From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753349Ab2AZUZ7 (ORCPT ); Thu, 26 Jan 2012 15:25:59 -0500 Received: from terminus.zytor.com ([198.137.202.10]:39636 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751491Ab2AZUZ5 (ORCPT ); Thu, 26 Jan 2012 15:25:57 -0500 Date: Thu, 26 Jan 2012 12:25:33 -0800 From: tip-bot for Peter Zijlstra Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, kosaki.motohiro@gmail.com, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, kosaki.motohiro@gmail.com, tglx@linutronix.de, mingo@elte.hu In-Reply-To: <1327486224.2614.45.camel@laptop> References: <1327486224.2614.45.camel@laptop> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched: Fix rq->nr_uninterruptible update race Git-Commit-ID: 4ca9b72b71f10147bd21969c1805f5b2c4ca7b7b 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-4.2.6 (terminus.zytor.com [127.0.0.1]); Thu, 26 Jan 2012 12:25:40 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 4ca9b72b71f10147bd21969c1805f5b2c4ca7b7b Gitweb: http://git.kernel.org/tip/4ca9b72b71f10147bd21969c1805f5b2c4ca7b7b Author: Peter Zijlstra AuthorDate: Wed, 25 Jan 2012 11:50:51 +0100 Committer: Ingo Molnar CommitDate: Thu, 26 Jan 2012 19:38:09 +0100 sched: Fix rq->nr_uninterruptible update race KOSAKI Motohiro noticed the following race: > CPU0 CPU1 > -------------------------------------------------------- > deactivate_task() > task->state = TASK_UNINTERRUPTIBLE; > activate_task() > rq->nr_uninterruptible--; > > schedule() > deactivate_task() > rq->nr_uninterruptible++; > Kosaki-San's scenario is possible when CPU0 runs __sched_setscheduler() against CPU1's current @task. __sched_setscheduler() does a dequeue/enqueue in order to move the task to its new queue (position) to reflect the newly provided scheduling parameters. However it should be completely invariant to nr_uninterruptible accounting, sched_setscheduler() doesn't affect readyness to run, merely policy on when to run. So convert the inappropriate activate/deactivate_task usage to enqueue/dequeue_task, which avoids the nr_uninterruptible accounting. Also convert the two other sites: __migrate_task() and normalize_task() that still use activate/deactivate_task. These sites aren't really a problem since __migrate_task() will only be called on non-running task (and therefore are immume to the described problem) and normalize_task() isn't ever used on regular systems. Also remove the comments from activate/deactivate_task since they're misleading at best. Reported-by: KOSAKI Motohiro Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1327486224.2614.45.camel@laptop Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 18 ++++++------------ 1 files changed, 6 insertions(+), 12 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index df00cb0..e067df1 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -723,9 +723,6 @@ static void dequeue_task(struct rq *rq, struct task_struct *p, int flags) p->sched_class->dequeue_task(rq, p, flags); } -/* - * activate_task - move a task to the runqueue. - */ void activate_task(struct rq *rq, struct task_struct *p, int flags) { if (task_contributes_to_load(p)) @@ -734,9 +731,6 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags) enqueue_task(rq, p, flags); } -/* - * deactivate_task - remove a task from the runqueue. - */ void deactivate_task(struct rq *rq, struct task_struct *p, int flags) { if (task_contributes_to_load(p)) @@ -4134,7 +4128,7 @@ recheck: on_rq = p->on_rq; running = task_current(rq, p); if (on_rq) - deactivate_task(rq, p, 0); + dequeue_task(rq, p, 0); if (running) p->sched_class->put_prev_task(rq, p); @@ -4147,7 +4141,7 @@ recheck: if (running) p->sched_class->set_curr_task(rq); if (on_rq) - activate_task(rq, p, 0); + enqueue_task(rq, p, 0); check_class_changed(rq, p, prev_class, oldprio); task_rq_unlock(rq, p, &flags); @@ -4998,9 +4992,9 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu) * placed properly. */ if (p->on_rq) { - deactivate_task(rq_src, p, 0); + dequeue_task(rq_src, p, 0); set_task_cpu(p, dest_cpu); - activate_task(rq_dest, p, 0); + enqueue_task(rq_dest, p, 0); check_preempt_curr(rq_dest, p, 0); } done: @@ -7032,10 +7026,10 @@ static void normalize_task(struct rq *rq, struct task_struct *p) on_rq = p->on_rq; if (on_rq) - deactivate_task(rq, p, 0); + dequeue_task(rq, p, 0); __setscheduler(rq, p, SCHED_NORMAL, 0); if (on_rq) { - activate_task(rq, p, 0); + enqueue_task(rq, p, 0); resched_task(rq->curr); }