Re: [PATCH 2/2] nbd: don't start req until after the dead connection logic

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);

Thanks,

Bart.