Re: [RFC PATCH 3/3] blk-mq: Remove generation seqeunce

Keith Busch
2018-07-13T15:43:46Z

On Thu, Jul 12, 2018 at 10:24:42PM +0000, Bart Van Assche wrote:
> Before commit 12f5b9314545 ("blk-mq: Remove generation seqeunce"), if a
> request completion was reported after request timeout processing had
> started, completion handling was skipped. The following code in
> blk_mq_complete_request() realized that:
>
> if (blk_mq_rq_aborted_gstate(rq) != rq->gstate)
> __blk_mq_complete_request(rq);
>
> Since commit 12f5b9314545, if a completion occurs after request timeout
> processing has started, that completion is processed if the request has the
> state MQ_RQ_IN_FLIGHT. blk_mq_rq_timed_out() does not modify the request
> state unless the block driver timeout handler modifies it, e.g. by calling
> blk_mq_end_request() or by calling blk_mq_requeue_request(). The typical
> behavior of scsi_times_out() is to queue sending of a SCSI abort and hence
> not to change the request state immediately. In other words, if a request
> completion occurs during or shortly after a timeout occurred then
> blk_mq_complete_request() will call __blk_mq_complete_request() and will
> complete the request, although that is not allowed because timeout handling
> has already started. Do you agree with this analysis?

Yes, it's different, and that was the whole point. No one made that a
secret either. Are you saying you want timeout software to take priority
over handling hardware events?