Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755327AbYKJNjo (ORCPT ); Mon, 10 Nov 2008 08:39:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755023AbYKJNje (ORCPT ); Mon, 10 Nov 2008 08:39:34 -0500 Received: from mx2.redhat.com ([66.187.237.31]:57188 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754913AbYKJNje (ORCPT ); Mon, 10 Nov 2008 08:39:34 -0500 Date: Mon, 10 Nov 2008 15:39:30 +0100 From: Oleg Nesterov To: Andrew Morton , Ingo Molnar , Peter Zijlstra Cc: adobriyan@gmail.com, Doug Chapman , Roland McGrath , linux-kernel@vger.kernel.org Subject: [PATCH] for account_group_exec_runtime(), make sure ->signal can't be freed under rq->lock Message-ID: <20081110143930.GA28275@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2292 Lines: 65 The patch is ugly, but I don't see the better fix for now. Needs the review from Peter/Ingo. Unlike other similar routines, account_group_exec_runtime() could be called "implicitly" from within scheduler after exit_notify(). This means we can race with the parent doing release_task(), we can't just check ->signal != NULL. Change __exit_signal() to do spin_unlock_wait(&task_rq(tsk)->lock) before __cleanup_signal() to make sure ->signal can't be freed under task_rq(tsk)->lock. Note that task_rq_unlock_wait() doesn't care about the case when tsk changes cpu/rq under us, this should be OK. Thanks to Ingo who nacked my previous buggy patch. Signed-off-by: Oleg Nesterov Reported-by: Doug Chapman --- K-28/include/linux/sched.h~SIG_RQ_LOCK 2008-11-06 19:12:44.000000000 +0100 +++ K-28/include/linux/sched.h 2008-11-10 13:13:07.000000000 +0100 @@ -247,6 +247,7 @@ extern void init_idle(struct task_struct extern void init_idle_bootup_task(struct task_struct *idle); extern int runqueue_is_locked(void); +extern void task_rq_unlock_wait(struct task_struct *p); extern cpumask_t nohz_cpu_mask; #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ) --- K-28/kernel/sched.c~SIG_RQ_LOCK 2008-11-06 19:12:44.000000000 +0100 +++ K-28/kernel/sched.c 2008-11-10 13:05:09.000000000 +0100 @@ -969,6 +969,14 @@ static struct rq *task_rq_lock(struct ta } } +void task_rq_unlock_wait(struct task_struct *p) +{ + struct rq *rq = task_rq(p); + + smp_mb(); + spin_unlock_wait(&rq->lock); +} + static void __task_rq_unlock(struct rq *rq) __releases(rq->lock) { --- K-28/kernel/exit.c~SIG_RQ_LOCK 2008-11-06 19:11:02.000000000 +0100 +++ K-28/kernel/exit.c 2008-11-10 15:07:22.000000000 +0100 @@ -141,6 +141,11 @@ static void __exit_signal(struct task_st if (sig) { flush_sigqueue(&sig->shared_pending); taskstats_tgid_free(sig); + /* + * Make sure ->signal can't go away under rq->lock, + * see account_group_exec_runtime(). + */ + task_rq_unlock_wait(tsk); __cleanup_signal(sig); } } -- 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/