Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753217Ab1CNIr1 (ORCPT ); Mon, 14 Mar 2011 04:47:27 -0400 Received: from e36.co.us.ibm.com ([32.97.110.154]:54724 "EHLO e36.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752279Ab1CNIrZ (ORCPT ); Mon, 14 Mar 2011 04:47:25 -0400 Date: Mon, 14 Mar 2011 01:47:18 -0700 From: "Paul E. McKenney" To: Joe Korty Cc: fweisbec@gmail.com, peterz@infradead.org, laijs@cn.fujitsu.com, mathieu.desnoyers@efficios.com, dhowells@redhat.com, loic.minier@linaro.org, dhaval.giani@gmail.com, tglx@linutronix.de, josh@joshtriplett.org, houston.jim@comcast.net, andi@firstfloor.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 8/9] jrcu: fix broken rcu_barrier Message-ID: <20110314084718.GH2167@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20110314035044.GA12990@tsunami.ccur.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110314035044.GA12990@tsunami.ccur.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2888 Lines: 82 On Sun, Mar 13, 2011 at 11:50:44PM -0400, Joe Korty wrote: > jrcu: fix bug in rcu_barrier. > > It is not equivalent to synchronize_rcu. But it > can be implemented by a pair of synchronize_rcu's, > so do so. > > Thanks go to Paul E McKenney for finding this. > > Signed-off-by: Joe Korty > > Index: b/kernel/jrcu.c > =================================================================== > --- a/kernel/jrcu.c > +++ b/kernel/jrcu.c > @@ -183,7 +183,7 @@ void rcu_note_might_resched(void) > } > EXPORT_SYMBOL(rcu_note_might_resched); > > -void rcu_barrier(void) > +void synchronize_sched(void) > { > struct rcu_synchronize rcu; > > @@ -196,6 +196,13 @@ void rcu_barrier(void) > atomic_inc(&rcu_stats.nbarriers); > > } > +EXPORT_SYMBOL_GPL(synchronize_sched); > + > +void rcu_barrier(void) > +{ > + synchronize_sched(); > + synchronize_sched(); > +} This is still broken. You need to wait until all pre-existing RCU callbacks on all CPUs have been invoked. Although this does guarantee that all callbacks on the current CPU have been invoked, if one of the other CPUs is busy, it might not yet have processed the callbacks from earlier grace periods. The usual way to take care of this is to post a callback on each CPU, then wait for them all to be invoked. Thanx, Paul > EXPORT_SYMBOL_GPL(rcu_barrier); > > void rcu_force_quiescent_state(void) > Index: b/include/linux/jrcu.h > =================================================================== > --- a/include/linux/jrcu.h > +++ b/include/linux/jrcu.h > @@ -39,12 +39,13 @@ extern void rcu_barrier(void); > #define rcu_barrier_sched rcu_barrier > #define rcu_barrier_bh rcu_barrier > > -#define synchronize_rcu rcu_barrier > -#define synchronize_sched rcu_barrier > -#define synchronize_sched_expedited rcu_barrier > -#define synchronize_rcu_bh rcu_barrier > -#define synchronize_rcu_expedited rcu_barrier > -#define synchronize_rcu_bh_expedited rcu_barrier > +extern void synchronize_sched(void); > + > +#define synchronize_rcu synchronize_sched > +#define synchronize_sched_expedited synchronize_sched > +#define synchronize_rcu_bh synchronize_sched > +#define synchronize_rcu_expedited synchronize_sched > +#define synchronize_rcu_bh_expedited synchronize_sched > > #define rcu_init(cpu) do { } while (0) > #define rcu_init_sched() do { } while (0) > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/