xfs: fix imprecise logic in xchk_btree_check_block_owner

BugLink: https://bugs.launchpad.net/bugs/2074091
commit c0afba9a8363f17d4efed22a8764df33389aebe8 upstream.

A reviewer was confused by the init_sa logic in this function.  Upon
checking the logic, I discovered that the code is imprecise.  What we
want to do here is check that there is an ownership record in the rmap
btree for the AG that contains a btree block.

For an inode-rooted btree (e.g. the bmbt) the per-AG btree cursors have
not been initialized because inode btrees can span multiple AGs.
Therefore, we must initialize the per-AG btree cursors in sc->sa before
proceeding.  That is what init_sa controls, and hence the logic should
be gated on XFS_BTREE_ROOT_IN_INODE, not XFS_BTREE_LONG_PTRS.

In practice, ROOT_IN_INODE and LONG_PTRS are coincident so this hasn't
mattered.  However, we're about to refactor both of those flags into
separate btree_ops fields so we want this the logic to make sense
afterwards.

Fixes: 858333dcf021a ("xfs: check btree block ownership with bnobt/rmapbt when scrubbing btree")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

diff --git a/fs/xfs/scrub/btree.c b/fs/xfs/scrub/btree.c
index 1935b9ce1885c9437545bcf0404c78883f569ceb..c3a9f33e5a8d127d8afab3d5b1e77ed6a323fbea 100644 (file)
--- a/fs/xfs/scrub/btree.c
+++ b/fs/xfs/scrub/btree.c
@@ -385,7 +385,12 @@ xchk_btree_check_block_owner(
        agno = xfs_daddr_to_agno(bs->cur->bc_mp, daddr);
        agbno = xfs_daddr_to_agbno(bs->cur->bc_mp, daddr);
 
-       init_sa = bs->cur->bc_flags & XFS_BTREE_LONG_PTRS;
+       /*
+        * If the btree being examined is not itself a per-AG btree, initialize
+        * sc->sa so that we can check for the presence of an ownership record
+        * in the rmap btree for the AG containing the block.
+        */
+       init_sa = bs->cur->bc_flags & XFS_BTREE_ROOT_IN_INODE;
        if (init_sa) {
                error = xchk_ag_init_existing(bs->sc, agno, &bs->sc->sa);
                if (!xchk_btree_xref_process_error(bs->sc, bs->cur,