nvmet: never fail double namespace enablement

In case we create N namespaces while N < NVMET_MAX_NAMESPACES, we can
perform "echo 1 > <nsid>/enable" as much as we want. In case N ==
NVMET_MAX_NAMESPACES we fail. Make sure we have the same flow for any N.

Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/core.c

@@ -494,13 +494,14 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
 	int ret;
 
 	mutex_lock(&subsys->lock);
-	ret = -EMFILE;
-	if (subsys->nr_namespaces == NVMET_MAX_NAMESPACES)
-		goto out_unlock;
 	ret = 0;
 	if (ns->enabled)
 		goto out_unlock;
 
+	ret = -EMFILE;
+	if (subsys->nr_namespaces == NVMET_MAX_NAMESPACES)
+		goto out_unlock;
+
 	ret = nvmet_bdev_ns_enable(ns);
 	if (ret == -ENOTBLK)
 		ret = nvmet_file_ns_enable(ns);