path: root/kernel/rcu/update.c
diff options
authorPaul E. McKenney <>2014-03-16 21:36:25 -0700
committerPaul E. McKenney <>2014-05-14 09:46:11 -0700
commitac1bea85781e9004da9b3e8a4b097c18492d857c (patch)
treee28ea65bf56d1624371885954a46ab64cab1524b /kernel/rcu/update.c
parent0e980234c97f98be6619b9281d83777f725b94ff (diff)
sched,rcu: Make cond_resched() report RCU quiescent states
Given a CPU running a loop containing cond_resched(), with no other tasks runnable on that CPU, RCU will eventually report RCU CPU stall warnings due to lack of quiescent states. Fortunately, every call to cond_resched() is a perfectly good quiescent state. Unfortunately, invoking rcu_note_context_switch() is a bit heavyweight for cond_resched(), especially given the need to disable preemption, and, for RCU-preempt, interrupts as well. This commit therefore maintains a per-CPU counter that causes cond_resched(), cond_resched_lock(), and cond_resched_softirq() to call rcu_note_context_switch(), but only about once per 256 invocations. This ratio was chosen in keeping with the relative time constants of RCU grace periods. Signed-off-by: Paul E. McKenney <> Reviewed-by: Josh Triplett <>
Diffstat (limited to 'kernel/rcu/update.c')
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 4c0a9b0af469..ed7a0d72562c 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -338,3 +338,21 @@ static int __init check_cpu_stall_init(void)
#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
+ * Hooks for cond_resched() and friends to avoid RCU CPU stall warnings.
+ */
+DEFINE_PER_CPU(int, rcu_cond_resched_count);
+ * Report a set of RCU quiescent states, for use by cond_resched()
+ * and friends. Out of line due to being called infrequently.
+ */
+void rcu_resched(void)
+ preempt_disable();
+ __this_cpu_write(rcu_cond_resched_count, 0);
+ rcu_note_context_switch(smp_processor_id());
+ preempt_enable();