nvme-multipath: add error handling support for add_disk()

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.

Since we now can tell for sure when a disk was added, move
setting the bit NVME_NSHEAD_DISK_LIVE only when we did
add the disk successfully.

Nothing to do here as the cleanup is done elsewhere. We take
care and use test_and_set_bit() because it is protects against
two nvme paths simultaneously calling device_add_disk() on the
same namespace head.
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/multipath.c

@@ -509,13 +509,23 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
 static void nvme_mpath_set_live(struct nvme_ns *ns)
 {
 	struct nvme_ns_head *head = ns->head;
+	int rc;
 
 	if (!head->disk)
 		return;
 
+	/*
+	 * test_and_set_bit() is used because it is protecting against two nvme
+	 * paths simultaneously calling device_add_disk() on the same namespace
+	 * head.
+	 */
 	if (!test_and_set_bit(NVME_NSHEAD_DISK_LIVE, &head->flags)) {
-		device_add_disk(&head->subsys->dev, head->disk,
+		rc = device_add_disk(&head->subsys->dev, head->disk,
 				     nvme_ns_id_attr_groups);
+		if (rc) {
+			clear_bit(NVME_NSHEAD_DISK_LIVE, &ns->flags);
+			return;
+		}
 		nvme_add_ns_head_cdev(head);
 	}