Although cond_resched_rcu_qs() supplies quiescent states to all flavors of normal RCU grace periods, it does nothing for expedited RCU-sched grace periods. This commit therefore adds a check for a need for a quiescent state from the current CPU by an expedited RCU-sched grace period, and invokes rcu_sched_qs() to supply that quiescent state if so.
Note that the check is racy in that we might be migrated to some other CPU just after checking the per-CPU variable. This is OK because the act of migration will do a context switch, which will supply the needed quiescent state. The only downside is that we might do an unnecessary call to rcu_sched_qs(), but the probability is low and the overhead is small. Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 687d8a5f35c7..178575c01d09 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -370,6 +370,21 @@ void rcu_all_qs(void) rcu_momentary_dyntick_idle(); local_irq_restore(flags); } + if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))) { + /* + * Yes, we just checked a per-CPU variable with preemption + * enabled, so we might be migrated to some other CPU at + * this point. That is OK because in that case, the + * migration will supply the needed quiescent state. + * We might end up needlessly disabling preemption and + * invoking rcu_sched_qs() on the destination CPU, but + * the probability and cost are both quite low, so this + * should not be a problem in practice. + */ + preempt_disable(); + rcu_sched_qs(); + preempt_enable(); + } this_cpu_inc(rcu_qs_ctr); barrier(); /* Avoid RCU read-side critical sections leaking up. */ } -- 2.5.2
