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rcu: Diagnostics for grace-period startup hangs 

This commit causes a splat if RCU is idle and a request for a new grace
period is ignored for more than one second.  This splat normally indicates
that some code path asked for a new grace period, but failed to wake up
the RCU grace-period kthread.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Fix bug located by Dan Carpenter and his static checker. ]
[ paulmck: Fix self-deadlock bug located 0day test robot. ]
[ paulmck: Disable unless CONFIG_PROVE_RCU=y. ]
This commit is contained in:
Paul E. McKenney 2018-04-21 20:44:11 -07:00
parent 8c42b1f39f
commit 26d950a945
2 changed files with 66 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
kernel/rcu/tree.c
View File

@ -1681,6 +1681,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
}
trace_rcu_this_gp(rnp_root, rdp, c, TPS("Startedroot"));
WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
rsp->gp_req_activity = jiffies;
if (!rsp->gp_kthread) {
trace_rcu_this_gp(rnp_root, rdp, c, TPS("NoGPkthread"));
goto unlock_out;
@ -2113,6 +2114,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
/* Advance CBs to reduce false positives below. */
if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
rsp->gp_req_activity = jiffies;
trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
TPS("newreq"));
}
@ -2744,6 +2746,65 @@ static void force_quiescent_state(struct rcu_state *rsp)
rcu_gp_kthread_wake(rsp);
}
/*
* This function checks for grace-period requests that fail to motivate
* RCU to come out of its idle mode.
*/
static void
rcu_check_gp_start_stall(struct rcu_state *rsp, struct rcu_node *rnp,
struct rcu_data *rdp)
{
unsigned long flags;
unsigned long j;
struct rcu_node *rnp_root = rcu_get_root(rsp);
static atomic_t warned = ATOMIC_INIT(0);
if (!IS_ENABLED(CONFIG_PROVE_RCU) ||
rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)))
return;
j = jiffies; /* Expensive access, and in common case don't get here. */
if (time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
atomic_read(&warned))
return;
raw_spin_lock_irqsave_rcu_node(rnp, flags);
j = jiffies;
if (rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)) ||
time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
atomic_read(&warned)) {
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
/* Hold onto the leaf lock to make others see warned==1. */
if (rnp_root != rnp)
raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
j = jiffies;
if (rcu_gp_in_progress(rsp) || !need_any_future_gp(rcu_get_root(rsp)) ||
time_before(j, rsp->gp_req_activity + HZ) ||
time_before(j, rsp->gp_activity + HZ) ||
atomic_xchg(&warned, 1)) {
raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return;
}
pr_alert("%s: g%lu %d%d%d%d gar:%lu ga:%lu f%#x %s->state:%#lx\n",
__func__, READ_ONCE(rsp->gpnum),
need_future_gp_element(rcu_get_root(rsp), 0),
need_future_gp_element(rcu_get_root(rsp), 1),
need_future_gp_element(rcu_get_root(rsp), 2),
need_future_gp_element(rcu_get_root(rsp), 3),
j - rsp->gp_req_activity, j - rsp->gp_activity,
rsp->gp_flags, rsp->name,
rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL);
WARN_ON(1);
if (rnp_root != rnp)
raw_spin_unlock_rcu_node(rnp_root);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
}
/*
* This does the RCU core processing work for the specified rcu_state
* and rcu_data structures. This may be called only from the CPU to
@ -2755,7 +2816,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
unsigned long flags;
bool needwake;
struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
struct rcu_node *rnp;
struct rcu_node *rnp = rdp->mynode;
WARN_ON_ONCE(!rdp->beenonline);
@ -2769,7 +2830,6 @@ __rcu_process_callbacks(struct rcu_state *rsp)
if (rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) {
local_irq_restore(flags);
} else {
rnp = rdp->mynode;
raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
@ -2778,6 +2838,8 @@ __rcu_process_callbacks(struct rcu_state *rsp)
}
}
rcu_check_gp_start_stall(rsp, rnp, rdp);
/* If there are callbacks ready, invoke them. */
if (rcu_segcblist_ready_cbs(&rdp->cblist))
invoke_rcu_callbacks(rsp, rdp);

2
kernel/rcu/tree.h
View File

@ -374,6 +374,8 @@ struct rcu_state {
/* but in jiffies. */
unsigned long gp_activity; /* Time of last GP kthread */
/* activity in jiffies. */
unsigned long gp_req_activity; /* Time of last GP request */
/* in jiffies. */
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
unsigned long jiffies_resched; /* Time at which to resched */