2020-10-14 08:56:03

by Zhang, Qiang

Subject: [PATCH v4] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled

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.

Cc: <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Zqiang <[email protected]>
---
v1->v2->v3:
Change the description of the problem and add 'Reviewed-by' tags.
v3->v4:
Add 'stable' and 'Acked-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

2020-10-15 12:43:49

by Petr Mladek

Subject: Re: [PATCH v4] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled

On Wed 2020-10-14 15:50:48, Zqiang wrote:
> 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.
>
> Cc: <[email protected]>
> Reviewed-by: Petr Mladek <[email protected]>
> Acked-by: Tejun Heo <[email protected]>
> Signed-off-by: Zqiang <[email protected]>

Andrew, are you going to take this patch with -mm tree, please?

I think that you usually take the changes in kthread.c.

Best Regards,
Petr