Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934438AbaFIXGS (ORCPT ); Mon, 9 Jun 2014 19:06:18 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56884 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933681AbaFIWpk (ORCPT ); Mon, 9 Jun 2014 18:45:40 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kirill Tkhai , Peter Zijlstra , Linus Torvalds , Ingo Molnar Subject: [PATCH 3.14 37/78] sched/dl: Fix race in dl_task_timer() Date: Mon, 9 Jun 2014 15:48:17 -0700 Message-Id: <20140609224814.540854196@linuxfoundation.org> X-Mailer: git-send-email 1.9.0 In-Reply-To: <20140609224813.282275135@linuxfoundation.org> References: <20140609224813.282275135@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill Tkhai commit 0f397f2c90ce68821ee864c2c53baafe78de765d upstream. Throttled task is still on rq, and it may be moved to other cpu if user is playing with sched_setaffinity(). Therefore, unlocked task_rq() access makes the race. Juri Lelli reports he got this race when dl_bandwidth_enabled() was not set. Other thing, pointed by Peter Zijlstra: "Now I suppose the problem can still actually happen when you change the root domain and trigger a effective affinity change that way". To fix that we do the same as made in __task_rq_lock(). We do not use __task_rq_lock() itself, because it has a useful lockdep check, which is not correct in case of dl_task_timer(). We do not need pi_lock locked here. This case is an exception (PeterZ): "The only reason we don't strictly need ->pi_lock now is because we're guaranteed to have p->state == TASK_RUNNING here and are thus free of ttwu races". Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra Cc: Linus Torvalds Link: http://lkml.kernel.org/r/3056991400578422@web14g.yandex.ru Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/deadline.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -490,9 +490,17 @@ static enum hrtimer_restart dl_task_time struct sched_dl_entity, dl_timer); struct task_struct *p = dl_task_of(dl_se); - struct rq *rq = task_rq(p); + struct rq *rq; +again: + rq = task_rq(p); raw_spin_lock(&rq->lock); + if (rq != task_rq(p)) { + /* Task was moved, retrying. */ + 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 -- 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/