Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761592AbXHGSnZ (ORCPT ); Tue, 7 Aug 2007 14:43:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751802AbXHGSnR (ORCPT ); Tue, 7 Aug 2007 14:43:17 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:53636 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751558AbXHGSnQ (ORCPT ); Tue, 7 Aug 2007 14:43:16 -0400 Date: Tue, 7 Aug 2007 11:43:14 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: linux-rt-users@vger.kernel.org, mingo@elte.hu, akpm@linux-foundation.org, dipankar@in.ibm.com, josht@linux.vnet.ibm.com, tytso@us.ibm.com, dvhltc@us.ibm.com, tglx@linutronix.de Subject: [PATCH 1/4 RFC] RCU: Fix barriers Message-ID: <20070807184314.GB10068@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20070807183946.GA32110@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070807183946.GA32110@linux.vnet.ibm.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2354 Lines: 52 Fix rcu_barrier() to work properly in preemptive kernel environment. Also, the ordering of callback must be preserved while moving callbacks to another CPU during CPU hotplug. Signed-off-by: Dipankar Sarma Signed-off-by: Paul E. McKenney --- rcuclassic.c | 2 +- rcupdate.c | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff -urpNa -X dontdiff linux-2.6.22-a-splitclassic/kernel/rcuclassic.c linux-2.6.22-b-fixbarriers/kernel/rcuclassic.c --- linux-2.6.22-a-splitclassic/kernel/rcuclassic.c 2007-07-19 15:03:51.000000000 -0700 +++ linux-2.6.22-b-fixbarriers/kernel/rcuclassic.c 2007-07-19 17:10:46.000000000 -0700 @@ -349,9 +349,9 @@ static void __rcu_offline_cpu(struct rcu if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp); spin_unlock_bh(&rcp->lock); + rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); - rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); } static void rcu_offline_cpu(int cpu) diff -urpNa -X dontdiff linux-2.6.22-a-splitclassic/kernel/rcupdate.c linux-2.6.22-b-fixbarriers/kernel/rcupdate.c --- linux-2.6.22-a-splitclassic/kernel/rcupdate.c 2007-07-19 14:19:03.000000000 -0700 +++ linux-2.6.22-b-fixbarriers/kernel/rcupdate.c 2007-07-19 17:13:31.000000000 -0700 @@ -115,7 +115,17 @@ void rcu_barrier(void) mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); atomic_set(&rcu_barrier_cpu_count, 0); + /* + * The queueing of callbacks in all CPUs must be atomic with + * respect to RCU, otherwise one CPU may queue a callback, + * wait for a grace period, decrement barrier count and call + * complete(), while other CPUs have not yet queued anything. + * So, we need to make sure that grace periods cannot complete + * until all the callbacks are queued. + */ + rcu_read_lock(); on_each_cpu(rcu_barrier_func, NULL, 0, 1); + rcu_read_unlock(); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } - 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/