lock the getter instead ??? c/o M

src/service/rooms/event_handler/upgrade_outlier_pdu.rs

@@ -149,7 +149,7 @@ where
 	let extremities: Vec<_> = self
 		.services
 		.state
-		.get_forward_extremities(room_id)
+		.get_forward_extremities(room_id, &state_lock)
 		.map(ToOwned::to_owned)
 		.ready_filter(|event_id| {
 			// Remove any that are referenced by this incoming event's prev_events

src/service/rooms/state/mod.rs

@@ -388,6 +388,7 @@ impl Service {
 	pub fn get_forward_extremities<'a>(
 		&'a self,
 		room_id: &'a RoomId,
+		_state_lock: &'a RoomMutexGuard,
 	) -> impl Stream<Item = &EventId> + Send + '_ {
 		let prefix = (room_id, Interfix);