btrfs: hold a ref on the root in create_reloc_inode

We're creating a reloc inode in the data reloc tree, we need to hold a
ref on the root while we're doing that.
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/relocation.c

@@ -4351,10 +4351,14 @@ struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
 	root = read_fs_root(fs_info, BTRFS_DATA_RELOC_TREE_OBJECTID);
 	if (IS_ERR(root))
 		return ERR_CAST(root);
+	if (!btrfs_grab_fs_root(root))
+		return ERR_PTR(-ENOENT);
 
 	trans = btrfs_start_transaction(root, 6);
-	if (IS_ERR(trans))
+	if (IS_ERR(trans)) {
+		btrfs_put_fs_root(root);
 		return ERR_CAST(trans);
+	}
 
 	err = btrfs_find_free_objectid(root, &objectid);
 	if (err)
@@ -4372,6 +4376,7 @@ struct inode *create_reloc_inode(struct btrfs_fs_info *fs_info,
 
 	err = btrfs_orphan_add(trans, BTRFS_I(inode));
 out:
+	btrfs_put_fs_root(root);
 	btrfs_end_transaction(trans);
 	btrfs_btree_balance_dirty(fs_info);
 	if (err) {