[XFS] Flush the block device before closing it on unmount.

SGI-PV: 965630
SGI-Modid: xfs-linux-melb:xfs-kern:28774a
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/linux-2.6/xfs_buf.c

@@ -1447,6 +1447,7 @@ xfs_free_buftarg(
 	int			external)
 {
 	xfs_flush_buftarg(btp, 1);
+	xfs_blkdev_issue_flush(btp);
 	if (external)
 		xfs_blkdev_put(btp->bt_bdev);
 	xfs_free_bufhash(btp);