From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756140Ab0IRTMq (ORCPT ); Sat, 18 Sep 2010 15:12:46 -0400 Received: from kroah.org ([198.145.64.141]:51730 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756001Ab0IRTCN (ORCPT ); Sat, 18 Sep 2010 15:02:13 -0400 X-Mailbox-Line: From gregkh@clark.site Sat Sep 18 12:00:00 2010 Message-Id: <20100918190000.870917770@clark.site> User-Agent: quilt/0.48-11.2 Date: Sat, 18 Sep 2010 11:58:58 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Ingo Molnar , Peter Zijlstra , Greg KH , Oleg Nesterov , Mike Galbraith Subject: [094/123] sched: move_task_off_dead_cpu(): Take rq->lock around select_fallback_rq() References: <20100918185724.290702750@clark.site> Content-Disposition: inline; filename=sched-move_task_off_dead_cpu-take-rq-lock-around-select_fallback_rq.patch In-Reply-To: <20100918190024.GA14388@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Oleg Nesterov commit 1445c08d06c5594895b4fae952ef8a457e89c390 upstream move_task_off_dead_cpu()->select_fallback_rq() reads/updates ->cpus_allowed lockless. We can race with set_cpus_allowed() running in parallel. Change it to take rq->lock around select_fallback_rq(). Note that it is not trivial to move this spin_lock() into select_fallback_rq(), we must recheck the task was not migrated after we take the lock and other callers do not need this lock. To avoid the races with other callers of select_fallback_rq() which rely on TASK_WAKING, we also check p->state != TASK_WAKING and do nothing otherwise. The owner of TASK_WAKING must update ->cpus_allowed and choose the correct CPU anyway, and the subsequent __migrate_task() is just meaningless because p->se.on_rq must be false. Alternatively, we could change select_task_rq() to take rq->lock right after it calls sched_class->select_task_rq(), but this looks a bit ugly. Also, change it to not assume irqs are disabled and absorb __migrate_task_irq(). Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra LKML-Reference: <20100315091010.GA9131@redhat.com> Signed-off-by: Ingo Molnar Signed-off-by: Mike Galbraith Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) --- a/kernel/sched.c +++ b/kernel/sched.c @@ -7399,29 +7399,29 @@ static int migration_thread(void *data) } #ifdef CONFIG_HOTPLUG_CPU - -static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu) -{ - int ret; - - local_irq_disable(); - ret = __migrate_task(p, src_cpu, dest_cpu); - local_irq_enable(); - return ret; -} - /* * Figure out where task on dead CPU should go, use force if necessary. */ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) { - int dest_cpu; - + struct rq *rq = cpu_rq(dead_cpu); + int needs_cpu, uninitialized_var(dest_cpu); + unsigned long flags; again: - dest_cpu = select_fallback_rq(dead_cpu, p); + local_irq_save(flags); + + spin_lock(&rq->lock); + needs_cpu = (task_cpu(p) == dead_cpu) && (p->state != TASK_WAKING); + if (needs_cpu) + dest_cpu = select_fallback_rq(dead_cpu, p); + spin_unlock(&rq->lock); /* It can have affinity changed while we were choosing. */ - if (unlikely(!__migrate_task_irq(p, dead_cpu, dest_cpu))) + if (needs_cpu) + needs_cpu = !__migrate_task(p, dead_cpu, dest_cpu); + local_irq_restore(flags); + + if (unlikely(needs_cpu)) goto again; }