xfs: always scrub record/key order of interior records

In commit d47fef93, we removed the firstrec and firstkey fields of
struct xchk_btree because Christoph thought they were unnecessary
because we could use the record index in the btree cursor.  This is
incorrect because bc_ptrs (now bc_levels[].ptr) tracks the cursor
position within a specific btree block, not within the entire level.

The end result is that scrub no longer detects situations where the
rightmost record of a block is identical to the leftmost record of that
block's right sibling.  Fix this regression by reintroducing record
validity booleans so that order checking skips *only* the leftmost
record/key in each level.

Fixes: d47fef93 ("xfs: don't track firstrec/firstkey separately in xchk_btree")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/scrub/btree.c

@@ -151,11 +151,12 @@ xchk_btree_rec(
 
 	trace_xchk_btree_rec(bs->sc, cur, 0);
 
-	/* If this isn't the first record, are they in order? */
-	if (cur->bc_levels[0].ptr > 1 &&
+	/* Are all records across all record blocks in order? */
+	if (bs->lastrec_valid &&
 	    !cur->bc_ops->recs_inorder(cur, &bs->lastrec, rec))
 		xchk_btree_set_corrupt(bs->sc, cur, 0);
 	memcpy(&bs->lastrec, rec, cur->bc_ops->rec_len);
+	bs->lastrec_valid = true;
 
 	if (cur->bc_nlevels == 1)
 		return;
@@ -198,11 +199,12 @@ xchk_btree_key(
 
 	trace_xchk_btree_key(bs->sc, cur, level);
 
-	/* If this isn't the first key, are they in order? */
-	if (cur->bc_levels[level].ptr > 1 &&
-	    !cur->bc_ops->keys_inorder(cur, &bs->lastkey[level - 1], key))
+	/* Are all low keys across all node blocks in order? */
+	if (bs->lastkey[level - 1].valid &&
+	    !cur->bc_ops->keys_inorder(cur, &bs->lastkey[level - 1].key, key))
 		xchk_btree_set_corrupt(bs->sc, cur, level);
-	memcpy(&bs->lastkey[level - 1], key, cur->bc_ops->key_len);
+	memcpy(&bs->lastkey[level - 1].key, key, cur->bc_ops->key_len);
+	bs->lastkey[level - 1].valid = true;
 
 	if (level + 1 >= cur->bc_nlevels)
 		return;

fs/xfs/scrub/btree.h

@@ -31,6 +31,11 @@ typedef int (*xchk_btree_rec_fn)(
 	struct xchk_btree		*bs,
 	const union xfs_btree_rec	*rec);
 
+struct xchk_btree_key {
+	union xfs_btree_key		key;
+	bool				valid;
+};
+
 struct xchk_btree {
 	/* caller-provided scrub state */
 	struct xfs_scrub		*sc;
@@ -40,11 +45,12 @@ struct xchk_btree {
 	void				*private;
 
 	/* internal scrub state */
+	bool				lastrec_valid;
 	union xfs_btree_rec		lastrec;
 	struct list_head		to_check;
 
 	/* this element must come last! */
-	union xfs_btree_key		lastkey[];
+	struct xchk_btree_key		lastkey[];
 };
 
 /*