btrfs: hold a ref for the root in btrfs_find_orphan_roots

We lookup roots for every orphan item we have, we need to hold a ref on
the root while we're doing this work.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/root-tree.c

@@ -257,6 +257,8 @@ int btrfs_find_orphan_roots(struct btrfs_fs_info *fs_info)
 
 		root = btrfs_get_fs_root(fs_info, &root_key, false);
 		err = PTR_ERR_OR_ZERO(root);
+		if (!err && !btrfs_grab_fs_root(root))
+			err = -ENOENT;
 		if (err && err != -ENOENT) {
 			break;
 		} else if (err == -ENOENT) {
@@ -287,6 +289,7 @@ int btrfs_find_orphan_roots(struct btrfs_fs_info *fs_info)
 			set_bit(BTRFS_ROOT_DEAD_TREE, &root->state);
 			btrfs_add_dead_root(root);
 		}
+		btrfs_put_fs_root(root);
 	}
 
 	btrfs_free_path(path);