From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gautham R Shenoy Subject: [RFC PATCH 3/6] Preempt-RCU: Fix rcu_barrier for preemptive environment Date: Thu, 13 Dec 2007 22:46:06 +0530 Message-ID: <20071213171606.GD25981@in.ibm.com> References: <20071213170348.GA25981@in.ibm.com> Reply-To: ego@in.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paul E McKenney , Dipankar Sarma , Ted Tso , dvhltc@us.ibm.com, Oleg Nesterov , Andrew Morton , bunk@kernel.org, Josh Triplett , Thomas Gleixner , Peter Zijlstra To: linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Ingo Molnar , Steven Rostedt Return-path: Received: from E23SMTP06.au.ibm.com ([202.81.18.175]:58461 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759538AbXLMRQk (ORCPT ); Thu, 13 Dec 2007 12:16:40 -0500 Content-Disposition: inline In-Reply-To: <20071213170348.GA25981@in.ibm.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Preempt-RCU: Fix rcu_barrier for preemptive environment. From: Paul E. McKenney 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: Gautham R Shenoy Signed-off-by: Dipankar Sarma Signed-off-by: Paul E. McKenney --- kernel/rcuclassic.c | 2 +- kernel/rcupdate.c | 10 ++++++++++ 2 files changed, 11 insertions(+), 1 deletions(-) diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c index 11c16aa..deb2acc 100644 --- a/kernel/rcuclassic.c +++ b/kernel/rcuclassic.c @@ -371,9 +371,9 @@ static void __rcu_offline_cpu(struct rcu_data *this_rdp, 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 --git a/kernel/rcupdate.c b/kernel/rcupdate.c index 0ccd009..760dfc2 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -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); } -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!"