This is a note to let you know that I've just added the patch titled
workqueue: make rescuer_thread() empty wq->maydays list before exiting
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
workqueue-make-rescuer_thread-empty-wq-maydays-list-before-exiting.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4d595b866d2c653dc90a492b9973a834eabfa354 Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Date: Fri, 18 Apr 2014 11:04:16 -0400
Subject: workqueue: make rescuer_thread() empty wq->maydays list before exiting
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
commit 4d595b866d2c653dc90a492b9973a834eabfa354 upstream.
After a @pwq is scheduled for emergency execution, other workers may
consume the affectd work items before the rescuer gets to them. This
means that a workqueue many have pwqs queued on @wq->maydays list
while not having any work item pending or in-flight. If
destroy_workqueue() executes in such condition, the rescuer may exit
without emptying @wq->maydays.
This currently doesn't cause any actual harm. destroy_workqueue() can
safely destroy all the involved data structures whether @wq->maydays
is populated or not as nobody access the list once the rescuer exits.
However, this is nasty and makes future development difficult. Let's
update rescuer_thread() so that it empties @wq->maydays after seeing
should_stop to guarantee that the list is empty on rescuer exit.
tj: Updated comment and patch description.
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/workqueue.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2362,6 +2362,7 @@ static int rescuer_thread(void *__rescue
struct worker *rescuer = __rescuer;
struct workqueue_struct *wq = rescuer->rescue_wq;
struct list_head *scheduled = &rescuer->scheduled;
+ bool should_stop;
set_user_nice(current, RESCUER_NICE_LEVEL);
@@ -2373,11 +2374,15 @@ static int rescuer_thread(void *__rescue
repeat:
set_current_state(TASK_INTERRUPTIBLE);
- if (kthread_should_stop()) {
- __set_current_state(TASK_RUNNING);
- rescuer->task->flags &= ~PF_WQ_WORKER;
- return 0;
- }
+ /*
+ * By the time the rescuer is requested to stop, the workqueue
+ * shouldn't have any work pending, but @wq->maydays may still have
+ * pwq(s) queued. This can happen by non-rescuer workers consuming
+ * all the work items before the rescuer got to them. Go through
+ * @wq->maydays processing before acting on should_stop so that the
+ * list is always empty on exit.
+ */
+ should_stop = kthread_should_stop();
/* see whether any pwq is asking for help */
spin_lock_irq(&wq_mayday_lock);
@@ -2429,6 +2434,12 @@ repeat:
spin_unlock_irq(&wq_mayday_lock);
+ if (should_stop) {
+ __set_current_state(TASK_RUNNING);
+ rescuer->task->flags &= ~PF_WQ_WORKER;
+ return 0;
+ }
+
/* rescuers should never participate in concurrency management */
WARN_ON_ONCE(!(rescuer->flags & WORKER_NOT_RUNNING));
schedule();
Patches currently in stable-queue which might be from laijs@xxxxxxxxxxxxxx are
queue-3.10/futex-add-another-early-deadlock-detection-check.patch
queue-3.10/futex-prevent-attaching-to-kernel-threads.patch
queue-3.10/workqueue-make-rescuer_thread-empty-wq-maydays-list-before-exiting.patch
queue-3.10/workqueue-fix-bugs-in-wq_update_unbound_numa-failure-path.patch
queue-3.10/workqueue-fix-a-possible-race-condition-between-rescuer-and-pwq-release.patch
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