Dear all, would you mind helping me understand how workers and workqueues act in a seemingly simple scenario? I'm calling queue_work(my_queue, my_worker) to add a worker to a queue that was created by calling create_singlethread_workqueue(). This goes into queue_work queue_work_on ... if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) { __queue_work(cpu, wq, work); ret = true; } ... return false if __queue_work hasn't been called... with static void __queue_work(int cpu, struct workqueue_struct *wq, struct work_struct *work) ... /* if draining, only works from the same workqueue are allowed */ if (unlikely(wq->flags & __WQ_DRAINING) && WARN_ON_ONCE(!is_chained_work(wq))) return; If drain_workqueue(my_queue) is running while queue_work(my_queue, my_worker) is called, my_worker will have WORK_STRUCT_PENDING_BIT set, but it's not queued and no error is returned. With WORK_STRUCT_PENDING_BIT set, all further attempts to queue_work(my_queue, my_worker) later, after draining is done, will fail. This code has been unchanged since at least 4.14. Could anyone shed some light on this, where am I getting things wrong? Thanks and best regards, Martin