[added to the 4.1 stable tree] xfs: Don't wrap growfs AGFL indexes

From: Dave Chinner <redacted>

This patch has been added to the 4.1 stable tree. If you have any
objections, please let us know.

===============

[ Upstream commit ad747e3b299671e1a53db74963cc6c5f6cdb9f6d ]

Commit 96f859d ("libxfs: pack the agfl header structure so
XFS_AGFL_SIZE is correct") allowed the freelist to use the empty
slot at the end of the freelist on 64 bit systems that was not
being used due to sizeof() rounding up the structure size.

This has caused versions of xfs_repair prior to 4.5.0 (which also
has the fix) to report this as a corruption once the filesystem has
been grown. Older kernels can also have problems (seen from a whacky
container/vm management environment) mounting filesystems grown on a
system with a newer kernel than the vm/container it is deployed on.

To avoid this problem, change the initial free list indexes not to
wrap across the end of the AGFL, hence avoiding the initialisation
of agf_fllast to the last index in the AGFL.

cc: <redacted> # 4.4-4.5
Signed-off-by: Dave Chinner <redacted>
Reviewed-by: Carlos Maiolino <redacted>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Sasha Levin <redacted>
---
 fs/xfs/xfs_fsops.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index cb7e8a2..1a89b34 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c

@@ -241,8 +241,8 @@ xfs_growfs_data_private(
 		agf->agf_roots[XFS_BTNUM_CNTi] = cpu_to_be32(XFS_CNT_BLOCK(mp));
 		agf->agf_levels[XFS_BTNUM_BNOi] = cpu_to_be32(1);
 		agf->agf_levels[XFS_BTNUM_CNTi] = cpu_to_be32(1);
-		agf->agf_flfirst = 0;
-		agf->agf_fllast = cpu_to_be32(XFS_AGFL_SIZE(mp) - 1);
+		agf->agf_flfirst = cpu_to_be32(1);
+		agf->agf_fllast = 0;
 		agf->agf_flcount = 0;
 		tmpsize = agsize - XFS_PREALLOC_BLOCKS(mp);
 		agf->agf_freeblks = cpu_to_be32(tmpsize);

-- 
2.5.0