nvme: always search for namespace head

Even if a namespace reports it is not capable of sharing, search the
subsystem for a matching namespace head. If found, the driver should
reject that namespace since it's coming from an invalid configuration.
Signed-off-by: Keith Busch <kbusch@kernel.org>
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/core.c

@@ -3489,7 +3489,6 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
 		goto out;
 
 	mutex_lock(&ctrl->subsys->lock);
-	if (is_shared)
 	head = nvme_find_ns_head(ctrl->subsys, nsid);
 	if (!head) {
 		head = nvme_alloc_ns_head(ctrl, nsid, &ids);
@@ -3498,6 +3497,14 @@ static int nvme_init_ns_head(struct nvme_ns *ns, unsigned nsid,
 			goto out_unlock;
 		}
 	} else {
+		if (!is_shared) {
+			dev_err(ctrl->device,
+				"Duplicate unshared namespace %d\n",
+					nsid);
+			ret = -EINVAL;
+			nvme_put_ns_head(head);
+			goto out_unlock;
+		}
 		if (!nvme_ns_ids_equal(&head->ids, &ids)) {
 			dev_err(ctrl->device,
 				"IDs don't match for shared namespace %d\n",