Re: [PATCH v3 11/17] rv: Retry when da monitor detects race conditions

On Tue, Jul 15, 2025 at 09:14:28AM +0200, Gabriele Monaco wrote:

 static inline bool										\
 da_event_##name(struct da_monitor *da_mon, enum events_##name event)				\
 {												\
-	type curr_state = da_monitor_curr_state_##name(da_mon);					\
-	type next_state = model_get_next_state_##name(curr_state, event);			\
-												\
-	if (next_state != INVALID_STATE) {							\
-		da_monitor_set_state_##name(da_mon, next_state);				\
-												\
-		trace_event_##name(model_get_state_name_##name(curr_state),			\
-				   model_get_event_name_##name(event),				\
-				   model_get_state_name_##name(next_state),			\
-				   model_is_final_state_##name(next_state));			\
-												\
-		return true;									\
+	enum states_##name curr_state, next_state;						\
+												\
+	curr_state = READ_ONCE(da_mon->curr_state);						\
+	for (int i = 0; i < MAX_DA_RETRY_RACING_EVENTS; i++) {					\
+		next_state = model_get_next_state_##name(curr_state, event);			\
+		if (next_state == INVALID_STATE)						\
+			goto out_react;								\
+		if (likely(try_cmpxchg(&da_mon->curr_state, &curr_state, next_state)))		\
+			goto out_success;							\
 	}											\
+	/* Special invalid transition if we run out of retries. */				\
+	curr_state = INVALID_STATE;								\
 												\
+out_react:											\
 	cond_react_##name(curr_state, event);							\
 												\
 	trace_error_##name(model_get_state_name_##name(curr_state),				\
 			   model_get_event_name_##name(event));					\

If I understand correctly, if after 3 tries and we still fail to change the
state, we will invoke the reactor and trace_error? Doesn't that cause a
false positive? Because it is not a violation of the model, it is just a
race making us fail to change the state.

Same below.

Also, I wouldn't use goto unless necessary. Perhaps it is better to put the
code at "out_react:" and "out_success:" into the loop. But that's just my
personal preference, up to you.

Nam