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.