xfs: remove the truncate short cut in xfs_map_blocks

		xfs_iunlock(ip, XFS_ILOCK_SHARED);

		wpc->fork = XFS_COW_FORK;

		/*

		 * Truncate can race with writeback since writeback doesn't

		 * take the iolock and truncate decreases the file size before

		 * it starts truncating the pages between new_size and old_size.

		 * Therefore, we can end up in the situation where writeback

		 * gets a CoW fork mapping but the truncate makes the mapping

		 * invalid and we end up in here trying to get a new mapping.

		 * bail out here so that we simply never get a valid mapping

		 * and so we drop the write altogether.  The page truncation

		 * will kill the contents anyway.

		 */

		if (offset > i_size_read(inode)) {

			wpc->imap.br_blockcount = end_fsb - offset_fsb;

			wpc->imap.br_startoff = offset_fsb;

			wpc->imap.br_startblock = HOLESTARTBLOCK;

			wpc->imap.br_state = XFS_EXT_NORM;

			return 0;

		}

		goto allocate_blocks;

	}