xfs: Fix xfs_flush_unmap_range() range for RT

Currently xfs_flush_unmap_range() does unmap for a full RT extent range,
which we also want to ensure is clean and idle.

This code change is originally from Dave Chinner.

Reviewed-by: Christoph Hellwig <hch@lst.de>4
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/xfs_bmap_util.c

@@ -808,14 +808,18 @@ xfs_flush_unmap_range(
 	xfs_off_t		offset,
 	xfs_off_t		len)
 {
-	struct xfs_mount	*mp = ip->i_mount;
 	struct inode		*inode = VFS_I(ip);
 	xfs_off_t		rounding, start, end;
 	int			error;
 
-	rounding = max_t(xfs_off_t, mp->m_sb.sb_blocksize, PAGE_SIZE);
-	start = round_down(offset, rounding);
-	end = round_up(offset + len, rounding) - 1;
+	/*
+	 * Make sure we extend the flush out to extent alignment
+	 * boundaries so any extent range overlapping the start/end
+	 * of the modification we are about to do is clean and idle.
+	 */
+	rounding = max_t(xfs_off_t, xfs_inode_alloc_unitsize(ip), PAGE_SIZE);
+	start = rounddown_64(offset, rounding);
+	end = roundup_64(offset + len, rounding) - 1;
 
 	error = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (error)