Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752998AbaBMHqk (ORCPT ); Thu, 13 Feb 2014 02:46:40 -0500 Received: from mail-pb0-f52.google.com ([209.85.160.52]:41881 "EHLO mail-pb0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752783AbaBMHqj (ORCPT ); Thu, 13 Feb 2014 02:46:39 -0500 Message-ID: <52FC7858.3070000@linaro.org> Date: Thu, 13 Feb 2014 15:46:32 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Daniel Lezcano , peterz@infradead.org, mingo@kernel.org CC: linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH V2 2/3] sched: Fix race in idle_balance() References: <1391728237-4441-1-git-send-email-daniel.lezcano@linaro.org> <1391728237-4441-3-git-send-email-daniel.lezcano@linaro.org> In-Reply-To: <1391728237-4441-3-git-send-email-daniel.lezcano@linaro.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/07/2014 07:10 AM, Daniel Lezcano wrote: > The scheduler main function 'schedule()' checks if there are no more tasks > on the runqueue. Then it checks if a task should be pulled in the current > runqueue in idle_balance() assuming it will go to idle otherwise. > > But the idle_balance() releases the rq->lock in order to lookup in the sched > domains and takes the lock again right after. That opens a window where > another cpu may put a task in our runqueue, so we won't go to idle but > we have filled the idle_stamp, thinking we will. > > This patch closes the window by checking if the runqueue has been modified > but without pulling a task after taking the lock again, so we won't go to idle > right after in the __schedule() function. > > Cc: alex.shi@linaro.org > Cc: peterz@infradead.org > Cc: mingo@kernel.org > Signed-off-by: Daniel Lezcano > Signed-off-by: Peter Zijlstra > --- > kernel/sched/fair.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 428bc9d..5ebc681 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6589,6 +6589,13 @@ void idle_balance(struct rq *this_rq) > > raw_spin_lock(&this_rq->lock); > > + /* > + * While browsing the domains, we released the rq lock. > + * A task could have be enqueued in the meantime > + */ Mind to move the following line up to here? if (curr_cost > this_rq->max_idle_balance_cost) this_rq->max_idle_balance_cost = curr_cost; > + if (this_rq->nr_running && !pulled_task) > + return; > + > if (pulled_task || time_after(jiffies, this_rq->next_balance)) { > /* > * We are going idle. next_balance may be set based on > -- Thanks Alex -- 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/