From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753800Ab2LBBH7 (ORCPT ); Sat, 1 Dec 2012 20:07:59 -0500 Received: from mail-pa0-f46.google.com ([209.85.220.46]:41737 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753600Ab2LBBH6 (ORCPT ); Sat, 1 Dec 2012 20:07:58 -0500 Date: Sat, 1 Dec 2012 17:07:51 -0800 From: Tejun Heo To: Linus Torvalds Cc: linux-kernel@vger.kernel.org, Mike Galbraith , Anders Kaseorg , Zlatko Calusic , Joonsoo Kim Subject: [GIT PULL] workqueue fixes for 3.7-rc7 Message-ID: <20121202010751.GD2685@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Linus. Unfortunately, I have two really late fixes. One was for a long-standing bug and queued for 3.8 but I found out about a regression introduced during 3.7-rc1 two days ago, so I'm sending out the two fixes together. The first (long-standing) one is rescuer_thread() entering exit path w/ TASK_INTERRUPTIBLE. It only triggers on workqueue destructions which isn't very frequent and the exit path can usually survive being called with TASK_INTERRUPT, so it was hidden pretty well. Apparently, if you're reiserfs, this could lead to the exiting kthread sleeping indefinitely holding a mutex, which is never good. The fix is simple - restoring TASK_RUNNING before returning from the kthread function. The second one is introduced by the new mod_delayed_work(). mod_delayed_work() was missing special case handling for 0 delay. Instead of queueing the work item immediately, it queued the timer which expires on the closest next tick. Some users of the new function converted from "[__]cancel_delayed_work() + queue_delayed_work()" combination became unhappy with the extra delay. Block unplugging led to noticeably higher number of context switches and intel 6250 wireless failed to associate with WPA-Enterprise network. The fix, again, is fairly simple. The 0 delay special case logic from queue_delayed_work_on() should be moved to __queue_delayed_work() which is shared by both queue_delayed_work_on() and mod_delayed_work_on(). The first one is difficult to trigger and the failure mode for the latter isn't completely catastrophic, so missing these two for 3.7 wouldn't make it a disastrous release, but both bugs are nasty and the fixes are fairly safe, so please consider pulling the following branch. git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-3.7-fixes Thanks. --- Mike Galbraith (1): workqueue: exit rescuer_thread() as TASK_RUNNING Tejun Heo (1): workqueue: mod_delayed_work_on() shouldn't queue timer on 0 delay kernel/workqueue.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 042d221..084aa47 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1364,6 +1364,17 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, BUG_ON(timer_pending(timer)); BUG_ON(!list_empty(&work->entry)); + /* + * If @delay is 0, queue @dwork->work immediately. This is for + * both optimization and correctness. The earliest @timer can + * expire is on the closest next tick and delayed_work users depend + * on that there's no such delay when @delay is 0. + */ + if (!delay) { + __queue_work(cpu, wq, &dwork->work); + return; + } + timer_stats_timer_set_start_info(&dwork->timer); /* @@ -1417,9 +1428,6 @@ bool queue_delayed_work_on(int cpu, struct workqueue_struct *wq, bool ret = false; unsigned long flags; - if (!delay) - return queue_work_on(cpu, wq, &dwork->work); - /* read the comment in __queue_work() */ local_irq_save(flags); @@ -2407,8 +2415,10 @@ static int rescuer_thread(void *__wq) repeat: set_current_state(TASK_INTERRUPTIBLE); - if (kthread_should_stop()) + if (kthread_should_stop()) { + __set_current_state(TASK_RUNNING); return 0; + } /* * See whether any cpu is asking for help. Unbounded