Re: [PATCH RFC] v7 expedited "big hammer" RCU grace periods
From: Lai Jiangshan <hidden>
Date: 2009-05-26 01:07:56
Also in:
lkml, netfilter-devel
Paul E. McKenney wrote:
Good point -- I should at the very least add a comment to synchronize_sched_expedited() stating that it cannot be called holding any lock that is acquired in a CPU hotplug notifier. If this restriction causes any problems, then your approach seems like a promising fix.
Reviewed-by: Lai Jiangshan <redacted>
quoted
The coupling of synchronize_sched_expedited() and migration_req is largely increased: 1) The offline cpu's per_cpu(rcu_migration_req, cpu) is handled. See migration_call::CPU_DEADGood. ;-)quoted
2) migration_call() is the highest priority of cpu notifiers, So even any other cpu notifier calls synchronize_sched_expedited(), It'll not cause DEADLOCK.You mean if using your preempt_disable() approach, right? Unless I am missing something, the current get_online_cpus() approach would deadlock in this case.
Yes, I mean if using my preempt_disable() approach. The current get_online_cpus() approach would NOT deadlock in this case also, we can require get_online_cpus() in cpu notifiers.
quoted hunk ↗ jump to hunk
diff --git a/include/linux/rcupreempt.h b/include/linux/rcupreempt.h index fce5227..78117ed 100644 --- a/include/linux/rcupreempt.h +++ b/include/linux/rcupreempt.h@@ -74,6 +74,16 @@ extern int rcu_needs_cpu(int cpu); extern void __synchronize_sched(void); +static inline void synchronize_rcu_expedited(void) +{ + synchronize_rcu(); /* Placeholder for new rcupreempt implementation. */ +} + +static inline void synchronize_rcu_bh_expedited(void) +{ + synchronize_rcu(); /* Placeholder for new rcupreempt implementation. */ +} +
Why not synchronize_rcu_bh() ? In mainline, rcu_read_lock_bh() is not preemptable, So I think synchronize_sched_expedited() is better. Anyway, synchronize_rcu() is OK for me, because it is "Placeholder for new rcupreempt implementation". Lai