btrfs: Explicitly handle btrfs_update_root failure

btrfs_udpate_root can fail and it aborts the transaction, the correct
way to handle an aborted transaction is to explicitly end with
btrfs_end_transaction.  Even now the code is correct since
btrfs_commit_transaction would handle an aborted transaction but this is
more of an implementation detail. So let's be explicit in handling
failure in btrfs_update_root.

Furthermore btrfs_commit_transaction can also fail and by ignoring it's
return value we could have left the in-memory copy of the root item in
an inconsistent state. So capture the error value which allows us to
correctly revert the RO/RW flags in case of commit failure.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -1827,8 +1827,13 @@ static noinline int btrfs_ioctl_subvol_setflags(struct file *file,
 
 	ret = btrfs_update_root(trans, fs_info->tree_root,
 				&root->root_key, &root->root_item);
+	if (ret < 0) {
+		btrfs_end_transaction(trans);
+		goto out_reset;
+	}
+
+	ret = btrfs_commit_transaction(trans);
 
-	btrfs_commit_transaction(trans);
 out_reset:
 	if (ret)
 		btrfs_set_root_flags(&root->root_item, root_flags);