Delete slow-work timers properly

Slow-work appears to delete its timer as soon as the first user
unregisters, even though other users could be active.  At the same time, it
never seems to delete slow_work_oom_timer.  Arrange for both to happen in
the shutdown path.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/slow-work.c

@@ -609,14 +609,14 @@ void slow_work_unregister_user(void)
 	if (slow_work_user_count == 0) {
 		printk(KERN_NOTICE "Slow work thread pool: Shutting down\n");
 		slow_work_threads_should_exit = true;
+		del_timer_sync(&slow_work_cull_timer);
+		del_timer_sync(&slow_work_oom_timer);
 		wake_up_all(&slow_work_thread_wq);
 		wait_for_completion(&slow_work_last_thread_exited);
 		printk(KERN_NOTICE "Slow work thread pool:"
 		       " Shut down complete\n");
 	}
 
-	del_timer_sync(&slow_work_cull_timer);
-
 	mutex_unlock(&slow_work_user_lock);
 }
 EXPORT_SYMBOL(slow_work_unregister_user);