[PATCH v3] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled

[PATCH v3] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled

[qiang.zhang]

From: Zqiang <qiang.zhang@windriver.com>

There is a small race window when a delayed work is being canceled and
the work still might be queued from the timer_fn:

	CPU0						CPU1
kthread_cancel_delayed_work_sync()
   __kthread_cancel_work_sync()
     __kthread_cancel_work()
        work->canceling++;
					      kthread_delayed_work_timer_fn()
						   kthread_insert_work();

BUG: kthread_insert_work() should not get called when work->canceling
is set.

Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
--- 
 v1->v2->v3:
 Change the description of the problem and add 'Reviewed-by' tags.

 kernel/kthread.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 3edaa380dc7b..85a2c9b32049 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -897,7 +897,8 @@ void kthread_delayed_work_timer_fn(struct timer_list *t)
 	/* Move the work from worker->delayed_work_list. */
 	WARN_ON_ONCE(list_empty(&work->node));
 	list_del_init(&work->node);
-	kthread_insert_work(worker, work, &worker->work_list);
+	if (!work->canceling)
+		kthread_insert_work(worker, work, &worker->work_list);
 
 	raw_spin_unlock_irqrestore(&worker->lock, flags);
 }
-- 
2.17.1

Re: [PATCH v3] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled

[Tejun Heo]

On Sun, Sep 27, 2020 at 01:54:49PM +0800, qiang.zhang@windriver.com wrote:
> From: Zqiang <qiang.zhang@windriver.com>
> 
> There is a small race window when a delayed work is being canceled and
> the work still might be queued from the timer_fn:
> 
> 	CPU0						CPU1
> kthread_cancel_delayed_work_sync()
>    __kthread_cancel_work_sync()
>      __kthread_cancel_work()
>         work->canceling++;
> 					      kthread_delayed_work_timer_fn()
> 						   kthread_insert_work();
> 
> BUG: kthread_insert_work() should not get called when work->canceling
> is set.
> 
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Zqiang <qiang.zhang@windriver.com>

Acked-by: Tejun Heo <tj@kernel.org>

This prolly should go throgh -mm. Can you please also add a stable: tag?

Thanks.

-- 
tejun