From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754861AbaESNLj (ORCPT ); Mon, 19 May 2014 09:11:39 -0400 Received: from mail-wi0-f175.google.com ([209.85.212.175]:48037 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754279AbaESNLg (ORCPT ); Mon, 19 May 2014 09:11:36 -0400 Date: Mon, 19 May 2014 15:12:33 +0200 From: Juri Lelli To: Kirill Tkhai Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, stable@vger.kernel.org Subject: Re: [PATCH] sched/dl: Fix race between dl_task_timer() and sched_setaffinity() Message-Id: <20140519151233.5043b749361e1b384f1e5562@gmail.com> In-Reply-To: <20140516213003.10384.7946.stgit@localhost> References: <20140516213003.10384.7946.stgit@localhost> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 17 May 2014 01:30:03 +0400 Kirill Tkhai wrote: > The race is in unlocked task_rq() access. In pair with parallel > call of sched_setaffinity() it may be a reason of corruption > of internal rq's data. > Sure, the thing can happen! > Signed-off-by: Kirill Tkhai > CC: Juri Lelli > CC: Peter Zijlstra > CC: Ingo Molnar > Cc: # v3.14 > --- > kernel/sched/deadline.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 800e99b..ffb023a 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -513,9 +513,16 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer) > struct sched_dl_entity, > dl_timer); > struct task_struct *p = dl_task_of(dl_se); > - struct rq *rq = task_rq(p); > + struct rq *rq; We could maybe add a comment here, in line with what we have below, to document why we need this. Thanks, - Juri > +again: > + rq = task_rq(p); > raw_spin_lock(&rq->lock); > > + if (unlikely(rq != task_rq(p))) { > + raw_spin_unlock(&rq->lock); > + goto again; > + } > + > /* > * We need to take care of a possible races here. In fact, the > * task might have changed its scheduling policy to something >