btrfs: hold a ref on the root in record_reloc_root_in_trans

We are recording this root in the transaction, so we need to hold a ref
on it until we do that.
Signed-off-by: NJosef Bacik <josef@toxicpanda.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -2648,15 +2648,19 @@ static int record_reloc_root_in_trans(struct btrfs_trans_handle *trans,
 {
 	struct btrfs_fs_info *fs_info = reloc_root->fs_info;
 	struct btrfs_root *root;
+	int ret;
 
 	if (reloc_root->last_trans == trans->transid)
 		return 0;
 
 	root = read_fs_root(fs_info, reloc_root->root_key.offset);
 	BUG_ON(IS_ERR(root));
+	BUG_ON(!btrfs_grab_fs_root(root));
 	BUG_ON(root->reloc_root != reloc_root);
+	ret = btrfs_record_root_in_trans(trans, root);
+	btrfs_put_fs_root(root);
 
-	return btrfs_record_root_in_trans(trans, root);
+	return ret;
 }
 
 static noinline_for_stack