Re: [PATCH] nbd: make starting request more reasonable
On Mon, Mar 16, 2020 at 11:30:33PM +0800, Ming Lei wrote:
> On Mon, Mar 16, 2020 at 08:26:35PM +0800, Yufen Yu wrote:
> > > + blk_mq_start_request(req);
> > > +
> > > if (req->cmd_flags & REQ_FUA)
> > > nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
> > > @@ -879,7 +881,6 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
> > > if (!refcount_inc_not_zero(&nbd->config_refs)) {
> > > dev_err_ratelimited(disk_to_dev(nbd->disk),
> > > "Socks array is empty\n");
> > > - blk_mq_start_request(req);
>
> I think it is fine to not start request in case of failure, given
> __blk_mq_end_request() doesn't check rq's state.
Not only is it fine to not start it, blk-mq expects the low level
driver will not tell it to start a request that the lld doesn't
actually start. A started request should be completed through
blk_mq_complete_request(). Returning an error from your queue_rq()
doesn't do that, and starting it will have blk-mq track the request as
an in-flight request.
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