bcachefs: CONFIG_BCACHEFS_INJECT_TRANSACTION_RESTARTS

Incorrectly handled transaction restarts can be a source of heisenbugs;
add a mode where we randomly inject them to shake them out.

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

Author: Kent Overstreet

fs/bcachefs/Kconfig

@@ -61,6 +61,13 @@ config BCACHEFS_DEBUG
 	The resulting code will be significantly slower than normal; you
 	probably shouldn't select this option unless you're a developer.
 
+config BCACHEFS_INJECT_TRANSACTION_RESTARTS
+	bool "Randomly inject transaction restarts"
+	depends on BCACHEFS_DEBUG
+	help
+	Randomly inject transaction restarts in a few core paths - may have a
+	significant performance penalty
+
 config BCACHEFS_TESTS
 	bool "bcachefs unit and performance tests"
 	depends on BCACHEFS_FS

fs/bcachefs/btree_iter.c

@@ -2357,6 +2357,12 @@ struct bkey_s_c bch2_btree_iter_peek_max(struct btree_iter *iter, struct bpos en
 	bch2_btree_iter_verify_entry_exit(iter);
 	EBUG_ON((iter->flags & BTREE_ITER_filter_snapshots) && bkey_eq(end, POS_MAX));
 
+	ret = trans_maybe_inject_restart(trans, _RET_IP_);
+	if (unlikely(ret)) {
+		k = bkey_s_c_err(ret);
+		goto out_no_locked;
+	}
+
 	if (iter->update_path) {
 		bch2_path_put_nokeep(trans, iter->update_path,
 				     iter->flags & BTREE_ITER_intent);
@@ -2622,6 +2628,12 @@ struct bkey_s_c bch2_btree_iter_peek_prev_min(struct btree_iter *iter, struct bp
 	bch2_btree_iter_verify_entry_exit(iter);
 	EBUG_ON((iter->flags & BTREE_ITER_filter_snapshots) && bpos_eq(end, POS_MIN));
 
+	int ret = trans_maybe_inject_restart(trans, _RET_IP_);
+	if (unlikely(ret)) {
+		k = bkey_s_c_err(ret);
+		goto out_no_locked;
+	}
+
 	while (1) {
 		k = __bch2_btree_iter_peek_prev(iter, search_key);
 		if (unlikely(!k.k))
@@ -2749,6 +2761,12 @@ struct bkey_s_c bch2_btree_iter_peek_slot(struct btree_iter *iter)
 	bch2_btree_iter_verify_entry_exit(iter);
 	EBUG_ON(btree_iter_path(trans, iter)->level && (iter->flags & BTREE_ITER_with_key_cache));
 
+	ret = trans_maybe_inject_restart(trans, _RET_IP_);
+	if (unlikely(ret)) {
+		k = bkey_s_c_err(ret);
+		goto out_no_locked;
+	}
+
 	/* extents can't span inode numbers: */
 	if ((iter->flags & BTREE_ITER_is_extents) &&
 	    unlikely(iter->pos.offset == KEY_OFFSET_MAX)) {
@@ -3106,6 +3124,10 @@ void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size)
 
 	WARN_ON_ONCE(new_bytes > BTREE_TRANS_MEM_MAX);
 
+	ret = trans_maybe_inject_restart(trans, _RET_IP_);
+	if (ret)
+		return ERR_PTR(ret);
+
 	struct btree_transaction_stats *s = btree_trans_stats(trans);
 	s->max_mem = max(s->max_mem, new_bytes);
 
@@ -3163,7 +3185,8 @@ void *__bch2_trans_kmalloc(struct btree_trans *trans, size_t size)
 
 	if (old_bytes) {
 		trace_and_count(c, trans_restart_mem_realloced, trans, _RET_IP_, new_bytes);
-		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_mem_realloced));
+		return ERR_PTR(btree_trans_restart_ip(trans,
+					BCH_ERR_transaction_restart_mem_realloced, _RET_IP_));
 	}
 out_change_top:
 	p = trans->mem + trans->mem_top;
@@ -3271,6 +3294,14 @@ u32 bch2_trans_begin(struct btree_trans *trans)
 
 	trans->last_begin_ip = _RET_IP_;
 
+#ifdef CONFIG_BCACHEFS_INJECT_TRANSACTION_RESTARTS
+	if (trans->restarted) {
+		trans->restart_count_this_trans++;
+	} else {
+		trans->restart_count_this_trans = 0;
+	}
+#endif
+
 	trans_set_locked(trans, false);
 
 	if (trans->restarted) {

fs/bcachefs/btree_iter.h

@@ -355,6 +355,18 @@ static int btree_trans_restart(struct btree_trans *trans, int err)
 	return btree_trans_restart_ip(trans, err, _THIS_IP_);
 }
 
+static inline int trans_maybe_inject_restart(struct btree_trans *trans, unsigned long ip)
+{
+#ifdef CONFIG_BCACHEFS_INJECT_TRANSACTION_RESTARTS
+	if (!(ktime_get_ns() & ~(~0ULL << min(63, (10 + trans->restart_count_this_trans))))) {
+		trace_and_count(trans->c, trans_restart_injected, trans, ip);
+		return btree_trans_restart_ip(trans,
+					BCH_ERR_transaction_restart_fault_inject, ip);
+	}
+#endif
+	return 0;
+}
+
 bool bch2_btree_node_upgrade(struct btree_trans *,
 			     struct btree_path *, unsigned);
 

fs/bcachefs/btree_trans_commit.c

@@ -999,6 +999,10 @@ int __bch2_trans_commit(struct btree_trans *trans, unsigned flags)
 
 	bch2_trans_verify_not_unlocked_or_in_restart(trans);
 
+	ret = trans_maybe_inject_restart(trans, _RET_IP_);
+	if (unlikely(ret))
+		goto out_reset;
+
 	if (!trans->nr_updates &&
 	    !trans->journal_entries_u64s)
 		goto out_reset;

fs/bcachefs/btree_types.h

@@ -509,6 +509,9 @@ struct btree_trans {
 	bool			notrace_relock_fail:1;
 	enum bch_errcode	restarted:16;
 	u32			restart_count;
+#ifdef CONFIG_BCACHEFS_INJECT_TRANSACTION_RESTARTS
+	u32			restart_count_this_trans;
+#endif
 
 	u64			last_begin_time;
 	unsigned long		last_begin_ip;