bcachefs: Iterator debug code improvements

More aggressively checking iterator invariants, and fixing the resulting
bugs. Also greatly simplifying iter_next() and iter_next_slot() - they
were hyper optimized before, but the optimizations were getting too
brittle.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bset.c

@@ -1665,6 +1665,7 @@ struct bkey_packed *bch2_btree_node_iter_prev_all(struct btree_node_iter *iter,
 	struct bset_tree *t;
 	unsigned end = 0;
 
+	if (btree_keys_expensive_checks(b))
 		bch2_btree_node_iter_verify(iter, b);
 
 	for_each_bset(b, t) {
@@ -1700,6 +1701,7 @@ struct bkey_packed *bch2_btree_node_iter_prev_all(struct btree_node_iter *iter,
 	iter->data[0].k = __btree_node_key_to_offset(b, prev);
 	iter->data[0].end = end;
 
+	if (btree_keys_expensive_checks(b))
 		bch2_btree_node_iter_verify(iter, b);
 	return prev;
 }

fs/bcachefs/btree_iter.h

@@ -96,10 +96,10 @@ __trans_next_iter_with_node(struct btree_trans *trans, struct btree *b,
 						 (_iter)->idx + 1))
 
 #ifdef CONFIG_BCACHEFS_DEBUG
-void bch2_btree_iter_verify(struct btree_iter *, struct btree *);
+void bch2_btree_trans_verify_iters(struct btree_trans *, struct btree *);
 void bch2_btree_trans_verify_locks(struct btree_trans *);
 #else
-static inline void bch2_btree_iter_verify(struct btree_iter *iter,
+static inline void bch2_btree_trans_verify_iters(struct btree_trans *trans,
 						 struct btree *b) {}
 static inline void bch2_btree_trans_verify_locks(struct btree_trans *iter) {}
 #endif
@@ -154,7 +154,7 @@ bch2_btree_iter_traverse(struct btree_iter *iter)
 int bch2_btree_iter_traverse_all(struct btree_trans *);
 
 struct btree *bch2_btree_iter_peek_node(struct btree_iter *);
-struct btree *bch2_btree_iter_next_node(struct btree_iter *, unsigned);
+struct btree *bch2_btree_iter_next_node(struct btree_iter *);
 
 struct bkey_s_c bch2_btree_iter_peek(struct btree_iter *);
 struct bkey_s_c bch2_btree_iter_next(struct btree_iter *);
@@ -231,7 +231,7 @@ static inline int bch2_trans_cond_resched(struct btree_trans *trans)
 				_start, _locks_want, _depth, _flags),	\
 	     _b = bch2_btree_iter_peek_node(_iter);			\
 	     (_b);							\
-	     (_b) = bch2_btree_iter_next_node(_iter, _depth))
+	     (_b) = bch2_btree_iter_next_node(_iter))
 
 #define for_each_btree_node(_trans, _iter, _btree_id, _start,		\
 			    _flags, _b)					\

fs/bcachefs/btree_types.h

@@ -238,9 +238,10 @@ struct btree_iter {
 	u16			flags;
 	u8			idx;
 
-	enum btree_iter_uptodate uptodate:4;
 	enum btree_id		btree_id:4;
+	enum btree_iter_uptodate uptodate:4;
 	unsigned		level:4,
+				min_depth:4,
 				locks_want:4,
 				nodes_locked:4,
 				nodes_intent_locked:4;

fs/bcachefs/btree_update_interior.c

@@ -1557,7 +1557,7 @@ bch2_btree_insert_keys_interior(struct btree_update *as, struct btree *b,
 	trans_for_each_iter_with_node(iter->trans, b, linked)
 		bch2_btree_node_iter_peek(&linked->l[b->c.level].iter, b);
 
-	bch2_btree_iter_verify(iter, b);
+	bch2_btree_trans_verify_iters(iter->trans, b);
 }
 
 /**
@@ -1827,7 +1827,7 @@ void __bch2_foreground_maybe_merge(struct bch_fs *c,
 
 	bch2_btree_iter_node_replace(iter, n);
 
-	bch2_btree_iter_verify(iter, n);
+	bch2_btree_trans_verify_iters(trans, n);
 
 	bch2_btree_node_free_inmem(c, b, iter);
 	bch2_btree_node_free_inmem(c, m, iter);