xfs: check the ir_startino alignment directly

In xchk_iallocbt_rec, check the alignment of ir_startino by converting
the inode cluster block alignment into units of inodes instead of the
other way around (converting ir_startino to blocks).  This prevents us
from tripping over off-by-one errors in ir_startino which are obscured
by the inode -> block conversion.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/scrub/ialloc.c

@@ -265,6 +265,53 @@ xchk_iallocbt_check_freemask(
 	return error;
 }
 
+/*
+ * Make sure this inode btree record is aligned properly.  Because a fs block
+ * contains multiple inodes, we check that the inobt record is aligned to the
+ * correct inode, not just the correct block on disk.  This results in a finer
+ * grained corruption check.
+ */
+STATIC void
+xchk_iallocbt_rec_alignment(
+	struct xchk_btree		*bs,
+	struct xfs_inobt_rec_incore	*irec)
+{
+	struct xfs_mount		*mp = bs->sc->mp;
+
+	/*
+	 * finobt records have different positioning requirements than inobt
+	 * records: each finobt record must have a corresponding inobt record.
+	 * That is checked in the xref function, so for now we only catch the
+	 * obvious case where the record isn't at all aligned properly.
+	 *
+	 * Note that if a fs block contains more than a single chunk of inodes,
+	 * we will have finobt records only for those chunks containing free
+	 * inodes, and therefore expect chunk alignment of finobt records.
+	 * Otherwise, we expect that the finobt record is aligned to the
+	 * cluster alignment as told by the superblock.
+	 */
+	if (bs->cur->bc_btnum == XFS_BTNUM_FINO) {
+		unsigned int	imask;
+
+		imask = min_t(unsigned int, XFS_INODES_PER_CHUNK,
+				mp->m_cluster_align_inodes) - 1;
+		if (irec->ir_startino & imask)
+			xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+		return;
+	}
+
+	/* inobt records must be aligned to cluster and inoalignmnt size. */
+	if (irec->ir_startino & (mp->m_cluster_align_inodes - 1)) {
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+		return;
+	}
+
+	if (irec->ir_startino & (mp->m_inodes_per_cluster - 1)) {
+		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+		return;
+	}
+}
+
 /* Scrub an inobt/finobt record. */
 STATIC int
 xchk_iallocbt_rec(
@@ -277,7 +324,6 @@ xchk_iallocbt_rec(
 	uint64_t			holes;
 	xfs_agnumber_t			agno = bs->cur->bc_private.a.agno;
 	xfs_agino_t			agino;
-	xfs_agblock_t			agbno;
 	xfs_extlen_t			len;
 	int				holecount;
 	int				i;
@@ -304,11 +350,9 @@ xchk_iallocbt_rec(
 		goto out;
 	}
 
-	/* Make sure this record is aligned to cluster and inoalignmnt size. */
-	agbno = XFS_AGINO_TO_AGBNO(mp, irec.ir_startino);
-	if ((agbno & (mp->m_cluster_align - 1)) ||
-	    (agbno & (mp->m_blocks_per_cluster - 1)))
-		xchk_btree_set_corrupt(bs->sc, bs->cur, 0);
+	xchk_iallocbt_rec_alignment(bs, &irec);
+	if (bs->sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
+		goto out;
 
 	iabt->inodes += irec.ir_count;