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From:   Zqiang <qiang.zhang@windriver.com>
To:     tj@kernel.org, pmladek@suse.com, hdanton@sina.com
Cc:     akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: [PATCH v4] kthread_worker: Prevent queuing delayed work from timer_fn when it is being canceled
Date:   Wed, 14 Oct 2020 15:50:48 +0800
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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: <stable@vger.kernel.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
--- 
 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