From 5d01bbd111d6ff9ea9d9847774f66dff39633776 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:35 +0000 Subject: [PATCH 01/73] rcu: Yield simpler The rcu_yield() code is amazing. It's there to avoid starvation of the system when lots of (boosting) work is to be done. Now looking at the code it's functionality is: Make the thread SCHED_OTHER and very nice, i.e. get it out of the way Arm a timer with 2 ticks schedule() Now if the system goes idle the rcu task returns, regains SCHED_FIFO and plugs on. If the systems stays busy the timer fires and wakes a per node kthread which in turn makes the per cpu thread SCHED_FIFO and brings it back on the cpu. For the boosting thread the "make it FIFO" bit is missing and it just runs some magic boost checks. Now this is a lot of code with extra threads and complexity. It's way simpler to let the tasks when they detect overload schedule away for 2 ticks and defer the normal wakeup as long as they are in yielded state and the cpu is not idle. That solves the same problem and the only difference is that when the cpu goes idle it's not guaranteed that the thread returns right away, but it won't be longer out than two ticks, so no harm is done. If that's an issue than it is way simpler just to wake the task from idle as RCU has callbacks there anyway. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: Rusty Russell Cc: Namhyung Kim Reviewed-by: Paul E. McKenney Link: http://lkml.kernel.org/r/20120716103948.131256723@linutronix.de Signed-off-by: Thomas Gleixner --- kernel/rcutree.c | 8 +- kernel/rcutree.h | 7 +- kernel/rcutree_plugin.h | 210 +++++++--------------------------------- 3 files changed, 41 insertions(+), 184 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f280e542e3e9..f08ee3bc5741 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -139,7 +139,7 @@ DEFINE_PER_CPU(char, rcu_cpu_has_work); #endif /* #ifdef CONFIG_RCU_BOOST */ -static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); static void invoke_rcu_core(void); static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); @@ -1469,7 +1469,7 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) /* Adjust any no-longer-needed kthreads. */ rcu_stop_cpu_kthread(cpu); - rcu_node_kthread_setaffinity(rnp, -1); + rcu_boost_kthread_setaffinity(rnp, -1); /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */ @@ -2594,11 +2594,11 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, break; case CPU_ONLINE: case CPU_DOWN_FAILED: - rcu_node_kthread_setaffinity(rnp, -1); + rcu_boost_kthread_setaffinity(rnp, -1); rcu_cpu_kthread_setrt(cpu, 1); break; case CPU_DOWN_PREPARE: - rcu_node_kthread_setaffinity(rnp, cpu); + rcu_boost_kthread_setaffinity(rnp, cpu); rcu_cpu_kthread_setrt(cpu, 0); break; case CPU_DYING: diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 4d29169f2124..f08176172546 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -491,13 +491,8 @@ static void invoke_rcu_callbacks_kthread(void); static bool rcu_is_callbacks_kthread(void); #ifdef CONFIG_RCU_BOOST static void rcu_preempt_do_callbacks(void); -static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, - cpumask_var_t cm); static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, - struct rcu_node *rnp, - int rnp_index); -static void invoke_rcu_node_kthread(struct rcu_node *rnp); -static void rcu_yield(void (*f)(unsigned long), unsigned long arg); + struct rcu_node *rnp); #endif /* #ifdef CONFIG_RCU_BOOST */ static void rcu_cpu_kthread_setrt(int cpu, int to_rt); static void __cpuinit rcu_prepare_kthreads(int cpu); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7f3244c0df01..0f8b5ec64a7d 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1069,6 +1069,16 @@ static void rcu_initiate_boost_trace(struct rcu_node *rnp) #endif /* #else #ifdef CONFIG_RCU_TRACE */ +static void rcu_wake_cond(struct task_struct *t, int status) +{ + /* + * If the thread is yielding, only wake it when this + * is invoked from idle + */ + if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) + wake_up_process(t); +} + /* * Carry out RCU priority boosting on the task indicated by ->exp_tasks * or ->boost_tasks, advancing the pointer to the next task in the @@ -1140,17 +1150,6 @@ static int rcu_boost(struct rcu_node *rnp) ACCESS_ONCE(rnp->boost_tasks) != NULL; } -/* - * Timer handler to initiate waking up of boost kthreads that - * have yielded the CPU due to excessive numbers of tasks to - * boost. We wake up the per-rcu_node kthread, which in turn - * will wake up the booster kthread. - */ -static void rcu_boost_kthread_timer(unsigned long arg) -{ - invoke_rcu_node_kthread((struct rcu_node *)arg); -} - /* * Priority-boosting kthread. One per leaf rcu_node and one for the * root rcu_node. @@ -1174,8 +1173,9 @@ static int rcu_boost_kthread(void *arg) else spincnt = 0; if (spincnt > 10) { + rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; trace_rcu_utilization("End boost kthread@rcu_yield"); - rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp); + schedule_timeout_interruptible(2); trace_rcu_utilization("Start boost kthread@rcu_yield"); spincnt = 0; } @@ -1213,8 +1213,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) rnp->boost_tasks = rnp->gp_tasks; raw_spin_unlock_irqrestore(&rnp->lock, flags); t = rnp->boost_kthread_task; - if (t != NULL) - wake_up_process(t); + if (t) + rcu_wake_cond(t, rnp->boost_kthread_status); } else { rcu_initiate_boost_trace(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); @@ -1231,8 +1231,10 @@ static void invoke_rcu_callbacks_kthread(void) local_irq_save(flags); __this_cpu_write(rcu_cpu_has_work, 1); if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && - current != __this_cpu_read(rcu_cpu_kthread_task)) - wake_up_process(__this_cpu_read(rcu_cpu_kthread_task)); + current != __this_cpu_read(rcu_cpu_kthread_task)) { + rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), + __this_cpu_read(rcu_cpu_kthread_status)); + } local_irq_restore(flags); } @@ -1245,21 +1247,6 @@ static bool rcu_is_callbacks_kthread(void) return __get_cpu_var(rcu_cpu_kthread_task) == current; } -/* - * Set the affinity of the boost kthread. The CPU-hotplug locks are - * held, so no one should be messing with the existence of the boost - * kthread. - */ -static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, - cpumask_var_t cm) -{ - struct task_struct *t; - - t = rnp->boost_kthread_task; - if (t != NULL) - set_cpus_allowed_ptr(rnp->boost_kthread_task, cm); -} - #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) /* @@ -1276,15 +1263,19 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) * Returns zero if all is well, a negated errno otherwise. */ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, - struct rcu_node *rnp, - int rnp_index) + struct rcu_node *rnp) { + int rnp_index = rnp - &rsp->node[0]; unsigned long flags; struct sched_param sp; struct task_struct *t; if (&rcu_preempt_state != rsp) return 0; + + if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) + return 0; + rsp->boost = 1; if (rnp->boost_kthread_task != NULL) return 0; @@ -1327,20 +1318,6 @@ static void rcu_kthread_do_work(void) rcu_preempt_do_callbacks(); } -/* - * Wake up the specified per-rcu_node-structure kthread. - * Because the per-rcu_node kthreads are immortal, we don't need - * to do anything to keep them alive. - */ -static void invoke_rcu_node_kthread(struct rcu_node *rnp) -{ - struct task_struct *t; - - t = rnp->node_kthread_task; - if (t != NULL) - wake_up_process(t); -} - /* * Set the specified CPU's kthread to run RT or not, as specified by * the to_rt argument. The CPU-hotplug locks are held, so the task @@ -1365,45 +1342,6 @@ static void rcu_cpu_kthread_setrt(int cpu, int to_rt) sched_setscheduler_nocheck(t, policy, &sp); } -/* - * Timer handler to initiate the waking up of per-CPU kthreads that - * have yielded the CPU due to excess numbers of RCU callbacks. - * We wake up the per-rcu_node kthread, which in turn will wake up - * the booster kthread. - */ -static void rcu_cpu_kthread_timer(unsigned long arg) -{ - struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg); - struct rcu_node *rnp = rdp->mynode; - - atomic_or(rdp->grpmask, &rnp->wakemask); - invoke_rcu_node_kthread(rnp); -} - -/* - * Drop to non-real-time priority and yield, but only after posting a - * timer that will cause us to regain our real-time priority if we - * remain preempted. Either way, we restore our real-time priority - * before returning. - */ -static void rcu_yield(void (*f)(unsigned long), unsigned long arg) -{ - struct sched_param sp; - struct timer_list yield_timer; - int prio = current->rt_priority; - - setup_timer_on_stack(&yield_timer, f, arg); - mod_timer(&yield_timer, jiffies + 2); - sp.sched_priority = 0; - sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp); - set_user_nice(current, 19); - schedule(); - set_user_nice(current, 0); - sp.sched_priority = prio; - sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); - del_timer(&yield_timer); -} - /* * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU. * This can happen while the corresponding CPU is either coming online @@ -1476,7 +1414,7 @@ static int rcu_cpu_kthread(void *arg) if (spincnt > 10) { *statusp = RCU_KTHREAD_YIELDING; trace_rcu_utilization("End CPU kthread@rcu_yield"); - rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu); + schedule_timeout_interruptible(2); trace_rcu_utilization("Start CPU kthread@rcu_yield"); spincnt = 0; } @@ -1532,48 +1470,6 @@ static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) return 0; } -/* - * Per-rcu_node kthread, which is in charge of waking up the per-CPU - * kthreads when needed. We ignore requests to wake up kthreads - * for offline CPUs, which is OK because force_quiescent_state() - * takes care of this case. - */ -static int rcu_node_kthread(void *arg) -{ - int cpu; - unsigned long flags; - unsigned long mask; - struct rcu_node *rnp = (struct rcu_node *)arg; - struct sched_param sp; - struct task_struct *t; - - for (;;) { - rnp->node_kthread_status = RCU_KTHREAD_WAITING; - rcu_wait(atomic_read(&rnp->wakemask) != 0); - rnp->node_kthread_status = RCU_KTHREAD_RUNNING; - raw_spin_lock_irqsave(&rnp->lock, flags); - mask = atomic_xchg(&rnp->wakemask, 0); - rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */ - for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) { - if ((mask & 0x1) == 0) - continue; - preempt_disable(); - t = per_cpu(rcu_cpu_kthread_task, cpu); - if (!cpu_online(cpu) || t == NULL) { - preempt_enable(); - continue; - } - per_cpu(rcu_cpu_has_work, cpu) = 1; - sp.sched_priority = RCU_KTHREAD_PRIO; - sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); - preempt_enable(); - } - } - /* NOTREACHED */ - rnp->node_kthread_status = RCU_KTHREAD_STOPPED; - return 0; -} - /* * Set the per-rcu_node kthread's affinity to cover all CPUs that are * served by the rcu_node in question. The CPU hotplug lock is still @@ -1583,17 +1479,17 @@ static int rcu_node_kthread(void *arg) * no outgoing CPU. If there are no CPUs left in the affinity set, * this function allows the kthread to execute on any CPU. */ -static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { + struct task_struct *t = rnp->boost_kthread_task; + unsigned long mask = rnp->qsmaskinit; cpumask_var_t cm; int cpu; - unsigned long mask = rnp->qsmaskinit; - if (rnp->node_kthread_task == NULL) + if (!t) return; - if (!alloc_cpumask_var(&cm, GFP_KERNEL)) + if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) return; - cpumask_clear(cm); for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) if ((mask & 0x1) && cpu != outgoingcpu) cpumask_set_cpu(cpu, cm); @@ -1603,50 +1499,17 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) cpumask_clear_cpu(cpu, cm); WARN_ON_ONCE(cpumask_weight(cm) == 0); } - set_cpus_allowed_ptr(rnp->node_kthread_task, cm); - rcu_boost_kthread_setaffinity(rnp, cm); + set_cpus_allowed_ptr(t, cm); free_cpumask_var(cm); } -/* - * Spawn a per-rcu_node kthread, setting priority and affinity. - * Called during boot before online/offline can happen, or, if - * during runtime, with the main CPU-hotplug locks held. So only - * one of these can be executing at a time. - */ -static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp, - struct rcu_node *rnp) -{ - unsigned long flags; - int rnp_index = rnp - &rsp->node[0]; - struct sched_param sp; - struct task_struct *t; - - if (!rcu_scheduler_fully_active || - rnp->qsmaskinit == 0) - return 0; - if (rnp->node_kthread_task == NULL) { - t = kthread_create(rcu_node_kthread, (void *)rnp, - "rcun/%d", rnp_index); - if (IS_ERR(t)) - return PTR_ERR(t); - raw_spin_lock_irqsave(&rnp->lock, flags); - rnp->node_kthread_task = t; - raw_spin_unlock_irqrestore(&rnp->lock, flags); - sp.sched_priority = 99; - sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); - wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ - } - return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index); -} - /* * Spawn all kthreads -- called as soon as the scheduler is running. */ static int __init rcu_spawn_kthreads(void) { - int cpu; struct rcu_node *rnp; + int cpu; rcu_scheduler_fully_active = 1; for_each_possible_cpu(cpu) { @@ -1655,10 +1518,10 @@ static int __init rcu_spawn_kthreads(void) (void)rcu_spawn_one_cpu_kthread(cpu); } rnp = rcu_get_root(rcu_state); - (void)rcu_spawn_one_node_kthread(rcu_state, rnp); + (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); if (NUM_RCU_NODES > 1) { rcu_for_each_leaf_node(rcu_state, rnp) - (void)rcu_spawn_one_node_kthread(rcu_state, rnp); + (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); } return 0; } @@ -1672,8 +1535,7 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ if (rcu_scheduler_fully_active) { (void)rcu_spawn_one_cpu_kthread(cpu); - if (rnp->node_kthread_task == NULL) - (void)rcu_spawn_one_node_kthread(rcu_state, rnp); + (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); } } @@ -1706,7 +1568,7 @@ static void rcu_stop_cpu_kthread(int cpu) #endif /* #ifdef CONFIG_HOTPLUG_CPU */ -static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { } From 2a1d446019f9a5983ec5a335b95e8593fdb6fa2e Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:36 +0000 Subject: [PATCH 02/73] kthread: Implement park/unpark facility To avoid the full teardown/setup of per cpu kthreads in the case of cpu hot(un)plug, provide a facility which allows to put the kthread into a park position and unpark it when the cpu comes online again. Signed-off-by: Thomas Gleixner Reviewed-by: Namhyung Kim Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Link: http://lkml.kernel.org/r/20120716103948.236618824@linutronix.de Signed-off-by: Thomas Gleixner --- include/linux/kthread.h | 11 ++- kernel/kthread.c | 185 +++++++++++++++++++++++++++++++++++----- 2 files changed, 176 insertions(+), 20 deletions(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 22ccf9dee177..8d816646f766 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -14,6 +14,11 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), kthread_create_on_node(threadfn, data, -1, namefmt, ##arg) +struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), + void *data, + unsigned int cpu, + const char *namefmt); + /** * kthread_run - create and wake a thread. * @threadfn: the function to run until signal_pending(current). @@ -34,9 +39,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), void kthread_bind(struct task_struct *k, unsigned int cpu); int kthread_stop(struct task_struct *k); -int kthread_should_stop(void); +bool kthread_should_stop(void); +bool kthread_should_park(void); bool kthread_freezable_should_stop(bool *was_frozen); void *kthread_data(struct task_struct *k); +int kthread_park(struct task_struct *k); +void kthread_unpark(struct task_struct *k); +void kthread_parkme(void); int kthreadd(void *unused); extern struct task_struct *kthreadd_task; diff --git a/kernel/kthread.c b/kernel/kthread.c index b579af57ea10..146a6fa96825 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -37,11 +37,20 @@ struct kthread_create_info }; struct kthread { - int should_stop; + unsigned long flags; + unsigned int cpu; void *data; + struct completion parked; struct completion exited; }; +enum KTHREAD_BITS { + KTHREAD_IS_PER_CPU = 0, + KTHREAD_SHOULD_STOP, + KTHREAD_SHOULD_PARK, + KTHREAD_IS_PARKED, +}; + #define to_kthread(tsk) \ container_of((tsk)->vfork_done, struct kthread, exited) @@ -52,12 +61,28 @@ struct kthread { * and this will return true. You should then return, and your return * value will be passed through to kthread_stop(). */ -int kthread_should_stop(void) +bool kthread_should_stop(void) { - return to_kthread(current)->should_stop; + return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags); } EXPORT_SYMBOL(kthread_should_stop); +/** + * kthread_should_park - should this kthread park now? + * + * When someone calls kthread_park() on your kthread, it will be woken + * and this will return true. You should then do the necessary + * cleanup and call kthread_parkme() + * + * Similar to kthread_should_stop(), but this keeps the thread alive + * and in a park position. kthread_unpark() "restarts" the thread and + * calls the thread function again. + */ +bool kthread_should_park(void) +{ + return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags); +} + /** * kthread_freezable_should_stop - should this freezable kthread return now? * @was_frozen: optional out parameter, indicates whether %current was frozen @@ -96,6 +121,24 @@ void *kthread_data(struct task_struct *task) return to_kthread(task)->data; } +static void __kthread_parkme(struct kthread *self) +{ + __set_current_state(TASK_INTERRUPTIBLE); + while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) { + if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags)) + complete(&self->parked); + schedule(); + __set_current_state(TASK_INTERRUPTIBLE); + } + clear_bit(KTHREAD_IS_PARKED, &self->flags); + __set_current_state(TASK_RUNNING); +} + +void kthread_parkme(void) +{ + __kthread_parkme(to_kthread(current)); +} + static int kthread(void *_create) { /* Copy data: it's on kthread's stack */ @@ -105,9 +148,10 @@ static int kthread(void *_create) struct kthread self; int ret; - self.should_stop = 0; + self.flags = 0; self.data = data; init_completion(&self.exited); + init_completion(&self.parked); current->vfork_done = &self.exited; /* OK, tell user we're spawned, wait for stop or wakeup */ @@ -117,9 +161,11 @@ static int kthread(void *_create) schedule(); ret = -EINTR; - if (!self.should_stop) - ret = threadfn(data); + if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) { + __kthread_parkme(&self); + ret = threadfn(data); + } /* we can't just return, we must preserve "self" on stack */ do_exit(ret); } @@ -172,8 +218,7 @@ static void create_kthread(struct kthread_create_info *create) * Returns a task_struct or ERR_PTR(-ENOMEM). */ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), - void *data, - int node, + void *data, int node, const char namefmt[], ...) { @@ -210,6 +255,13 @@ struct task_struct *kthread_create_on_node(int (*threadfn)(void *data), } EXPORT_SYMBOL(kthread_create_on_node); +static void __kthread_bind(struct task_struct *p, unsigned int cpu) +{ + /* It's safe because the task is inactive. */ + do_set_cpus_allowed(p, cpumask_of(cpu)); + p->flags |= PF_THREAD_BOUND; +} + /** * kthread_bind - bind a just-created kthread to a cpu. * @p: thread created by kthread_create(). @@ -226,13 +278,111 @@ void kthread_bind(struct task_struct *p, unsigned int cpu) WARN_ON(1); return; } - - /* It's safe because the task is inactive. */ - do_set_cpus_allowed(p, cpumask_of(cpu)); - p->flags |= PF_THREAD_BOUND; + __kthread_bind(p, cpu); } EXPORT_SYMBOL(kthread_bind); +/** + * kthread_create_on_cpu - Create a cpu bound kthread + * @threadfn: the function to run until signal_pending(current). + * @data: data ptr for @threadfn. + * @cpu: The cpu on which the thread should be bound, + * @namefmt: printf-style name for the thread. Format is restricted + * to "name.*%u". Code fills in cpu number. + * + * Description: This helper function creates and names a kernel thread + * The thread will be woken and put into park mode. + */ +struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data), + void *data, unsigned int cpu, + const char *namefmt) +{ + struct task_struct *p; + + p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt, + cpu); + if (IS_ERR(p)) + return p; + set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags); + to_kthread(p)->cpu = cpu; + /* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */ + kthread_park(p); + return p; +} + +static struct kthread *task_get_live_kthread(struct task_struct *k) +{ + struct kthread *kthread; + + get_task_struct(k); + kthread = to_kthread(k); + /* It might have exited */ + barrier(); + if (k->vfork_done != NULL) + return kthread; + return NULL; +} + +/** + * kthread_unpark - unpark a thread created by kthread_create(). + * @k: thread created by kthread_create(). + * + * Sets kthread_should_park() for @k to return false, wakes it, and + * waits for it to return. If the thread is marked percpu then its + * bound to the cpu again. + */ +void kthread_unpark(struct task_struct *k) +{ + struct kthread *kthread = task_get_live_kthread(k); + + if (kthread) { + clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags); + /* + * We clear the IS_PARKED bit here as we don't wait + * until the task has left the park code. So if we'd + * park before that happens we'd see the IS_PARKED bit + * which might be about to be cleared. + */ + if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) { + if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags)) + __kthread_bind(k, kthread->cpu); + wake_up_process(k); + } + } + put_task_struct(k); +} + +/** + * kthread_park - park a thread created by kthread_create(). + * @k: thread created by kthread_create(). + * + * Sets kthread_should_park() for @k to return true, wakes it, and + * waits for it to return. This can also be called after kthread_create() + * instead of calling wake_up_process(): the thread will park without + * calling threadfn(). + * + * Returns 0 if the thread is parked, -ENOSYS if the thread exited. + * If called by the kthread itself just the park bit is set. + */ +int kthread_park(struct task_struct *k) +{ + struct kthread *kthread = task_get_live_kthread(k); + int ret = -ENOSYS; + + if (kthread) { + if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) { + set_bit(KTHREAD_SHOULD_PARK, &kthread->flags); + if (k != current) { + wake_up_process(k); + wait_for_completion(&kthread->parked); + } + } + ret = 0; + } + put_task_struct(k); + return ret; +} + /** * kthread_stop - stop a thread created by kthread_create(). * @k: thread created by kthread_create(). @@ -250,16 +400,13 @@ EXPORT_SYMBOL(kthread_bind); */ int kthread_stop(struct task_struct *k) { - struct kthread *kthread; + struct kthread *kthread = task_get_live_kthread(k); int ret; trace_sched_kthread_stop(k); - get_task_struct(k); - - kthread = to_kthread(k); - barrier(); /* it might have exited */ - if (k->vfork_done != NULL) { - kthread->should_stop = 1; + if (kthread) { + set_bit(KTHREAD_SHOULD_STOP, &kthread->flags); + clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags); wake_up_process(k); wait_for_completion(&kthread->exited); } From f97f8f06a49febbc3cb3635172efbe64ddc79700 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:36 +0000 Subject: [PATCH 03/73] smpboot: Provide infrastructure for percpu hotplug threads Provide a generic interface for setting up and tearing down percpu threads. On registration the threads for already online cpus are created and started. On deregistration (modules) the threads are stoppped. During hotplug operations the threads are created, started, parked and unparked. The datastructure for registration provides a pointer to percpu storage space and optional setup, cleanup, park, unpark functions. These functions are called when the thread state changes. Each implementation has to provide a function which is queried and returns whether the thread should run and the thread function itself. The core code handles all state transitions and avoids duplicated code in the call sites. [ paulmck: Preemption leak fix ] Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Reviewed-by: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.352501068@linutronix.de Signed-off-by: Thomas Gleixner --- include/linux/smpboot.h | 43 ++++++++ kernel/cpu.c | 10 +- kernel/smpboot.c | 229 ++++++++++++++++++++++++++++++++++++++++ kernel/smpboot.h | 4 + 4 files changed, 285 insertions(+), 1 deletion(-) create mode 100644 include/linux/smpboot.h diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h new file mode 100644 index 000000000000..e0106d8581d3 --- /dev/null +++ b/include/linux/smpboot.h @@ -0,0 +1,43 @@ +#ifndef _LINUX_SMPBOOT_H +#define _LINUX_SMPBOOT_H + +#include + +struct task_struct; +/* Cookie handed to the thread_fn*/ +struct smpboot_thread_data; + +/** + * struct smp_hotplug_thread - CPU hotplug related thread descriptor + * @store: Pointer to per cpu storage for the task pointers + * @list: List head for core management + * @thread_should_run: Check whether the thread should run or not. Called with + * preemption disabled. + * @thread_fn: The associated thread function + * @setup: Optional setup function, called when the thread gets + * operational the first time + * @cleanup: Optional cleanup function, called when the thread + * should stop (module exit) + * @park: Optional park function, called when the thread is + * parked (cpu offline) + * @unpark: Optional unpark function, called when the thread is + * unparked (cpu online) + * @thread_comm: The base name of the thread + */ +struct smp_hotplug_thread { + struct task_struct __percpu **store; + struct list_head list; + int (*thread_should_run)(unsigned int cpu); + void (*thread_fn)(unsigned int cpu); + void (*setup)(unsigned int cpu); + void (*cleanup)(unsigned int cpu, bool online); + void (*park)(unsigned int cpu); + void (*unpark)(unsigned int cpu); + const char *thread_comm; +}; + +int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread); +void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread); +int smpboot_thread_schedule(void); + +#endif diff --git a/kernel/cpu.c b/kernel/cpu.c index 14d32588cccd..e615dfbcf794 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -280,12 +280,13 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) __func__, cpu); goto out_release; } + smpboot_park_threads(cpu); err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); if (err) { /* CPU didn't die: tell everyone. Can't complain. */ + smpboot_unpark_threads(cpu); cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu); - goto out_release; } BUG_ON(cpu_online(cpu)); @@ -354,6 +355,10 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out; } + ret = smpboot_create_threads(cpu); + if (ret) + goto out; + ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls); if (ret) { nr_calls--; @@ -368,6 +373,9 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) goto out_notify; BUG_ON(!cpu_online(cpu)); + /* Wake the per cpu threads */ + smpboot_unpark_threads(cpu); + /* Now call notifier in preparation. */ cpu_notify(CPU_ONLINE | mod, hcpu); diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 98f60c5caa1b..9d5f7b04025d 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -1,11 +1,17 @@ /* * Common SMP CPU bringup/teardown functions */ +#include #include #include #include +#include +#include #include +#include #include +#include +#include #include "smpboot.h" @@ -65,3 +71,226 @@ void __init idle_threads_init(void) } } #endif + +static LIST_HEAD(hotplug_threads); +static DEFINE_MUTEX(smpboot_threads_lock); + +struct smpboot_thread_data { + unsigned int cpu; + unsigned int status; + struct smp_hotplug_thread *ht; +}; + +enum { + HP_THREAD_NONE = 0, + HP_THREAD_ACTIVE, + HP_THREAD_PARKED, +}; + +/** + * smpboot_thread_fn - percpu hotplug thread loop function + * @data: thread data pointer + * + * Checks for thread stop and park conditions. Calls the necessary + * setup, cleanup, park and unpark functions for the registered + * thread. + * + * Returns 1 when the thread should exit, 0 otherwise. + */ +static int smpboot_thread_fn(void *data) +{ + struct smpboot_thread_data *td = data; + struct smp_hotplug_thread *ht = td->ht; + + while (1) { + set_current_state(TASK_INTERRUPTIBLE); + preempt_disable(); + if (kthread_should_stop()) { + set_current_state(TASK_RUNNING); + preempt_enable(); + if (ht->cleanup) + ht->cleanup(td->cpu, cpu_online(td->cpu)); + kfree(td); + return 0; + } + + if (kthread_should_park()) { + __set_current_state(TASK_RUNNING); + preempt_enable(); + if (ht->park && td->status == HP_THREAD_ACTIVE) { + BUG_ON(td->cpu != smp_processor_id()); + ht->park(td->cpu); + td->status = HP_THREAD_PARKED; + } + kthread_parkme(); + /* We might have been woken for stop */ + continue; + } + + BUG_ON(td->cpu != smp_processor_id()); + + /* Check for state change setup */ + switch (td->status) { + case HP_THREAD_NONE: + preempt_enable(); + if (ht->setup) + ht->setup(td->cpu); + td->status = HP_THREAD_ACTIVE; + preempt_disable(); + break; + case HP_THREAD_PARKED: + preempt_enable(); + if (ht->unpark) + ht->unpark(td->cpu); + td->status = HP_THREAD_ACTIVE; + preempt_disable(); + break; + } + + if (!ht->thread_should_run(td->cpu)) { + preempt_enable(); + schedule(); + } else { + set_current_state(TASK_RUNNING); + preempt_enable(); + ht->thread_fn(td->cpu); + } + } +} + +static int +__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + struct smpboot_thread_data *td; + + if (tsk) + return 0; + + td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu)); + if (!td) + return -ENOMEM; + td->cpu = cpu; + td->ht = ht; + + tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, + ht->thread_comm); + if (IS_ERR(tsk)) { + kfree(td); + return PTR_ERR(tsk); + } + + get_task_struct(tsk); + *per_cpu_ptr(ht->store, cpu) = tsk; + return 0; +} + +int smpboot_create_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + int ret = 0; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry(cur, &hotplug_threads, list) { + ret = __smpboot_create_thread(cur, cpu); + if (ret) + break; + } + mutex_unlock(&smpboot_threads_lock); + return ret; +} + +static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + kthread_unpark(tsk); +} + +void smpboot_unpark_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry(cur, &hotplug_threads, list) + smpboot_unpark_thread(cur, cpu); + mutex_unlock(&smpboot_threads_lock); +} + +static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) +{ + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + if (tsk) + kthread_park(tsk); +} + +void smpboot_park_threads(unsigned int cpu) +{ + struct smp_hotplug_thread *cur; + + mutex_lock(&smpboot_threads_lock); + list_for_each_entry_reverse(cur, &hotplug_threads, list) + smpboot_park_thread(cur, cpu); + mutex_unlock(&smpboot_threads_lock); +} + +static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) +{ + unsigned int cpu; + + /* We need to destroy also the parked threads of offline cpus */ + for_each_possible_cpu(cpu) { + struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); + + if (tsk) { + kthread_stop(tsk); + put_task_struct(tsk); + *per_cpu_ptr(ht->store, cpu) = NULL; + } + } +} + +/** + * smpboot_register_percpu_thread - Register a per_cpu thread related to hotplug + * @plug_thread: Hotplug thread descriptor + * + * Creates and starts the threads on all online cpus. + */ +int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) +{ + unsigned int cpu; + int ret = 0; + + mutex_lock(&smpboot_threads_lock); + for_each_online_cpu(cpu) { + ret = __smpboot_create_thread(plug_thread, cpu); + if (ret) { + smpboot_destroy_threads(plug_thread); + goto out; + } + smpboot_unpark_thread(plug_thread, cpu); + } + list_add(&plug_thread->list, &hotplug_threads); +out: + mutex_unlock(&smpboot_threads_lock); + return ret; +} +EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); + +/** + * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug + * @plug_thread: Hotplug thread descriptor + * + * Stops all threads on all possible cpus. + */ +void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) +{ + get_online_cpus(); + mutex_lock(&smpboot_threads_lock); + list_del(&plug_thread->list); + smpboot_destroy_threads(plug_thread); + mutex_unlock(&smpboot_threads_lock); + put_online_cpus(); +} +EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); diff --git a/kernel/smpboot.h b/kernel/smpboot.h index 6ef9433e1c70..72415a0eb955 100644 --- a/kernel/smpboot.h +++ b/kernel/smpboot.h @@ -13,4 +13,8 @@ static inline void idle_thread_set_boot_cpu(void) { } static inline void idle_threads_init(void) { } #endif +int smpboot_create_threads(unsigned int cpu); +void smpboot_park_threads(unsigned int cpu); +void smpboot_unpark_threads(unsigned int cpu); + #endif From 3180d89b47701072cf129f800a735baf3acdbb8a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Jul 2012 01:55:54 -0700 Subject: [PATCH 04/73] hotplug: Fix UP bug in smpboot hotplug code Because kernel subsystems need their per-CPU kthreads on UP systems as well as on SMP systems, the smpboot hotplug kthread functions must be provided in UP builds as well as in SMP builds. This commit therefore adds smpboot.c to UP builds and excludes irrelevant code via #ifdef. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner --- kernel/Makefile | 3 +-- kernel/smpboot.c | 4 ++++ 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/Makefile b/kernel/Makefile index c0cc67ad764c..e5602d32acb3 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -10,7 +10,7 @@ obj-y = fork.o exec_domain.o panic.o printk.o \ kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \ hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \ notifier.o ksysfs.o cred.o \ - async.o range.o groups.o lglock.o + async.o range.o groups.o lglock.o smpboot.o ifdef CONFIG_FUNCTION_TRACER # Do not trace debug files and internal ftrace files @@ -46,7 +46,6 @@ obj-$(CONFIG_DEBUG_RT_MUTEXES) += rtmutex-debug.o obj-$(CONFIG_RT_MUTEX_TESTER) += rtmutex-tester.o obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o obj-$(CONFIG_SMP) += smp.o -obj-$(CONFIG_SMP) += smpboot.o ifneq ($(CONFIG_SMP),y) obj-y += up.o endif diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 9d5f7b04025d..d6c5fc054242 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -15,6 +15,8 @@ #include "smpboot.h" +#ifdef CONFIG_SMP + #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD /* * For the hotplug case we keep the task structs around and reuse @@ -72,6 +74,8 @@ void __init idle_threads_init(void) } #endif +#endif /* #ifdef CONFIG_SMP */ + static LIST_HEAD(hotplug_threads); static DEFINE_MUTEX(smpboot_threads_lock); From 3e339b5dae24a7065e196eb8d0145ab2f8cc2d2d Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:37 +0000 Subject: [PATCH 05/73] softirq: Use hotplug thread infrastructure [ paulmck: Call rcu_note_context_switch() with interrupts enabled. ] Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.456416747@linutronix.de Signed-off-by: Thomas Gleixner --- kernel/softirq.c | 111 ++++++++++++----------------------------------- 1 file changed, 27 insertions(+), 84 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index b73e681df09e..5c6a5bd8462f 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #define CREATE_TRACE_POINTS @@ -742,49 +743,22 @@ void __init softirq_init(void) open_softirq(HI_SOFTIRQ, tasklet_hi_action); } -static int run_ksoftirqd(void * __bind_cpu) +static int ksoftirqd_should_run(unsigned int cpu) { - set_current_state(TASK_INTERRUPTIBLE); + return local_softirq_pending(); +} - while (!kthread_should_stop()) { - preempt_disable(); - if (!local_softirq_pending()) { - schedule_preempt_disabled(); - } - - __set_current_state(TASK_RUNNING); - - while (local_softirq_pending()) { - /* Preempt disable stops cpu going offline. - If already offline, we'll be on wrong CPU: - don't process */ - if (cpu_is_offline((long)__bind_cpu)) - goto wait_to_die; - local_irq_disable(); - if (local_softirq_pending()) - __do_softirq(); - local_irq_enable(); - sched_preempt_enable_no_resched(); - cond_resched(); - preempt_disable(); - rcu_note_context_switch((long)__bind_cpu); - } - preempt_enable(); - set_current_state(TASK_INTERRUPTIBLE); +static void run_ksoftirqd(unsigned int cpu) +{ + local_irq_disable(); + if (local_softirq_pending()) { + __do_softirq(); + rcu_note_context_switch(cpu); + local_irq_enable(); + cond_resched(); + return; } - __set_current_state(TASK_RUNNING); - return 0; - -wait_to_die: - preempt_enable(); - /* Wait for kthread_stop */ - set_current_state(TASK_INTERRUPTIBLE); - while (!kthread_should_stop()) { - schedule(); - set_current_state(TASK_INTERRUPTIBLE); - } - __set_current_state(TASK_RUNNING); - return 0; + local_irq_enable(); } #ifdef CONFIG_HOTPLUG_CPU @@ -850,50 +824,14 @@ static int __cpuinit cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) { - int hotcpu = (unsigned long)hcpu; - struct task_struct *p; - switch (action) { - case CPU_UP_PREPARE: - case CPU_UP_PREPARE_FROZEN: - p = kthread_create_on_node(run_ksoftirqd, - hcpu, - cpu_to_node(hotcpu), - "ksoftirqd/%d", hotcpu); - if (IS_ERR(p)) { - printk("ksoftirqd for %i failed\n", hotcpu); - return notifier_from_errno(PTR_ERR(p)); - } - kthread_bind(p, hotcpu); - per_cpu(ksoftirqd, hotcpu) = p; - break; - case CPU_ONLINE: - case CPU_ONLINE_FROZEN: - wake_up_process(per_cpu(ksoftirqd, hotcpu)); - break; #ifdef CONFIG_HOTPLUG_CPU - case CPU_UP_CANCELED: - case CPU_UP_CANCELED_FROZEN: - if (!per_cpu(ksoftirqd, hotcpu)) - break; - /* Unbind so it can run. Fall thru. */ - kthread_bind(per_cpu(ksoftirqd, hotcpu), - cpumask_any(cpu_online_mask)); case CPU_DEAD: - case CPU_DEAD_FROZEN: { - static const struct sched_param param = { - .sched_priority = MAX_RT_PRIO-1 - }; - - p = per_cpu(ksoftirqd, hotcpu); - per_cpu(ksoftirqd, hotcpu) = NULL; - sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m); - kthread_stop(p); - takeover_tasklets(hotcpu); + case CPU_DEAD_FROZEN: + takeover_tasklets((unsigned long)hcpu); break; - } #endif /* CONFIG_HOTPLUG_CPU */ - } + } return NOTIFY_OK; } @@ -901,14 +839,19 @@ static struct notifier_block __cpuinitdata cpu_nfb = { .notifier_call = cpu_callback }; +static struct smp_hotplug_thread softirq_threads = { + .store = &ksoftirqd, + .thread_should_run = ksoftirqd_should_run, + .thread_fn = run_ksoftirqd, + .thread_comm = "ksoftirqd/%u", +}; + static __init int spawn_ksoftirqd(void) { - void *cpu = (void *)(long)smp_processor_id(); - int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu); - - BUG_ON(err != NOTIFY_OK); - cpu_callback(&cpu_nfb, CPU_ONLINE, cpu); register_cpu_notifier(&cpu_nfb); + + BUG_ON(smpboot_register_percpu_thread(&softirq_threads)); + return 0; } early_initcall(spawn_ksoftirqd); From bcd951cf10f24e341defcd002c15a1f4eea13ddb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:38 +0000 Subject: [PATCH 06/73] watchdog: Use hotplug thread infrastructure Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.563736676@linutronix.de Signed-off-by: Thomas Gleixner --- kernel/watchdog.c | 269 ++++++++++++++++------------------------------ 1 file changed, 92 insertions(+), 177 deletions(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 4b1dfba70f7c..9d4c8d5a1f53 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -29,16 +30,18 @@ int watchdog_enabled = 1; int __read_mostly watchdog_thresh = 10; +static int __read_mostly watchdog_disabled; static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts); static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog); static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer); static DEFINE_PER_CPU(bool, softlockup_touch_sync); static DEFINE_PER_CPU(bool, soft_watchdog_warn); +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); +static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt); #ifdef CONFIG_HARDLOCKUP_DETECTOR static DEFINE_PER_CPU(bool, hard_watchdog_warn); static DEFINE_PER_CPU(bool, watchdog_nmi_touch); -static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); static DEFINE_PER_CPU(struct perf_event *, watchdog_ev); #endif @@ -248,13 +251,15 @@ static void watchdog_overflow_callback(struct perf_event *event, __this_cpu_write(hard_watchdog_warn, false); return; } +#endif /* CONFIG_HARDLOCKUP_DETECTOR */ + static void watchdog_interrupt_count(void) { __this_cpu_inc(hrtimer_interrupts); } -#else -static inline void watchdog_interrupt_count(void) { return; } -#endif /* CONFIG_HARDLOCKUP_DETECTOR */ + +static int watchdog_nmi_enable(unsigned int cpu); +static void watchdog_nmi_disable(unsigned int cpu); /* watchdog kicker functions */ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) @@ -327,49 +332,68 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) return HRTIMER_RESTART; } - -/* - * The watchdog thread - touches the timestamp. - */ -static int watchdog(void *unused) +static void watchdog_set_prio(unsigned int policy, unsigned int prio) +{ + struct sched_param param = { .sched_priority = prio }; + + sched_setscheduler(current, policy, ¶m); +} + +static void watchdog_enable(unsigned int cpu) { - struct sched_param param = { .sched_priority = 0 }; struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer); - /* initialize timestamp */ - __touch_watchdog(); + if (!watchdog_enabled) { + kthread_park(current); + return; + } + + /* Enable the perf event */ + watchdog_nmi_enable(cpu); /* kick off the timer for the hardlockup detector */ + hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + hrtimer->function = watchdog_timer_fn; + /* done here because hrtimer_start can only pin to smp_processor_id() */ hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()), HRTIMER_MODE_REL_PINNED); - set_current_state(TASK_INTERRUPTIBLE); - /* - * Run briefly (kicked by the hrtimer callback function) once every - * get_sample_period() seconds (4 seconds by default) to reset the - * softlockup timestamp. If this gets delayed for more than - * 2*watchdog_thresh seconds then the debug-printout triggers in - * watchdog_timer_fn(). - */ - while (!kthread_should_stop()) { - __touch_watchdog(); - schedule(); - - if (kthread_should_stop()) - break; - - set_current_state(TASK_INTERRUPTIBLE); - } - /* - * Drop the policy/priority elevation during thread exit to avoid a - * scheduling latency spike. - */ - __set_current_state(TASK_RUNNING); - sched_setscheduler(current, SCHED_NORMAL, ¶m); - return 0; + /* initialize timestamp */ + watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1); + __touch_watchdog(); } +static void watchdog_disable(unsigned int cpu) +{ + struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer); + + watchdog_set_prio(SCHED_NORMAL, 0); + hrtimer_cancel(hrtimer); + /* disable the perf event */ + watchdog_nmi_disable(cpu); +} + +static int watchdog_should_run(unsigned int cpu) +{ + return __this_cpu_read(hrtimer_interrupts) != + __this_cpu_read(soft_lockup_hrtimer_cnt); +} + +/* + * The watchdog thread function - touches the timestamp. + * + * It only runs once every get_sample_period() seconds (4 seconds by + * default) to reset the softlockup timestamp. If this gets delayed + * for more than 2*watchdog_thresh seconds then the debug-printout + * triggers in watchdog_timer_fn(). + */ +static void watchdog(unsigned int cpu) +{ + __this_cpu_write(soft_lockup_hrtimer_cnt, + __this_cpu_read(hrtimer_interrupts)); + __touch_watchdog(); +} #ifdef CONFIG_HARDLOCKUP_DETECTOR /* @@ -379,7 +403,7 @@ static int watchdog(void *unused) */ static unsigned long cpu0_err; -static int watchdog_nmi_enable(int cpu) +static int watchdog_nmi_enable(unsigned int cpu) { struct perf_event_attr *wd_attr; struct perf_event *event = per_cpu(watchdog_ev, cpu); @@ -433,7 +457,7 @@ out: return 0; } -static void watchdog_nmi_disable(int cpu) +static void watchdog_nmi_disable(unsigned int cpu) { struct perf_event *event = per_cpu(watchdog_ev, cpu); @@ -447,107 +471,35 @@ static void watchdog_nmi_disable(int cpu) return; } #else -static int watchdog_nmi_enable(int cpu) { return 0; } -static void watchdog_nmi_disable(int cpu) { return; } +static int watchdog_nmi_enable(unsigned int cpu) { return 0; } +static void watchdog_nmi_disable(unsigned int cpu) { return; } #endif /* CONFIG_HARDLOCKUP_DETECTOR */ /* prepare/enable/disable routines */ -static void watchdog_prepare_cpu(int cpu) -{ - struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu); - - WARN_ON(per_cpu(softlockup_watchdog, cpu)); - hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); - hrtimer->function = watchdog_timer_fn; -} - -static int watchdog_enable(int cpu) -{ - struct task_struct *p = per_cpu(softlockup_watchdog, cpu); - int err = 0; - - /* enable the perf event */ - err = watchdog_nmi_enable(cpu); - - /* Regardless of err above, fall through and start softlockup */ - - /* create the watchdog thread */ - if (!p) { - struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 }; - p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu); - if (IS_ERR(p)) { - pr_err("softlockup watchdog for %i failed\n", cpu); - if (!err) { - /* if hardlockup hasn't already set this */ - err = PTR_ERR(p); - /* and disable the perf event */ - watchdog_nmi_disable(cpu); - } - goto out; - } - sched_setscheduler(p, SCHED_FIFO, ¶m); - kthread_bind(p, cpu); - per_cpu(watchdog_touch_ts, cpu) = 0; - per_cpu(softlockup_watchdog, cpu) = p; - wake_up_process(p); - } - -out: - return err; -} - -static void watchdog_disable(int cpu) -{ - struct task_struct *p = per_cpu(softlockup_watchdog, cpu); - struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu); - - /* - * cancel the timer first to stop incrementing the stats - * and waking up the kthread - */ - hrtimer_cancel(hrtimer); - - /* disable the perf event */ - watchdog_nmi_disable(cpu); - - /* stop the watchdog thread */ - if (p) { - per_cpu(softlockup_watchdog, cpu) = NULL; - kthread_stop(p); - } -} - /* sysctl functions */ #ifdef CONFIG_SYSCTL static void watchdog_enable_all_cpus(void) { - int cpu; - - watchdog_enabled = 0; - - for_each_online_cpu(cpu) - if (!watchdog_enable(cpu)) - /* if any cpu succeeds, watchdog is considered - enabled for the system */ - watchdog_enabled = 1; - - if (!watchdog_enabled) - pr_err("failed to be enabled on some cpus\n"); + unsigned int cpu; + if (watchdog_disabled) { + watchdog_disabled = 0; + for_each_online_cpu(cpu) + kthread_unpark(per_cpu(softlockup_watchdog, cpu)); + } } static void watchdog_disable_all_cpus(void) { - int cpu; + unsigned int cpu; - for_each_online_cpu(cpu) - watchdog_disable(cpu); - - /* if all watchdogs are disabled, then they are disabled for the system */ - watchdog_enabled = 0; + if (!watchdog_disabled) { + watchdog_disabled = 1; + for_each_online_cpu(cpu) + kthread_park(per_cpu(softlockup_watchdog, cpu)); + } } - /* * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh */ @@ -557,73 +509,36 @@ int proc_dowatchdog(struct ctl_table *table, int write, { int ret; + if (watchdog_disabled < 0) + return -ENODEV; + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); if (ret || !write) - goto out; + return ret; if (watchdog_enabled && watchdog_thresh) watchdog_enable_all_cpus(); else watchdog_disable_all_cpus(); -out: return ret; } #endif /* CONFIG_SYSCTL */ - -/* - * Create/destroy watchdog threads as CPUs come and go: - */ -static int __cpuinit -cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) -{ - int hotcpu = (unsigned long)hcpu; - - switch (action) { - case CPU_UP_PREPARE: - case CPU_UP_PREPARE_FROZEN: - watchdog_prepare_cpu(hotcpu); - break; - case CPU_ONLINE: - case CPU_ONLINE_FROZEN: - if (watchdog_enabled) - watchdog_enable(hotcpu); - break; -#ifdef CONFIG_HOTPLUG_CPU - case CPU_UP_CANCELED: - case CPU_UP_CANCELED_FROZEN: - watchdog_disable(hotcpu); - break; - case CPU_DEAD: - case CPU_DEAD_FROZEN: - watchdog_disable(hotcpu); - break; -#endif /* CONFIG_HOTPLUG_CPU */ - } - - /* - * hardlockup and softlockup are not important enough - * to block cpu bring up. Just always succeed and - * rely on printk output to flag problems. - */ - return NOTIFY_OK; -} - -static struct notifier_block __cpuinitdata cpu_nfb = { - .notifier_call = cpu_callback +static struct smp_hotplug_thread watchdog_threads = { + .store = &softlockup_watchdog, + .thread_should_run = watchdog_should_run, + .thread_fn = watchdog, + .thread_comm = "watchdog/%u", + .setup = watchdog_enable, + .park = watchdog_disable, + .unpark = watchdog_enable, }; void __init lockup_detector_init(void) { - void *cpu = (void *)(long)smp_processor_id(); - int err; - - err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu); - WARN_ON(notifier_to_errno(err)); - - cpu_callback(&cpu_nfb, CPU_ONLINE, cpu); - register_cpu_notifier(&cpu_nfb); - - return; + if (smpboot_register_percpu_thread(&watchdog_threads)) { + pr_err("Failed to create watchdog threads, disabled\n"); + watchdog_disabled = -ENODEV; + } } From 62ab7072476ae1600e877cc62b43758e485f4f1e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 16 Jul 2012 10:42:38 +0000 Subject: [PATCH 07/73] rcu: Use smp_hotplug_thread facility for RCUs per-CPU kthread Bring RCU into the new-age CPU-hotplug fold by modifying RCU's per-CPU kthread code to use the new smp_hotplug_thread facility. [ tglx: Adapted it to use callbacks and to the simplified rcu yield ] Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: Rusty Russell Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.673354828@linutronix.de Signed-off-by: Thomas Gleixner --- kernel/rcutree.c | 4 - kernel/rcutree.h | 8 -- kernel/rcutree_plugin.h | 203 ++++++++-------------------------------- kernel/rcutree_trace.c | 3 +- 4 files changed, 41 insertions(+), 177 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f08ee3bc5741..11a4fdca1df7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -133,7 +133,6 @@ static int rcu_scheduler_fully_active __read_mostly; */ static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); -DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu); DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); DEFINE_PER_CPU(char, rcu_cpu_has_work); @@ -1468,7 +1467,6 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ /* Adjust any no-longer-needed kthreads. */ - rcu_stop_cpu_kthread(cpu); rcu_boost_kthread_setaffinity(rnp, -1); /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */ @@ -2595,11 +2593,9 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, case CPU_ONLINE: case CPU_DOWN_FAILED: rcu_boost_kthread_setaffinity(rnp, -1); - rcu_cpu_kthread_setrt(cpu, 1); break; case CPU_DOWN_PREPARE: rcu_boost_kthread_setaffinity(rnp, cpu); - rcu_cpu_kthread_setrt(cpu, 0); break; case CPU_DYING: case CPU_DYING_FROZEN: diff --git a/kernel/rcutree.h b/kernel/rcutree.h index f08176172546..1224d4c05382 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -196,12 +196,6 @@ struct rcu_node { /* Refused to boost: not sure why, though. */ /* This can happen due to race conditions. */ #endif /* #ifdef CONFIG_RCU_BOOST */ - struct task_struct *node_kthread_task; - /* kthread that takes care of this rcu_node */ - /* structure, for example, awakening the */ - /* per-CPU kthreads as needed. */ - unsigned int node_kthread_status; - /* State of node_kthread_task for tracing. */ } ____cacheline_internodealigned_in_smp; /* @@ -468,7 +462,6 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp); #ifdef CONFIG_HOTPLUG_CPU static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags); -static void rcu_stop_cpu_kthread(int cpu); #endif /* #ifdef CONFIG_HOTPLUG_CPU */ static void rcu_print_detail_task_stall(struct rcu_state *rsp); static int rcu_print_task_stall(struct rcu_node *rnp); @@ -494,7 +487,6 @@ static void rcu_preempt_do_callbacks(void); static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, struct rcu_node *rnp); #endif /* #ifdef CONFIG_RCU_BOOST */ -static void rcu_cpu_kthread_setrt(int cpu, int to_rt); static void __cpuinit rcu_prepare_kthreads(int cpu); static void rcu_prepare_for_idle_init(int cpu); static void rcu_cleanup_after_idle(int cpu); diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 0f8b5ec64a7d..c1961aed1213 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,6 +25,7 @@ */ #include +#include #define RCU_KTHREAD_PRIO 1 @@ -1292,25 +1293,6 @@ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, return 0; } -#ifdef CONFIG_HOTPLUG_CPU - -/* - * Stop the RCU's per-CPU kthread when its CPU goes offline,. - */ -static void rcu_stop_cpu_kthread(int cpu) -{ - struct task_struct *t; - - /* Stop the CPU's kthread. */ - t = per_cpu(rcu_cpu_kthread_task, cpu); - if (t != NULL) { - per_cpu(rcu_cpu_kthread_task, cpu) = NULL; - kthread_stop(t); - } -} - -#endif /* #ifdef CONFIG_HOTPLUG_CPU */ - static void rcu_kthread_do_work(void) { rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); @@ -1318,59 +1300,22 @@ static void rcu_kthread_do_work(void) rcu_preempt_do_callbacks(); } -/* - * Set the specified CPU's kthread to run RT or not, as specified by - * the to_rt argument. The CPU-hotplug locks are held, so the task - * is not going away. - */ -static void rcu_cpu_kthread_setrt(int cpu, int to_rt) +static void rcu_cpu_kthread_setup(unsigned int cpu) { - int policy; struct sched_param sp; - struct task_struct *t; - t = per_cpu(rcu_cpu_kthread_task, cpu); - if (t == NULL) - return; - if (to_rt) { - policy = SCHED_FIFO; - sp.sched_priority = RCU_KTHREAD_PRIO; - } else { - policy = SCHED_NORMAL; - sp.sched_priority = 0; - } - sched_setscheduler_nocheck(t, policy, &sp); + sp.sched_priority = RCU_KTHREAD_PRIO; + sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); } -/* - * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU. - * This can happen while the corresponding CPU is either coming online - * or going offline. We cannot wait until the CPU is fully online - * before starting the kthread, because the various notifier functions - * can wait for RCU grace periods. So we park rcu_cpu_kthread() until - * the corresponding CPU is online. - * - * Return 1 if the kthread needs to stop, 0 otherwise. - * - * Caller must disable bh. This function can momentarily enable it. - */ -static int rcu_cpu_kthread_should_stop(int cpu) +static void rcu_cpu_kthread_park(unsigned int cpu) { - while (cpu_is_offline(cpu) || - !cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu)) || - smp_processor_id() != cpu) { - if (kthread_should_stop()) - return 1; - per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; - per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id(); - local_bh_enable(); - schedule_timeout_uninterruptible(1); - if (!cpumask_equal(¤t->cpus_allowed, cpumask_of(cpu))) - set_cpus_allowed_ptr(current, cpumask_of(cpu)); - local_bh_disable(); - } - per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; - return 0; + per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; +} + +static int rcu_cpu_kthread_should_run(unsigned int cpu) +{ + return __get_cpu_var(rcu_cpu_has_work); } /* @@ -1378,96 +1323,35 @@ static int rcu_cpu_kthread_should_stop(int cpu) * RCU softirq used in flavors and configurations of RCU that do not * support RCU priority boosting. */ -static int rcu_cpu_kthread(void *arg) +static void rcu_cpu_kthread(unsigned int cpu) { - int cpu = (int)(long)arg; - unsigned long flags; - int spincnt = 0; - unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu); - char work; - char *workp = &per_cpu(rcu_cpu_has_work, cpu); + unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status); + char work, *workp = &__get_cpu_var(rcu_cpu_has_work); + int spincnt; - trace_rcu_utilization("Start CPU kthread@init"); - for (;;) { - *statusp = RCU_KTHREAD_WAITING; - trace_rcu_utilization("End CPU kthread@rcu_wait"); - rcu_wait(*workp != 0 || kthread_should_stop()); + for (spincnt = 0; spincnt < 10; spincnt++) { trace_rcu_utilization("Start CPU kthread@rcu_wait"); local_bh_disable(); - if (rcu_cpu_kthread_should_stop(cpu)) { - local_bh_enable(); - break; - } *statusp = RCU_KTHREAD_RUNNING; - per_cpu(rcu_cpu_kthread_loops, cpu)++; - local_irq_save(flags); + this_cpu_inc(rcu_cpu_kthread_loops); + local_irq_disable(); work = *workp; *workp = 0; - local_irq_restore(flags); + local_irq_enable(); if (work) rcu_kthread_do_work(); local_bh_enable(); - if (*workp != 0) - spincnt++; - else - spincnt = 0; - if (spincnt > 10) { - *statusp = RCU_KTHREAD_YIELDING; - trace_rcu_utilization("End CPU kthread@rcu_yield"); - schedule_timeout_interruptible(2); - trace_rcu_utilization("Start CPU kthread@rcu_yield"); - spincnt = 0; + if (*workp == 0) { + trace_rcu_utilization("End CPU kthread@rcu_wait"); + *statusp = RCU_KTHREAD_WAITING; + return; } } - *statusp = RCU_KTHREAD_STOPPED; - trace_rcu_utilization("End CPU kthread@term"); - return 0; -} - -/* - * Spawn a per-CPU kthread, setting up affinity and priority. - * Because the CPU hotplug lock is held, no other CPU will be attempting - * to manipulate rcu_cpu_kthread_task. There might be another CPU - * attempting to access it during boot, but the locking in kthread_bind() - * will enforce sufficient ordering. - * - * Please note that we cannot simply refuse to wake up the per-CPU - * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state, - * which can result in softlockup complaints if the task ends up being - * idle for more than a couple of minutes. - * - * However, please note also that we cannot bind the per-CPU kthread to its - * CPU until that CPU is fully online. We also cannot wait until the - * CPU is fully online before we create its per-CPU kthread, as this would - * deadlock the system when CPU notifiers tried waiting for grace - * periods. So we bind the per-CPU kthread to its CPU only if the CPU - * is online. If its CPU is not yet fully online, then the code in - * rcu_cpu_kthread() will wait until it is fully online, and then do - * the binding. - */ -static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu) -{ - struct sched_param sp; - struct task_struct *t; - - if (!rcu_scheduler_fully_active || - per_cpu(rcu_cpu_kthread_task, cpu) != NULL) - return 0; - t = kthread_create_on_node(rcu_cpu_kthread, - (void *)(long)cpu, - cpu_to_node(cpu), - "rcuc/%d", cpu); - if (IS_ERR(t)) - return PTR_ERR(t); - if (cpu_online(cpu)) - kthread_bind(t, cpu); - per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu; - WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL); - sp.sched_priority = RCU_KTHREAD_PRIO; - sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); - per_cpu(rcu_cpu_kthread_task, cpu) = t; - wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */ - return 0; + *statusp = RCU_KTHREAD_YIELDING; + trace_rcu_utilization("Start CPU kthread@rcu_yield"); + schedule_timeout_interruptible(2); + trace_rcu_utilization("End CPU kthread@rcu_yield"); + *statusp = RCU_KTHREAD_WAITING; } /* @@ -1503,6 +1387,15 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) free_cpumask_var(cm); } +static struct smp_hotplug_thread rcu_cpu_thread_spec = { + .store = &rcu_cpu_kthread_task, + .thread_should_run = rcu_cpu_kthread_should_run, + .thread_fn = rcu_cpu_kthread, + .thread_comm = "rcuc/%u", + .setup = rcu_cpu_kthread_setup, + .park = rcu_cpu_kthread_park, +}; + /* * Spawn all kthreads -- called as soon as the scheduler is running. */ @@ -1512,11 +1405,9 @@ static int __init rcu_spawn_kthreads(void) int cpu; rcu_scheduler_fully_active = 1; - for_each_possible_cpu(cpu) { + for_each_possible_cpu(cpu) per_cpu(rcu_cpu_has_work, cpu) = 0; - if (cpu_online(cpu)) - (void)rcu_spawn_one_cpu_kthread(cpu); - } + BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); rnp = rcu_get_root(rcu_state); (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); if (NUM_RCU_NODES > 1) { @@ -1533,10 +1424,8 @@ static void __cpuinit rcu_prepare_kthreads(int cpu) struct rcu_node *rnp = rdp->mynode; /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ - if (rcu_scheduler_fully_active) { - (void)rcu_spawn_one_cpu_kthread(cpu); + if (rcu_scheduler_fully_active) (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); - } } #else /* #ifdef CONFIG_RCU_BOOST */ @@ -1560,22 +1449,10 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) { } -#ifdef CONFIG_HOTPLUG_CPU - -static void rcu_stop_cpu_kthread(int cpu) -{ -} - -#endif /* #ifdef CONFIG_HOTPLUG_CPU */ - static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { } -static void rcu_cpu_kthread_setrt(int cpu, int to_rt) -{ -} - static int __init rcu_scheduler_really_started(void) { rcu_scheduler_fully_active = 1; diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index abffb486e94e..31968931f146 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -108,11 +108,10 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp) rdp->nxttail[RCU_WAIT_TAIL]], ".D"[&rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL]]); #ifdef CONFIG_RCU_BOOST - seq_printf(m, " kt=%d/%c/%d ktl=%x", + seq_printf(m, " kt=%d/%c ktl=%x", per_cpu(rcu_cpu_has_work, rdp->cpu), convert_kthread_status(per_cpu(rcu_cpu_kthread_status, rdp->cpu)), - per_cpu(rcu_cpu_kthread_cpu, rdp->cpu), per_cpu(rcu_cpu_kthread_loops, rdp->cpu) & 0xffff); #endif /* #ifdef CONFIG_RCU_BOOST */ seq_printf(m, " b=%ld", rdp->blimit); From 81942621bd6b70b1a1ac4692b3f8f3be65a91b44 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 16 Jul 2012 10:42:39 +0000 Subject: [PATCH 08/73] infiniband: Ehca: Use hotplug thread infrastructure Get rid of the hotplug notifiers and use the generic hotplug thread infrastructure. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: Rusty Russell Reviewed-by: Paul E. McKenney Cc: Namhyung Kim Link: http://lkml.kernel.org/r/20120716103948.775527032@linutronix.de Signed-off-by: Thomas Gleixner --- drivers/infiniband/hw/ehca/ehca_irq.c | 266 ++++++++++---------------- drivers/infiniband/hw/ehca/ehca_irq.h | 6 +- 2 files changed, 100 insertions(+), 172 deletions(-) diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c index 53589000fd07..4eeac40cd943 100644 --- a/drivers/infiniband/hw/ehca/ehca_irq.c +++ b/drivers/infiniband/hw/ehca/ehca_irq.c @@ -42,6 +42,7 @@ */ #include +#include #include "ehca_classes.h" #include "ehca_irq.h" @@ -652,7 +653,7 @@ void ehca_tasklet_eq(unsigned long data) ehca_process_eq((struct ehca_shca*)data, 1); } -static inline int find_next_online_cpu(struct ehca_comp_pool *pool) +static int find_next_online_cpu(struct ehca_comp_pool *pool) { int cpu; unsigned long flags; @@ -662,17 +663,20 @@ static inline int find_next_online_cpu(struct ehca_comp_pool *pool) ehca_dmp(cpu_online_mask, cpumask_size(), ""); spin_lock_irqsave(&pool->last_cpu_lock, flags); - cpu = cpumask_next(pool->last_cpu, cpu_online_mask); - if (cpu >= nr_cpu_ids) - cpu = cpumask_first(cpu_online_mask); - pool->last_cpu = cpu; + do { + cpu = cpumask_next(pool->last_cpu, cpu_online_mask); + if (cpu >= nr_cpu_ids) + cpu = cpumask_first(cpu_online_mask); + pool->last_cpu = cpu; + } while (!per_cpu_ptr(pool->cpu_comp_tasks, cpu)->active) spin_unlock_irqrestore(&pool->last_cpu_lock, flags); return cpu; } static void __queue_comp_task(struct ehca_cq *__cq, - struct ehca_cpu_comp_task *cct) + struct ehca_cpu_comp_task *cct, + struct task_struct *thread) { unsigned long flags; @@ -683,7 +687,7 @@ static void __queue_comp_task(struct ehca_cq *__cq, __cq->nr_callbacks++; list_add_tail(&__cq->entry, &cct->cq_list); cct->cq_jobs++; - wake_up(&cct->wait_queue); + wake_up_process(thread); } else __cq->nr_callbacks++; @@ -695,6 +699,7 @@ static void queue_comp_task(struct ehca_cq *__cq) { int cpu_id; struct ehca_cpu_comp_task *cct; + struct task_struct *thread; int cq_jobs; unsigned long flags; @@ -702,7 +707,8 @@ static void queue_comp_task(struct ehca_cq *__cq) BUG_ON(!cpu_online(cpu_id)); cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu_id); - BUG_ON(!cct); + thread = per_cpu_ptr(pool->cpu_comp_threads, cpu_id); + BUG_ON(!cct || !thread); spin_lock_irqsave(&cct->task_lock, flags); cq_jobs = cct->cq_jobs; @@ -710,28 +716,25 @@ static void queue_comp_task(struct ehca_cq *__cq) if (cq_jobs > 0) { cpu_id = find_next_online_cpu(pool); cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu_id); - BUG_ON(!cct); + thread = per_cpu_ptr(pool->cpu_comp_threads, cpu_id); + BUG_ON(!cct || !thread); } - - __queue_comp_task(__cq, cct); + __queue_comp_task(__cq, cct, thread); } static void run_comp_task(struct ehca_cpu_comp_task *cct) { struct ehca_cq *cq; - unsigned long flags; - - spin_lock_irqsave(&cct->task_lock, flags); while (!list_empty(&cct->cq_list)) { cq = list_entry(cct->cq_list.next, struct ehca_cq, entry); - spin_unlock_irqrestore(&cct->task_lock, flags); + spin_unlock_irq(&cct->task_lock); comp_event_callback(cq); if (atomic_dec_and_test(&cq->nr_events)) wake_up(&cq->wait_completion); - spin_lock_irqsave(&cct->task_lock, flags); + spin_lock_irq(&cct->task_lock); spin_lock(&cq->task_lock); cq->nr_callbacks--; if (!cq->nr_callbacks) { @@ -740,159 +743,76 @@ static void run_comp_task(struct ehca_cpu_comp_task *cct) } spin_unlock(&cq->task_lock); } - - spin_unlock_irqrestore(&cct->task_lock, flags); } -static int comp_task(void *__cct) -{ - struct ehca_cpu_comp_task *cct = __cct; - int cql_empty; - DECLARE_WAITQUEUE(wait, current); - - set_current_state(TASK_INTERRUPTIBLE); - while (!kthread_should_stop()) { - add_wait_queue(&cct->wait_queue, &wait); - - spin_lock_irq(&cct->task_lock); - cql_empty = list_empty(&cct->cq_list); - spin_unlock_irq(&cct->task_lock); - if (cql_empty) - schedule(); - else - __set_current_state(TASK_RUNNING); - - remove_wait_queue(&cct->wait_queue, &wait); - - spin_lock_irq(&cct->task_lock); - cql_empty = list_empty(&cct->cq_list); - spin_unlock_irq(&cct->task_lock); - if (!cql_empty) - run_comp_task(__cct); - - set_current_state(TASK_INTERRUPTIBLE); - } - __set_current_state(TASK_RUNNING); - - return 0; -} - -static struct task_struct *create_comp_task(struct ehca_comp_pool *pool, - int cpu) -{ - struct ehca_cpu_comp_task *cct; - - cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - spin_lock_init(&cct->task_lock); - INIT_LIST_HEAD(&cct->cq_list); - init_waitqueue_head(&cct->wait_queue); - cct->task = kthread_create_on_node(comp_task, cct, cpu_to_node(cpu), - "ehca_comp/%d", cpu); - - return cct->task; -} - -static void destroy_comp_task(struct ehca_comp_pool *pool, - int cpu) -{ - struct ehca_cpu_comp_task *cct; - struct task_struct *task; - unsigned long flags_cct; - - cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - - spin_lock_irqsave(&cct->task_lock, flags_cct); - - task = cct->task; - cct->task = NULL; - cct->cq_jobs = 0; - - spin_unlock_irqrestore(&cct->task_lock, flags_cct); - - if (task) - kthread_stop(task); -} - -static void __cpuinit take_over_work(struct ehca_comp_pool *pool, int cpu) +static void comp_task_park(unsigned int cpu) { struct ehca_cpu_comp_task *cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); + struct ehca_cpu_comp_task *target; + struct task_struct *thread; + struct ehca_cq *cq, *tmp; LIST_HEAD(list); - struct ehca_cq *cq; - unsigned long flags_cct; - - spin_lock_irqsave(&cct->task_lock, flags_cct); + spin_lock_irq(&cct->task_lock); + cct->cq_jobs = 0; + cct->active = 0; list_splice_init(&cct->cq_list, &list); + spin_unlock_irq(&cct->task_lock); - while (!list_empty(&list)) { - cq = list_entry(cct->cq_list.next, struct ehca_cq, entry); - + cpu = find_next_online_cpu(pool); + target = per_cpu_ptr(pool->cpu_comp_tasks, cpu); + thread = per_cpu_ptr(pool->cpu_comp_threads, cpu); + spin_lock_irq(&target->task_lock); + list_for_each_entry_safe(cq, tmp, &list, entry) { list_del(&cq->entry); - __queue_comp_task(cq, this_cpu_ptr(pool->cpu_comp_tasks)); + __queue_comp_task(cq, target, thread); } - - spin_unlock_irqrestore(&cct->task_lock, flags_cct); - + spin_unlock_irq(&target->task_lock); } -static int __cpuinit comp_pool_callback(struct notifier_block *nfb, - unsigned long action, - void *hcpu) +static void comp_task_stop(unsigned int cpu, bool online) { - unsigned int cpu = (unsigned long)hcpu; - struct ehca_cpu_comp_task *cct; + struct ehca_cpu_comp_task *cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - switch (action) { - case CPU_UP_PREPARE: - case CPU_UP_PREPARE_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_PREPARE)", cpu); - if (!create_comp_task(pool, cpu)) { - ehca_gen_err("Can't create comp_task for cpu: %x", cpu); - return notifier_from_errno(-ENOMEM); - } - break; - case CPU_UP_CANCELED: - case CPU_UP_CANCELED_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_CANCELED)", cpu); - cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - kthread_bind(cct->task, cpumask_any(cpu_online_mask)); - destroy_comp_task(pool, cpu); - break; - case CPU_ONLINE: - case CPU_ONLINE_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_ONLINE)", cpu); - cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - kthread_bind(cct->task, cpu); - wake_up_process(cct->task); - break; - case CPU_DOWN_PREPARE: - case CPU_DOWN_PREPARE_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_DOWN_PREPARE)", cpu); - break; - case CPU_DOWN_FAILED: - case CPU_DOWN_FAILED_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_DOWN_FAILED)", cpu); - break; - case CPU_DEAD: - case CPU_DEAD_FROZEN: - ehca_gen_dbg("CPU: %x (CPU_DEAD)", cpu); - destroy_comp_task(pool, cpu); - take_over_work(pool, cpu); - break; - } - - return NOTIFY_OK; + spin_lock_irq(&cct->task_lock); + cct->cq_jobs = 0; + cct->active = 0; + WARN_ON(!list_empty(&cct->cq_list)); + spin_unlock_irq(&cct->task_lock); } -static struct notifier_block comp_pool_callback_nb __cpuinitdata = { - .notifier_call = comp_pool_callback, - .priority = 0, +static int comp_task_should_run(unsigned int cpu) +{ + struct ehca_cpu_comp_task *cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); + + return cct->cq_jobs; +} + +static int comp_task(unsigned int cpu) +{ + struct ehca_cpu_comp_task *cct = this_cpu_ptr(pool->cpu_comp_tasks); + int cql_empty; + + spin_lock_irq(&cct->task_lock); + cql_empty = list_empty(&cct->cq_list); + if (!cql_empty) { + __set_current_state(TASK_RUNNING); + run_comp_task(cct); + } + spin_unlock_irq(&cct->task_lock); +} + +static struct smp_hotplug_thread comp_pool_threads = { + .thread_should_run = comp_task_should_run, + .thread_fn = comp_task, + .thread_comm = "ehca_comp/%u", + .cleanup = comp_task_stop, + .park = comp_task_park, }; int ehca_create_comp_pool(void) { - int cpu; - struct task_struct *task; + int cpu, ret = -ENOMEM; if (!ehca_scaling_code) return 0; @@ -905,38 +825,46 @@ int ehca_create_comp_pool(void) pool->last_cpu = cpumask_any(cpu_online_mask); pool->cpu_comp_tasks = alloc_percpu(struct ehca_cpu_comp_task); - if (pool->cpu_comp_tasks == NULL) { - kfree(pool); - return -EINVAL; + if (!pool->cpu_comp_tasks) + goto out_pool; + + pool->cpu_comp_threads = alloc_percpu(struct task_struct *); + if (!pool->cpu_comp_threads) + goto out_tasks; + + for_each_present_cpu(cpu) { + struct ehca_cpu_comp_task *cct; + + cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu); + spin_lock_init(&cct->task_lock); + INIT_LIST_HEAD(&cct->cq_list); } - for_each_online_cpu(cpu) { - task = create_comp_task(pool, cpu); - if (task) { - kthread_bind(task, cpu); - wake_up_process(task); - } - } + comp_pool_threads.store = pool->cpu_comp_threads; + ret = smpboot_register_percpu_thread(&comp_pool_threads); + if (ret) + goto out_threads; - register_hotcpu_notifier(&comp_pool_callback_nb); + pr_info("eHCA scaling code enabled\n"); + return ret; - printk(KERN_INFO "eHCA scaling code enabled\n"); - - return 0; +out_threads: + free_percpu(pool->cpu_comp_threads); +out_tasks: + free_percpu(pool->cpu_comp_tasks); +out_pool: + kfree(pool); + return ret; } void ehca_destroy_comp_pool(void) { - int i; - if (!ehca_scaling_code) return; - unregister_hotcpu_notifier(&comp_pool_callback_nb); - - for_each_online_cpu(i) - destroy_comp_task(pool, i); + smpboot_unregister_percpu_thread(&comp_pool_threads); + free_percpu(pool->cpu_comp_threads); free_percpu(pool->cpu_comp_tasks); kfree(pool); } diff --git a/drivers/infiniband/hw/ehca/ehca_irq.h b/drivers/infiniband/hw/ehca/ehca_irq.h index 3346cb06cea6..5370199f08c7 100644 --- a/drivers/infiniband/hw/ehca/ehca_irq.h +++ b/drivers/infiniband/hw/ehca/ehca_irq.h @@ -58,15 +58,15 @@ void ehca_tasklet_eq(unsigned long data); void ehca_process_eq(struct ehca_shca *shca, int is_irq); struct ehca_cpu_comp_task { - wait_queue_head_t wait_queue; struct list_head cq_list; - struct task_struct *task; spinlock_t task_lock; int cq_jobs; + int active; }; struct ehca_comp_pool { - struct ehca_cpu_comp_task *cpu_comp_tasks; + struct ehca_cpu_comp_task __percpu *cpu_comp_tasks; + struct task_struct * __percpu *cpu_comp_threads; int last_cpu; spinlock_t last_cpu_lock; }; From c0e12e51b0522f7f5f09ea90273dbb724afb054d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 16 Aug 2012 12:45:05 -0700 Subject: [PATCH 09/73] infiniband: ehca: Fix while->do-while conversion typo This commit just adds a needed semicolon. Reported-by: Stephen Rothwell Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Stephen Rothwell --- drivers/infiniband/hw/ehca/ehca_irq.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c index 4eeac40cd943..83a00955146b 100644 --- a/drivers/infiniband/hw/ehca/ehca_irq.c +++ b/drivers/infiniband/hw/ehca/ehca_irq.c @@ -668,7 +668,7 @@ static int find_next_online_cpu(struct ehca_comp_pool *pool) if (cpu >= nr_cpu_ids) cpu = cpumask_first(cpu_online_mask); pool->last_cpu = cpu; - } while (!per_cpu_ptr(pool->cpu_comp_tasks, cpu)->active) + } while (!per_cpu_ptr(pool->cpu_comp_tasks, cpu)->active); spin_unlock_irqrestore(&pool->last_cpu_lock, flags); return cpu; From bff4a394795add6b919debc009f72b7607f5d4bf Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 17 Aug 2012 04:43:11 -0700 Subject: [PATCH 10/73] infiniband: ehca: Fix compiler warnings Fix comp_task() to return void to match smp_hotplug_thread's thread_fn member, and adjust indirection on the ->cpu_comp_threads per-CPU member of the ehca_comp_pool structure. Reported-by: Stephen Rothwell Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Stephen Rothwell --- drivers/infiniband/hw/ehca/ehca_irq.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/infiniband/hw/ehca/ehca_irq.c b/drivers/infiniband/hw/ehca/ehca_irq.c index 83a00955146b..8615d7cf7e01 100644 --- a/drivers/infiniband/hw/ehca/ehca_irq.c +++ b/drivers/infiniband/hw/ehca/ehca_irq.c @@ -707,7 +707,7 @@ static void queue_comp_task(struct ehca_cq *__cq) BUG_ON(!cpu_online(cpu_id)); cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu_id); - thread = per_cpu_ptr(pool->cpu_comp_threads, cpu_id); + thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu_id); BUG_ON(!cct || !thread); spin_lock_irqsave(&cct->task_lock, flags); @@ -716,7 +716,7 @@ static void queue_comp_task(struct ehca_cq *__cq) if (cq_jobs > 0) { cpu_id = find_next_online_cpu(pool); cct = per_cpu_ptr(pool->cpu_comp_tasks, cpu_id); - thread = per_cpu_ptr(pool->cpu_comp_threads, cpu_id); + thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu_id); BUG_ON(!cct || !thread); } __queue_comp_task(__cq, cct, thread); @@ -761,7 +761,7 @@ static void comp_task_park(unsigned int cpu) cpu = find_next_online_cpu(pool); target = per_cpu_ptr(pool->cpu_comp_tasks, cpu); - thread = per_cpu_ptr(pool->cpu_comp_threads, cpu); + thread = *per_cpu_ptr(pool->cpu_comp_threads, cpu); spin_lock_irq(&target->task_lock); list_for_each_entry_safe(cq, tmp, &list, entry) { list_del(&cq->entry); @@ -788,7 +788,7 @@ static int comp_task_should_run(unsigned int cpu) return cct->cq_jobs; } -static int comp_task(unsigned int cpu) +static void comp_task(unsigned int cpu) { struct ehca_cpu_comp_task *cct = this_cpu_ptr(pool->cpu_comp_tasks); int cql_empty; From a10d206ef1a83121ab7430cb196e0376a7145b22 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 22 Sep 2012 13:55:30 -0700 Subject: [PATCH 11/73] rcu: Fix day-one dyntick-idle stall-warning bug Each grace period is supposed to have at least one callback waiting for that grace period to complete. However, if CONFIG_NO_HZ=n, an extra callback-free grace period is no big problem -- it will chew up a tiny bit of CPU time, but it will complete normally. In contrast, CONFIG_NO_HZ=y kernels have the potential for all the CPUs to go to sleep indefinitely, in turn indefinitely delaying completion of the callback-free grace period. Given that nothing is waiting on this grace period, this is also not a problem. That is, unless RCU CPU stall warnings are also enabled, as they are in recent kernels. In this case, if a CPU wakes up after at least one minute of inactivity, an RCU CPU stall warning will result. The reason that no one noticed until quite recently is that most systems have enough OS noise that they will never remain absolutely idle for a full minute. But there are some embedded systems with cut-down userspace configurations that consistently get into this situation. All this begs the question of exactly how a callback-free grace period gets started in the first place. This can happen due to the fact that CPUs do not necessarily agree on which grace period is in progress. If a CPU still believes that the grace period that just completed is still ongoing, it will believe that it has callbacks that need to wait for another grace period, never mind the fact that the grace period that they were waiting for just completed. This CPU can therefore erroneously decide to start a new grace period. Note that this can happen in TREE_RCU and TREE_PREEMPT_RCU even on a single-CPU system: Deadlock considerations mean that the CPU that detected the end of the grace period is not necessarily officially informed of this fact for some time. Once this CPU notices that the earlier grace period completed, it will invoke its callbacks. It then won't have any callbacks left. If no other CPU has any callbacks, we now have a callback-free grace period. This commit therefore makes CPUs check more carefully before starting a new grace period. This new check relies on an array of tail pointers into each CPU's list of callbacks. If the CPU is up to date on which grace periods have completed, it checks to see if any callbacks follow the RCU_DONE_TAIL segment, otherwise it checks to see if any callbacks follow the RCU_WAIT_TAIL segment. The reason that this works is that the RCU_WAIT_TAIL segment will be promoted to the RCU_DONE_TAIL segment as soon as the CPU is officially notified that the old grace period has ended. This change is to cpu_needs_another_gp(), which is called in a number of places. The only one that really matters is in rcu_start_gp(), where the root rcu_node structure's ->lock is held, which prevents any other CPU from starting or completing a grace period, so that the comparison that determines whether the CPU is missing the completion of a grace period is stable. Reported-by: Becky Bruce Reported-by: Subodh Nijsure Reported-by: Paul Walmsley Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Paul Walmsley # OMAP3730, OMAP4430 Cc: stable@vger.kernel.org --- kernel/rcutree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f280e542e3e9..f7bcd9e6c054 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -305,7 +305,9 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) static int cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) { - return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp); + return *rdp->nxttail[RCU_DONE_TAIL + + ACCESS_ONCE(rsp->completed) != rdp->completed] && + !rcu_gp_in_progress(rsp); } /* From b3dbec76e5334fbb063987dea14e7b255602d7e4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 18 Jun 2012 18:36:08 -0700 Subject: [PATCH 12/73] rcu: Move RCU grace-period initialization into a kthread As the first step towards allowing grace-period initialization to be preemptible, this commit moves the RCU grace-period initialization into its own kthread. This is needed to keep large-system scheduling latency at reasonable levels. Also change raw_spin_lock_irqsave() to raw_spin_lock_irq() as suggested by Peter Zijlstra in review comments. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 190 +++++++++++++++++++++++++++++++---------------- kernel/rcutree.h | 3 + 2 files changed, 129 insertions(+), 64 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f7bcd9e6c054..4792f1642bf2 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1041,6 +1041,102 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat __note_new_gpnum(rsp, rnp, rdp); } +/* + * Body of kthread that handles grace periods. + */ +static int rcu_gp_kthread(void *arg) +{ + struct rcu_data *rdp; + struct rcu_node *rnp; + struct rcu_state *rsp = arg; + + for (;;) { + + /* Handle grace-period start. */ + rnp = rcu_get_root(rsp); + for (;;) { + wait_event_interruptible(rsp->gp_wq, rsp->gp_flags); + if (rsp->gp_flags) + break; + flush_signals(current); + } + raw_spin_lock_irq(&rnp->lock); + rsp->gp_flags = 0; + rdp = this_cpu_ptr(rsp->rda); + + if (rcu_gp_in_progress(rsp)) { + /* + * A grace period is already in progress, so + * don't start another one. + */ + raw_spin_unlock_irq(&rnp->lock); + continue; + } + + if (rsp->fqs_active) { + /* + * We need a grace period, but force_quiescent_state() + * is running. Tell it to start one on our behalf. + */ + rsp->fqs_need_gp = 1; + raw_spin_unlock_irq(&rnp->lock); + continue; + } + + /* Advance to a new grace period and initialize state. */ + rsp->gpnum++; + trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); + WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); + rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ + rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; + record_gp_stall_check_time(rsp); + raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ + + /* Exclude any concurrent CPU-hotplug operations. */ + raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ + + /* + * Set the quiescent-state-needed bits in all the rcu_node + * structures for all currently online CPUs in breadth-first + * order, starting from the root rcu_node structure. + * This operation relies on the layout of the hierarchy + * within the rsp->node[] array. Note that other CPUs will + * access only the leaves of the hierarchy, which still + * indicate that no grace period is in progress, at least + * until the corresponding leaf node has been initialized. + * In addition, we have excluded CPU-hotplug operations. + * + * Note that the grace period cannot complete until + * we finish the initialization process, as there will + * be at least one qsmask bit set in the root node until + * that time, namely the one corresponding to this CPU, + * due to the fact that we have irqs disabled. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + rcu_preempt_check_blocked_tasks(rnp); + rnp->qsmask = rnp->qsmaskinit; + rnp->gpnum = rsp->gpnum; + rnp->completed = rsp->completed; + if (rnp == rdp->mynode) + rcu_start_gp_per_cpu(rsp, rnp, rdp); + rcu_preempt_boost_start_gp(rnp); + trace_rcu_grace_period_init(rsp->name, rnp->gpnum, + rnp->level, rnp->grplo, + rnp->grphi, rnp->qsmask); + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + } + + rnp = rcu_get_root(rsp); + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + /* force_quiescent_state() now OK. */ + rsp->fqs_state = RCU_SIGNAL_INIT; + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irq(&rsp->onofflock); + } + return 0; +} + /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold @@ -1058,77 +1154,20 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); - if (!rcu_scheduler_fully_active || + if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* - * Either the scheduler hasn't yet spawned the first - * non-idle task or this CPU does not need another - * grace period. Either way, don't start a new grace - * period. + * Either we have not yet spawned the grace-period + * task or this CPU does not need another grace period. + * Either way, don't start a new grace period. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } - if (rsp->fqs_active) { - /* - * This CPU needs a grace period, but force_quiescent_state() - * is running. Tell it to start one on this CPU's behalf. - */ - rsp->fqs_need_gp = 1; - raw_spin_unlock_irqrestore(&rnp->lock, flags); - return; - } - - /* Advance to a new grace period and initialize state. */ - rsp->gpnum++; - trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); - WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); - rsp->fqs_state = RCU_GP_INIT; /* Hold off force_quiescent_state. */ - rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; - record_gp_stall_check_time(rsp); - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ - - /* Exclude any concurrent CPU-hotplug operations. */ - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ - - /* - * Set the quiescent-state-needed bits in all the rcu_node - * structures for all currently online CPUs in breadth-first - * order, starting from the root rcu_node structure. This - * operation relies on the layout of the hierarchy within the - * rsp->node[] array. Note that other CPUs will access only - * the leaves of the hierarchy, which still indicate that no - * grace period is in progress, at least until the corresponding - * leaf node has been initialized. In addition, we have excluded - * CPU-hotplug operations. - * - * Note that the grace period cannot complete until we finish - * the initialization process, as there will be at least one - * qsmask bit set in the root node until that time, namely the - * one corresponding to this CPU, due to the fact that we have - * irqs disabled. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - rcu_preempt_check_blocked_tasks(rnp); - rnp->qsmask = rnp->qsmaskinit; - rnp->gpnum = rsp->gpnum; - rnp->completed = rsp->completed; - if (rnp == rdp->mynode) - rcu_start_gp_per_cpu(rsp, rnp, rdp); - rcu_preempt_boost_start_gp(rnp); - trace_rcu_grace_period_init(rsp->name, rnp->gpnum, - rnp->level, rnp->grplo, - rnp->grphi, rnp->qsmask); - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - } - - rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - rsp->fqs_state = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */ - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + rsp->gp_flags = 1; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + wake_up(&rsp->gp_wq); } /* @@ -2628,6 +2667,28 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self, return NOTIFY_OK; } +/* + * Spawn the kthread that handles this RCU flavor's grace periods. + */ +static int __init rcu_spawn_gp_kthread(void) +{ + unsigned long flags; + struct rcu_node *rnp; + struct rcu_state *rsp; + struct task_struct *t; + + for_each_rcu_flavor(rsp) { + t = kthread_run(rcu_gp_kthread, rsp, rsp->name); + BUG_ON(IS_ERR(t)); + rnp = rcu_get_root(rsp); + raw_spin_lock_irqsave(&rnp->lock, flags); + rsp->gp_kthread = t; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + } + return 0; +} +early_initcall(rcu_spawn_gp_kthread); + /* * This function is invoked towards the end of the scheduler's initialization * process. Before this is called, the idle task might contain @@ -2729,6 +2790,7 @@ static void __init rcu_init_one(struct rcu_state *rsp, } rsp->rda = rda; + init_waitqueue_head(&rsp->gp_wq); rnp = rsp->level[rcu_num_lvls - 1]; for_each_possible_cpu(i) { while (i > rnp->grphi) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 4d29169f2124..117a15019e99 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -385,6 +385,9 @@ struct rcu_state { u8 boost; /* Subject to priority boost. */ unsigned long gpnum; /* Current gp number. */ unsigned long completed; /* # of last completed gp. */ + struct task_struct *gp_kthread; /* Task for grace periods. */ + wait_queue_head_t gp_wq; /* Where GP task waits. */ + int gp_flags; /* Commands for GP task. */ /* End of fields guarded by root rcu_node's lock. */ From 79bce6724366b3827c5c673fb07d7063082873cf Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 17 Sep 2012 14:32:58 -0700 Subject: [PATCH 13/73] rcu: Prevent initialization-time quiescent-state race The next step in reducing RCU's grace-period initialization latency on large systems will make this initialization preemptible. Unfortunately, making the grace-period initialization subject to interrupts (let alone preemption) exposes the following race on systems whose rcu_node tree contains more than one node: 1. CPU 31 starts initializing the grace period, including the first leaf rcu_node structures, and is then preempted. 2. CPU 0 refers to the first leaf rcu_node structure, and notes that a new grace period has started. It passes through a quiescent state shortly thereafter, and informs the RCU core of this rite of passage. 3. CPU 0 enters an RCU read-side critical section, acquiring a pointer to an RCU-protected data item. 4. CPU 31 takes an interrupt whose handler removes the data item referenced by CPU 0 from the data structure, and registers an RCU callback in order to free it. 5. CPU 31 resumes initializing the grace period, including its own rcu_node structure. In invokes rcu_start_gp_per_cpu(), which advances all callbacks, including the one registered in #4 above, to be handled by the current grace period. 6. The remaining CPUs pass through quiescent states and inform the RCU core, but CPU 0 remains in its RCU read-side critical section, still referencing the now-removed data item. 7. The grace period completes and all the callbacks are invoked, including the one that frees the data item that CPU 0 is still referencing. Oops!!! One way to avoid this race is to remove grace-period acceleration from rcu_start_gp_per_cpu(). Now, the only reason for this acceleration was to allow CPUs bringing RCU out of idle state to have their callbacks invoked after only one grace period, rather than the two grace periods that would otherwise be required. But this acceleration does not work when RCU grace-period initialization is moved to a kthread because the CPU posting the callback is no longer necessarily the CPU that is initializing the resulting grace period. This commit therefore removes this now-pointless (and soon to be dangerous) grace-period acceleration, thus avoiding the above race. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 14 -------------- 1 file changed, 14 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 4792f1642bf2..e7a534498aa0 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1023,20 +1023,6 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat /* Prior grace period ended, so advance callbacks for current CPU. */ __rcu_process_gp_end(rsp, rnp, rdp); - /* - * Because this CPU just now started the new grace period, we know - * that all of its callbacks will be covered by this upcoming grace - * period, even the ones that were registered arbitrarily recently. - * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL. - * - * Other CPUs cannot be sure exactly when the grace period started. - * Therefore, their recently registered callbacks must pass through - * an additional RCU_NEXT_READY stage, so that they will be handled - * by the next RCU grace period. - */ - rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; - rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL]; - /* Set state so that this CPU will detect the next quiescent state. */ __note_new_gpnum(rsp, rnp, rdp); } From 755609a9087fa983f567dc5452b2fa7b089b591f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 19 Jun 2012 17:18:20 -0700 Subject: [PATCH 14/73] rcu: Allow RCU grace-period initialization to be preempted RCU grace-period initialization is currently carried out with interrupts disabled, which can result in 200-microsecond latency spikes on systems on which RCU has been configured for 4096 CPUs. This patch therefore makes the RCU grace-period initialization be preemptible, which should eliminate those latency spikes. Similar spikes from grace-period cleanup and the forcing of quiescent states will be dealt with similarly by later patches. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e7a534498aa0..781e5f0b7b17 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1030,7 +1030,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat /* * Body of kthread that handles grace periods. */ -static int rcu_gp_kthread(void *arg) +static int __noreturn rcu_gp_kthread(void *arg) { struct rcu_data *rdp; struct rcu_node *rnp; @@ -1056,6 +1056,7 @@ static int rcu_gp_kthread(void *arg) * don't start another one. */ raw_spin_unlock_irq(&rnp->lock); + cond_resched(); continue; } @@ -1066,6 +1067,7 @@ static int rcu_gp_kthread(void *arg) */ rsp->fqs_need_gp = 1; raw_spin_unlock_irq(&rnp->lock); + cond_resched(); continue; } @@ -1076,10 +1078,10 @@ static int rcu_gp_kthread(void *arg) rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); - raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */ + raw_spin_unlock_irq(&rnp->lock); /* Exclude any concurrent CPU-hotplug operations. */ - raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */ + get_online_cpus(); /* * Set the quiescent-state-needed bits in all the rcu_node @@ -1091,15 +1093,9 @@ static int rcu_gp_kthread(void *arg) * indicate that no grace period is in progress, at least * until the corresponding leaf node has been initialized. * In addition, we have excluded CPU-hotplug operations. - * - * Note that the grace period cannot complete until - * we finish the initialization process, as there will - * be at least one qsmask bit set in the root node until - * that time, namely the one corresponding to this CPU, - * due to the fact that we have irqs disabled. */ rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irq(&rnp->lock); rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; @@ -1110,17 +1106,17 @@ static int rcu_gp_kthread(void *arg) trace_rcu_grace_period_init(rsp->name, rnp->gpnum, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irq(&rnp->lock); + cond_resched(); } rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irq(&rnp->lock); /* force_quiescent_state() now OK. */ rsp->fqs_state = RCU_SIGNAL_INIT; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - raw_spin_unlock_irq(&rsp->onofflock); + raw_spin_unlock_irq(&rnp->lock); + put_online_cpus(); } - return 0; } /* From cabc49c1ff51baaf1958d501a7a616ce91245c93 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 20 Jun 2012 17:07:14 -0700 Subject: [PATCH 15/73] rcu: Move RCU grace-period cleanup into kthread As a first step towards allowing grace-period cleanup to be preemptible, this commit moves the RCU grace-period cleanup into the same kthread that is now used to initialize grace periods. This is needed to keep scheduling latency down to a dull roar. [ paulmck: Get rid of stray spin_lock_irqsave() calls. ] Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 112 ++++++++++++++++++++++++++--------------------- 1 file changed, 62 insertions(+), 50 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 781e5f0b7b17..52c3102dc5f7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1032,6 +1032,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat */ static int __noreturn rcu_gp_kthread(void *arg) { + unsigned long gp_duration; struct rcu_data *rdp; struct rcu_node *rnp; struct rcu_state *rsp = arg; @@ -1116,6 +1117,65 @@ static int __noreturn rcu_gp_kthread(void *arg) rsp->fqs_state = RCU_SIGNAL_INIT; raw_spin_unlock_irq(&rnp->lock); put_online_cpus(); + + /* Handle grace-period end. */ + rnp = rcu_get_root(rsp); + for (;;) { + wait_event_interruptible(rsp->gp_wq, + !ACCESS_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)); + if (!ACCESS_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)) + break; + flush_signals(current); + } + + raw_spin_lock_irq(&rnp->lock); + gp_duration = jiffies - rsp->gp_start; + if (gp_duration > rsp->gp_max) + rsp->gp_max = gp_duration; + + /* + * We know the grace period is complete, but to everyone else + * it appears to still be ongoing. But it is also the case + * that to everyone else it looks like there is nothing that + * they can do to advance the grace period. It is therefore + * safe for us to drop the lock in order to mark the grace + * period as completed in all of the rcu_node structures. + * + * But if this CPU needs another grace period, it will take + * care of this while initializing the next grace period. + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL + * because the callbacks have not yet been advanced: Those + * callbacks are waiting on the grace period that just now + * completed. + */ + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + + /* + * Propagate new ->completed value to rcu_node + * structures so that other CPUs don't have to + * wait until the start of the next grace period + * to process their callbacks. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + /* irqs already disabled. */ + raw_spin_lock(&rnp->lock); + rnp->completed = rsp->gpnum; + /* irqs remain disabled. */ + raw_spin_unlock(&rnp->lock); + } + rnp = rcu_get_root(rsp); + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + } + + rsp->completed = rsp->gpnum; /* Declare grace period done. */ + trace_rcu_grace_period(rsp->name, rsp->completed, "end"); + rsp->fqs_state = RCU_GP_IDLE; + if (cpu_needs_another_gp(rsp, rdp)) + rsp->gp_flags = 1; + raw_spin_unlock_irq(&rnp->lock); } } @@ -1162,57 +1222,9 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { - unsigned long gp_duration; - struct rcu_node *rnp = rcu_get_root(rsp); - struct rcu_data *rdp = this_cpu_ptr(rsp->rda); - WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); - - /* - * Ensure that all grace-period and pre-grace-period activity - * is seen before the assignment to rsp->completed. - */ - smp_mb(); /* See above block comment. */ - gp_duration = jiffies - rsp->gp_start; - if (gp_duration > rsp->gp_max) - rsp->gp_max = gp_duration; - - /* - * We know the grace period is complete, but to everyone else - * it appears to still be ongoing. But it is also the case - * that to everyone else it looks like there is nothing that - * they can do to advance the grace period. It is therefore - * safe for us to drop the lock in order to mark the grace - * period as completed in all of the rcu_node structures. - * - * But if this CPU needs another grace period, it will take - * care of this while initializing the next grace period. - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL - * because the callbacks have not yet been advanced: Those - * callbacks are waiting on the grace period that just now - * completed. - */ - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - - /* - * Propagate new ->completed value to rcu_node structures - * so that other CPUs don't have to wait until the start - * of the next grace period to process their callbacks. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - rnp->completed = rsp->gpnum; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - } - rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - } - - rsp->completed = rsp->gpnum; /* Declare the grace period complete. */ - trace_rcu_grace_period(rsp->name, rsp->completed, "end"); - rsp->fqs_state = RCU_GP_IDLE; - rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); + wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ } /* From c856bafae7f5b3f59ac1d99279a9b99b3b36ad12 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 21 Jun 2012 08:19:05 -0700 Subject: [PATCH 16/73] rcu: Allow RCU grace-period cleanup to be preempted RCU grace-period cleanup is currently carried out with interrupts disabled, which can result in excessive latency spikes on large systems (many hundreds or thousands of CPUs). This patch therefore makes the RCU grace-period cleanup be preemptible, including voluntary preemption points, which should eliminate those latency spikes. Similar spikes from forcing of quiescent states will be dealt with similarly by later patches. Updated to replace uses of spin_lock_irqsave() with spin_lock_irq(), as suggested by Peter Zijlstra. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 52c3102dc5f7..ddc6acc85d26 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1151,7 +1151,7 @@ static int __noreturn rcu_gp_kthread(void *arg) * completed. */ if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irq(&rnp->lock); /* * Propagate new ->completed value to rcu_node @@ -1160,14 +1160,13 @@ static int __noreturn rcu_gp_kthread(void *arg) * to process their callbacks. */ rcu_for_each_node_breadth_first(rsp, rnp) { - /* irqs already disabled. */ - raw_spin_lock(&rnp->lock); + raw_spin_lock_irq(&rnp->lock); rnp->completed = rsp->gpnum; - /* irqs remain disabled. */ - raw_spin_unlock(&rnp->lock); + raw_spin_unlock_irq(&rnp->lock); + cond_resched(); } rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irq(&rnp->lock); } rsp->completed = rsp->gpnum; /* Declare grace period done. */ From 7fdefc10e1d730d4608cc59d386bc446f5b9ee99 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 22 Jun 2012 11:08:41 -0700 Subject: [PATCH 17/73] rcu: Break up rcu_gp_kthread() into subfunctions Then rcu_gp_kthread() function is too large and furthermore needs to have the force_quiescent_state() code pulled in. This commit therefore breaks up rcu_gp_kthread() into rcu_gp_init() and rcu_gp_cleanup(). Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 264 +++++++++++++++++++++++++---------------------- 1 file changed, 142 insertions(+), 122 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index ddc6acc85d26..f0c0c1b4b6d4 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1027,96 +1027,160 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat __note_new_gpnum(rsp, rnp, rdp); } +/* + * Initialize a new grace period. + */ +static int rcu_gp_init(struct rcu_state *rsp) +{ + struct rcu_data *rdp; + struct rcu_node *rnp = rcu_get_root(rsp); + + raw_spin_lock_irq(&rnp->lock); + rsp->gp_flags = 0; + + if (rcu_gp_in_progress(rsp)) { + /* Grace period already in progress, don't start another. */ + raw_spin_unlock_irq(&rnp->lock); + return 0; + } + + if (rsp->fqs_active) { + /* + * We need a grace period, but force_quiescent_state() + * is running. Tell it to start one on our behalf. + */ + rsp->fqs_need_gp = 1; + raw_spin_unlock_irq(&rnp->lock); + return 0; + } + + /* Advance to a new grace period and initialize state. */ + rsp->gpnum++; + trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); + WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); + rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ + rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; + record_gp_stall_check_time(rsp); + raw_spin_unlock_irq(&rnp->lock); + + /* Exclude any concurrent CPU-hotplug operations. */ + get_online_cpus(); + + /* + * Set the quiescent-state-needed bits in all the rcu_node + * structures for all currently online CPUs in breadth-first order, + * starting from the root rcu_node structure, relying on the layout + * of the tree within the rsp->node[] array. Note that other CPUs + * will access only the leaves of the hierarchy, thus seeing that no + * grace period is in progress, at least until the corresponding + * leaf node has been initialized. In addition, we have excluded + * CPU-hotplug operations. + * + * The grace period cannot complete until the initialization + * process finishes, because this kthread handles both. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock_irq(&rnp->lock); + rdp = this_cpu_ptr(rsp->rda); + rcu_preempt_check_blocked_tasks(rnp); + rnp->qsmask = rnp->qsmaskinit; + rnp->gpnum = rsp->gpnum; + rnp->completed = rsp->completed; + if (rnp == rdp->mynode) + rcu_start_gp_per_cpu(rsp, rnp, rdp); + rcu_preempt_boost_start_gp(rnp); + trace_rcu_grace_period_init(rsp->name, rnp->gpnum, + rnp->level, rnp->grplo, + rnp->grphi, rnp->qsmask); + raw_spin_unlock_irq(&rnp->lock); + cond_resched(); + } + + rnp = rcu_get_root(rsp); + raw_spin_lock_irq(&rnp->lock); + /* force_quiescent_state() now OK. */ + rsp->fqs_state = RCU_SIGNAL_INIT; + raw_spin_unlock_irq(&rnp->lock); + put_online_cpus(); + return 1; +} + +/* + * Clean up after the old grace period. + */ +static int rcu_gp_cleanup(struct rcu_state *rsp) +{ + unsigned long gp_duration; + struct rcu_data *rdp; + struct rcu_node *rnp = rcu_get_root(rsp); + + raw_spin_lock_irq(&rnp->lock); + gp_duration = jiffies - rsp->gp_start; + if (gp_duration > rsp->gp_max) + rsp->gp_max = gp_duration; + + /* + * We know the grace period is complete, but to everyone else + * it appears to still be ongoing. But it is also the case + * that to everyone else it looks like there is nothing that + * they can do to advance the grace period. It is therefore + * safe for us to drop the lock in order to mark the grace + * period as completed in all of the rcu_node structures. + * + * But if this CPU needs another grace period, it will take + * care of this while initializing the next grace period. + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL + * because the callbacks have not yet been advanced: Those + * callbacks are waiting on the grace period that just now + * completed. + */ + rdp = this_cpu_ptr(rsp->rda); + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { + raw_spin_unlock_irq(&rnp->lock); + + /* + * Propagate new ->completed value to rcu_node + * structures so that other CPUs don't have to + * wait until the start of the next grace period + * to process their callbacks. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + raw_spin_lock_irq(&rnp->lock); + rnp->completed = rsp->gpnum; + raw_spin_unlock_irq(&rnp->lock); + cond_resched(); + } + rnp = rcu_get_root(rsp); + raw_spin_lock_irq(&rnp->lock); + } + + rsp->completed = rsp->gpnum; /* Declare grace period done. */ + trace_rcu_grace_period(rsp->name, rsp->completed, "end"); + rsp->fqs_state = RCU_GP_IDLE; + if (cpu_needs_another_gp(rsp, rdp)) + rsp->gp_flags = 1; + raw_spin_unlock_irq(&rnp->lock); + return 1; +} + /* * Body of kthread that handles grace periods. */ static int __noreturn rcu_gp_kthread(void *arg) { - unsigned long gp_duration; - struct rcu_data *rdp; - struct rcu_node *rnp; struct rcu_state *rsp = arg; + struct rcu_node *rnp = rcu_get_root(rsp); for (;;) { /* Handle grace-period start. */ - rnp = rcu_get_root(rsp); for (;;) { wait_event_interruptible(rsp->gp_wq, rsp->gp_flags); - if (rsp->gp_flags) + if (rsp->gp_flags && rcu_gp_init(rsp)) break; + cond_resched(); flush_signals(current); } - raw_spin_lock_irq(&rnp->lock); - rsp->gp_flags = 0; - rdp = this_cpu_ptr(rsp->rda); - - if (rcu_gp_in_progress(rsp)) { - /* - * A grace period is already in progress, so - * don't start another one. - */ - raw_spin_unlock_irq(&rnp->lock); - cond_resched(); - continue; - } - - if (rsp->fqs_active) { - /* - * We need a grace period, but force_quiescent_state() - * is running. Tell it to start one on our behalf. - */ - rsp->fqs_need_gp = 1; - raw_spin_unlock_irq(&rnp->lock); - cond_resched(); - continue; - } - - /* Advance to a new grace period and initialize state. */ - rsp->gpnum++; - trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); - WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); - rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ - rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; - record_gp_stall_check_time(rsp); - raw_spin_unlock_irq(&rnp->lock); - - /* Exclude any concurrent CPU-hotplug operations. */ - get_online_cpus(); - - /* - * Set the quiescent-state-needed bits in all the rcu_node - * structures for all currently online CPUs in breadth-first - * order, starting from the root rcu_node structure. - * This operation relies on the layout of the hierarchy - * within the rsp->node[] array. Note that other CPUs will - * access only the leaves of the hierarchy, which still - * indicate that no grace period is in progress, at least - * until the corresponding leaf node has been initialized. - * In addition, we have excluded CPU-hotplug operations. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock_irq(&rnp->lock); - rcu_preempt_check_blocked_tasks(rnp); - rnp->qsmask = rnp->qsmaskinit; - rnp->gpnum = rsp->gpnum; - rnp->completed = rsp->completed; - if (rnp == rdp->mynode) - rcu_start_gp_per_cpu(rsp, rnp, rdp); - rcu_preempt_boost_start_gp(rnp); - trace_rcu_grace_period_init(rsp->name, rnp->gpnum, - rnp->level, rnp->grplo, - rnp->grphi, rnp->qsmask); - raw_spin_unlock_irq(&rnp->lock); - cond_resched(); - } - - rnp = rcu_get_root(rsp); - raw_spin_lock_irq(&rnp->lock); - /* force_quiescent_state() now OK. */ - rsp->fqs_state = RCU_SIGNAL_INIT; - raw_spin_unlock_irq(&rnp->lock); - put_online_cpus(); /* Handle grace-period end. */ rnp = rcu_get_root(rsp); @@ -1125,56 +1189,12 @@ static int __noreturn rcu_gp_kthread(void *arg) !ACCESS_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)); if (!ACCESS_ONCE(rnp->qsmask) && - !rcu_preempt_blocked_readers_cgp(rnp)) + !rcu_preempt_blocked_readers_cgp(rnp) && + rcu_gp_cleanup(rsp)) break; + cond_resched(); flush_signals(current); } - - raw_spin_lock_irq(&rnp->lock); - gp_duration = jiffies - rsp->gp_start; - if (gp_duration > rsp->gp_max) - rsp->gp_max = gp_duration; - - /* - * We know the grace period is complete, but to everyone else - * it appears to still be ongoing. But it is also the case - * that to everyone else it looks like there is nothing that - * they can do to advance the grace period. It is therefore - * safe for us to drop the lock in order to mark the grace - * period as completed in all of the rcu_node structures. - * - * But if this CPU needs another grace period, it will take - * care of this while initializing the next grace period. - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL - * because the callbacks have not yet been advanced: Those - * callbacks are waiting on the grace period that just now - * completed. - */ - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { - raw_spin_unlock_irq(&rnp->lock); - - /* - * Propagate new ->completed value to rcu_node - * structures so that other CPUs don't have to - * wait until the start of the next grace period - * to process their callbacks. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock_irq(&rnp->lock); - rnp->completed = rsp->gpnum; - raw_spin_unlock_irq(&rnp->lock); - cond_resched(); - } - rnp = rcu_get_root(rsp); - raw_spin_lock_irq(&rnp->lock); - } - - rsp->completed = rsp->gpnum; /* Declare grace period done. */ - trace_rcu_grace_period(rsp->name, rsp->completed, "end"); - rsp->fqs_state = RCU_GP_IDLE; - if (cpu_needs_another_gp(rsp, rdp)) - rsp->gp_flags = 1; - raw_spin_unlock_irq(&rnp->lock); } } From bfa00b4c4028f39357d16279ff0fddf550241593 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 21 Jun 2012 09:54:10 -0700 Subject: [PATCH 18/73] rcu: Prevent offline CPUs from executing RCU core code Earlier versions of RCU invoked the RCU core from the CPU_DYING notifier in order to note a quiescent state for the outgoing CPU. Because the CPU is marked "offline" during the execution of the CPU_DYING notifiers, the RCU core had to tolerate being invoked from an offline CPU. However, commit b1420f1c (Make rcu_barrier() less disruptive) left only tracing code in the CPU_DYING notifier, so the RCU core need no longer execute on offline CPUs. This commit therefore enforces this restriction. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f0c0c1b4b6d4..340a5f54b6af 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1892,6 +1892,8 @@ static void rcu_process_callbacks(struct softirq_action *unused) { struct rcu_state *rsp; + if (cpu_is_offline(smp_processor_id())) + return; trace_rcu_utilization("Start RCU core"); for_each_rcu_flavor(rsp) __rcu_process_callbacks(rsp); From b626c1b689364859ccd2e86d5e043aeadfeb2cd4 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 11 Jun 2012 17:39:43 -0700 Subject: [PATCH 19/73] rcu: Provide OOM handler to motivate lazy RCU callbacks In kernels built with CONFIG_RCU_FAST_NO_HZ=y, CPUs can accumulate a large number of lazy callbacks, which as the name implies will be slow to be invoked. This can be a problem on small-memory systems, where the default 6-second sleep for CPUs having only lazy RCU callbacks could well be fatal. This commit therefore installs an OOM hander that ensures that every CPU with lazy callbacks has at least one non-lazy callback, in turn ensuring timely advancement for these callbacks. Updated to fix bug that disabled OOM killing, noted by Lai Jiangshan. Updated to push the for_each_rcu_flavor() loop into rcu_oom_notify_cpu(), thus reducing the number of IPIs, as suggested by Steven Rostedt. Also to make the for_each_online_cpu() loop be preemptible. (Later, it might be good to use smp_call_function(), as suggested by Peter Zijlstra.) Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Sasha Levin Reviewed-by: Josh Triplett --- kernel/rcutree.h | 5 ++- kernel/rcutree_plugin.h | 83 +++++++++++++++++++++++++++++++++++++++++ 2 files changed, 87 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 117a15019e99..effb2733b7fc 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -315,8 +315,11 @@ struct rcu_data { unsigned long n_rp_need_fqs; unsigned long n_rp_need_nothing; - /* 6) _rcu_barrier() callback. */ + /* 6) _rcu_barrier() and OOM callbacks. */ struct rcu_head barrier_head; +#ifdef CONFIG_RCU_FAST_NO_HZ + struct rcu_head oom_head; +#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ int cpu; struct rcu_state *rsp; diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7f3244c0df01..587963689328 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -25,6 +25,7 @@ */ #include +#include #define RCU_KTHREAD_PRIO 1 @@ -2112,6 +2113,88 @@ static void rcu_idle_count_callbacks_posted(void) __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); } +/* + * Data for flushing lazy RCU callbacks at OOM time. + */ +static atomic_t oom_callback_count; +static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); + +/* + * RCU OOM callback -- decrement the outstanding count and deliver the + * wake-up if we are the last one. + */ +static void rcu_oom_callback(struct rcu_head *rhp) +{ + if (atomic_dec_and_test(&oom_callback_count)) + wake_up(&oom_callback_wq); +} + +/* + * Post an rcu_oom_notify callback on the current CPU if it has at + * least one lazy callback. This will unnecessarily post callbacks + * to CPUs that already have a non-lazy callback at the end of their + * callback list, but this is an infrequent operation, so accept some + * extra overhead to keep things simple. + */ +static void rcu_oom_notify_cpu(void *unused) +{ + struct rcu_state *rsp; + struct rcu_data *rdp; + + for_each_rcu_flavor(rsp) { + rdp = __this_cpu_ptr(rsp->rda); + if (rdp->qlen_lazy != 0) { + atomic_inc(&oom_callback_count); + rsp->call(&rdp->oom_head, rcu_oom_callback); + } + } +} + +/* + * If low on memory, ensure that each CPU has a non-lazy callback. + * This will wake up CPUs that have only lazy callbacks, in turn + * ensuring that they free up the corresponding memory in a timely manner. + * Because an uncertain amount of memory will be freed in some uncertain + * timeframe, we do not claim to have freed anything. + */ +static int rcu_oom_notify(struct notifier_block *self, + unsigned long notused, void *nfreed) +{ + int cpu; + + /* Wait for callbacks from earlier instance to complete. */ + wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); + + /* + * Prevent premature wakeup: ensure that all increments happen + * before there is a chance of the counter reaching zero. + */ + atomic_set(&oom_callback_count, 1); + + get_online_cpus(); + for_each_online_cpu(cpu) { + smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); + cond_resched(); + } + put_online_cpus(); + + /* Unconditionally decrement: no need to wake ourselves up. */ + atomic_dec(&oom_callback_count); + + return NOTIFY_OK; +} + +static struct notifier_block rcu_oom_nb = { + .notifier_call = rcu_oom_notify +}; + +static int __init rcu_register_oom_notifier(void) +{ + register_oom_notifier(&rcu_oom_nb); + return 0; +} +early_initcall(rcu_register_oom_notifier); + #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ #ifdef CONFIG_RCU_CPU_STALL_INFO From b402b73b3afe3614bc0e921ebe18013ea103115a Mon Sep 17 00:00:00 2001 From: Dimitri Sivanich Date: Fri, 29 Jun 2012 14:17:29 -0700 Subject: [PATCH 20/73] rcu: Segregate rcu_state fields to improve cache locality The fields in the rcu_state structure that are protected by the root rcu_node structure's ->lock can share a cache line with the fields protected by ->onofflock. This can result in excessive memory contention on large systems, so this commit applies ____cacheline_internodealigned_in_smp to the ->onofflock field in order to segregate them. Signed-off-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Tested-by: Dimitri Sivanich Reviewed-by: Josh Triplett --- kernel/rcutree.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.h b/kernel/rcutree.h index effb2733b7fc..5d92b80a0a28 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -394,7 +394,8 @@ struct rcu_state { /* End of fields guarded by root rcu_node's lock. */ - raw_spinlock_t onofflock; /* exclude on/offline and */ + raw_spinlock_t onofflock ____cacheline_internodealigned_in_smp; + /* exclude on/offline and */ /* starting new GP. */ struct rcu_head *orphan_nxtlist; /* Orphaned callbacks that */ /* need a grace period. */ From 4cdfc175c25c89eedc08460b5e6239c2ec67fcb6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 22 Jun 2012 17:06:26 -0700 Subject: [PATCH 21/73] rcu: Move quiescent-state forcing into kthread As the first step towards allowing quiescent-state forcing to be preemptible, this commit moves RCU quiescent-state forcing into the same kthread that is now used to initialize and clean up after grace periods. This is yet another step towards keeping scheduling latency down to a dull roar. Updated to change from raw_spin_lock_irqsave() to raw_spin_lock_irq() and to remove the now-unused rcu_state structure fields as suggested by Peter Zijlstra. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 199 +++++++++++++++------------------------- kernel/rcutree.h | 13 +-- kernel/rcutree_plugin.h | 8 +- 3 files changed, 82 insertions(+), 138 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 340a5f54b6af..6182686de4a6 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -72,7 +72,6 @@ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; .orphan_nxttail = &sname##_state.orphan_nxtlist, \ .orphan_donetail = &sname##_state.orphan_donelist, \ .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ - .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \ .name = #sname, \ } @@ -226,7 +225,8 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_suppress, int, 0644); module_param(rcu_cpu_stall_timeout, int, 0644); -static void force_quiescent_state(struct rcu_state *rsp, int relaxed); +static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); +static void force_quiescent_state(struct rcu_state *rsp); static int rcu_pending(int cpu); /* @@ -252,7 +252,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); */ void rcu_bh_force_quiescent_state(void) { - force_quiescent_state(&rcu_bh_state, 0); + force_quiescent_state(&rcu_bh_state); } EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); @@ -286,7 +286,7 @@ EXPORT_SYMBOL_GPL(rcutorture_record_progress); */ void rcu_sched_force_quiescent_state(void) { - force_quiescent_state(&rcu_sched_state, 0); + force_quiescent_state(&rcu_sched_state); } EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); @@ -784,11 +784,11 @@ static void print_other_cpu_stall(struct rcu_state *rsp) else if (!trigger_all_cpu_backtrace()) dump_stack(); - /* If so configured, complain about tasks blocking the grace period. */ + /* Complain about tasks blocking the grace period. */ rcu_print_detail_task_stall(rsp); - force_quiescent_state(rsp, 0); /* Kick them all. */ + force_quiescent_state(rsp); /* Kick them all. */ } static void print_cpu_stall(struct rcu_state *rsp) @@ -1036,7 +1036,7 @@ static int rcu_gp_init(struct rcu_state *rsp) struct rcu_node *rnp = rcu_get_root(rsp); raw_spin_lock_irq(&rnp->lock); - rsp->gp_flags = 0; + rsp->gp_flags = 0; /* Clear all flags: New grace period. */ if (rcu_gp_in_progress(rsp)) { /* Grace period already in progress, don't start another. */ @@ -1044,22 +1044,9 @@ static int rcu_gp_init(struct rcu_state *rsp) return 0; } - if (rsp->fqs_active) { - /* - * We need a grace period, but force_quiescent_state() - * is running. Tell it to start one on our behalf. - */ - rsp->fqs_need_gp = 1; - raw_spin_unlock_irq(&rnp->lock); - return 0; - } - /* Advance to a new grace period and initialize state. */ rsp->gpnum++; trace_rcu_grace_period(rsp->name, rsp->gpnum, "start"); - WARN_ON_ONCE(rsp->fqs_state == RCU_GP_INIT); - rsp->fqs_state = RCU_GP_INIT; /* Stop force_quiescent_state. */ - rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; record_gp_stall_check_time(rsp); raw_spin_unlock_irq(&rnp->lock); @@ -1096,19 +1083,40 @@ static int rcu_gp_init(struct rcu_state *rsp) cond_resched(); } - rnp = rcu_get_root(rsp); - raw_spin_lock_irq(&rnp->lock); - /* force_quiescent_state() now OK. */ - rsp->fqs_state = RCU_SIGNAL_INIT; - raw_spin_unlock_irq(&rnp->lock); put_online_cpus(); return 1; } +/* + * Do one round of quiescent-state forcing. + */ +int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in) +{ + int fqs_state = fqs_state_in; + struct rcu_node *rnp = rcu_get_root(rsp); + + rsp->n_force_qs++; + if (fqs_state == RCU_SAVE_DYNTICK) { + /* Collect dyntick-idle snapshots. */ + force_qs_rnp(rsp, dyntick_save_progress_counter); + fqs_state = RCU_FORCE_QS; + } else { + /* Handle dyntick-idle and offline CPUs. */ + force_qs_rnp(rsp, rcu_implicit_dynticks_qs); + } + /* Clear flag to prevent immediate re-entry. */ + if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { + raw_spin_lock_irq(&rnp->lock); + rsp->gp_flags &= ~RCU_GP_FLAG_FQS; + raw_spin_unlock_irq(&rnp->lock); + } + return fqs_state; +} + /* * Clean up after the old grace period. */ -static int rcu_gp_cleanup(struct rcu_state *rsp) +static void rcu_gp_cleanup(struct rcu_state *rsp) { unsigned long gp_duration; struct rcu_data *rdp; @@ -1160,7 +1168,6 @@ static int rcu_gp_cleanup(struct rcu_state *rsp) if (cpu_needs_another_gp(rsp, rdp)) rsp->gp_flags = 1; raw_spin_unlock_irq(&rnp->lock); - return 1; } /* @@ -1168,6 +1175,8 @@ static int rcu_gp_cleanup(struct rcu_state *rsp) */ static int __noreturn rcu_gp_kthread(void *arg) { + int fqs_state; + int ret; struct rcu_state *rsp = arg; struct rcu_node *rnp = rcu_get_root(rsp); @@ -1175,26 +1184,43 @@ static int __noreturn rcu_gp_kthread(void *arg) /* Handle grace-period start. */ for (;;) { - wait_event_interruptible(rsp->gp_wq, rsp->gp_flags); - if (rsp->gp_flags && rcu_gp_init(rsp)) + wait_event_interruptible(rsp->gp_wq, + rsp->gp_flags & + RCU_GP_FLAG_INIT); + if ((rsp->gp_flags & RCU_GP_FLAG_INIT) && + rcu_gp_init(rsp)) break; cond_resched(); flush_signals(current); } - /* Handle grace-period end. */ - rnp = rcu_get_root(rsp); + /* Handle quiescent-state forcing. */ + fqs_state = RCU_SAVE_DYNTICK; for (;;) { - wait_event_interruptible(rsp->gp_wq, - !ACCESS_ONCE(rnp->qsmask) && - !rcu_preempt_blocked_readers_cgp(rnp)); + rsp->jiffies_force_qs = jiffies + + RCU_JIFFIES_TILL_FORCE_QS; + ret = wait_event_interruptible_timeout(rsp->gp_wq, + (rsp->gp_flags & RCU_GP_FLAG_FQS) || + (!ACCESS_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)), + RCU_JIFFIES_TILL_FORCE_QS); + /* If grace period done, leave loop. */ if (!ACCESS_ONCE(rnp->qsmask) && - !rcu_preempt_blocked_readers_cgp(rnp) && - rcu_gp_cleanup(rsp)) + !rcu_preempt_blocked_readers_cgp(rnp)) break; - cond_resched(); - flush_signals(current); + /* If time for quiescent-state forcing, do it. */ + if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) { + fqs_state = rcu_gp_fqs(rsp, fqs_state); + cond_resched(); + } else { + /* Deal with stray signal. */ + cond_resched(); + flush_signals(current); + } } + + /* Handle grace-period end. */ + rcu_gp_cleanup(rsp); } } @@ -1226,7 +1252,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) return; } - rsp->gp_flags = 1; + rsp->gp_flags = RCU_GP_FLAG_INIT; raw_spin_unlock_irqrestore(&rnp->lock, flags); wake_up(&rsp->gp_wq); } @@ -1777,72 +1803,20 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) * Force quiescent states on reluctant CPUs, and also detect which * CPUs are in dyntick-idle mode. */ -static void force_quiescent_state(struct rcu_state *rsp, int relaxed) +static void force_quiescent_state(struct rcu_state *rsp) { unsigned long flags; struct rcu_node *rnp = rcu_get_root(rsp); - trace_rcu_utilization("Start fqs"); - if (!rcu_gp_in_progress(rsp)) { - trace_rcu_utilization("End fqs"); - return; /* No grace period in progress, nothing to force. */ - } - if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) { + if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) + return; /* Someone beat us to it. */ + if (!raw_spin_trylock_irqsave(&rnp->lock, flags)) { rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */ - trace_rcu_utilization("End fqs"); - return; /* Someone else is already on the job. */ - } - if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies)) - goto unlock_fqs_ret; /* no emergency and done recently. */ - rsp->n_force_qs++; - raw_spin_lock(&rnp->lock); /* irqs already disabled */ - rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS; - if(!rcu_gp_in_progress(rsp)) { - rsp->n_force_qs_ngp++; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ - goto unlock_fqs_ret; /* no GP in progress, time updated. */ - } - rsp->fqs_active = 1; - switch (rsp->fqs_state) { - case RCU_GP_IDLE: - case RCU_GP_INIT: - - break; /* grace period idle or initializing, ignore. */ - - case RCU_SAVE_DYNTICK: - - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ - - /* Record dyntick-idle state. */ - force_qs_rnp(rsp, dyntick_save_progress_counter); - raw_spin_lock(&rnp->lock); /* irqs already disabled */ - if (rcu_gp_in_progress(rsp)) - rsp->fqs_state = RCU_FORCE_QS; - break; - - case RCU_FORCE_QS: - - /* Check dyntick-idle state, send IPI to laggarts. */ - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ - force_qs_rnp(rsp, rcu_implicit_dynticks_qs); - - /* Leave state in case more forcing is required. */ - - raw_spin_lock(&rnp->lock); /* irqs already disabled */ - break; - } - rsp->fqs_active = 0; - if (rsp->fqs_need_gp) { - raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */ - rsp->fqs_need_gp = 0; - rcu_start_gp(rsp, flags); /* releases rnp->lock */ - trace_rcu_utilization("End fqs"); return; } - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ -unlock_fqs_ret: - raw_spin_unlock_irqrestore(&rsp->fqslock, flags); - trace_rcu_utilization("End fqs"); + rsp->gp_flags |= RCU_GP_FLAG_FQS; + raw_spin_unlock_irqrestore(&rnp->lock, flags); + wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ } /* @@ -1858,13 +1832,6 @@ __rcu_process_callbacks(struct rcu_state *rsp) WARN_ON_ONCE(rdp->beenonline == 0); - /* - * If an RCU GP has gone long enough, go check for dyntick - * idle CPUs and, if needed, send resched IPIs. - */ - if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) - force_quiescent_state(rsp, 1); - /* * Advance callbacks in response to end of earlier grace * period that some other CPU ended. @@ -1965,12 +1932,11 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, rdp->blimit = LONG_MAX; if (rsp->n_force_qs == rdp->n_force_qs_snap && *rdp->nxttail[RCU_DONE_TAIL] != head) - force_quiescent_state(rsp, 0); + force_quiescent_state(rsp); rdp->n_force_qs_snap = rsp->n_force_qs; rdp->qlen_last_fqs_check = rdp->qlen; } - } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) - force_quiescent_state(rsp, 1); + } } static void @@ -2251,17 +2217,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) /* Is the RCU core waiting for a quiescent state from this CPU? */ if (rcu_scheduler_fully_active && rdp->qs_pending && !rdp->passed_quiesce) { - - /* - * If force_quiescent_state() coming soon and this CPU - * needs a quiescent state, and this is either RCU-sched - * or RCU-bh, force a local reschedule. - */ rdp->n_rp_qs_pending++; - if (!rdp->preemptible && - ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1, - jiffies)) - set_need_resched(); } else if (rdp->qs_pending && rdp->passed_quiesce) { rdp->n_rp_report_qs++; return 1; @@ -2291,13 +2247,6 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) return 1; } - /* Has an RCU GP gone long enough to send resched IPIs &c? */ - if (rcu_gp_in_progress(rsp) && - ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) { - rdp->n_rp_need_fqs++; - return 1; - } - /* nothing to do */ rdp->n_rp_need_nothing++; return 0; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 5d92b80a0a28..2d04106d1533 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -378,13 +378,6 @@ struct rcu_state { u8 fqs_state ____cacheline_internodealigned_in_smp; /* Force QS state. */ - u8 fqs_active; /* force_quiescent_state() */ - /* is running. */ - u8 fqs_need_gp; /* A CPU was prevented from */ - /* starting a new grace */ - /* period because */ - /* force_quiescent_state() */ - /* was running. */ u8 boost; /* Subject to priority boost. */ unsigned long gpnum; /* Current gp number. */ unsigned long completed; /* # of last completed gp. */ @@ -413,8 +406,6 @@ struct rcu_state { struct completion barrier_completion; /* Wake at barrier end. */ unsigned long n_barrier_done; /* ++ at start and end of */ /* _rcu_barrier(). */ - raw_spinlock_t fqslock; /* Only one task forcing */ - /* quiescent states. */ unsigned long jiffies_force_qs; /* Time at which to invoke */ /* force_quiescent_state(). */ unsigned long n_force_qs; /* Number of calls to */ @@ -433,6 +424,10 @@ struct rcu_state { struct list_head flavors; /* List of RCU flavors. */ }; +/* Values for rcu_state structure's gp_flags field. */ +#define RCU_GP_FLAG_INIT 0x1 /* Need grace-period initialization. */ +#define RCU_GP_FLAG_FQS 0x2 /* Need grace-period quiescent-state forcing. */ + extern struct list_head rcu_struct_flavors; #define for_each_rcu_flavor(rsp) \ list_for_each_entry((rsp), &rcu_struct_flavors, flavors) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 587963689328..eb8dcd1bc4b5 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -119,7 +119,7 @@ EXPORT_SYMBOL_GPL(rcu_batches_completed); */ void rcu_force_quiescent_state(void) { - force_quiescent_state(&rcu_preempt_state, 0); + force_quiescent_state(&rcu_preempt_state); } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); @@ -2076,16 +2076,16 @@ static void rcu_prepare_for_idle(int cpu) #ifdef CONFIG_TREE_PREEMPT_RCU if (per_cpu(rcu_preempt_data, cpu).nxtlist) { rcu_preempt_qs(cpu); - force_quiescent_state(&rcu_preempt_state, 0); + force_quiescent_state(&rcu_preempt_state); } #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ if (per_cpu(rcu_sched_data, cpu).nxtlist) { rcu_sched_qs(cpu); - force_quiescent_state(&rcu_sched_state, 0); + force_quiescent_state(&rcu_sched_state); } if (per_cpu(rcu_bh_data, cpu).nxtlist) { rcu_bh_qs(cpu); - force_quiescent_state(&rcu_bh_state, 0); + force_quiescent_state(&rcu_bh_state); } /* From b4be093fee0200789df59b6c90e2d099a20f55b3 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 25 Jun 2012 08:41:11 -0700 Subject: [PATCH 22/73] rcu: Allow RCU quiescent-state forcing to be preempted RCU quiescent-state forcing is currently carried out without preemption points, which can result in excessive latency spikes on large systems (many hundreds or thousands of CPUs). This patch therefore inserts a voluntary preemption point into force_qs_rnp(), which should greatly reduce the magnitude of these spikes. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6182686de4a6..723e2e723074 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1767,6 +1767,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) struct rcu_node *rnp; rcu_for_each_leaf_node(rsp, rnp) { + cond_resched(); mask = 0; raw_spin_lock_irqsave(&rnp->lock, flags); if (!rcu_gp_in_progress(rsp)) { From 4605c0143c6d611b3076025ba3a7e04293c01d69 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 26 Jun 2012 14:00:48 -0700 Subject: [PATCH 23/73] rcu: Adjust debugfs tracing for kthread-based quiescent-state forcing Moving quiescent-state forcing into a kthread dispenses with the need for the ->n_rp_need_fqs field, so this commit removes it. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/RCU/trace.txt | 43 ++++++++++++++----------------------- kernel/rcutree.h | 1 - kernel/rcutree_trace.c | 3 +-- 3 files changed, 17 insertions(+), 30 deletions(-) diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt index f6f15ce39903..672d19083252 100644 --- a/Documentation/RCU/trace.txt +++ b/Documentation/RCU/trace.txt @@ -333,23 +333,23 @@ o Each element of the form "1/1 0:127 ^0" represents one struct The output of "cat rcu/rcu_pending" looks as follows: rcu_sched: - 0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nf=6445 nn=146741 - 1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nf=5912 nn=155792 - 2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nf=1201 nn=136629 - 3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nf=207 nn=137723 - 4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nf=3529 nn=123110 - 5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nf=201 nn=137456 - 6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nf=4202 nn=120834 - 7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nf=41 nn=144888 + 0 np=255892 qsp=53936 rpq=85 cbr=0 cng=14417 gpc=10033 gps=24320 nn=146741 + 1 np=261224 qsp=54638 rpq=33 cbr=0 cng=25723 gpc=16310 gps=2849 nn=155792 + 2 np=237496 qsp=49664 rpq=23 cbr=0 cng=2762 gpc=45478 gps=1762 nn=136629 + 3 np=236249 qsp=48766 rpq=98 cbr=0 cng=286 gpc=48049 gps=1218 nn=137723 + 4 np=221310 qsp=46850 rpq=7 cbr=0 cng=26 gpc=43161 gps=4634 nn=123110 + 5 np=237332 qsp=48449 rpq=9 cbr=0 cng=54 gpc=47920 gps=3252 nn=137456 + 6 np=219995 qsp=46718 rpq=12 cbr=0 cng=50 gpc=42098 gps=6093 nn=120834 + 7 np=249893 qsp=49390 rpq=42 cbr=0 cng=72 gpc=38400 gps=17102 nn=144888 rcu_bh: - 0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nf=2 nn=145314 - 1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nf=3 nn=143180 - 2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nf=0 nn=117936 - 3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nf=0 nn=134863 - 4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nf=0 nn=110671 - 5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nf=0 nn=133235 - 6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nf=2 nn=110921 - 7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nf=0 nn=118542 + 0 np=146741 qsp=1419 rpq=6 cbr=0 cng=6 gpc=0 gps=0 nn=145314 + 1 np=155792 qsp=12597 rpq=3 cbr=0 cng=0 gpc=4 gps=8 nn=143180 + 2 np=136629 qsp=18680 rpq=1 cbr=0 cng=0 gpc=7 gps=6 nn=117936 + 3 np=137723 qsp=2843 rpq=0 cbr=0 cng=0 gpc=10 gps=7 nn=134863 + 4 np=123110 qsp=12433 rpq=0 cbr=0 cng=0 gpc=4 gps=2 nn=110671 + 5 np=137456 qsp=4210 rpq=1 cbr=0 cng=0 gpc=6 gps=5 nn=133235 + 6 np=120834 qsp=9902 rpq=2 cbr=0 cng=0 gpc=6 gps=3 nn=110921 + 7 np=144888 qsp=26336 rpq=0 cbr=0 cng=0 gpc=8 gps=2 nn=118542 As always, this is once again split into "rcu_sched" and "rcu_bh" portions, with CONFIG_TREE_PREEMPT_RCU kernels having an additional @@ -377,17 +377,6 @@ o "gpc" is the number of times that an old grace period had o "gps" is the number of times that a new grace period had started, but this CPU was not yet aware of it. -o "nf" is the number of times that this CPU suspected that the - current grace period had run for too long, and thus needed to - be forced. - - Please note that "forcing" consists of sending resched IPIs - to holdout CPUs. If that CPU really still is in an old RCU - read-side critical section, then we really do have to wait for it. - The assumption behing "forcing" is that the CPU is not still in - an old RCU read-side critical section, but has not yet responded - for some other reason. - o "nn" is the number of times that this CPU needed nothing. Alert readers will note that the rcu "nn" number for a given CPU very closely matches the rcu_bh "np" number for that same CPU. This diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 2d04106d1533..7fb93cedc76a 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -312,7 +312,6 @@ struct rcu_data { unsigned long n_rp_cpu_needs_gp; unsigned long n_rp_gp_completed; unsigned long n_rp_gp_started; - unsigned long n_rp_need_fqs; unsigned long n_rp_need_nothing; /* 6) _rcu_barrier() and OOM callbacks. */ diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index abffb486e94e..f54f0ceda0cf 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -386,10 +386,9 @@ static void print_one_rcu_pending(struct seq_file *m, struct rcu_data *rdp) rdp->n_rp_report_qs, rdp->n_rp_cb_ready, rdp->n_rp_cpu_needs_gp); - seq_printf(m, "gpc=%ld gps=%ld nf=%ld nn=%ld\n", + seq_printf(m, "gpc=%ld gps=%ld nn=%ld\n", rdp->n_rp_gp_completed, rdp->n_rp_gp_started, - rdp->n_rp_need_fqs, rdp->n_rp_need_nothing); } From 394f2769aa0dbcf027bae6fb52835e25e05d332e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 26 Jun 2012 17:00:35 -0700 Subject: [PATCH 24/73] rcu: Prevent force_quiescent_state() memory contention Large systems running RCU_FAST_NO_HZ kernels see extreme memory contention on the rcu_state structure's ->fqslock field. This can be avoided by disabling RCU_FAST_NO_HZ, either at compile time or at boot time (via the nohz kernel boot parameter), but large systems will no doubt become sensitive to energy consumption. This commit therefore uses a combining-tree approach to spread the memory contention across new cache lines in the leaf rcu_node structures. This can be thought of as a tournament lock that has only a try-lock acquisition primitive. The effect on small systems is minimal, because such systems have an rcu_node "tree" consisting of a single node. In addition, this functionality is not used on fastpaths. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 47 +++++++++++++++++++++++++++++++++++++---------- kernel/rcutree.h | 1 + 2 files changed, 38 insertions(+), 10 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 723e2e723074..43d57a17fcc5 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -61,6 +61,7 @@ /* Data structures. */ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; +static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; #define RCU_STATE_INITIALIZER(sname, cr) { \ .level = { &sname##_state.node[0] }, \ @@ -1807,16 +1808,35 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)) static void force_quiescent_state(struct rcu_state *rsp) { unsigned long flags; - struct rcu_node *rnp = rcu_get_root(rsp); + bool ret; + struct rcu_node *rnp; + struct rcu_node *rnp_old = NULL; - if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) + /* Funnel through hierarchy to reduce memory contention. */ + rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode; + for (; rnp != NULL; rnp = rnp->parent) { + ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) || + !raw_spin_trylock(&rnp->fqslock); + if (rnp_old != NULL) + raw_spin_unlock(&rnp_old->fqslock); + if (ret) { + rsp->n_force_qs_lh++; + return; + } + rnp_old = rnp; + } + /* rnp_old == rcu_get_root(rsp), rnp == NULL. */ + + /* Reached the root of the rcu_node tree, acquire lock. */ + raw_spin_lock_irqsave(&rnp_old->lock, flags); + raw_spin_unlock(&rnp_old->fqslock); + if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { + rsp->n_force_qs_lh++; + raw_spin_unlock_irqrestore(&rnp_old->lock, flags); return; /* Someone beat us to it. */ - if (!raw_spin_trylock_irqsave(&rnp->lock, flags)) { - rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */ - return; } rsp->gp_flags |= RCU_GP_FLAG_FQS; - raw_spin_unlock_irqrestore(&rnp->lock, flags); + raw_spin_unlock_irqrestore(&rnp_old->lock, flags); wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ } @@ -2704,10 +2724,14 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) static void __init rcu_init_one(struct rcu_state *rsp, struct rcu_data __percpu *rda) { - static char *buf[] = { "rcu_node_level_0", - "rcu_node_level_1", - "rcu_node_level_2", - "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */ + static char *buf[] = { "rcu_node_0", + "rcu_node_1", + "rcu_node_2", + "rcu_node_3" }; /* Match MAX_RCU_LVLS */ + static char *fqs[] = { "rcu_node_fqs_0", + "rcu_node_fqs_1", + "rcu_node_fqs_2", + "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */ int cpustride = 1; int i; int j; @@ -2732,6 +2756,9 @@ static void __init rcu_init_one(struct rcu_state *rsp, raw_spin_lock_init(&rnp->lock); lockdep_set_class_and_name(&rnp->lock, &rcu_node_class[i], buf[i]); + raw_spin_lock_init(&rnp->fqslock); + lockdep_set_class_and_name(&rnp->fqslock, + &rcu_fqs_class[i], fqs[i]); rnp->gpnum = 0; rnp->qsmask = 0; rnp->qsmaskinit = 0; diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 7fb93cedc76a..8f0293ce1517 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -202,6 +202,7 @@ struct rcu_node { /* per-CPU kthreads as needed. */ unsigned int node_kthread_status; /* State of node_kthread_task for tracing. */ + raw_spinlock_t fqslock ____cacheline_internodealigned_in_smp; } ____cacheline_internodealigned_in_smp; /* From d40011f601b450396104de42c631981502946cf0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 26 Jun 2012 20:45:57 -0700 Subject: [PATCH 25/73] rcu: Control grace-period duration from sysfs Although almost everyone is well-served by the defaults, some uses of RCU benefit from shorter grace periods, while others benefit more from the greater efficiency provided by longer grace periods. Situations requiring a large number of grace periods to elapse (and wireshark startup has been called out as an example of this) are helped by lower-latency grace periods. Furthermore, in some embedded applications, people are willing to accept a small degradation in update efficiency (due to there being more of the shorter grace-period operations) in order to gain the lower latency. In contrast, those few systems with thousands of CPUs need longer grace periods because the CPU overhead of a grace period rises roughly linearly with the number of CPUs. Such systems normally do not make much use of facilities that require large numbers of grace periods to elapse, so this is a good tradeoff. Therefore, this commit allows the durations to be controlled from sysfs. There are two sysfs parameters, one named "jiffies_till_first_fqs" that specifies the delay in jiffies from the end of grace-period initialization until the first attempt to force quiescent states, and the other named "jiffies_till_next_fqs" that specifies the delay (again in jiffies) between subsequent attempts to force quiescent states. They both default to three jiffies, which is compatible with the old hard-coded behavior. At some future time, it may be possible to automatically increase the grace-period length with the number of CPUs, but we do not yet have sufficient data to do a good job. Preliminary data indicates that we should add an addiitonal jiffy to each of the delays for every 200 CPUs in the system, but more experimentation is needed. For now, the number of systems with more than 1,000 CPUs is small enough that this can be relegated to boot-time hand tuning. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- Documentation/kernel-parameters.txt | 11 +++++++++++ kernel/rcutree.c | 25 ++++++++++++++++++++++--- 2 files changed, 33 insertions(+), 3 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index ad7e2e5088c1..55ada0471f93 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2385,6 +2385,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted. rcutree.rcu_cpu_stall_timeout= [KNL,BOOT] Set timeout for RCU CPU stall warning messages. + rcutree.jiffies_till_first_fqs= [KNL,BOOT] + Set delay from grace-period initialization to + first attempt to force quiescent states. + Units are jiffies, minimum value is zero, + and maximum value is HZ. + + rcutree.jiffies_till_next_fqs= [KNL,BOOT] + Set delay between subsequent attempts to force + quiescent states. Units are jiffies, minimum + value is one, and maximum value is HZ. + rcutorture.fqs_duration= [KNL,BOOT] Set duration of force_quiescent_state bursts. diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 43d57a17fcc5..c0d3d56f0404 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -226,6 +226,12 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_suppress, int, 0644); module_param(rcu_cpu_stall_timeout, int, 0644); +static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS; +static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; + +module_param(jiffies_till_first_fqs, ulong, 0644); +module_param(jiffies_till_next_fqs, ulong, 0644); + static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); static void force_quiescent_state(struct rcu_state *rsp); static int rcu_pending(int cpu); @@ -1177,6 +1183,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) static int __noreturn rcu_gp_kthread(void *arg) { int fqs_state; + unsigned long j; int ret; struct rcu_state *rsp = arg; struct rcu_node *rnp = rcu_get_root(rsp); @@ -1197,14 +1204,18 @@ static int __noreturn rcu_gp_kthread(void *arg) /* Handle quiescent-state forcing. */ fqs_state = RCU_SAVE_DYNTICK; + j = jiffies_till_first_fqs; + if (j > HZ) { + j = HZ; + jiffies_till_first_fqs = HZ; + } for (;;) { - rsp->jiffies_force_qs = jiffies + - RCU_JIFFIES_TILL_FORCE_QS; + rsp->jiffies_force_qs = jiffies + j; ret = wait_event_interruptible_timeout(rsp->gp_wq, (rsp->gp_flags & RCU_GP_FLAG_FQS) || (!ACCESS_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)), - RCU_JIFFIES_TILL_FORCE_QS); + j); /* If grace period done, leave loop. */ if (!ACCESS_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) @@ -1218,6 +1229,14 @@ static int __noreturn rcu_gp_kthread(void *arg) cond_resched(); flush_signals(current); } + j = jiffies_till_next_fqs; + if (j > HZ) { + j = HZ; + jiffies_till_next_fqs = HZ; + } else if (j < 1) { + j = 1; + jiffies_till_next_fqs = 1; + } } /* Handle grace-period end. */ From 7e5c2dfb4de15e21f62c956ec32cda9372ca993b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sun, 1 Jul 2012 15:42:33 -0700 Subject: [PATCH 26/73] rcu: Make rcutree module parameters visible in sysfs The module parameters blimit, qhimark, and qlomark (and more recently, rcu_fanout_leaf) have permission masks of zero, so that their values are not visible from sysfs. This is unnecessary and inconvenient to administrators who might like an easy way to see what these values are on a running system. This commit therefore sets their permission masks to 0444, allowing them to be read but not written. Reported-by: Rusty Russell Reported-by: Josh Triplett Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index c0d3d56f0404..f91a20c652b5 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -88,7 +88,7 @@ LIST_HEAD(rcu_struct_flavors); /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */ static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF; -module_param(rcu_fanout_leaf, int, 0); +module_param(rcu_fanout_leaf, int, 0444); int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */ NUM_RCU_LVL_0, @@ -216,9 +216,9 @@ static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */ static int qhimark = 10000; /* If this many pending, ignore blimit. */ static int qlowmark = 100; /* Once only this many pending, use blimit. */ -module_param(blimit, int, 0); -module_param(qhimark, int, 0); -module_param(qlowmark, int, 0); +module_param(blimit, int, 0444); +module_param(qhimark, int, 0444); +module_param(qlowmark, int, 0444); int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; From 5d4b86594984d8746b01487c768d8548463c173f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 7 Jul 2012 07:56:57 -0700 Subject: [PATCH 27/73] rcu: Fix day-zero grace-period initialization/cleanup race The current approach to grace-period initialization is vulnerable to extremely low-probability races. These races stem from the fact that the old grace period is marked completed on the same traversal through the rcu_node structure that is marking the start of the new grace period. This means that some rcu_node structures will believe that the old grace period is still in effect at the same time that other rcu_node structures believe that the new grace period has already started. These sorts of disagreements can result in too-short grace periods, as shown in the following scenario: 1. CPU 0 completes a grace period, but needs an additional grace period, so starts initializing one, initializing all the non-leaf rcu_node structures and the first leaf rcu_node structure. Because CPU 0 is both completing the old grace period and starting a new one, it marks the completion of the old grace period and the start of the new grace period in a single traversal of the rcu_node structures. Therefore, CPUs corresponding to the first rcu_node structure can become aware that the prior grace period has completed, but CPUs corresponding to the other rcu_node structures will see this same prior grace period as still being in progress. 2. CPU 1 passes through a quiescent state, and therefore informs the RCU core. Because its leaf rcu_node structure has already been initialized, this CPU's quiescent state is applied to the new (and only partially initialized) grace period. 3. CPU 1 enters an RCU read-side critical section and acquires a reference to data item A. Note that this CPU believes that its critical section started after the beginning of the new grace period, and therefore will not block this new grace period. 4. CPU 16 exits dyntick-idle mode. Because it was in dyntick-idle mode, other CPUs informed the RCU core of its extended quiescent state for the past several grace periods. This means that CPU 16 is not yet aware that these past grace periods have ended. Assume that CPU 16 corresponds to the second leaf rcu_node structure -- which has not yet been made aware of the new grace period. 5. CPU 16 removes data item A from its enclosing data structure and passes it to call_rcu(), which queues a callback in the RCU_NEXT_TAIL segment of the callback queue. 6. CPU 16 enters the RCU core, possibly because it has taken a scheduling-clock interrupt, or alternatively because it has more than 10,000 callbacks queued. It notes that the second most recent grace period has completed (recall that because it corresponds to the second as-yet-uninitialized rcu_node structure, it cannot yet become aware that the most recent grace period has completed), and therefore advances its callbacks. The callback for data item A is therefore in the RCU_NEXT_READY_TAIL segment of the callback queue. 7. CPU 0 completes initialization of the remaining leaf rcu_node structures for the new grace period, including the structure corresponding to CPU 16. 8. CPU 16 again enters the RCU core, again, possibly because it has taken a scheduling-clock interrupt, or alternatively because it now has more than 10,000 callbacks queued. It notes that the most recent grace period has ended, and therefore advances its callbacks. The callback for data item A is therefore in the RCU_DONE_TAIL segment of the callback queue. 9. All CPUs other than CPU 1 pass through quiescent states. Because CPU 1 already passed through its quiescent state, the new grace period completes. Note that CPU 1 is still in its RCU read-side critical section, still referencing data item A. 10. Suppose that CPU 2 wais the last CPU to pass through a quiescent state for the new grace period, and suppose further that CPU 2 did not have any callbacks queued, therefore not needing an additional grace period. CPU 2 therefore traverses all of the rcu_node structures, marking the new grace period as completed, but does not initialize a new grace period. 11. CPU 16 yet again enters the RCU core, yet again possibly because it has taken a scheduling-clock interrupt, or alternatively because it now has more than 10,000 callbacks queued. It notes that the new grace period has ended, and therefore advances its callbacks. The callback for data item A is therefore in the RCU_DONE_TAIL segment of the callback queue. This means that this callback is now considered ready to be invoked. 12. CPU 16 invokes the callback, freeing data item A while CPU 1 is still referencing it. This scenario represents a day-zero bug for TREE_RCU. This commit therefore ensures that the old grace period is marked completed in all leaf rcu_node structures before a new grace period is marked started in any of them. That said, it would have been insanely difficult to force this race to happen before the grace-period initialization process was preemptible. Therefore, this commit is not a candidate for -stable. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Conflicts: kernel/rcutree.c --- kernel/rcutree.c | 40 +++++++++++++++++----------------------- 1 file changed, 17 insertions(+), 23 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f91a20c652b5..145f27fe3a1f 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1141,37 +1141,31 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) * they can do to advance the grace period. It is therefore * safe for us to drop the lock in order to mark the grace * period as completed in all of the rcu_node structures. - * - * But if this CPU needs another grace period, it will take - * care of this while initializing the next grace period. - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL - * because the callbacks have not yet been advanced: Those - * callbacks are waiting on the grace period that just now - * completed. */ - rdp = this_cpu_ptr(rsp->rda); - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { - raw_spin_unlock_irq(&rnp->lock); + raw_spin_unlock_irq(&rnp->lock); - /* - * Propagate new ->completed value to rcu_node - * structures so that other CPUs don't have to - * wait until the start of the next grace period - * to process their callbacks. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock_irq(&rnp->lock); - rnp->completed = rsp->gpnum; - raw_spin_unlock_irq(&rnp->lock); - cond_resched(); - } - rnp = rcu_get_root(rsp); + /* + * Propagate new ->completed value to rcu_node structures so + * that other CPUs don't have to wait until the start of the next + * grace period to process their callbacks. This also avoids + * some nasty RCU grace-period initialization races by forcing + * the end of the current grace period to be completely recorded in + * all of the rcu_node structures before the beginning of the next + * grace period is recorded in any of the rcu_node structures. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq(&rnp->lock); + rnp->completed = rsp->gpnum; + raw_spin_unlock_irq(&rnp->lock); + cond_resched(); } + rnp = rcu_get_root(rsp); + raw_spin_lock_irq(&rnp->lock); rsp->completed = rsp->gpnum; /* Declare grace period done. */ trace_rcu_grace_period(rsp->name, rsp->completed, "end"); rsp->fqs_state = RCU_GP_IDLE; + rdp = this_cpu_ptr(rsp->rda); if (cpu_needs_another_gp(rsp, rdp)) rsp->gp_flags = 1; raw_spin_unlock_irq(&rnp->lock); From 661a85dc0d2ec0404e3b80909e413a9d5e42a239 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 7 Jul 2012 05:57:03 -0700 Subject: [PATCH 28/73] rcu: Add random PROVE_RCU_DELAY to grace-period initialization Preemption greatly raised the probability of certain types of race conditions, so this commit adds an anti-heisenbug to greatly increase the collision cross section, also known as the probability of occurrence. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 145f27fe3a1f..f0f3a18c0a20 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -52,6 +52,7 @@ #include #include #include +#include #include "rcutree.h" #include @@ -1087,6 +1088,10 @@ static int rcu_gp_init(struct rcu_state *rsp) rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); raw_spin_unlock_irq(&rnp->lock); +#ifdef CONFIG_PROVE_RCU_DELAY + if ((random32() % (rcu_num_nodes * 8)) == 0) + schedule_timeout_uninterruptible(2); +#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ cond_resched(); } From 25d30cf4250f74e5ceb35f8f39739782408db633 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jul 2012 05:23:18 -0700 Subject: [PATCH 29/73] rcu: Adjust for unconditional ->completed assignment Now that the rcu_node structures' ->completed fields are unconditionally assigned at grace-period cleanup time, they should already have the correct value for the new grace period at grace-period initialization time. This commit therefore inserts a WARN_ON_ONCE() to verify this invariant. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f0f3a18c0a20..a2eadd04fb29 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1080,6 +1080,7 @@ static int rcu_gp_init(struct rcu_state *rsp) rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; + WARN_ON_ONCE(rnp->completed != rsp->completed); rnp->completed = rsp->completed; if (rnp == rdp->mynode) rcu_start_gp_per_cpu(rsp, rnp, rdp); @@ -2777,7 +2778,8 @@ static void __init rcu_init_one(struct rcu_state *rsp, raw_spin_lock_init(&rnp->fqslock); lockdep_set_class_and_name(&rnp->fqslock, &rcu_fqs_class[i], fqs[i]); - rnp->gpnum = 0; + rnp->gpnum = rsp->gpnum; + rnp->completed = rsp->completed; rnp->qsmask = 0; rnp->qsmaskinit = 0; rnp->grplo = j * cpustride; From bcfa57ce10d3d53d37a6e324f3010b1ce6a2784a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Jul 2012 16:03:51 -0700 Subject: [PATCH 30/73] rcu: Eliminate signed overflow in synchronize_rcu_expedited() In the C language, signed overflow is undefined. It is true that twos-complement arithmetic normally comes to the rescue, but if the compiler can subvert this any time it has any information about the values being compared. For example, given "if (a - b > 0)", if the compiler has enough information to realize that (for example) the value of "a" is positive and that of "b" is negative, the compiler is within its rights to optimize to a simple "if (1)", which might not be what you want. This commit therefore converts synchronize_rcu_expedited()'s work-done detection counter from signed to unsigned. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index eb8dcd1bc4b5..cb5879386a02 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -677,7 +677,7 @@ void synchronize_rcu(void) EXPORT_SYMBOL_GPL(synchronize_rcu); static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); -static long sync_rcu_preempt_exp_count; +static unsigned long sync_rcu_preempt_exp_count; static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); /* @@ -792,7 +792,7 @@ void synchronize_rcu_expedited(void) unsigned long flags; struct rcu_node *rnp; struct rcu_state *rsp = &rcu_preempt_state; - long snap; + unsigned long snap; int trycount = 0; smp_mb(); /* Caller's modifications seen first by other CPUs. */ @@ -811,10 +811,10 @@ void synchronize_rcu_expedited(void) synchronize_rcu(); return; } - if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) + if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) goto mb_ret; /* Others did our work for us. */ } - if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0) + if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) goto unlock_mb_ret; /* Others did our work for us. */ /* force all RCU readers onto ->blkd_tasks lists. */ From 1943c89de700248d68385300a9b5588a1e314f90 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 30 Jul 2012 17:19:25 -0700 Subject: [PATCH 31/73] rcu: Reduce synchronize_rcu_expedited() latency The synchronize_rcu_expedited() function disables interrupts across a scan of all leaf rcu_node structures, which is not good for real-time scheduling latency on large systems (hundreds or especially thousands of CPUs). This commit therefore holds off CPU-hotplug operations using get_online_cpus(), and removes the prior acquisiion of the ->onofflock (which required disabling interrupts). Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index cb5879386a02..b4e8eb24a5f1 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -799,34 +799,48 @@ void synchronize_rcu_expedited(void) snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; smp_mb(); /* Above access cannot bleed into critical section. */ + /* + * Block CPU-hotplug operations. This means that any CPU-hotplug + * operation that finds an rcu_node structure with tasks in the + * process of being boosted will know that all tasks blocking + * this expedited grace period will already be in the process of + * being boosted. This simplifies the process of moving tasks + * from leaf to root rcu_node structures. + */ + get_online_cpus(); + /* * Acquire lock, falling back to synchronize_rcu() if too many * lock-acquisition failures. Of course, if someone does the * expedited grace period for us, just leave. */ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { + if (ULONG_CMP_LT(snap, + ACCESS_ONCE(sync_rcu_preempt_exp_count))) { + put_online_cpus(); + goto mb_ret; /* Others did our work for us. */ + } if (trycount++ < 10) { udelay(trycount * num_online_cpus()); } else { + put_online_cpus(); synchronize_rcu(); return; } - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) - goto mb_ret; /* Others did our work for us. */ } - if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) + if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { + put_online_cpus(); goto unlock_mb_ret; /* Others did our work for us. */ + } /* force all RCU readers onto ->blkd_tasks lists. */ synchronize_sched_expedited(); - raw_spin_lock_irqsave(&rsp->onofflock, flags); - /* Initialize ->expmask for all non-leaf rcu_node structures. */ rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + raw_spin_lock_irqsave(&rnp->lock, flags); rnp->expmask = rnp->qsmaskinit; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* Snapshot current state of ->blkd_tasks lists. */ @@ -835,7 +849,7 @@ void synchronize_rcu_expedited(void) if (NUM_RCU_NODES > 1) sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + put_online_cpus(); /* Wait for snapshotted ->blkd_tasks lists to drain. */ rnp = rcu_get_root(rsp); From d7d6a11e8609f0319d4a2d8ede348f8b3374b652 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 21 Aug 2012 15:00:05 -0700 Subject: [PATCH 32/73] rcu: Simplify quiescent-state detection The current quiescent-state detection algorithm is needlessly complex. It records the grace-period number corresponding to the quiescent state at the time of the quiescent state, which works, but it seems better to simply erase any record of previous quiescent states at the time that the CPU notices the new grace period. This has the further advantage of removing another piece of RCU for which lockless reasoning is required. Therefore, this commit makes this change. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 27 +++++++++++---------------- kernel/rcutree.h | 2 -- kernel/rcutree_plugin.h | 2 -- kernel/rcutree_trace.c | 12 +++++------- 4 files changed, 16 insertions(+), 27 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index a2eadd04fb29..6194402ec853 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -176,8 +176,6 @@ void rcu_sched_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu); - rdp->passed_quiesce_gpnum = rdp->gpnum; - barrier(); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; @@ -187,8 +185,6 @@ void rcu_bh_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); - rdp->passed_quiesce_gpnum = rdp->gpnum; - barrier(); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; @@ -899,12 +895,8 @@ static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct */ rdp->gpnum = rnp->gpnum; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart"); - if (rnp->qsmask & rdp->grpmask) { - rdp->qs_pending = 1; - rdp->passed_quiesce = 0; - } else { - rdp->qs_pending = 0; - } + rdp->passed_quiesce = 0; + rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask); zero_cpu_stall_ticks(rdp); } } @@ -984,10 +976,13 @@ __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat * our behalf. Catch up with this state to avoid noting * spurious new grace periods. If another grace period * has started, then rnp->gpnum will have advanced, so - * we will detect this later on. + * we will detect this later on. Of course, any quiescent + * states we found for the old GP are now invalid. */ - if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) + if (ULONG_CMP_LT(rdp->gpnum, rdp->completed)) { rdp->gpnum = rdp->completed; + rdp->passed_quiesce = 0; + } /* * If RCU does not need a quiescent state from this CPU, @@ -1358,7 +1353,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, * based on quiescent states detected in an earlier grace period! */ static void -rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp) +rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; unsigned long mask; @@ -1366,7 +1361,8 @@ rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long las rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); - if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) { + if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum || + rnp->completed == rnp->gpnum) { /* * The grace period in which this quiescent state was @@ -1425,7 +1421,7 @@ rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) * Tell RCU we are done (but rcu_report_qs_rdp() will be the * judge of that). */ - rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum); + rcu_report_qs_rdp(rdp->cpu, rsp, rdp); } #ifdef CONFIG_HOTPLUG_CPU @@ -2600,7 +2596,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->completed = rnp->completed; rdp->passed_quiesce = 0; rdp->qs_pending = 0; - rdp->passed_quiesce_gpnum = rnp->gpnum - 1; trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl"); } raw_spin_unlock(&rnp->lock); /* irqs already disabled. */ diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 8f0293ce1517..935dd4ca6816 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -246,8 +246,6 @@ struct rcu_data { /* in order to detect GP end. */ unsigned long gpnum; /* Highest gp number that this CPU */ /* is aware of having started. */ - unsigned long passed_quiesce_gpnum; - /* gpnum at time of quiescent state. */ bool passed_quiesce; /* User-mode/idle loop etc. */ bool qs_pending; /* Core waits for quiesc state. */ bool beenonline; /* CPU online at least once. */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index b4e8eb24a5f1..4734afbea73a 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -137,8 +137,6 @@ static void rcu_preempt_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); - rdp->passed_quiesce_gpnum = rdp->gpnum; - barrier(); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index f54f0ceda0cf..bd4df13d4afb 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -86,12 +86,11 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp) { if (!rdp->beenonline) return; - seq_printf(m, "%3d%cc=%lu g=%lu pq=%d pgp=%lu qp=%d", + seq_printf(m, "%3d%cc=%lu g=%lu pq=%d qp=%d", rdp->cpu, cpu_is_offline(rdp->cpu) ? '!' : ' ', rdp->completed, rdp->gpnum, - rdp->passed_quiesce, rdp->passed_quiesce_gpnum, - rdp->qs_pending); + rdp->passed_quiesce, rdp->qs_pending); seq_printf(m, " dt=%d/%llx/%d df=%lu", atomic_read(&rdp->dynticks->dynticks), rdp->dynticks->dynticks_nesting, @@ -150,12 +149,11 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp) { if (!rdp->beenonline) return; - seq_printf(m, "%d,%s,%lu,%lu,%d,%lu,%d", + seq_printf(m, "%d,%s,%lu,%lu,%d,%d", rdp->cpu, cpu_is_offline(rdp->cpu) ? "\"N\"" : "\"Y\"", rdp->completed, rdp->gpnum, - rdp->passed_quiesce, rdp->passed_quiesce_gpnum, - rdp->qs_pending); + rdp->passed_quiesce, rdp->qs_pending); seq_printf(m, ",%d,%llx,%d,%lu", atomic_read(&rdp->dynticks->dynticks), rdp->dynticks->dynticks_nesting, @@ -186,7 +184,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused) int cpu; struct rcu_state *rsp; - seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\","); + seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pq\","); seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\","); seq_puts(m, "\"of\",\"qll\",\"ql\",\"qs\""); #ifdef CONFIG_RCU_BOOST From 4dbd6bb38dd1cbfa5cb21e56e51dffc74aa20038 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 5 Sep 2012 21:43:57 -0700 Subject: [PATCH 33/73] rcu: Handle unbalanced rcu_node configurations with few CPUs If CONFIG_RCU_FANOUT_EXACT=y, if there are not enough CPUs (according to nr_cpu_ids) to require more than a single rcu_node structure, but if NR_CPUS is larger than would fit into a single rcu_node structure, then the current rcu_init_levelspread() code is subject to integer overflow in the eight-bit ->levelspread[] array in the rcu_state structure. In this case, the solution is -not- to increase the size of the elements in this array because the values in that array should be constrained to the number of bits in an unsigned long. Instead, this commit replaces NR_CPUS with nr_cpu_ids in the rcu_init_levelspread() function's initialization of the cprv local variable. This results in all of the arithmetic being consistently based off of the nr_cpu_ids value, thus avoiding the overflow, which was caused by the mixing of nr_cpu_ids and NR_CPUS. Reported-by: Mike Galbraith Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 6194402ec853..8b9496fee235 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2723,7 +2723,7 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) int cprv; int i; - cprv = NR_CPUS; + cprv = nr_cpu_ids; for (i = rcu_num_lvls - 1; i >= 0; i--) { ccur = rsp->levelcnt[i]; rsp->levelspread[i] = (cprv + ccur - 1) / ccur; From b17c7035f37f47c7f7cb08a5555ab2aebfa31f91 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 6 Sep 2012 15:38:02 -0700 Subject: [PATCH 34/73] rcu: Shrink RCU based on number of CPUs Currently, rcu_init_geometry() only reshapes RCU's combining trees if the leaf fanout is changed at boot time. This means that by default, kernels compiled with (say) NR_CPUS=4096 will keep oversized data structures, even when running on systems with (say) four CPUs. This commit therefore checks to see if the maximum number of CPUs on the actual running system (nr_cpu_ids) differs from NR_CPUS, and if so reshapes the combining trees accordingly. Reported-by: Mike Galbraith Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 8b9496fee235..b703989148e4 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2821,7 +2821,8 @@ static void __init rcu_init_geometry(void) int rcu_capacity[MAX_RCU_LVLS + 1]; /* If the compile-time values are accurate, just leave. */ - if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF) + if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF && + nr_cpu_ids == NR_CPUS) return; /* From ab840f7a06df780c4db01f34a5660b1e472d9ca6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 23 Jul 2012 12:30:22 -0700 Subject: [PATCH 35/73] rcu: Update rcutorture defaults A number of new features have been added to rcutorture over the years, but the defaults have not been updated to include them. This commit therefore turns on a couple of them that have proven helpful and trustworthy, namely periodic progress reports and testing of NO_HZ. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutorture.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 25b15033c61f..53c548c39265 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -53,10 +53,11 @@ MODULE_AUTHOR("Paul E. McKenney and Josh Triplett Date: Mon, 23 Jul 2012 12:05:55 -0700 Subject: [PATCH 36/73] rcu: Track CPU-hotplug duration statistics Many rcutorture runs include CPU-hotplug operations in their stress testing. This commit accumulates statistics on the durations of these operations in deference to the recent concern about the overhead and latency of these operations. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutorture.c | 42 +++++++++++++++++++++++++++++++++++++----- 1 file changed, 37 insertions(+), 5 deletions(-) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 53c548c39265..2736cc878ba2 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -177,8 +177,14 @@ static long n_rcu_torture_boosts; static long n_rcu_torture_timers; static long n_offline_attempts; static long n_offline_successes; +static unsigned long sum_offline; +static int min_offline = -1; +static int max_offline; static long n_online_attempts; static long n_online_successes; +static unsigned long sum_online; +static int min_online = -1; +static int max_online; static long n_barrier_attempts; static long n_barrier_successes; static struct list_head rcu_torture_removed; @@ -1215,11 +1221,13 @@ rcu_torture_printk(char *page) n_rcu_torture_boost_failure, n_rcu_torture_boosts, n_rcu_torture_timers); - cnt += sprintf(&page[cnt], "onoff: %ld/%ld:%ld/%ld ", - n_online_successes, - n_online_attempts, - n_offline_successes, - n_offline_attempts); + cnt += sprintf(&page[cnt], + "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ", + n_online_successes, n_online_attempts, + n_offline_successes, n_offline_attempts, + min_online, max_online, + min_offline, max_offline, + sum_online, sum_offline, HZ); cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld", n_barrier_successes, n_barrier_attempts, @@ -1491,8 +1499,10 @@ static int __cpuinit rcu_torture_onoff(void *arg) { int cpu; + unsigned long delta; int maxcpu = -1; DEFINE_RCU_RANDOM(rand); + unsigned long starttime; VERBOSE_PRINTK_STRING("rcu_torture_onoff task started"); for_each_online_cpu(cpu) @@ -1510,6 +1520,7 @@ rcu_torture_onoff(void *arg) printk(KERN_ALERT "%s" TORTURE_FLAG "rcu_torture_onoff task: offlining %d\n", torture_type, cpu); + starttime = jiffies; n_offline_attempts++; if (cpu_down(cpu) == 0) { if (verbose) @@ -1517,12 +1528,23 @@ rcu_torture_onoff(void *arg) "rcu_torture_onoff task: offlined %d\n", torture_type, cpu); n_offline_successes++; + delta = jiffies - starttime; + sum_offline += delta; + if (min_offline < 0) { + min_offline = delta; + max_offline = delta; + } + if (min_offline > delta) + min_offline = delta; + if (max_offline < delta) + max_offline = delta; } } else if (cpu_is_hotpluggable(cpu)) { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG "rcu_torture_onoff task: onlining %d\n", torture_type, cpu); + starttime = jiffies; n_online_attempts++; if (cpu_up(cpu) == 0) { if (verbose) @@ -1530,6 +1552,16 @@ rcu_torture_onoff(void *arg) "rcu_torture_onoff task: onlined %d\n", torture_type, cpu); n_online_successes++; + delta = jiffies - starttime; + sum_online += delta; + if (min_online < 0) { + min_online = delta; + max_online = delta; + } + if (min_online > delta) + min_online = delta; + if (max_online < delta) + max_online = delta; } } schedule_timeout_interruptible(onoff_interval * HZ); From 2aef619c7524d73d18ff7b102a1706066b69141d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 3 Aug 2012 16:41:23 -0700 Subject: [PATCH 37/73] rcu: Document SRCU dead-CPU capabilities, emphasize read-side limits The current documentation did not help someone grepping for SRCU to learn that disabling preemption is not a replacement for srcu_read_lock(), so upgrade the documentation to bring this out, not just for SRCU, but also for RCU-bh. Also document the fact that SRCU readers are respected on CPUs executing in user mode, idle CPUs, and even on offline CPUs. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Reviewed-by: Lai Jiangshan --- Documentation/RCU/checklist.txt | 6 ++++++ Documentation/RCU/whatisRCU.txt | 9 +++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt index fc103d7a0474..cdb20d41a44a 100644 --- a/Documentation/RCU/checklist.txt +++ b/Documentation/RCU/checklist.txt @@ -310,6 +310,12 @@ over a rather long period of time, but improvements are always welcome! code under the influence of preempt_disable(), you instead need to use synchronize_irq() or synchronize_sched(). + This same limitation also applies to synchronize_rcu_bh() + and synchronize_srcu(), as well as to the asynchronous and + expedited forms of the three primitives, namely call_rcu(), + call_rcu_bh(), call_srcu(), synchronize_rcu_expedited(), + synchronize_rcu_bh_expedited(), and synchronize_srcu_expedited(). + 12. Any lock acquired by an RCU callback must be acquired elsewhere with softirq disabled, e.g., via spin_lock_irqsave(), spin_lock_bh(), etc. Failing to disable irq on a given diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt index 69ee188515e7..bf0f6de2aa00 100644 --- a/Documentation/RCU/whatisRCU.txt +++ b/Documentation/RCU/whatisRCU.txt @@ -873,7 +873,7 @@ d. Do you need to treat NMI handlers, hardirq handlers, and code segments with preemption disabled (whether via preempt_disable(), local_irq_save(), local_bh_disable(), or some other mechanism) as if they were explicit RCU readers? - If so, you need RCU-sched. + If so, RCU-sched is the only choice that will work for you. e. Do you need RCU grace periods to complete even in the face of softirq monopolization of one or more of the CPUs? For @@ -884,7 +884,12 @@ f. Is your workload too update-intensive for normal use of RCU, but inappropriate for other synchronization mechanisms? If so, consider SLAB_DESTROY_BY_RCU. But please be careful! -g. Otherwise, use RCU. +g. Do you need read-side critical sections that are respected + even though they are in the middle of the idle loop, during + user-mode execution, or on an offlined CPU? If so, SRCU is the + only choice that will work for you. + +h. Otherwise, use RCU. Of course, this all assumes that you have determined that RCU is in fact the right tool for your job. From 2caa1e4432be7260dca60c3de6949b77eb007515 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 9 Aug 2012 16:30:45 -0700 Subject: [PATCH 38/73] rcu: Switch rcutorture to pr_alert() and friends Drop a few characters by switching kernel/rcutorture.c from "printk(KERN_ALERT" to "pr_alert(". Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 100 ++++++++++++++++++++++---------------------- 1 file changed, 50 insertions(+), 50 deletions(-) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 2736cc878ba2..61be03ba598d 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -120,11 +120,11 @@ MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)"); #define TORTURE_FLAG "-torture:" #define PRINTK_STRING(s) \ - do { printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0) + do { pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0) #define VERBOSE_PRINTK_STRING(s) \ - do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0) + do { if (verbose) pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0) #define VERBOSE_PRINTK_ERRSTRING(s) \ - do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0) + do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0) static char printk_buf[4096]; @@ -242,7 +242,7 @@ rcutorture_shutdown_notify(struct notifier_block *unused1, if (fullstop == FULLSTOP_DONTSTOP) fullstop = FULLSTOP_SHUTDOWN; else - printk(KERN_WARNING /* but going down anyway, so... */ + pr_warn(/* but going down anyway, so... */ "Concurrent 'rmmod rcutorture' and shutdown illegal!\n"); mutex_unlock(&fullstop_mutex); return NOTIFY_DONE; @@ -255,7 +255,7 @@ rcutorture_shutdown_notify(struct notifier_block *unused1, static void rcutorture_shutdown_absorb(char *title) { if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) { - printk(KERN_NOTICE + pr_notice( "rcutorture thread %s parking due to system shutdown\n", title); schedule_timeout_uninterruptible(MAX_SCHEDULE_TIMEOUT); @@ -1276,7 +1276,7 @@ rcu_torture_stats_print(void) int cnt; cnt = rcu_torture_printk(printk_buf); - printk(KERN_ALERT "%s", printk_buf); + pr_alert("%s", printk_buf); } /* @@ -1389,20 +1389,20 @@ rcu_torture_stutter(void *arg) static inline void rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag) { - printk(KERN_ALERT "%s" TORTURE_FLAG - "--- %s: nreaders=%d nfakewriters=%d " - "stat_interval=%d verbose=%d test_no_idle_hz=%d " - "shuffle_interval=%d stutter=%d irqreader=%d " - "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d " - "test_boost=%d/%d test_boost_interval=%d " - "test_boost_duration=%d shutdown_secs=%d " - "onoff_interval=%d onoff_holdoff=%d\n", - torture_type, tag, nrealreaders, nfakewriters, - stat_interval, verbose, test_no_idle_hz, shuffle_interval, - stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter, - test_boost, cur_ops->can_boost, - test_boost_interval, test_boost_duration, shutdown_secs, - onoff_interval, onoff_holdoff); + pr_alert("%s" TORTURE_FLAG + "--- %s: nreaders=%d nfakewriters=%d " + "stat_interval=%d verbose=%d test_no_idle_hz=%d " + "shuffle_interval=%d stutter=%d irqreader=%d " + "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d " + "test_boost=%d/%d test_boost_interval=%d " + "test_boost_duration=%d shutdown_secs=%d " + "onoff_interval=%d onoff_holdoff=%d\n", + torture_type, tag, nrealreaders, nfakewriters, + stat_interval, verbose, test_no_idle_hz, shuffle_interval, + stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter, + test_boost, cur_ops->can_boost, + test_boost_interval, test_boost_duration, shutdown_secs, + onoff_interval, onoff_holdoff); } static struct notifier_block rcutorture_shutdown_nb = { @@ -1469,9 +1469,9 @@ rcu_torture_shutdown(void *arg) !kthread_should_stop()) { delta = shutdown_time - jiffies_snap; if (verbose) - printk(KERN_ALERT "%s" TORTURE_FLAG - "rcu_torture_shutdown task: %lu jiffies remaining\n", - torture_type, delta); + pr_alert("%s" TORTURE_FLAG + "rcu_torture_shutdown task: %lu jiffies remaining\n", + torture_type, delta); schedule_timeout_interruptible(delta); jiffies_snap = ACCESS_ONCE(jiffies); } @@ -1517,16 +1517,16 @@ rcu_torture_onoff(void *arg) cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1); if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) { if (verbose) - printk(KERN_ALERT "%s" TORTURE_FLAG - "rcu_torture_onoff task: offlining %d\n", - torture_type, cpu); + pr_alert("%s" TORTURE_FLAG + "rcu_torture_onoff task: offlining %d\n", + torture_type, cpu); starttime = jiffies; n_offline_attempts++; if (cpu_down(cpu) == 0) { if (verbose) - printk(KERN_ALERT "%s" TORTURE_FLAG - "rcu_torture_onoff task: offlined %d\n", - torture_type, cpu); + pr_alert("%s" TORTURE_FLAG + "rcu_torture_onoff task: offlined %d\n", + torture_type, cpu); n_offline_successes++; delta = jiffies - starttime; sum_offline += delta; @@ -1541,16 +1541,16 @@ rcu_torture_onoff(void *arg) } } else if (cpu_is_hotpluggable(cpu)) { if (verbose) - printk(KERN_ALERT "%s" TORTURE_FLAG - "rcu_torture_onoff task: onlining %d\n", - torture_type, cpu); + pr_alert("%s" TORTURE_FLAG + "rcu_torture_onoff task: onlining %d\n", + torture_type, cpu); starttime = jiffies; n_online_attempts++; if (cpu_up(cpu) == 0) { if (verbose) - printk(KERN_ALERT "%s" TORTURE_FLAG - "rcu_torture_onoff task: onlined %d\n", - torture_type, cpu); + pr_alert("%s" TORTURE_FLAG + "rcu_torture_onoff task: onlined %d\n", + torture_type, cpu); n_online_successes++; delta = jiffies - starttime; sum_online += delta; @@ -1626,14 +1626,14 @@ static int __cpuinit rcu_torture_stall(void *args) if (!kthread_should_stop()) { stop_at = get_seconds() + stall_cpu; /* RCU CPU stall is expected behavior in following code. */ - printk(KERN_ALERT "rcu_torture_stall start.\n"); + pr_alert("rcu_torture_stall start.\n"); rcu_read_lock(); preempt_disable(); while (ULONG_CMP_LT(get_seconds(), stop_at)) continue; /* Induce RCU CPU stall warning. */ preempt_enable(); rcu_read_unlock(); - printk(KERN_ALERT "rcu_torture_stall end.\n"); + pr_alert("rcu_torture_stall end.\n"); } rcutorture_shutdown_absorb("rcu_torture_stall"); while (!kthread_should_stop()) @@ -1749,12 +1749,12 @@ static int rcu_torture_barrier_init(void) if (n_barrier_cbs == 0) return 0; if (cur_ops->call == NULL || cur_ops->cb_barrier == NULL) { - printk(KERN_ALERT "%s" TORTURE_FLAG - " Call or barrier ops missing for %s,\n", - torture_type, cur_ops->name); - printk(KERN_ALERT "%s" TORTURE_FLAG - " RCU barrier testing omitted from run.\n", - torture_type); + pr_alert("%s" TORTURE_FLAG + " Call or barrier ops missing for %s,\n", + torture_type, cur_ops->name); + pr_alert("%s" TORTURE_FLAG + " RCU barrier testing omitted from run.\n", + torture_type); return 0; } atomic_set(&barrier_cbs_count, 0); @@ -1847,7 +1847,7 @@ rcu_torture_cleanup(void) mutex_lock(&fullstop_mutex); rcutorture_record_test_transition(); if (fullstop == FULLSTOP_SHUTDOWN) { - printk(KERN_WARNING /* but going down anyway, so... */ + pr_warn(/* but going down anyway, so... */ "Concurrent 'rmmod rcutorture' and shutdown illegal!\n"); mutex_unlock(&fullstop_mutex); schedule_timeout_uninterruptible(10); @@ -1971,17 +1971,17 @@ rcu_torture_init(void) break; } if (i == ARRAY_SIZE(torture_ops)) { - printk(KERN_ALERT "rcu-torture: invalid torture type: \"%s\"\n", - torture_type); - printk(KERN_ALERT "rcu-torture types:"); + pr_alert("rcu-torture: invalid torture type: \"%s\"\n", + torture_type); + pr_alert("rcu-torture types:"); for (i = 0; i < ARRAY_SIZE(torture_ops); i++) - printk(KERN_ALERT " %s", torture_ops[i]->name); - printk(KERN_ALERT "\n"); + pr_alert(" %s", torture_ops[i]->name); + pr_alert("\n"); mutex_unlock(&fullstop_mutex); return -EINVAL; } if (cur_ops->fqs == NULL && fqs_duration != 0) { - printk(KERN_ALERT "rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n"); + pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n"); fqs_duration = 0; } if (cur_ops->init) From 60f53782c51f27c695840ce90c6c432284319eef Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Sat, 25 Aug 2012 15:27:40 -0700 Subject: [PATCH 39/73] rcu: Prevent initialization race in rcutorture kthreads When you do something like "t = kthread_run(...)", it is possible that the kthread will start running before the assignment to "t" happens. If the child kthread expects to find a pointer to its task_struct in "t", it will then be fatally disappointed. This commit therefore switches such cases to kthread_create() followed by wake_up_process(), guaranteeing that the assignment happens before the child kthread starts running. Reported-by: Fengguang Wu Signed-off-by: Paul E. McKenney --- kernel/rcutorture.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c index 61be03ba598d..aaa7b9f3532a 100644 --- a/kernel/rcutorture.c +++ b/kernel/rcutorture.c @@ -2029,14 +2029,15 @@ rcu_torture_init(void) /* Start up the kthreads. */ VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task"); - writer_task = kthread_run(rcu_torture_writer, NULL, - "rcu_torture_writer"); + writer_task = kthread_create(rcu_torture_writer, NULL, + "rcu_torture_writer"); if (IS_ERR(writer_task)) { firsterr = PTR_ERR(writer_task); VERBOSE_PRINTK_ERRSTRING("Failed to create writer"); writer_task = NULL; goto unwind; } + wake_up_process(writer_task); fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]), GFP_KERNEL); if (fakewriter_tasks == NULL) { @@ -2151,14 +2152,15 @@ rcu_torture_init(void) } if (shutdown_secs > 0) { shutdown_time = jiffies + shutdown_secs * HZ; - shutdown_task = kthread_run(rcu_torture_shutdown, NULL, - "rcu_torture_shutdown"); + shutdown_task = kthread_create(rcu_torture_shutdown, NULL, + "rcu_torture_shutdown"); if (IS_ERR(shutdown_task)) { firsterr = PTR_ERR(shutdown_task); VERBOSE_PRINTK_ERRSTRING("Failed to create shutdown"); shutdown_task = NULL; goto unwind; } + wake_up_process(shutdown_task); } i = rcu_torture_onoff_init(); if (i != 0) { From e3ebfb96f396731ca2d0b108785d5da31b53ab00 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 2 Jul 2012 14:42:01 -0700 Subject: [PATCH 40/73] rcu: Add PROVE_RCU_DELAY to provoke difficult races There have been some recent bugs that were triggered only when preemptible RCU's __rcu_read_unlock() was preempted just after setting ->rcu_read_lock_nesting to INT_MIN, which is a low-probability event. Therefore, reproducing those bugs (to say nothing of gaining confidence in alleged fixes) was quite difficult. This commit therefore creates a new debug-only RCU kernel config option that forces a short delay in __rcu_read_unlock() to increase the probability of those sorts of bugs occurring. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcupdate.c | 4 ++++ lib/Kconfig.debug | 14 ++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 4e6a61b15e86..29ca1c6da594 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -45,6 +45,7 @@ #include #include #include +#include #define CREATE_TRACE_POINTS #include @@ -81,6 +82,9 @@ void __rcu_read_unlock(void) } else { barrier(); /* critical section before exit code. */ t->rcu_read_lock_nesting = INT_MIN; +#ifdef CONFIG_PROVE_RCU_DELAY + udelay(10); /* Make preemption more probable. */ +#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */ barrier(); /* assign before ->rcu_read_unlock_special load */ if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special))) rcu_read_unlock_special(t); diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 2403a63b5da5..dacbbe4d7a80 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -629,6 +629,20 @@ config PROVE_RCU_REPEATEDLY Say N if you are unsure. +config PROVE_RCU_DELAY + bool "RCU debugging: preemptible RCU race provocation" + depends on DEBUG_KERNEL && PREEMPT_RCU + default n + help + There is a class of races that involve an unlikely preemption + of __rcu_read_unlock() just after ->rcu_read_lock_nesting has + been set to INT_MIN. This feature inserts a delay at that + point to increase the probability of these races. + + Say Y to increase probability of preemption of __rcu_read_unlock(). + + Say N if you are unsure. + config SPARSE_RCU_POINTER bool "RCU debugging: sparse-based checks for pointer usage" default n From 818615c4cde2a71a5857007b134cce89d506cc3f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 11 Jul 2012 00:24:57 -0700 Subject: [PATCH 41/73] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region Because TINY_RCU's idle detection keys directly off of the nesting level, rather than from a separate variable as in TREE_RCU, the TINY_RCU dyntick-idle tracing on transition to idle must happen before the change to the nesting level. This commit therefore makes this change by passing the desired new value (rather than the old value) of the nesting level in to rcu_idle_enter_common(). [ paulmck: Add fix for wrong-variable bug spotted by Michael Wang . ] Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutiny.c | 31 ++++++++++++++++--------------- 1 file changed, 16 insertions(+), 15 deletions(-) diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 547b1fe5b052..e4163c5af1de 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -56,24 +56,27 @@ static void __call_rcu(struct rcu_head *head, static long long rcu_dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */ -static void rcu_idle_enter_common(long long oldval) +static void rcu_idle_enter_common(long long newval) { - if (rcu_dynticks_nesting) { + if (newval) { RCU_TRACE(trace_rcu_dyntick("--=", - oldval, rcu_dynticks_nesting)); + rcu_dynticks_nesting, newval)); + rcu_dynticks_nesting = newval; return; } - RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting)); + RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting, newval)); if (!is_idle_task(current)) { struct task_struct *idle = idle_task(smp_processor_id()); RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task", - oldval, rcu_dynticks_nesting)); + rcu_dynticks_nesting, newval)); ftrace_dump(DUMP_ALL); WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } + barrier(); + rcu_dynticks_nesting = newval; rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ } @@ -84,17 +87,16 @@ static void rcu_idle_enter_common(long long oldval) void rcu_idle_enter(void) { unsigned long flags; - long long oldval; + long long newval; local_irq_save(flags); - oldval = rcu_dynticks_nesting; WARN_ON_ONCE((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); if ((rcu_dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) - rcu_dynticks_nesting = 0; + newval = 0; else - rcu_dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; - rcu_idle_enter_common(oldval); + newval = rcu_dynticks_nesting - DYNTICK_TASK_NEST_VALUE; + rcu_idle_enter_common(newval); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_enter); @@ -105,13 +107,12 @@ EXPORT_SYMBOL_GPL(rcu_idle_enter); void rcu_irq_exit(void) { unsigned long flags; - long long oldval; + long long newval; local_irq_save(flags); - oldval = rcu_dynticks_nesting; - rcu_dynticks_nesting--; - WARN_ON_ONCE(rcu_dynticks_nesting < 0); - rcu_idle_enter_common(oldval); + newval = rcu_dynticks_nesting - 1; + WARN_ON_ONCE(newval < 0); + rcu_idle_enter_common(newval); local_irq_restore(flags); } From 1e3fd2b38cea41f5386bf23440f2cbdd74cf13d0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 27 Jul 2012 13:41:47 -0700 Subject: [PATCH 42/73] rcu: Properly initialize ->boost_tasks on CPU offline When rcu_preempt_offline_tasks() clears tasks from a leaf rcu_node structure, it does not NULL out the structure's ->boost_tasks field. This commit therefore fixes this issue. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 7f3244c0df01..b1b485111321 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -584,8 +584,11 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ } + rnp->gp_tasks = NULL; + rnp->exp_tasks = NULL; #ifdef CONFIG_RCU_BOOST - /* In case root is being boosted and leaf is not. */ + rnp->boost_tasks = NULL; + /* In case root is being boosted and leaf was not. */ raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ if (rnp_root->boost_tasks != NULL && rnp_root->boost_tasks != rnp_root->gp_tasks) @@ -593,8 +596,6 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ #endif /* #ifdef CONFIG_RCU_BOOST */ - rnp->gp_tasks = NULL; - rnp->exp_tasks = NULL; return retval; } From b4270ee356e5ecef5394ab80c0a0301c1676b7f0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 31 Jul 2012 10:12:48 -0700 Subject: [PATCH 43/73] rcu: Permit RCU_NONIDLE() to be used from interrupt context There is a need to use RCU from interrupt context, but either before rcu_irq_enter() is called or after rcu_irq_exit() is called. If the interrupt occurs from idle, then lockdep-RCU will complain about such uses, as they appear to be illegal uses of RCU from the idle loop. In other environments, RCU_NONIDLE() could be used to properly protect the use of RCU, but RCU_NONIDLE() currently cannot be invoked except from process context. This commit therefore modifies RCU_NONIDLE() to permit its use more globally. Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 6 ++---- kernel/rcutiny.c | 2 ++ 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 115ead2b5155..0fbbd52e01f9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -210,14 +210,12 @@ extern void exit_rcu(void); * to nest RCU_NONIDLE() wrappers, but the nesting level is currently * quite limited. If deeper nesting is required, it will be necessary * to adjust DYNTICK_TASK_NESTING_VALUE accordingly. - * - * This macro may be used from process-level code only. */ #define RCU_NONIDLE(a) \ do { \ - rcu_idle_exit(); \ + rcu_irq_enter(); \ do { a; } while (0); \ - rcu_idle_enter(); \ + rcu_irq_exit(); \ } while (0) /* diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index e4163c5af1de..2e073a24d250 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -115,6 +115,7 @@ void rcu_irq_exit(void) rcu_idle_enter_common(newval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_exit); /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */ static void rcu_idle_exit_common(long long oldval) @@ -172,6 +173,7 @@ void rcu_irq_enter(void) rcu_idle_exit_common(oldval); local_irq_restore(flags); } +EXPORT_SYMBOL_GPL(rcu_irq_enter); #ifdef CONFIG_DEBUG_LOCK_ALLOC From 5cc900cf55fe58aaad93767c5a526e2a69cbcbc6 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 31 Jul 2012 14:09:49 -0700 Subject: [PATCH 44/73] rcu: Improve boost selection when moving tasks to root rcu_node The rcu_preempt_offline_tasks() moves all tasks queued on a given leaf rcu_node structure to the root rcu_node, which is done when the last CPU corresponding the the leaf rcu_node structure goes offline. Now that RCU-preempt's synchronize_rcu_expedited() implementation blocks CPU-hotplug operations during the initialization of each rcu_node structure's ->boost_tasks pointer, rcu_preempt_offline_tasks() can do a better job of setting the root rcu_node's ->boost_tasks pointer. The key point is that rcu_preempt_offline_tasks() runs as part of the CPU-hotplug process, so that a concurrent synchronize_rcu_expedited() is guaranteed to either have not started on the one hand (in which case there is no boosting on behalf of the expedited grace period) or to be completely initialized on the other (in which case, in the absence of other priority boosting, all ->boost_tasks pointers will be initialized). Therefore, if rcu_preempt_offline_tasks() finds that the ->boost_tasks pointer is equal to the ->exp_tasks pointer, it can be sure that it is correctly placed. In the case where there was boosting ongoing at the time that the synchronize_rcu_expedited() function started, different nodes might start boosting the tasks blocking the expedited grace period at different times. In this mixed case, the root node will either be boosting tasks for the expedited grace period already, or it will start as soon as it gets done boosting for the normal grace period -- but in this latter case, the root node's tasks needed to be boosted in any case. This commit therefore adds a check of the ->boost_tasks pointer against the ->exp_tasks pointer to the list that prevents updating ->boost_tasks. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index b1b485111321..15d28febbbd4 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -588,10 +588,15 @@ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, rnp->exp_tasks = NULL; #ifdef CONFIG_RCU_BOOST rnp->boost_tasks = NULL; - /* In case root is being boosted and leaf was not. */ + /* + * In case root is being boosted and leaf was not. Make sure + * that we boost the tasks blocking the current grace period + * in this case. + */ raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ if (rnp_root->boost_tasks != NULL && - rnp_root->boost_tasks != rnp_root->gp_tasks) + rnp_root->boost_tasks != rnp_root->gp_tasks && + rnp_root->boost_tasks != rnp_root->exp_tasks) rnp_root->boost_tasks = rnp_root->gp_tasks; raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ #endif /* #ifdef CONFIG_RCU_BOOST */ From a82dcc76021e22c174ba85d90b7a8c750b7362d0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 1 Aug 2012 14:29:20 -0700 Subject: [PATCH 45/73] rcu: Make offline-CPU checking allow for indefinite delays The rcu_implicit_offline_qs() function implicitly assumed that execution would progress predictably when interrupts are disabled, which is of course not guaranteed when running on a hypervisor. Furthermore, this function is short, and is called from one place only in a short function. This commit therefore ensures that the timing is checked before checking the condition, which guarantees correct behavior even given indefinite delays. It also inlines rcu_implicit_offline_qs() into rcu_implicit_dynticks_qs(). Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 53 +++++++++++++++++++----------------------------- 1 file changed, 21 insertions(+), 32 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f7bcd9e6c054..2c4ee4cdbc0e 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -318,35 +318,6 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) return &rsp->node[0]; } -/* - * If the specified CPU is offline, tell the caller that it is in - * a quiescent state. Otherwise, whack it with a reschedule IPI. - * Grace periods can end up waiting on an offline CPU when that - * CPU is in the process of coming online -- it will be added to the - * rcu_node bitmasks before it actually makes it online. The same thing - * can happen while a CPU is in the process of coming online. Because this - * race is quite rare, we check for it after detecting that the grace - * period has been delayed rather than checking each and every CPU - * each and every time we start a new grace period. - */ -static int rcu_implicit_offline_qs(struct rcu_data *rdp) -{ - /* - * If the CPU is offline for more than a jiffy, it is in a quiescent - * state. We can trust its state not to change because interrupts - * are disabled. The reason for the jiffy's worth of slack is to - * handle CPUs initializing on the way up and finding their way - * to the idle loop on the way down. - */ - if (cpu_is_offline(rdp->cpu) && - ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) { - trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); - rdp->offline_fqs++; - return 1; - } - return 0; -} - /* * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle * @@ -675,7 +646,7 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp) * Return true if the specified CPU has passed through a quiescent * state by virtue of being in or having passed through an dynticks * idle state since the last call to dyntick_save_progress_counter() - * for this same CPU. + * for this same CPU, or by virtue of having been offline. */ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) { @@ -699,8 +670,26 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return 1; } - /* Go check for the CPU being offline. */ - return rcu_implicit_offline_qs(rdp); + /* + * Check for the CPU being offline, but only if the grace period + * is old enough. We don't need to worry about the CPU changing + * state: If we see it offline even once, it has been through a + * quiescent state. + * + * The reason for insisting that the grace period be at least + * one jiffy old is that CPUs that are not quite online and that + * have just gone offline can still execute RCU read-side critical + * sections. + */ + if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies)) + return 0; /* Grace period is not old enough. */ + barrier(); + if (cpu_is_offline(rdp->cpu)) { + trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl"); + rdp->offline_fqs++; + return 1; + } + return 0; } static int jiffies_till_stall_check(void) From b065a85354239cc96295f696eeace67ad3a55e5c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Wed, 1 Aug 2012 15:57:54 -0700 Subject: [PATCH 46/73] rcu: Fix obsolete rcu_initiate_boost() header comment Commit 1217ed1b (rcu: permit rcu_read_unlock() to be called while holding runqueue locks) made rcu_initiate_boost() restore irq state when releasing the rcu_node structure's ->lock, but failed to update the header comment accordingly. This commit therefore brings the header comment up to date. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree_plugin.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 15d28febbbd4..c47b28bf18ae 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1197,9 +1197,9 @@ static int rcu_boost_kthread(void *arg) * kthread to start boosting them. If there is an expedited grace * period in progress, it is always time to boost. * - * The caller must hold rnp->lock, which this function releases, - * but irqs remain disabled. The ->boost_kthread_task is immortal, - * so we don't need to worry about it going away. + * The caller must hold rnp->lock, which this function releases. + * The ->boost_kthread_task is immortal, so we don't need to worry + * about it going away. */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) { From 115f7a7ca0d412aab81acaaaa95eb1ab1c622e2f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 10 Aug 2012 13:55:03 -0700 Subject: [PATCH 47/73] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() The increment_cpu_stall_ticks() function listed each RCU flavor explicitly, with an ifdef to handle preemptible RCU. This commit therefore applies for_each_rcu_flavor() to save a line of code. Because this commit switches from a code-based enumeration of the flavors of RCU to an rcu_state-list-based enumeration, it is no longer possible to apply __get_cpu_var() to the per-CPU rcu_data structures. We instead use __this_cpu_var() on the rcu_state structure's ->rda field that references the corresponding rcu_data structures. Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index c47b28bf18ae..70b33bf780f0 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2200,11 +2200,10 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp) /* Increment ->ticks_this_gp for all flavors of RCU. */ static void increment_cpu_stall_ticks(void) { - __get_cpu_var(rcu_sched_data).ticks_this_gp++; - __get_cpu_var(rcu_bh_data).ticks_this_gp++; -#ifdef CONFIG_TREE_PREEMPT_RCU - __get_cpu_var(rcu_preempt_data).ticks_this_gp++; -#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ + struct rcu_state *rsp; + + for_each_rcu_flavor(rsp) + __this_cpu_ptr(rsp->rda)->ticks_this_gp++; } #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ From 5fd4dc068c4ded1339180dbcd1a99e15b1c0a728 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 10 Aug 2012 16:00:11 -0700 Subject: [PATCH 48/73] rcu: Avoid rcu_print_detail_task_stall_rnp() segfault The rcu_print_detail_task_stall_rnp() function invokes rcu_preempt_blocked_readers_cgp() to verify that there are some preempted RCU readers blocking the current grace period outside of the protection of the rcu_node structure's ->lock. This means that the last blocked reader might exit its RCU read-side critical section and remove itself from the ->blkd_tasks list before the ->lock is acquired, resulting in a segmentation fault when the subsequent code attempts to dereference the now-NULL gp_tasks pointer. This commit therefore moves the test under the lock. This will not have measurable effect on lock contention because this code is invoked only when printing RCU CPU stall warnings, in other words, in the common case, never. Signed-off-by: Paul E. McKenney --- kernel/rcutree_plugin.h | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index 70b33bf780f0..df47014e129d 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -422,9 +422,11 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) unsigned long flags; struct task_struct *t; - if (!rcu_preempt_blocked_readers_cgp(rnp)) - return; raw_spin_lock_irqsave(&rnp->lock, flags); + if (!rcu_preempt_blocked_readers_cgp(rnp)) { + raw_spin_unlock_irqrestore(&rnp->lock, flags); + return; + } t = list_entry(rnp->gp_tasks, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) From c8020a67e625c714c4dbedc8ae2944b461e204ec Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 10 Aug 2012 16:55:59 -0700 Subject: [PATCH 49/73] rcu: Protect rcu_node accesses during CPU stall warnings The print_other_cpu_stall() function accesses a number of rcu_node fields without protection from the ->lock. In theory, this is not a problem because the fields accessed are all integers, but in practice the compiler can get nasty. Therefore, the commit extends the existing critical section to cover the entire loop body. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2c4ee4cdbc0e..2cf8eb3e2d43 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -746,14 +746,15 @@ static void print_other_cpu_stall(struct rcu_state *rsp) rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); ndetected += rcu_print_task_stall(rnp); + if (rnp->qsmask != 0) { + for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) + if (rnp->qsmask & (1UL << cpu)) { + print_cpu_stall_info(rsp, + rnp->grplo + cpu); + ndetected++; + } + } raw_spin_unlock_irqrestore(&rnp->lock, flags); - if (rnp->qsmask == 0) - continue; - for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) - if (rnp->qsmask & (1UL << cpu)) { - print_cpu_stall_info(rsp, rnp->grplo + cpu); - ndetected++; - } } /* From c96ea7cfdd88d0a67c970502bc5313fede34b86b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 13 Aug 2012 11:17:06 -0700 Subject: [PATCH 50/73] rcu: Avoid spurious RCU CPU stall warnings If a given CPU avoids the idle loop but also avoids starting a new RCU grace period for a full minute, RCU can issue spurious RCU CPU stall warnings. This commit fixes this issue by adding a check for ongoing grace period to avoid these spurious stall warnings. Reported-by: Becky Bruce Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 2cf8eb3e2d43..98f275296c6d 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -819,7 +819,8 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) j = ACCESS_ONCE(jiffies); js = ACCESS_ONCE(rsp->jiffies_stall); rnp = rdp->mynode; - if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { + if (rcu_gp_in_progress(rsp) && + (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); From fdab649b1aa732cd6e79654349088465cdff49af Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 13 Aug 2012 16:34:12 -0700 Subject: [PATCH 51/73] rcu: Remove redundant memory barrier from __call_rcu() The first memory barrier in __call_rcu() is supposed to order any updates done beforehand by the caller against the actual queuing of the callback. However, the second memory barrier (which is intended to order incrementing the queue lengths before queuing the callback) is also between the caller's updates and the queuing of the callback. The second memory barrier can therefore serve both purposes. This commit therefore removes the first memory barrier. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 98f275296c6d..ba4f4b4c2382 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1922,8 +1922,6 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), head->func = func; head->next = NULL; - smp_mb(); /* Ensure RCU update seen before callback registry. */ - /* * Opportunistically note grace-period endings and beginnings. * Note that we might see a beginning right after we see an From 7a11e2058f02feb6884efb067f328012c318a13f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 21 Aug 2012 12:14:19 -0700 Subject: [PATCH 52/73] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() The use of raw_local_irq_save() is unnecessary, given that local_irq_save() really does disable interrupts. Also, it appears to interfere with lockdep. Therefore, this commit moves to local_irq_save(). Reported-by: Fengguang Wu Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Fengguang Wu --- kernel/rcutiny_plugin.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h index 918fd1e8509c..3d0190282204 100644 --- a/kernel/rcutiny_plugin.h +++ b/kernel/rcutiny_plugin.h @@ -278,7 +278,7 @@ static int rcu_boost(void) rcu_preempt_ctrlblk.exp_tasks == NULL) return 0; /* Nothing to boost. */ - raw_local_irq_save(flags); + local_irq_save(flags); /* * Recheck with irqs disabled: all tasks in need of boosting @@ -287,7 +287,7 @@ static int rcu_boost(void) */ if (rcu_preempt_ctrlblk.boost_tasks == NULL && rcu_preempt_ctrlblk.exp_tasks == NULL) { - raw_local_irq_restore(flags); + local_irq_restore(flags); return 0; } @@ -317,7 +317,7 @@ static int rcu_boost(void) t = container_of(tb, struct task_struct, rcu_node_entry); rt_mutex_init_proxy_locked(&mtx, t); t->rcu_boost_mutex = &mtx; - raw_local_irq_restore(flags); + local_irq_restore(flags); rt_mutex_lock(&mtx); rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ @@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n) { unsigned long flags; - raw_local_irq_save(flags); + local_irq_save(flags); rcp->qlen -= n; - raw_local_irq_restore(flags); + local_irq_restore(flags); } /* From 803b0ebae921714d1c36f0996db8125eda5fae53 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 23 Aug 2012 08:34:07 -0700 Subject: [PATCH 53/73] time: RCU permitted to stop idle entry via softirq The can_stop_idle_tick() function complains if a softirq vector is raised too late in the idle-entry process, presumably in order to prevent dangling softirq invocations from being delayed across the full idle period, which might be indefinitely long -- and if softirq was asserted any later than the call to this function, such a delay might well happen. However, RCU needs to be able to use softirq to stop idle entry in order to be able to drain RCU callbacks from the current CPU, which in turn enables faster entry into dyntick-idle mode, which in turn reduces power consumption. Because RCU takes this action at a well-defined point in the idle-entry path, it is safe for RCU to take this approach. This commit therefore silences the error message that is sometimes produced when the going-idle CPU suddenly finds that it has an RCU_SOFTIRQ to process. The error message will continue to be issued for other softirq vectors. Reported-by: Sedat Dilek Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Tested-by: Sedat Dilek Reviewed-by: Josh Triplett --- include/linux/interrupt.h | 2 ++ kernel/time/tick-sched.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index c5f856a040b9..5e4e6170f43a 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -430,6 +430,8 @@ enum NR_SOFTIRQS }; +#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) + /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. */ diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 024540f97f74..4b1785a7bb83 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -436,7 +436,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (unlikely(local_softirq_pending() && cpu_online(cpu))) { static int ratelimit; - if (ratelimit < 10) { + if (ratelimit < 10 && + (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", (unsigned int) local_softirq_pending()); ratelimit++; From 58fac09566bb48592a09ef0fe0c7dbefa0cd2109 Mon Sep 17 00:00:00 2001 From: Michael Wang Date: Fri, 17 Aug 2012 12:33:34 +0800 Subject: [PATCH 54/73] kmemleak: Replace list_for_each_continue_rcu with new interface This patch replaces list_for_each_continue_rcu() with list_for_each_entry_continue_rcu() to save a few lines of code and allow removing list_for_each_continue_rcu(). Signed-off-by: Michael Wang Acked-by: Catalin Marinas Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- mm/kmemleak.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 45eb6217bf38..0de83b4541e9 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -1483,13 +1483,11 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos) { struct kmemleak_object *prev_obj = v; struct kmemleak_object *next_obj = NULL; - struct list_head *n = &prev_obj->object_list; + struct kmemleak_object *obj = prev_obj; ++(*pos); - list_for_each_continue_rcu(n, &object_list) { - struct kmemleak_object *obj = - list_entry(n, struct kmemleak_object, object_list); + list_for_each_entry_continue_rcu(obj, &object_list, object_list) { if (get_object(obj)) { next_obj = obj; break; From 22a767269a767b3ee91e4aaea353ac6bec6a912d Mon Sep 17 00:00:00 2001 From: Li Zhong Date: Wed, 19 Sep 2012 08:52:32 -0700 Subject: [PATCH 55/73] rcu: Move TINY_RCU quiescent state out of extended quiescent state TINY_RCU's rcu_idle_enter_common() invokes rcu_sched_qs() in order to inform the RCU core of the quiescent state implied by idle entry. Of course, idle is also an extended quiescent state, so that the call to rcu_sched_qs() speeds up RCU's invoking of any callbacks that might be queued. This speed-up is important when entering into dyntick-idle mode -- if there are no further scheduling-clock interrupts, the callbacks might never be invoked, which could result in a system hang. However, processing callbacks does event tracing, which in turn implies RCU read-side critical sections, which are illegal in extended quiescent states. This patch therefore moves the call to rcu_sched_qs() so that it precedes the point at which we inform lockdep that RCU has entered an extended quiescent state. Signed-off-by: Li Zhong Signed-off-by: Paul E. McKenney --- kernel/rcutiny.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 2e073a24d250..e4c6a598d6f7 100644 --- a/kernel/rcutiny.c +++ b/kernel/rcutiny.c @@ -75,9 +75,9 @@ static void rcu_idle_enter_common(long long newval) current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } + rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ barrier(); rcu_dynticks_nesting = newval; - rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ } /* From 86f343b50bb9f56cce60fade22da9defff28934c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 21 Sep 2012 10:41:50 -0700 Subject: [PATCH 56/73] rcu: Fix CONFIG_RCU_FAST_NO_HZ stall warning message The print_cpu_stall_fast_no_hz() function attempts to print -1 when the ->idle_gp_timer is not pending, but unsigned arithmetic causes it to instead print ULONG_MAX, which is 4294967295 on 32-bit systems and 18446744073709551615 on 64-bit systems. Neither of these are the most reader-friendly values, so this commit instead causes "timer not pending" to be printed when ->idle_gp_timer is not pending. Reported-by: Paul Walmsley Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney --- Documentation/RCU/stallwarn.txt | 16 ++++++++-------- kernel/rcutree_plugin.h | 12 ++++++++---- 2 files changed, 16 insertions(+), 12 deletions(-) diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt index 523364e4e1f1..1927151b386b 100644 --- a/Documentation/RCU/stallwarn.txt +++ b/Documentation/RCU/stallwarn.txt @@ -99,7 +99,7 @@ In kernels with CONFIG_RCU_FAST_NO_HZ, even more information is printed: INFO: rcu_preempt detected stall on CPU - 0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer=-1 + 0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 drain=0 . timer not pending (t=65000 jiffies) The "(64628 ticks this GP)" indicates that this CPU has taken more @@ -116,13 +116,13 @@ number between the two "/"s is the value of the nesting, which will be a small positive number if in the idle loop and a very large positive number (as shown above) otherwise. -For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the -CPU is not in the process of trying to force itself into dyntick-idle -state, the "." indicates that the CPU has not given up forcing RCU -into dyntick-idle mode (it would be "H" otherwise), and the "timer=-1" -indicates that the CPU has not recented forced RCU into dyntick-idle -mode (it would otherwise indicate the number of microseconds remaining -in this forced state). +For CONFIG_RCU_FAST_NO_HZ kernels, the "drain=0" indicates that the CPU is +not in the process of trying to force itself into dyntick-idle state, the +"." indicates that the CPU has not given up forcing RCU into dyntick-idle +mode (it would be "H" otherwise), and the "timer not pending" indicates +that the CPU has not recently forced RCU into dyntick-idle mode (it +would otherwise indicate the number of microseconds remaining in this +forced state). Multiple Warnings From One Stall diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index df47014e129d..e12d07ba601a 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -2130,11 +2130,15 @@ static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); struct timer_list *tltp = &rdtp->idle_gp_timer; + char c; - sprintf(cp, "drain=%d %c timer=%lu", - rdtp->dyntick_drain, - rdtp->dyntick_holdoff == jiffies ? 'H' : '.', - timer_pending(tltp) ? tltp->expires - jiffies : -1); + c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.'; + if (timer_pending(tltp)) + sprintf(cp, "drain=%d %c timer=%lu", + rdtp->dyntick_drain, c, tltp->expires - jiffies); + else + sprintf(cp, "drain=%d %c timer not pending", + rdtp->dyntick_drain, c); } #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ From 1331e7a1bbe1f11b19c4327ba0853bee2a606543 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 2 Aug 2012 17:43:50 -0700 Subject: [PATCH 57/73] rcu: Remove _rcu_barrier() dependency on __stop_machine() Currently, _rcu_barrier() relies on preempt_disable() to prevent any CPU from going offline, which in turn depends on CPU hotplug's use of __stop_machine(). This patch therefore makes _rcu_barrier() use get_online_cpus() to block CPU-hotplug operations. This has the added benefit of removing the need for _rcu_barrier() to adopt callbacks: Because CPU-hotplug operations are excluded, there can be no callbacks to adopt. This commit simplifies the code accordingly. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 83 ++++++------------------------------------ kernel/rcutree.h | 3 -- kernel/rcutree_trace.c | 4 +- 3 files changed, 13 insertions(+), 77 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f7bcd9e6c054..c45d3f745302 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1392,17 +1392,6 @@ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) int i; struct rcu_data *rdp = __this_cpu_ptr(rsp->rda); - /* - * If there is an rcu_barrier() operation in progress, then - * only the task doing that operation is permitted to adopt - * callbacks. To do otherwise breaks rcu_barrier() and friends - * by causing them to fail to wait for the callbacks in the - * orphanage. - */ - if (rsp->rcu_barrier_in_progress && - rsp->rcu_barrier_in_progress != current) - return; - /* Do the accounting first. */ rdp->qlen_lazy += rsp->qlen_lazy; rdp->qlen += rsp->qlen; @@ -1457,9 +1446,8 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) * The CPU has been completely removed, and some other CPU is reporting * this fact from process context. Do the remainder of the cleanup, * including orphaning the outgoing CPU's RCU callbacks, and also - * adopting them, if there is no _rcu_barrier() instance running. - * There can only be one CPU hotplug operation at a time, so no other - * CPU can be attempting to update rcu_cpu_kthread_task. + * adopting them. There can only be one CPU hotplug operation at a time, + * so no other CPU can be attempting to update rcu_cpu_kthread_task. */ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { @@ -1521,10 +1509,6 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) #else /* #ifdef CONFIG_HOTPLUG_CPU */ -static void rcu_adopt_orphan_cbs(struct rcu_state *rsp) -{ -} - static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { } @@ -2328,13 +2312,10 @@ static void rcu_barrier_func(void *type) static void _rcu_barrier(struct rcu_state *rsp) { int cpu; - unsigned long flags; struct rcu_data *rdp; - struct rcu_data rd; unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done); unsigned long snap_done; - init_rcu_head_on_stack(&rd.barrier_head); _rcu_barrier_trace(rsp, "Begin", -1, snap); /* Take mutex to serialize concurrent rcu_barrier() requests. */ @@ -2374,70 +2355,30 @@ static void _rcu_barrier(struct rcu_state *rsp) /* * Initialize the count to one rather than to zero in order to * avoid a too-soon return to zero in case of a short grace period - * (or preemption of this task). Also flag this task as doing - * an rcu_barrier(). This will prevent anyone else from adopting - * orphaned callbacks, which could cause otherwise failure if a - * CPU went offline and quickly came back online. To see this, - * consider the following sequence of events: - * - * 1. We cause CPU 0 to post an rcu_barrier_callback() callback. - * 2. CPU 1 goes offline, orphaning its callbacks. - * 3. CPU 0 adopts CPU 1's orphaned callbacks. - * 4. CPU 1 comes back online. - * 5. We cause CPU 1 to post an rcu_barrier_callback() callback. - * 6. Both rcu_barrier_callback() callbacks are invoked, awakening - * us -- but before CPU 1's orphaned callbacks are invoked!!! + * (or preemption of this task). Exclude CPU-hotplug operations + * to ensure that no offline CPU has callbacks queued. */ init_completion(&rsp->barrier_completion); atomic_set(&rsp->barrier_cpu_count, 1); - raw_spin_lock_irqsave(&rsp->onofflock, flags); - rsp->rcu_barrier_in_progress = current; - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); + get_online_cpus(); /* - * Force every CPU with callbacks to register a new callback - * that will tell us when all the preceding callbacks have - * been invoked. If an offline CPU has callbacks, wait for - * it to either come back online or to finish orphaning those - * callbacks. + * Force each CPU with callbacks to register a new callback. + * When that callback is invoked, we will know that all of the + * corresponding CPU's preceding callbacks have been invoked. */ - for_each_possible_cpu(cpu) { - preempt_disable(); + for_each_online_cpu(cpu) { rdp = per_cpu_ptr(rsp->rda, cpu); - if (cpu_is_offline(cpu)) { - _rcu_barrier_trace(rsp, "Offline", cpu, - rsp->n_barrier_done); - preempt_enable(); - while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen)) - schedule_timeout_interruptible(1); - } else if (ACCESS_ONCE(rdp->qlen)) { + if (ACCESS_ONCE(rdp->qlen)) { _rcu_barrier_trace(rsp, "OnlineQ", cpu, rsp->n_barrier_done); smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); - preempt_enable(); } else { _rcu_barrier_trace(rsp, "OnlineNQ", cpu, rsp->n_barrier_done); - preempt_enable(); } } - - /* - * Now that all online CPUs have rcu_barrier_callback() callbacks - * posted, we can adopt all of the orphaned callbacks and place - * an rcu_barrier_callback() callback after them. When that is done, - * we are guaranteed to have an rcu_barrier_callback() callback - * following every callback that could possibly have been - * registered before _rcu_barrier() was called. - */ - raw_spin_lock_irqsave(&rsp->onofflock, flags); - rcu_adopt_orphan_cbs(rsp); - rsp->rcu_barrier_in_progress = NULL; - raw_spin_unlock_irqrestore(&rsp->onofflock, flags); - atomic_inc(&rsp->barrier_cpu_count); - smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */ - rd.rsp = rsp; - rsp->call(&rd.barrier_head, rcu_barrier_callback); + put_online_cpus(); /* * Now that we have an rcu_barrier_callback() callback on each @@ -2458,8 +2399,6 @@ static void _rcu_barrier(struct rcu_state *rsp) /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rsp->barrier_mutex); - - destroy_rcu_head_on_stack(&rd.barrier_head); } /** diff --git a/kernel/rcutree.h b/kernel/rcutree.h index 4d29169f2124..94dfdf1f31f5 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -398,9 +398,6 @@ struct rcu_state { struct rcu_head **orphan_donetail; /* Tail of above. */ long qlen_lazy; /* Number of lazy callbacks. */ long qlen; /* Total number of callbacks. */ - struct task_struct *rcu_barrier_in_progress; - /* Task doing rcu_barrier(), */ - /* or NULL if no barrier. */ struct mutex barrier_mutex; /* Guards barrier fields. */ atomic_t barrier_cpu_count; /* # CPUs waiting on. */ struct completion barrier_completion; /* Wake at barrier end. */ diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c index abffb486e94e..6a2e52a85d77 100644 --- a/kernel/rcutree_trace.c +++ b/kernel/rcutree_trace.c @@ -51,8 +51,8 @@ static int show_rcubarrier(struct seq_file *m, void *unused) struct rcu_state *rsp; for_each_rcu_flavor(rsp) - seq_printf(m, "%s: %c bcc: %d nbd: %lu\n", - rsp->name, rsp->rcu_barrier_in_progress ? 'B' : '.', + seq_printf(m, "%s: bcc: %d nbd: %lu\n", + rsp->name, atomic_read(&rsp->barrier_cpu_count), rsp->n_barrier_done); return 0; From 0d8ee37e2fcb7b77b9c5dee784beca5a215cad4c Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 3 Aug 2012 13:16:15 -0700 Subject: [PATCH 58/73] rcu: Disallow callback registry on offline CPUs Posting a callback after the CPU_DEAD notifier effectively leaks that callback unless/until that CPU comes back online. Silence is unhelpful when attempting to track down such leaks, so this commit emits a WARN_ON_ONCE() and unconditionally leaks the callback when an offline CPU attempts to register a callback. The rdp->nxttail[RCU_NEXT_TAIL] is set to NULL in the CPU_DEAD notifier and restored in the CPU_UP_PREPARE notifier, allowing _call_rcu() to determine exactly when posting callbacks is illegal. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcutree.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index c45d3f745302..be76c80a14d1 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1505,6 +1505,9 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL, "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n", cpu, rdp->qlen, rdp->nxtlist); + init_callback_list(rdp); + /* Disallow further callbacks on this CPU. */ + rdp->nxttail[RCU_NEXT_TAIL] = NULL; } #else /* #ifdef CONFIG_HOTPLUG_CPU */ @@ -1927,6 +1930,12 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ + if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL)) { + /* _call_rcu() is illegal on offline CPU; leak the callback. */ + WARN_ON_ONCE(1); + local_irq_restore(flags); + return; + } ACCESS_ONCE(rdp->qlen)++; if (lazy) rdp->qlen_lazy++; @@ -2464,6 +2473,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; + init_callback_list(rdp); /* Re-enable callbacks on this CPU. */ rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); From 5d18023294abc22984886bd7185344e0c2be0daf Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 20 Aug 2012 11:26:57 +0200 Subject: [PATCH 59/73] sched: Fix load avg vs cpu-hotplug Rabik and Paul reported two different issues related to the same few lines of code. Rabik's issue is that the nr_uninterruptible migration code is wrong in that he sees artifacts due to this (Rabik please do expand in more detail). Paul's issue is that this code as it stands relies on us using stop_machine() for unplug, we all would like to remove this assumption so that eventually we can remove this stop_machine() usage altogether. The only reason we'd have to migrate nr_uninterruptible is so that we could use for_each_online_cpu() loops in favour of for_each_possible_cpu() loops, however since nr_uninterruptible() is the only such loop and its using possible lets not bother at all. The problem Rabik sees is (probably) caused by the fact that by migrating nr_uninterruptible we screw rq->calc_load_active for both rqs involved. So don't bother with fancy migration schemes (meaning we now have to keep using for_each_possible_cpu()) and instead fold any nr_active delta after we migrate all tasks away to make sure we don't have any skewed nr_active accounting. [ paulmck: Move call to calc_load_migration to CPU_DEAD to avoid miscounting noted by Rakib. ] Reported-by: Rakib Mullick Reported-by: Paul E. McKenney Signed-off-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- kernel/sched/core.c | 41 ++++++++++++++++++++--------------------- 1 file changed, 20 insertions(+), 21 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fbf1fd098dc6..8c38b5e7ce47 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5304,27 +5304,17 @@ void idle_task_exit(void) } /* - * While a dead CPU has no uninterruptible tasks queued at this point, - * it might still have a nonzero ->nr_uninterruptible counter, because - * for performance reasons the counter is not stricly tracking tasks to - * their home CPUs. So we just add the counter to another CPU's counter, - * to keep the global sum constant after CPU-down: + * Since this CPU is going 'away' for a while, fold any nr_active delta + * we might have. Assumes we're called after migrate_tasks() so that the + * nr_active count is stable. + * + * Also see the comment "Global load-average calculations". */ -static void migrate_nr_uninterruptible(struct rq *rq_src) +static void calc_load_migrate(struct rq *rq) { - struct rq *rq_dest = cpu_rq(cpumask_any(cpu_active_mask)); - - rq_dest->nr_uninterruptible += rq_src->nr_uninterruptible; - rq_src->nr_uninterruptible = 0; -} - -/* - * remove the tasks which were accounted by rq from calc_load_tasks. - */ -static void calc_global_load_remove(struct rq *rq) -{ - atomic_long_sub(rq->calc_load_active, &calc_load_tasks); - rq->calc_load_active = 0; + long delta = calc_load_fold_active(rq); + if (delta) + atomic_long_add(delta, &calc_load_tasks); } /* @@ -5617,9 +5607,18 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) migrate_tasks(cpu); BUG_ON(rq->nr_running != 1); /* the migration thread */ raw_spin_unlock_irqrestore(&rq->lock, flags); + break; - migrate_nr_uninterruptible(rq); - calc_global_load_remove(rq); + case CPU_DEAD: + { + struct rq *dest_rq; + + local_irq_save(flags); + dest_rq = cpu_rq(smp_processor_id()); + raw_spin_lock(&dest_rq->lock); + calc_load_migrate(rq); + raw_spin_unlock_irqrestore(&dest_rq->lock, flags); + } break; #endif } From a2db672aa305a045404615e5222ba681bab6cf58 Mon Sep 17 00:00:00 2001 From: Silas Boyd-Wickizer Date: Fri, 3 Aug 2012 12:33:27 -0700 Subject: [PATCH 60/73] Use get_online_cpus to avoid races involving CPU hotplug If arch/x86/kernel/msr.c is a module, a CPU might offline or online between the for_each_online_cpu(i) loop and the call to register_hotcpu_notifier in msr_init or the call to unregister_hotcpu_notifier in msr_exit. The potential races can lead to leaks/duplicates, attempts to destroy non-existant devices, or random pointer dereferences. For example, in msr_init if: for_each_online_cpu(i) { err = msr_device_create(i); if (err != 0) goto out_class; } <----- CPU offlines register_hotcpu_notifier(&msr_class_cpu_notifier); and the CPU never onlines before msr_exit, then the module will never call msr_device_destroy for the associated CPU. This fix surrounds for_each_online_cpu and register_hotcpu_notifier or unregister_hotcpu_notifier with get_online_cpus+put_online_cpus. Tested on a VM. Signed-off-by: Silas Boyd-Wickizer Signed-off-by: Paul E. McKenney --- arch/x86/kernel/msr.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index eb113693f043..a7c5661f8496 100644 --- a/arch/x86/kernel/msr.c +++ b/arch/x86/kernel/msr.c @@ -257,12 +257,14 @@ static int __init msr_init(void) goto out_chrdev; } msr_class->devnode = msr_devnode; + get_online_cpus(); for_each_online_cpu(i) { err = msr_device_create(i); if (err != 0) goto out_class; } register_hotcpu_notifier(&msr_class_cpu_notifier); + put_online_cpus(); err = 0; goto out; @@ -271,6 +273,7 @@ out_class: i = 0; for_each_online_cpu(i) msr_device_destroy(i); + put_online_cpus(); class_destroy(msr_class); out_chrdev: __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); @@ -281,11 +284,13 @@ out: static void __exit msr_exit(void) { int cpu = 0; + get_online_cpus(); for_each_online_cpu(cpu) msr_device_destroy(cpu); class_destroy(msr_class); __unregister_chrdev(MSR_MAJOR, 0, NR_CPUS, "cpu/msr"); unregister_hotcpu_notifier(&msr_class_cpu_notifier); + put_online_cpus(); } module_init(msr_init); From 429227bbe55647aa42f8f63cac61e4544e248629 Mon Sep 17 00:00:00 2001 From: Silas Boyd-Wickizer Date: Fri, 3 Aug 2012 12:34:50 -0700 Subject: [PATCH 61/73] Use get_online_cpus to avoid races involving CPU hotplug If arch/x86/kernel/cpuid.c is a module, a CPU might offline or online between the for_each_online_cpu() loop and the call to register_hotcpu_notifier in cpuid_init or the call to unregister_hotcpu_notifier in cpuid_exit. The potential races can lead to leaks/duplicates, attempts to destroy non-existant devices, or random pointer dereferences. For example, in cpuid_exit if: for_each_online_cpu(cpu) cpuid_device_destroy(cpu); class_destroy(cpuid_class); __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); <----- CPU onlines unregister_hotcpu_notifier(&cpuid_class_cpu_notifier); the hotcpu notifier will attempt to create a device for the cpuid_class, which the module already destroyed. This fix surrounds for_each_online_cpu and register_hotcpu_notifier or unregister_hotcpu_notifier with get_online_cpus+put_online_cpus. Tested on a VM. Signed-off-by: Silas Boyd-Wickizer Signed-off-by: Paul E. McKenney --- arch/x86/kernel/cpuid.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/x86/kernel/cpuid.c b/arch/x86/kernel/cpuid.c index 39472dd2323f..60c78917190c 100644 --- a/arch/x86/kernel/cpuid.c +++ b/arch/x86/kernel/cpuid.c @@ -199,12 +199,14 @@ static int __init cpuid_init(void) goto out_chrdev; } cpuid_class->devnode = cpuid_devnode; + get_online_cpus(); for_each_online_cpu(i) { err = cpuid_device_create(i); if (err != 0) goto out_class; } register_hotcpu_notifier(&cpuid_class_cpu_notifier); + put_online_cpus(); err = 0; goto out; @@ -214,6 +216,7 @@ out_class: for_each_online_cpu(i) { cpuid_device_destroy(i); } + put_online_cpus(); class_destroy(cpuid_class); out_chrdev: __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); @@ -225,11 +228,13 @@ static void __exit cpuid_exit(void) { int cpu = 0; + get_online_cpus(); for_each_online_cpu(cpu) cpuid_device_destroy(cpu); class_destroy(cpuid_class); __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid"); unregister_hotcpu_notifier(&cpuid_class_cpu_notifier); + put_online_cpus(); } module_init(cpuid_init); From 6a6c0272f17cc80a8286d915f2ddf31557c2d559 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Thu, 23 Aug 2012 14:11:25 +0200 Subject: [PATCH 62/73] alpha: Fix preemption handling in idle loop cpu_idle() is called on the boot CPU by the init code with preemption disabled. But the cpu_idle() function in alpha doesn't handle this when it calls schedule() directly. Fix it by converting it into schedule_preempt_disabled(). Also disable preemption before calling cpu_idle() from secondary CPU entry code to stay consistent with this state. Signed-off-by: Frederic Weisbecker Tested-by: Michael Cree Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Matt Turner Cc: alpha Cc: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/alpha/kernel/process.c | 3 ++- arch/alpha/kernel/smp.c | 1 + 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c index d6fde98b74b3..db56f31dbf70 100644 --- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -56,7 +56,8 @@ cpu_idle(void) while (!need_resched()) cpu_relax(); - schedule(); + + schedule_preempt_disabled(); } } diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c index 35ddc02bfa4a..a41ad90a97a6 100644 --- a/arch/alpha/kernel/smp.c +++ b/arch/alpha/kernel/smp.c @@ -166,6 +166,7 @@ smp_callin(void) DBGS(("smp_callin: commencing CPU %d current %p active_mm %p\n", cpuid, current, current->active_mm)); + preempt_disable(); /* Do nothing. */ cpu_idle(); } From 4c94cada48f7c660eca582be6032427a5e367117 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 63/73] alpha: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the Alpha's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Tested-by: Michael Cree Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Matt Turner Cc: alpha Cc: Paul E. McKenney Cc: # 3.3+ Reviewed-by: Josh Triplett --- arch/alpha/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c index db56f31dbf70..83638aa096d5 100644 --- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -28,6 +28,7 @@ #include #include #include +#include #include #include @@ -54,9 +55,11 @@ cpu_idle(void) /* FIXME -- EV6 and LCA45 know how to power down the CPU. */ + rcu_idle_enter(); while (!need_resched()) cpu_relax(); + rcu_idle_exit(); schedule_preempt_disabled(); } } From c633f9e788928e91ad11f44df29b47bbbe9550b0 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 64/73] cris: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the Cris's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Mikael Starvik Cc: Jesper Nilsson Cc: Cris Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/cris/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/cris/kernel/process.c b/arch/cris/kernel/process.c index 66fd01728790..7f65be6f7f17 100644 --- a/arch/cris/kernel/process.c +++ b/arch/cris/kernel/process.c @@ -25,6 +25,7 @@ #include #include #include +#include //#define DEBUG @@ -74,6 +75,7 @@ void cpu_idle (void) { /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) { void (*idle)(void); /* @@ -86,6 +88,7 @@ void cpu_idle (void) idle = default_idle; idle(); } + rcu_idle_exit(); schedule_preempt_disabled(); } } From 41d8fe5bb3cf91ce2716ac8f43e4b40d802a99c8 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 65/73] frv: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the Frv's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: David Howells Cc: # 3.3+ Acked-by: David Howells Reviewed-by: Josh Triplett --- arch/frv/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/frv/kernel/process.c b/arch/frv/kernel/process.c index ff95f50efea5..2eb7fa5bf9d8 100644 --- a/arch/frv/kernel/process.c +++ b/arch/frv/kernel/process.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include @@ -69,12 +70,14 @@ void cpu_idle(void) { /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) { check_pgt_cache(); if (!frv_dma_inprogress && idle) idle(); } + rcu_idle_exit(); schedule_preempt_disabled(); } From b2fe1430d4115c74d007c825cb9dc3317f28bb16 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 66/73] h8300: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the h8300's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Yoshinori Sato Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/h8300/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/h8300/kernel/process.c b/arch/h8300/kernel/process.c index 0e9c315be104..f153ed1a4c08 100644 --- a/arch/h8300/kernel/process.c +++ b/arch/h8300/kernel/process.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -78,8 +79,10 @@ void (*idle)(void) = default_idle; void cpu_idle(void) { while (1) { + rcu_idle_enter(); while (!need_resched()) idle(); + rcu_idle_exit(); schedule_preempt_disabled(); } } From 48ae077cfce72591b8fc80e1dcc87806f86fed7f Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 67/73] m32r: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the m32r's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Hirokazu Takata Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/m32r/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/m32r/kernel/process.c b/arch/m32r/kernel/process.c index 3a4a32b27208..384e63f3a4c4 100644 --- a/arch/m32r/kernel/process.c +++ b/arch/m32r/kernel/process.c @@ -26,6 +26,7 @@ #include #include #include +#include #include #include @@ -82,6 +83,7 @@ void cpu_idle (void) { /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) { void (*idle)(void) = pm_idle; @@ -90,6 +92,7 @@ void cpu_idle (void) idle(); } + rcu_idle_exit(); schedule_preempt_disabled(); } } From 5b57ba37e82a15f345a6a2eb8c01a2b2d94c5eeb Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 68/73] m68k: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the m68k's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Acked-by: Geert Uytterhoeven Cc: m68k Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/m68k/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c index c488e3cfab53..ac2892e49c7c 100644 --- a/arch/m68k/kernel/process.c +++ b/arch/m68k/kernel/process.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include @@ -75,8 +76,10 @@ void cpu_idle(void) { /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) idle(); + rcu_idle_exit(); schedule_preempt_disabled(); } } From 5b0753a90b7a98bc613c3767e9263a1a76d4f900 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 69/73] mn10300: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the mn10300's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: David Howells Cc: Koichi Yasutake Cc: # 3.3+ Signed-off-by: Paul E. McKenney Acked-by: David Howells Reviewed-by: Josh Triplett --- arch/mn10300/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/mn10300/kernel/process.c b/arch/mn10300/kernel/process.c index 7dab0cd36466..e9cceba193b6 100644 --- a/arch/mn10300/kernel/process.c +++ b/arch/mn10300/kernel/process.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include #include @@ -107,6 +108,7 @@ void cpu_idle(void) { /* endless idle loop with no priority at all */ for (;;) { + rcu_idle_enter(); while (!need_resched()) { void (*idle)(void); @@ -121,6 +123,7 @@ void cpu_idle(void) } idle(); } + rcu_idle_exit(); schedule_preempt_disabled(); } From fbe752188d5589e7fcbb8e79824e560f77dccc92 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 70/73] parisc: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the parisc's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: James E.J. Bottomley Cc: Helge Deller Cc: Parisc Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/parisc/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c index 2c05a9292a81..8c6b6b6561f0 100644 --- a/arch/parisc/kernel/process.c +++ b/arch/parisc/kernel/process.c @@ -48,6 +48,7 @@ #include #include #include +#include #include #include @@ -69,8 +70,10 @@ void cpu_idle(void) /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) barrier(); + rcu_idle_exit(); schedule_preempt_disabled(); check_pgt_cache(); } From 0ee23fda59740767324b4340247ca41a2f498ca6 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 71/73] score: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in scores's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Chen Liqin Cc: Lennox Wu Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/score/kernel/process.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/score/kernel/process.c b/arch/score/kernel/process.c index 2707023c7563..637970cfd3f4 100644 --- a/arch/score/kernel/process.c +++ b/arch/score/kernel/process.c @@ -27,6 +27,7 @@ #include #include #include +#include void (*pm_power_off)(void); EXPORT_SYMBOL(pm_power_off); @@ -50,9 +51,10 @@ void __noreturn cpu_idle(void) { /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) barrier(); - + rcu_idle_exit(); schedule_preempt_disabled(); } } From 11ad47a0edbd62bfc0547cfcdf227a911433f207 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 22 Aug 2012 17:27:34 +0200 Subject: [PATCH 72/73] xtensa: Add missing RCU idle APIs on idle loop In the old times, the whole idle task was considered as an RCU quiescent state. But as RCU became more and more successful overtime, some RCU read side critical section have been added even in the code of some architectures idle tasks, for tracing for example. So nowadays, rcu_idle_enter() and rcu_idle_exit() must be called by the architecture to tell RCU about the part in the idle loop that doesn't make use of rcu read side critical sections, typically the part that puts the CPU in low power mode. This is necessary for RCU to find the quiescent states in idle in order to complete grace periods. Add this missing pair of calls in the xtensa's idle loop. Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Chris Zankel Cc: # 3.3+ Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- arch/xtensa/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/xtensa/kernel/process.c b/arch/xtensa/kernel/process.c index 2c8d6a3d250a..bc44311aa18c 100644 --- a/arch/xtensa/kernel/process.c +++ b/arch/xtensa/kernel/process.c @@ -31,6 +31,7 @@ #include #include #include +#include #include #include @@ -110,8 +111,10 @@ void cpu_idle(void) /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); while (!need_resched()) platform_idle(); + rcu_idle_exit(); schedule_preempt_disabled(); } } From 93482f4ef1093f5961a63359a34612183d6beea0 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 24 Aug 2012 13:22:13 -0700 Subject: [PATCH 73/73] ia64: Add missing RCU idle APIs on idle loop Traditionally, the entire idle task served as an RCU quiescent state. But when RCU read side critical sections started appearing within the idle loop, this traditional strategy became untenable. The fix was to create new RCU APIs named rcu_idle_enter() and rcu_idle_exit(), which must be called by each architecture's idle loop so that RCU can tell when it is safe to ignore a given idle CPU. Unfortunately, this fix was never applied to ia64, a shortcoming remedied by this commit. Reported by: Tony Luck Signed-off-by: Paul E. McKenney Cc: # 3.3+ Signed-off-by: Paul E. McKenney Tested by: Tony Luck Reviewed-by: Josh Triplett --- arch/ia64/kernel/process.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c index dd6fc1449741..3e316ec0b835 100644 --- a/arch/ia64/kernel/process.c +++ b/arch/ia64/kernel/process.c @@ -29,6 +29,7 @@ #include #include #include +#include #include #include @@ -279,6 +280,7 @@ cpu_idle (void) /* endless idle loop with no priority at all */ while (1) { + rcu_idle_enter(); if (can_do_pal_halt) { current_thread_info()->status &= ~TS_POLLING; /* @@ -309,6 +311,7 @@ cpu_idle (void) normal_xtp(); #endif } + rcu_idle_exit(); schedule_preempt_disabled(); check_pgt_cache(); if (cpu_is_offline(cpu))