kthread_worker: check all delayed works when destroy kthread worker

When destroying a kthread worker warn if there are still some pending
delayed works. This indicates that the caller should clear all pending
delayed works before destroying the kthread worker.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Zqiang <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Reviewed-by: Petr Mladek <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

kernel/kthread.c

···
  * Flush and destroy @worker.  The simple flush is enough because the kthread
  * worker API is used only in trivial scenarios.  There are no multi-step state
  * machines needed.
+ *
+ * Note that this function is not responsible for handling delayed work, so
+ * caller should be responsible for queuing or canceling all delayed work items
+ * before invoke this function.
  */
 void kthread_destroy_worker(struct kthread_worker *worker)
 {
···
 
 	kthread_flush_worker(worker);
 	kthread_stop(task);
+	WARN_ON(!list_empty(&worker->delayed_work_list));
 	WARN_ON(!list_empty(&worker->work_list));
 	kfree(worker);
 }