nvme-pci: refactor the tagset handling in nvme_reset_work

The code to create, update or delete a tagset and namespaces in
nvme_reset_work is a bit convoluted.  Refactor it with a two high-level
conditionals for first probe vs reset and I/O queues vs no I/O queues
to make the code flow more clear.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NChaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20221101150050.3510-3-hch@lst.de
[axboe: fix whitespace issue]
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/nvme/host/pci.c

@@ -2898,24 +2898,36 @@ static void nvme_reset_work(struct work_struct *work)
 	if (result)
 		goto out;
 
-	/*
-	 * Keep the controller around but remove all namespaces if we don't have
-	 * any working I/O queue.
-	 */
-	if (dev->online_queues < 2) {
-		dev_warn(dev->ctrl.device, "IO queues not created\n");
-		nvme_kill_queues(&dev->ctrl);
-		nvme_remove_namespaces(&dev->ctrl);
-		nvme_free_tagset(dev);
+	if (dev->ctrl.tagset) {
+		/*
+		 * This is a controller reset and we already have a tagset.
+		 * Freeze and update the number of I/O queues as thos might have
+		 * changed.  If there are no I/O queues left after this reset,
+		 * keep the controller around but remove all namespaces.
+		 */
+		if (dev->online_queues > 1) {
+			nvme_start_queues(&dev->ctrl);
+			nvme_wait_freeze(&dev->ctrl);
+			nvme_pci_update_nr_queues(dev);
+			nvme_dbbuf_set(dev);
+			nvme_unfreeze(&dev->ctrl);
+		} else {
+			dev_warn(dev->ctrl.device, "IO queues lost\n");
+			nvme_kill_queues(&dev->ctrl);
+			nvme_remove_namespaces(&dev->ctrl);
+			nvme_free_tagset(dev);
+		}
 	} else {
-		nvme_start_queues(&dev->ctrl);
-		nvme_wait_freeze(&dev->ctrl);
-		if (!dev->ctrl.tagset)
+		/*
+		 * First probe.  Still allow the controller to show up even if
+		 * there are no namespaces.
+		 */
+		if (dev->online_queues > 1) {
 			nvme_pci_alloc_tag_set(dev);
-		else
-			nvme_pci_update_nr_queues(dev);
-		nvme_dbbuf_set(dev);
-		nvme_unfreeze(&dev->ctrl);
+			nvme_dbbuf_set(dev);
+		} else {
+			dev_warn(dev->ctrl.device, "IO queues not created\n");
+		}
 	}
 
 	/*