| From 4d595b866d2c653dc90a492b9973a834eabfa354 Mon Sep 17 00:00:00 2001 |
| From: Lai Jiangshan <laijs@cn.fujitsu.com> |
| Date: Fri, 18 Apr 2014 11:04:16 -0400 |
| Subject: workqueue: make rescuer_thread() empty wq->maydays list before exiting |
| |
| From: Lai Jiangshan <laijs@cn.fujitsu.com> |
| |
| 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@cn.fujitsu.com> |
| Signed-off-by: Tejun Heo <tj@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| 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(); |