Re: [PATCH 1/2] blk-mq: don't complete un-started request in timeout handler

Ming Lei
2017-03-15T16:46:46Z

On Thu, Mar 16, 2017 at 12:22:01AM +0800, Ming Lei wrote:
> On Wed, Mar 15, 2017 at 03:36:31PM +0000, Bart Van Assche wrote:
>
> OK, this race should only exist in case that the requeue happens after dispatch
> busy, because COMPLETE flag isn't set. And if the requeue is from io completion,
> no such race because COMPLETE flag is set.
>
> One solution I thought of is to call blk_mark_rq_complete() before requeuing
> when dispatch busy happened, but that looks a bit silly. Another way is to
> set STARTED flag just after .queue_rq returns BLK_MQ_RQ_QUEUE_OK, which looks
> reasonable too. Any comments on the 2nd solution?

Actually it isn't possible to happen because rq->deadline is just set
in blk_mq_start_request() called from .queue_rq, and it won't trigger
timeout handling even STARTED is observed as true in blk_mq_check_expired()
because timeout period is often set as big enough. So it is still safe, isn't it?

But this situation should have been commented.

Thanks,
Ming