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

To: xfs@xxxxxxxxxxx
Subject: [PATCH 3/3] xfs: ensure btree root split sets blkno correctly
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Wed, 12 Jun 2013 12:19:08 +1000
Cc: bpm@xxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1371003548-4026-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1371003548-4026-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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

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