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
--
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