nvme-loop: kill timeout handler

Firstly it doesn't make sense to handle timeout for loop: 1) for admin
queue, the request is always completed in code path of queuing IO. 2)
for normal IO request, the timeout on these IOs have been handled by
underlying queue already.

Secondly nvme-loop's timeout handler is simply broken, and easy to
cause issue: 1) no any sync/protection between timeout and normal
completion, and now it is driver's responsibility to deal with
that; 2) bad reset implementation, blk_mq_update_nr_hw_queues()
is called after all NSs's queue is stopped(quiesced), and easy
to trigger deadlock.

So kill the timeout handler.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewd-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/loop.c

@@ -129,20 +129,6 @@ static void nvme_loop_execute_work(struct work_struct *work)
 	nvmet_req_execute(&iod->req);
 }
 
-static enum blk_eh_timer_return
-nvme_loop_timeout(struct request *rq, bool reserved)
-{
-	struct nvme_loop_iod *iod = blk_mq_rq_to_pdu(rq);
-
-	/* queue error recovery */
-	nvme_reset_ctrl(&iod->queue->ctrl->ctrl);
-
-	/* fail with DNR on admin cmd timeout */
-	nvme_req(rq)->status = NVME_SC_ABORT_REQ | NVME_SC_DNR;
-
-	return BLK_EH_DONE;
-}
-
 static blk_status_t nvme_loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 		const struct blk_mq_queue_data *bd)
 {
@@ -253,7 +239,6 @@ static const struct blk_mq_ops nvme_loop_mq_ops = {
 	.complete	= nvme_loop_complete_rq,
 	.init_request	= nvme_loop_init_request,
 	.init_hctx	= nvme_loop_init_hctx,
-	.timeout	= nvme_loop_timeout,
 };
 
 static const struct blk_mq_ops nvme_loop_admin_mq_ops = {
@@ -261,7 +246,6 @@ static const struct blk_mq_ops nvme_loop_admin_mq_ops = {
 	.complete	= nvme_loop_complete_rq,
 	.init_request	= nvme_loop_init_request,
 	.init_hctx	= nvme_loop_init_admin_hctx,
-	.timeout	= nvme_loop_timeout,
 };
 
 static void nvme_loop_destroy_admin_queue(struct nvme_loop_ctrl *ctrl)