[PATCH 4.19 38/71] kthread_worker: prevent queuing delayed work from timer_fn when it is being canceled

[Greg Kroah-Hartman]

From: Zqiang <qiang.zhang@xxxxxxxxxxxxx>

commit 6993d0fdbee0eb38bfac350aa016f65ad11ed3b1 upstream.

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.

Signed-off-by: Zqiang <qiang.zhang@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201014083030.16895-1-qiang.zhang@xxxxxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -863,7 +863,8 @@ void kthread_delayed_work_timer_fn(struc
 	/* 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);
 
 	spin_unlock(&worker->lock);
 }