From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754613AbaAUL37 (ORCPT ); Tue, 21 Jan 2014 06:29:59 -0500 Received: from merlin.infradead.org ([205.233.59.134]:51879 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754230AbaAUL30 (ORCPT ); Tue, 21 Jan 2014 06:29:26 -0500 Message-Id: <20140121112258.330689671@infradead.org> User-Agent: quilt/0.60-1 Date: Tue, 21 Jan 2014 12:17:56 +0100 From: Peter Zijlstra To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, daniel.lezcano@linaro.org, pjt@google.com, bsegall@google.com, Peter Zijlstra Subject: [PATCH 2/9] sched: Fix race in idle_balance() References: <20140121111754.580142558@infradead.org> Content-Disposition: inline; filename=daniel_lezcano-2_sched-fix_race_in_idle_balance.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel Lezcano 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 Link: http://lkml.kernel.org/r/1389949444-14821-2-git-send-email-daniel.lezcano@linaro.org --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6417,6 +6417,13 @@ 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