On Thu, May 17, 2018 at 06:21:40PM +0000, Bart Van Assche wrote:
On Thu, 2017-10-19 at 16:21 -0400, Josef Bacik wrote:
- blk_mq_start_request(req); if (unlikely(nsock->pending && nsock->pending != req)) { blk_mq_requeue_request(req, true); ret = 0;
(replying to an e-mail from seven months ago)
Hello Josef,
Are you aware that the nbd driver is one of the very few block drivers that calls blk_mq_requeue_request() after a request has been started? I think that can lead to the block layer core to undesired behavior, e.g. that the timeout handler fires concurrently with a request being reinstered. Can you or a colleague have a look at this? I would like to add the following code to the block layer core and I think that the nbd driver would trigger this warning:
void blk_mq_requeue_request(struct request *rq, bool kick_requeue_list) {
WARN_ON_ONCE(old_state != MQ_RQ_COMPLETE);__blk_mq_requeue_request(rq);
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,
Josef