Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751419AbXAOTZ1 (ORCPT ); Mon, 15 Jan 2007 14:25:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751425AbXAOTZ1 (ORCPT ); Mon, 15 Jan 2007 14:25:27 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:35917 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751419AbXAOTZ0 (ORCPT ); Mon, 15 Jan 2007 14:25:26 -0500 Date: Tue, 16 Jan 2007 00:54:46 +0530 From: Dipankar Sarma To: Andrew Morton Cc: Ingo Molnar , Paul E McKenney , linux-kernel@vger.kernel.org Subject: Re: [mm PATCH 3/6] RCU: Fix barriers Message-ID: <20070115192446.GD32238@in.ibm.com> Reply-To: dipankar@in.ibm.com References: <20070115191909.GA32238@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070115191909.GA32238@in.ibm.com> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2129 Lines: 54 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 --- diff -puN kernel/rcuclassic.c~rcu-fix-barriers kernel/rcuclassic.c --- linux-2.6.20-rc3-mm1-rcu/kernel/rcuclassic.c~rcu-fix-barriers 2007-01-15 15:36:47.000000000 +0530 +++ linux-2.6.20-rc3-mm1-rcu-dipankar/kernel/rcuclassic.c 2007-01-15 15:36:47.000000000 +0530 @@ -350,9 +350,9 @@ 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 -puN kernel/rcupdate.c~rcu-fix-barriers kernel/rcupdate.c --- linux-2.6.20-rc3-mm1-rcu/kernel/rcupdate.c~rcu-fix-barriers 2007-01-15 15:36:47.000000000 +0530 +++ linux-2.6.20-rc3-mm1-rcu-dipankar/kernel/rcupdate.c 2007-01-15 15:36:47.000000000 +0530 @@ -117,7 +117,18 @@ 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 + * haven't yet queued anything. So, we need to make sure + * that no grace period happens 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/