xfs: cross-reference with the bnobt

When we're scrubbing various btrees, cross-reference the records with
the bnobt to ensure that we don't also think the space is free.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/xfs/scrub/rmap.c b/fs/xfs/scrub/rmap.c
index 8655948..54b0eac 100644
--- a/fs/xfs/scrub/rmap.c
+++ b/fs/xfs/scrub/rmap.c
@@ -57,8 +57,13 @@ xfs_scrub_rmapbt_xref(
 	struct xfs_scrub_context	*sc,
 	struct xfs_rmap_irec		*irec)
 {
+	xfs_agblock_t			agbno = irec->rm_startblock;
+	xfs_extlen_t			len = irec->rm_blockcount;
+
 	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
 		return;
+
+	xfs_scrub_xref_is_used_space(sc, agbno, len);
 }
 
 /* Scrub an rmapbt record. */