From: Zqiang qiang.zhang@windriver.com Subject: 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.

Link: https://lkml.kernel.org/r/20201014083030.16895-1-qiang.zhang@windriver.com Signed-off-by: Zqiang qiang.zhang@windriver.com Reviewed-by: Petr Mladek pmladek@suse.com Acked-by: Tejun Heo tj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/kernel/kthread.c~kthread_worker-prevent-queuing-delayed-work-from-timer_fn-when-it-is-being-canceled +++ a/kernel/kthread.c @@ -897,7 +897,8 @@ 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);

raw_spin_unlock_irqrestore(&worker->lock, flags); } _