workqueue fixes for 3.7-rc7

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(-)

index 042d221..084aa47 100644
@@ -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