nvme-fc: reject reconnect if io queue count is reduced to zero

If:

 - A successful connect has occurred with an io queue count greater than
   zero and namespaces detected and running.
 - An error or something occurs which causes a termination of the prior
   association and then starts a reconnect,
 - The reconnect then creates a new controller, but for whatever reason,
   nvme_set_queue_count() results in io queue count set to zero.  This
   will skip io queue and tag set changes.
 - But... the controller will transition to live, calling
   nvme_start_ctrl, which calls nvme_start_queues(), which then releases
   I/Os into the transport which then sends them to the driver.

As there are no queues, things eventually hit the driver looking for a
handle, which was cleared when the original controller was reset, and it
can't proceed. Worst case, things progress, but everything fails.

In the failing scenario, the nvme_set_features(NVME_FEAT_NUM_QUEUES)
command actually failed with a NVME_SC_INTERNAL error.  For some reason,
although nvme_set_queue_count() saw the error and set io queue count to
zero, it doesn't return a failure status to the transport, which allows
the transport to continue using the controller.

Fix the problem by simply rejecting the new association if at least 1
I/O queue can't be created. The association reject will fail the
reconnect attempt and fall into the reconnect retry policy.
Signed-off-by: James Smart <jsmart2021@gmail.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/host/fc.c

@@ -2475,6 +2475,7 @@ static int
 nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
 {
 	struct nvmf_ctrl_options *opts = ctrl->ctrl.opts;
+	u32 prior_ioq_cnt = ctrl->ctrl.queue_count - 1;
 	unsigned int nr_io_queues;
 	int ret;
 
@@ -2487,6 +2488,13 @@ nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
 		return ret;
 	}
 
+	if (!nr_io_queues && prior_ioq_cnt) {
+		dev_info(ctrl->ctrl.device,
+			"Fail Reconnect: At least 1 io queue "
+			"required (was %d)\n", prior_ioq_cnt);
+		return -ENOSPC;
+	}
+
 	ctrl->ctrl.queue_count = nr_io_queues + 1;
 	/* check for io queues existing */
 	if (ctrl->ctrl.queue_count == 1)
@@ -2500,6 +2508,10 @@ nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
 	if (ret)
 		goto out_delete_hw_queues;
 
+	if (prior_ioq_cnt != nr_io_queues)
+		dev_info(ctrl->ctrl.device,
+			"reconnect: revising io queue count from %d to %d\n",
+			prior_ioq_cnt, nr_io_queues);
 	blk_mq_update_nr_hw_queues(&ctrl->tag_set, nr_io_queues);
 
 	return 0;