Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759313AbYFDRJN (ORCPT ); Wed, 4 Jun 2008 13:09:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755310AbYFDRIn (ORCPT ); Wed, 4 Jun 2008 13:08:43 -0400 Received: from x346.tv-sign.ru ([89.108.83.215]:47560 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755179AbYFDRIG (ORCPT ); Wed, 4 Jun 2008 13:08:06 -0400 Date: Wed, 4 Jun 2008 21:09:05 +0400 From: Oleg Nesterov To: Andrew Morton , Ingo Molnar Cc: Dmitry Adamushko , Matthew Wilcox , Peter Zijlstra , Roland McGrath , linux-kernel@vger.kernel.org Subject: [PATCH 1/2] schedule: fix TASK_WAKEKILL vs SIGKILL race Message-ID: <20080604170905.GA10273@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3107 Lines: 92 schedule() has the special "TASK_INTERRUPTIBLE && signal_pending()" case, this allows us to do current->state = TASK_INTERRUPTIBLE; schedule(); without fear to sleep with pending signal. However, the code like current->state = TASK_KILLABLE; schedule(); is not right, schedule() doesn't take TASK_WAKEKILL into account. This means that mutex_lock_killable(), wait_for_completion_killable(), down_killable(), schedule_timeout_killable() can miss SIGKILL (and btw the second SIGKILL has no effect). Introduce the new helper, signal_pending_state(), and change schedule() to use it. Note this "__TASK_STOPPED | __TASK_TRACED" check in signal_pending_state(). Probably it would be better to remove it, but this will change the current behaviour and thus needs a separate discussion. Note also that with or without this patch TASK_WAKEKILL is not exactly right wrt /sbin/init, but this is another issue. Signed-off-by: Oleg Nesterov include/linux/sched.h | 2 ++ kernel/signal.c | 14 ++++++++++++++ kernel/sched.c | 6 ++---- 3 files changed, 18 insertions(+), 4 deletions(-) --- 26-rc2/include/linux/sched.h~1_SCHED_KILLABLE 2008-06-01 16:44:39.000000000 +0400 +++ 26-rc2/include/linux/sched.h 2008-06-01 16:44:39.000000000 +0400 @@ -2020,6 +2020,8 @@ static inline int signal_pending(struct return unlikely(test_tsk_thread_flag(p,TIF_SIGPENDING)); } +extern int signal_pending_state(long state, struct task_struct *p); + extern int __fatal_signal_pending(struct task_struct *p); static inline int fatal_signal_pending(struct task_struct *p) --- 26-rc2/kernel/signal.c~1_SCHED_KILLABLE 2008-05-31 16:03:39.000000000 +0400 +++ 26-rc2/kernel/signal.c 2008-06-04 19:57:34.000000000 +0400 @@ -980,6 +980,20 @@ int __fatal_signal_pending(struct task_s } EXPORT_SYMBOL(__fatal_signal_pending); +int signal_pending_state(long state, struct task_struct *p) +{ + if (!(state & (TASK_INTERRUPTIBLE | TASK_WAKEKILL))) + return 0; + if (!signal_pending(p)) + return 0; + + if (state & TASK_INTERRUPTIBLE) + return 1; + if (state & (__TASK_STOPPED | __TASK_TRACED)) + return 0; + return __fatal_signal_pending(p); +} + struct sighand_struct *lock_task_sighand(struct task_struct *tsk, unsigned long *flags) { struct sighand_struct *sighand; --- 26-rc2/kernel/sched.c~1_SCHED_KILLABLE 2008-05-18 15:44:18.000000000 +0400 +++ 26-rc2/kernel/sched.c 2008-06-04 17:42:59.000000000 +0400 @@ -4510,12 +4510,10 @@ need_resched_nonpreemptible: clear_tsk_need_resched(prev); if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) { - if (unlikely((prev->state & TASK_INTERRUPTIBLE) && - signal_pending(prev))) { + if (unlikely(signal_pending_state(prev->state, prev))) prev->state = TASK_RUNNING; - } else { + else deactivate_task(rq, prev, 1); - } switch_count = &prev->nvcsw; } -- 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/