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rcu/tree: Keep kfree_rcu() awake during lock contention 

On PREEMPT_RT kernels, the krcp spinlock gets converted to an rt-mutex
and causes kfree_rcu() callers to sleep. This makes it unusable for
callers in purely atomic sections such as non-threaded IRQ handlers and
raw spinlock sections. Fix it by converting the spinlock to a raw
spinlock.

Vetting all code paths, there is no reason to believe that the raw
spinlock will hurt RT latencies as it is not held for a long time.

Cc: bigeasy@linutronix.de
Cc: Uladzislau Rezki <urezki@gmail.com>
Reviewed-by: Uladzislau Rezki <urezki@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2020-05-25 23:47:45 +02:00 committed by Paul E. McKenney
parent 8e11690d2f
commit 8ac88f7177
1 changed files with 15 additions and 15 deletions
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30
kernel/rcu/tree.c
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@ -3016,7 +3016,7 @@ struct kfree_rcu_cpu {
struct kfree_rcu_bulk_data *bhead; struct kfree_rcu_bulk_data *bhead;
struct kfree_rcu_bulk_data *bcached; struct kfree_rcu_bulk_data *bcached;
struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES]; struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
spinlock_t lock; raw_spinlock_t lock;
struct delayed_work monitor_work; struct delayed_work monitor_work;
bool monitor_todo; bool monitor_todo;
bool initialized; bool initialized;
@ -3049,12 +3049,12 @@ static void kfree_rcu_work(struct work_struct *work)
krwp = container_of(to_rcu_work(work), krwp = container_of(to_rcu_work(work),
struct kfree_rcu_cpu_work, rcu_work); struct kfree_rcu_cpu_work, rcu_work);
krcp = krwp->krcp; krcp = krwp->krcp;
spin_lock_irqsave(&krcp->lock, flags); raw_spin_lock_irqsave(&krcp->lock, flags);
head = krwp->head_free; head = krwp->head_free;
krwp->head_free = NULL; krwp->head_free = NULL;
bhead = krwp->bhead_free; bhead = krwp->bhead_free;
krwp->bhead_free = NULL; krwp->bhead_free = NULL;
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
/* "bhead" is now private, so traverse locklessly. */ /* "bhead" is now private, so traverse locklessly. */
for (; bhead; bhead = bnext) { for (; bhead; bhead = bnext) {
@ -3157,14 +3157,14 @@ static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp,
krcp->monitor_todo = false; krcp->monitor_todo = false;
if (queue_kfree_rcu_work(krcp)) { if (queue_kfree_rcu_work(krcp)) {
// Success! Our job is done here. // Success! Our job is done here.
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
return; return;
} }
// Previous RCU batch still in progress, try again later. // Previous RCU batch still in progress, try again later.
krcp->monitor_todo = true; krcp->monitor_todo = true;
schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
} }
/* /*
@ -3177,11 +3177,11 @@ static void kfree_rcu_monitor(struct work_struct *work)
struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu,
monitor_work.work); monitor_work.work);
spin_lock_irqsave(&krcp->lock, flags); raw_spin_lock_irqsave(&krcp->lock, flags);
if (krcp->monitor_todo) if (krcp->monitor_todo)
kfree_rcu_drain_unlock(krcp, flags); kfree_rcu_drain_unlock(krcp, flags);
else else
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
} }
static inline bool static inline bool
@ -3252,7 +3252,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
local_irq_save(flags); // For safely calling this_cpu_ptr(). local_irq_save(flags); // For safely calling this_cpu_ptr().
krcp = this_cpu_ptr(&krc); krcp = this_cpu_ptr(&krc);
if (krcp->initialized) if (krcp->initialized)
spin_lock(&krcp->lock); raw_spin_lock(&krcp->lock);
// Queue the object but don't yet schedule the batch. // Queue the object but don't yet schedule the batch.
if (debug_rcu_head_queue(head)) { if (debug_rcu_head_queue(head)) {
@ -3283,7 +3283,7 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
unlock_return: unlock_return:
if (krcp->initialized) if (krcp->initialized)
spin_unlock(&krcp->lock); raw_spin_unlock(&krcp->lock);
local_irq_restore(flags); local_irq_restore(flags);
} }
EXPORT_SYMBOL_GPL(kfree_call_rcu); EXPORT_SYMBOL_GPL(kfree_call_rcu);
@ -3315,11 +3315,11 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
count = krcp->count; count = krcp->count;
spin_lock_irqsave(&krcp->lock, flags); raw_spin_lock_irqsave(&krcp->lock, flags);
if (krcp->monitor_todo) if (krcp->monitor_todo)
kfree_rcu_drain_unlock(krcp, flags); kfree_rcu_drain_unlock(krcp, flags);
else else
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
sc->nr_to_scan -= count; sc->nr_to_scan -= count;
freed += count; freed += count;
@ -3346,15 +3346,15 @@ void __init kfree_rcu_scheduler_running(void)
for_each_online_cpu(cpu) { for_each_online_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
spin_lock_irqsave(&krcp->lock, flags); raw_spin_lock_irqsave(&krcp->lock, flags);
if (!krcp->head || krcp->monitor_todo) { if (!krcp->head || krcp->monitor_todo) {
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
continue; continue;
} }
krcp->monitor_todo = true; krcp->monitor_todo = true;
schedule_delayed_work_on(cpu, &krcp->monitor_work, schedule_delayed_work_on(cpu, &krcp->monitor_work,
KFREE_DRAIN_JIFFIES); KFREE_DRAIN_JIFFIES);
spin_unlock_irqrestore(&krcp->lock, flags); raw_spin_unlock_irqrestore(&krcp->lock, flags);
} }
} }
@ -4250,7 +4250,7 @@ static void __init kfree_rcu_batch_init(void)
for_each_possible_cpu(cpu) { for_each_possible_cpu(cpu) {
struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
spin_lock_init(&krcp->lock); raw_spin_lock_init(&krcp->lock);
for (i = 0; i < KFREE_N_BATCHES; i++) { for (i = 0; i < KFREE_N_BATCHES; i++) {
INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work); INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
krcp->krw_arr[i].krcp = krcp; krcp->krw_arr[i].krcp = krcp;