[PATCH 3/3] xfs: ensure btree root split sets blkno correctly

Dave Chinner
2013-06-12T02:19:30Z

From: Dave Chinner <dchinner@redhat.com>

For CRC enabled filesystems, the BMBT is rooted in an inode, so it
passes through a difference code path on root splits to the
freespace and inode btrees. This is much less traversed by xfstests
than the other trees. When testing on a 1k block size filesystem,
I've been seeing ASSERT failures in generic/234 like:

XFS: Assertion failed: cur->bc_btnum != XFS_BTNUM_BMAP || cur->bc_private.b.allocated == 0, file: fs/xfs/xfs_btree.c, line: 317

which are generally preceded by a lblock check failure. I noticed
this in the bmbt stats:

$ pminfo -f xfs.btree.block_map

xfs.btree.block_map.lookup
value 39135

xfs.btree.block_map.compare
value 268432

xfs.btree.block_map.insrec
value 15786

xfs.btree.block_map.delrec
value 13884

xfs.btree.block_map.newroot
value 2

xfs.btree.block_map.killroot
value 0
.....

Very little coverage of root splits and merges. Indeed, on a 4k
filesystem, block_map.newroot and block_map.killroot are both zero.
i.e the code is not exercised at all, and it's the only generic
btree infrastruct operation that is not exercised by a default run
of xfstests.

Turns out that on a 1k filesystem, generic/234 accounts for one of
those two root splits, and that is somewhat of a smoking gun. In
fact, it's the same problem we saw in the directory/attr code where
headers are memcpy()d from one block to another without updating the
self describing metadata.

Simple fix - when copying the header out of the root block, make
sure the block number is updated correctly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_btree.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/fs/xfs/xfs_btree.c b/fs/xfs/xfs_btree.c
index 8804b8a..0903960 100644
--- a/fs/xfs/xfs_btree.c
+++ b/fs/xfs/xfs_btree.c
@@ -2544,7 +2544,17 @@ xfs_btree_new_iroot(
if (error)
goto error0;

+ /*
+ * we can't just memcpy() the root in for CRC enabled btree blocks.
+ * In that case have to also ensure the blkno remains correct
+ */
memcpy(cblock, block, xfs_btree_block_len(cur));
+ if (cur->bc_flags & XFS_BTREE_CRC_BLOCKS) {
+ if (cur->bc_flags & XFS_BTREE_LONG_PTRS)
+ cblock->bb_u.l.bb_blkno = cpu_to_be64(cbp->b_bn);
+ else
+ cblock->bb_u.s.bb_blkno = cpu_to_be64(cbp->b_bn);
+ }

be16_add_cpu(&block->bb_level, 1);
xfs_btree_set_numrecs(block, 1);
--
1.7.10.4