Btrfs: remove BUG_ON()s in btrfs_ioctl_setflags()

We can recover from errors and return -errno to user space.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

fs/btrfs/ioctl.c

@@ -176,6 +176,8 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	struct btrfs_trans_handle *trans;
 	unsigned int flags, oldflags;
 	int ret;
+	u64 ip_oldflags;
+	unsigned int i_oldflags;
 
 	if (btrfs_root_readonly(root))
 		return -EROFS;
@@ -192,6 +194,9 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 
 	mutex_lock(&inode->i_mutex);
 
+	ip_oldflags = ip->flags;
+	i_oldflags = inode->i_flags;
+
 	flags = btrfs_mask_flags(inode->i_mode, flags);
 	oldflags = btrfs_flags_to_ioctl(ip->flags);
 	if ((flags ^ oldflags) & (FS_APPEND_FL | FS_IMMUTABLE_FL)) {
@@ -250,18 +255,23 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	}
 
 	trans = btrfs_join_transaction(root);
-	BUG_ON(IS_ERR(trans));
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto out_drop;
+	}
 
 	btrfs_update_iflags(inode);
 	inode->i_ctime = CURRENT_TIME;
 	ret = btrfs_update_inode(trans, root, inode);
-	BUG_ON(ret);
 
 	btrfs_end_transaction(trans, root);
+ out_drop:
+	if (ret) {
+		ip->flags = ip_oldflags;
+		inode->i_flags = i_oldflags;
+	}
 
 	mnt_drop_write(file->f_path.mnt);
-
-	ret = 0;
  out_unlock:
 	mutex_unlock(&inode->i_mutex);
 	return ret;