[PATCH 09/14] xfs: fix maxlevels comparisons in the btree staging code

Darrick J. Wong
2021-09-18T01:30:00Z

From: Darrick J. Wong <djwong@kernel.org>

The btree geometry computation function has an off-by-one error in that
it does not allow maximally tall btrees (nlevels == XFS_BTREE_MAXLEVELS).
This can result in repairs failing unnecessarily on very fragmented
filesystems. Subsequent patches to remove MAXLEVELS usage in favor of
the per-btree type computations will make this a much more likely
occurrence.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/libxfs/xfs_btree_staging.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_btree_staging.c b/fs/xfs/libxfs/xfs_btree_staging.c
index 26143297bb7b..cc56efc2b90a 100644
--- a/fs/xfs/libxfs/xfs_btree_staging.c
+++ b/fs/xfs/libxfs/xfs_btree_staging.c
@@ -662,7 +662,7 @@ xfs_btree_bload_compute_geometry(
xfs_btree_bload_ensure_slack(cur, &bbl->node_slack, 1);

bbl->nr_records = nr_this_level = nr_records;
- for (cur->bc_nlevels = 1; cur->bc_nlevels < XFS_BTREE_MAXLEVELS;) {
+ for (cur->bc_nlevels = 1; cur->bc_nlevels <= XFS_BTREE_MAXLEVELS;) {
uint64_t level_blocks;
uint64_t dontcare64;
unsigned int level = cur->bc_nlevels - 1;
@@ -726,7 +726,7 @@ xfs_btree_bload_compute_geometry(
nr_this_level = level_blocks;
}

- if (cur->bc_nlevels == XFS_BTREE_MAXLEVELS)
+ if (cur->bc_nlevels > XFS_BTREE_MAXLEVELS)
return -EOVERFLOW;

bbl->btree_height = cur->bc_nlevels;