bcachefs: Ensure bch2_btree_iter_next() always advances

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_iter.c

@@ -1110,7 +1110,8 @@ int __must_check bch2_btree_iter_traverse(struct btree_iter *iter)
 {
 	int ret;
 
-	ret = __bch2_btree_iter_traverse(iter);
+	ret =   bch2_trans_cond_resched(iter->trans) ?:
+		__bch2_btree_iter_traverse(iter);
 	if (unlikely(ret))
 		ret = __btree_iter_traverse_all(iter->trans, iter, ret);
 
@@ -1302,9 +1303,11 @@ struct bkey_s_c bch2_btree_iter_peek(struct btree_iter *iter)
 		return btree_iter_peek_uptodate(iter);
 
 	while (1) {
-		ret = bch2_btree_iter_traverse(iter);
-		if (unlikely(ret))
-			return bkey_s_c_err(ret);
+		if (iter->uptodate >= BTREE_ITER_NEED_RELOCK) {
+			ret = bch2_btree_iter_traverse(iter);
+			if (unlikely(ret))
+				return bkey_s_c_err(ret);
+		}
 
 		k = __btree_iter_peek(iter, l);
 		if (likely(k.k))
@@ -1356,10 +1359,17 @@ struct bkey_s_c bch2_btree_iter_next(struct btree_iter *iter)
 
 	bch2_btree_iter_checks(iter, BTREE_ITER_KEYS);
 
+	iter->pos = btree_type_successor(iter->btree_id, iter->k.p);
+
 	if (unlikely(iter->uptodate != BTREE_ITER_UPTODATE)) {
-		k = bch2_btree_iter_peek(iter);
-		if (IS_ERR_OR_NULL(k.k))
-			return k;
+		/*
+		 * XXX: when we just need to relock we should be able to avoid
+		 * calling traverse, but we need to kill BTREE_ITER_NEED_PEEK
+		 * for that to work
+		 */
+		btree_iter_set_dirty(iter, BTREE_ITER_NEED_TRAVERSE);
+
+		return bch2_btree_iter_peek(iter);
 	}
 
 	do {
@@ -1559,9 +1569,11 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 	if (iter->uptodate == BTREE_ITER_UPTODATE)
 		return btree_iter_peek_uptodate(iter);
 
-	ret = bch2_btree_iter_traverse(iter);
-	if (unlikely(ret))
-		return bkey_s_c_err(ret);
+	if (iter->uptodate >= BTREE_ITER_NEED_RELOCK) {
+		ret = bch2_btree_iter_traverse(iter);
+		if (unlikely(ret))
+			return bkey_s_c_err(ret);
+	}
 
 	return __bch2_btree_iter_peek_slot(iter);
 }

fs/bcachefs/btree_iter.h

@@ -195,13 +195,14 @@ static inline int btree_iter_cmp(const struct btree_iter *l,
  * Unlocks before scheduling
  * Note: does not revalidate iterator
  */
-static inline void bch2_trans_cond_resched(struct btree_trans *trans)
+static inline int bch2_trans_cond_resched(struct btree_trans *trans)
 {
-	if (need_resched()) {
+	if (need_resched() || race_fault()) {
 		bch2_trans_unlock(trans);
 		schedule();
-	} else if (race_fault()) {
-		bch2_trans_unlock(trans);
+		return bch2_trans_relock(trans) ? 0 : -EINTR;
+	} else {
+		return 0;
 	}
 }
 
@@ -229,8 +230,6 @@ static inline struct bkey_s_c __bch2_btree_iter_peek(struct btree_iter *iter,
 static inline struct bkey_s_c __bch2_btree_iter_next(struct btree_iter *iter,
 						     unsigned flags)
 {
-	bch2_trans_cond_resched(iter->trans);
-
 	return flags & BTREE_ITER_SLOTS
 		? bch2_btree_iter_next_slot(iter)
 		: bch2_btree_iter_next(iter);