Re: [PATCH 2/2] nbd: don't start req until after the dead connection logic
On Thu, 2018-05-17 at 14:41 -0400, Josef Bacik wrote:
> Yup I can tell you why, on 4.11 where I originally did this work
> __blk_mq_requeue_request() did this
>
> static void __blk_mq_requeue_request(struct request *rq)
> {
> struct request_queue *q = rq->q;
>
> trace_block_rq_requeue(q, rq);
> rq_qos_requeue(q, &rq->issue_stat);
> blk_mq_sched_requeue_request(rq);
>
> if (test_and_clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags)) {
> if (q->dma_drain_size && blk_rq_bytes(rq))
> rq->nr_phys_segments--;
> }
> }
>
> So it was clearing the started part when it did the requeue. If that's not what
> I'm supposed to be doing anymore then I can send a patch to fix it. What is
> supposed to be done if I did already do blk_mq_start_request, because I can
> avoid doing the start until after that chunk of code, but there's a part further
> down that needs to have start done before we reach it, so I'll have to do
> whatever the special thing is now there. Thanks,
Hello Josef,
After having had a closer look I think calling blk_mq_start_request() before
blk_mq_requeue_request() is fine anyway. The v4.16 block layer core namely defers
timeout processing until after .queue_rq() has returned. So the timeout code
shouldn't see the requests for which both blk_mq_start_request() and
blk_mq_requeue_request() are called from inside .queue_rq(). I will make sure this
behavior is preserved.
Bart.
Reply to: