On Mon, Apr 09, 2018 at 06:34:55PM -0700, Bart Van Assche wrote: > If a completion occurs after blk_mq_rq_timed_out() has reset > rq->aborted_gstate and the request is again in flight when the timeout Given rq->aborted_gstate is reset only for BLK_EH_RESET_TIMER, I think you are addressing the race between normal completion and the timeout of BLK_EH_RESET_TIMER. > expires then a request will be completed twice: a first time by the > timeout handler and a second time when the regular completion occurs. This patch looks simpler, and more like the previous model of using blk_mark_rq_complete(). I have one question: - with this patch, rq's state is updated atomically as cmpxchg. Suppose one rq is timed out, the rq's state is updated as MQ_RQ_COMPLETE by blk_mq_check_expired(), then ops->timeout() is run and BLK_EH_RESET_TIMER is returned, so blk_mq_add_timer(req, MQ_RQ_COMPLETE, MQ_RQ_IN_FLIGHT) is called to update rq's state into MQ_RQ_IN_FLIGHT. Now the original normal completion still may occur after rq's state becomes MQ_RQ_IN_FLIGHT, and seems there is still the double completion with this patch? Maybe I am wrong, please explain a bit. And synchronize_rcu() is needed by Tejun's approach between marking COMPLETE and handling this rq's timeout, and the time can be quite long, I guess it might be easier to trigger? Thanks, Ming
