From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751661AbaBKMQV (ORCPT ); Tue, 11 Feb 2014 07:16:21 -0500 Received: from terminus.zytor.com ([198.137.202.10]:46468 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750809AbaBKMQU (ORCPT ); Tue, 11 Feb 2014 07:16:20 -0500 Date: Tue, 11 Feb 2014 04:15:50 -0800 From: tip-bot for Daniel Lezcano Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, daniel.lezcano@linaro.org Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, daniel.lezcano@linaro.org In-Reply-To: <1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org> References: <1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: Fix race in idle_balance() Git-Commit-ID: e5fc66119ec97054eefc83f173a7ee9e133c3c3a X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.1 (terminus.zytor.com [127.0.0.1]); Tue, 11 Feb 2014 04:15:56 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: e5fc66119ec97054eefc83f173a7ee9e133c3c3a Gitweb: http://git.kernel.org/tip/e5fc66119ec97054eefc83f173a7ee9e133c3c3a Author: Daniel Lezcano AuthorDate: Fri, 17 Jan 2014 10:04:02 +0100 Committer: Ingo Molnar CommitDate: Mon, 10 Feb 2014 16:17:04 +0100 sched: Fix race in idle_balance() 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 idle_balance() releases the rq->lock in order to look up 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. Signed-off-by: Daniel Lezcano Cc: alex.shi@linaro.org Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org Signed-off-by: Ingo Molnar --- 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 + */ + 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