On Fri, 2018-07-27 at 10:46 -0600, Keith Busch wrote:
> On Fri, Jul 27, 2018 at 09:20:42AM -0700, Bart Van Assche wrote:
> > + ret = req->q->mq_ops->timeout(req, reserved);
> > + /*
> > + * BLK_EH_DONT_RESET_TIMER means that the block driver either
> > + * completed the request or still owns the request and will
> > + * continue processing the timeout asynchronously. In the
> > + * latter case, if blk_mq_complete_request() was called while
> > + * the timeout handler was in progress, ignore that call.
> > + */
> > + if (ret == BLK_EH_DONT_RESET_TIMER)
> > + return;
>
> This is how completions get lost.
The new approach for handling completions that occur while the .timeout()
callback in progress is as follows:
* blk_mq_complete_request() executes the following code:
if (blk_mq_change_rq_state(rq, MQ_RQ_TIMED_OUT, MQ_RQ_COMPLETE))
return;
* blk_mq_rq_timed_out() executes the following code:
if (blk_mq_rq_state(req) == MQ_RQ_COMPLETE) {
__blk_mq_complete_request(req);
return;
}
As one can see __blk_mq_complete_request() gets called if this race occurs.
Bart.
