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Date: Tue, 26 May 2009 09:03:55 +0800 From: Lai Jiangshan <laijs@...fujitsu.com> To: paulmck@...ux.vnet.ibm.com CC: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, netfilter-devel@...r.kernel.org, mingo@...e.hu, akpm@...ux-foundation.org, torvalds@...ux-foundation.org, davem@...emloft.net, dada1@...mosbay.com, zbr@...emap.net, jeff.chua.linux@...il.com, paulus@...ba.org, jengelh@...ozas.de, r000n@...0n.net, benh@...nel.crashing.org, mathieu.desnoyers@...ymtl.ca Subject: Re: [PATCH RFC] v7 expedited "big hammer" RCU grace periods 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 <laijs@...fujitsu.com> > >> 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_DEAD > > Good. ;-) > >> 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. > 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 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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