xfs: fix the calculation for "end" and "length"

The value of "end" should be "start + length - 1".
Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>

fs/xfs/xfs_notify_failure.c

@@ -114,7 +114,8 @@ xfs_dax_notify_ddev_failure(
 	int			error = 0;
 	xfs_fsblock_t		fsbno = XFS_DADDR_TO_FSB(mp, daddr);
 	xfs_agnumber_t		agno = XFS_FSB_TO_AGNO(mp, fsbno);
-	xfs_fsblock_t		end_fsbno = XFS_DADDR_TO_FSB(mp, daddr + bblen);
+	xfs_fsblock_t		end_fsbno = XFS_DADDR_TO_FSB(mp,
+							     daddr + bblen - 1);
 	xfs_agnumber_t		end_agno = XFS_FSB_TO_AGNO(mp, end_fsbno);
 
 	error = xfs_trans_alloc_empty(mp, &tp);
@@ -210,7 +211,7 @@ xfs_dax_notify_failure(
 	ddev_end = ddev_start + bdev_nr_bytes(mp->m_ddev_targp->bt_bdev) - 1;
 
 	/* Ignore the range out of filesystem area */
-	if (offset + len < ddev_start)
+	if (offset + len - 1 < ddev_start)
 		return -ENXIO;
 	if (offset > ddev_end)
 		return -ENXIO;
@@ -222,8 +223,8 @@ xfs_dax_notify_failure(
 		len -= ddev_start - offset;
 		offset = 0;
 	}
-	if (offset + len > ddev_end)
-		len -= ddev_end - offset;
+	if (offset + len - 1 > ddev_end)
+		len = ddev_end - offset + 1;
 
 	return xfs_dax_notify_ddev_failure(mp, BTOBB(offset), BTOBB(len),
 			mf_flags);