btrfs: do not BUG_ON() on failure to update inode when setting xattr

We are doing a BUG_ON() if we fail to update an inode after setting (or
clearing) a xattr, but there's really no reason to not instead simply
abort the transaction and return the error to the caller. This should be
a rare error because we have previously reserved enough metadata space to
update the inode and the delayed inode should have already been setup, so
an -ENOSPC or -ENOMEM, which are the possible errors, are very unlikely to
happen.

So replace the BUG_ON()s with a transaction abort.

CC: stable@vger.kernel.org # 4.9+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/xattr.c

@@ -262,7 +262,8 @@ int btrfs_setxattr_trans(struct inode *inode, const char *name,
 	inode_inc_iversion(inode);
 	inode->i_ctime = current_time(inode);
 	ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
-	BUG_ON(ret);
+	if (ret)
+		btrfs_abort_transaction(trans, ret);
 out:
 	if (start_trans)
 		btrfs_end_transaction(trans);
@@ -416,7 +417,8 @@ static int btrfs_xattr_handler_set_prop(const struct xattr_handler *handler,
 		inode_inc_iversion(inode);
 		inode->i_ctime = current_time(inode);
 		ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
-		BUG_ON(ret);
+		if (ret)
+			btrfs_abort_transaction(trans, ret);
 	}
 
 	btrfs_end_transaction(trans);