[Minor] Small improvements

src/lua/lua_common.c

@@ -1494,14 +1494,26 @@ rspamd_lua_traceback (lua_State *L)
 {
 
 	GString *tb;
+
+	tb = rspamd_lua_get_traceback_string (L);
+
+	lua_pushlightuserdata (L, tb);
+
+	return 1;
+}
+
+GString *
+rspamd_lua_get_traceback_string (lua_State *L)
+{
+	GString *tb;
 	const gchar *msg = lua_tostring (L, 1);
 
 	tb = g_string_sized_new (100);
 	g_string_append_printf (tb, "%s; trace:", msg);
+
 	rspamd_lua_traceback_string (L, tb);
-	lua_pushlightuserdata (L, tb);
 
-	return 1;
+	return tb;
 }
 
 guint

src/lua/lua_common.h

@@ -336,6 +336,14 @@ gboolean rspamd_lua_parse_table_arguments (lua_State *L, gint pos,
 
 gint rspamd_lua_traceback (lua_State *L);
 
+/**
+ * Returns stack trace as a string. Caller should clear memory.
+ * @param L
+ * @return
+ */
+GString *
+rspamd_lua_get_traceback_string (lua_State *L);
+
 /**
  * Returns size of table at position `tbl_pos`
  */

src/lua/lua_config.c

@@ -1257,6 +1257,13 @@ lua_resume_thread (struct rspamd_task *task, struct thread_entry *thread_entry,
 {
     g_assert (thread_entry->cd != NULL);
 
+    /*
+     * The only state where we can resume from is LUA_YIELD
+     * Another acceptable status is OK (0) but in that case we should push function on stack
+     * to start the thread from, which is happening in lua_metric_symbol_callback(), not in this function.
+     */
+    g_assert (lua_status (thread_entry->lua_state) == LUA_YIELD);
+
 	gint ret;
 
 	lua_thread_pool_set_running_entry (task->cfg->lua_thread_pool, thread_entry);
@@ -1277,15 +1284,12 @@ lua_metric_symbol_callback_return (struct rspamd_task *task, struct thread_entry
 	lua_State *thread = thread_entry->lua_state;
 
 	if (ret != 0) {
-		lua_pushcfunction (thread, rspamd_lua_traceback);
-		lua_call (thread, 0, LUA_MULTRET);
 
-		tb = lua_touserdata (thread, -1);
+		tb = rspamd_lua_get_traceback_string (thread);
 		msg_err_task ("call to (%s) failed (%d): %v", cd->symbol, ret, tb);
 
 		if (tb) {
 			g_string_free (tb, TRUE);
-			lua_pop (thread, 1);
 		}
 		g_assert (lua_gettop (thread) >= cd->stack_level);
 		/* maybe there is a way to recover here. For now, just remove faulty thread */