Don't allow two drawsyncs to be in play at once.

Core/CoreTiming.cpp

@@ -315,6 +315,52 @@ s64 UnscheduleEvent(int event_type, u64 userdata)
 	return result;
 }
 
+s64 UnscheduleThreadsafeEvent(int event_type, u64 userdata)
+{
+	s64 result = 0;
+	std::lock_guard<std::recursive_mutex> lk(externalEventSection);
+	if (!tsFirst)
+		return result;
+	while(tsFirst)
+	{
+		if (tsFirst->type == event_type && tsFirst->userdata == userdata)
+		{
+			result = tsFirst->time - globalTimer;
+
+			Event *next = tsFirst->next;
+			FreeTsEvent(tsFirst);
+			tsFirst = next;
+		}
+		else
+		{
+			break;
+		}
+	}
+	if (!tsFirst)
+		return result;
+
+	Event *prev = tsFirst;
+	Event *ptr = prev->next;
+	while (ptr)
+	{
+		if (ptr->type == event_type && ptr->userdata == userdata)
+		{
+			result = ptr->time - globalTimer;
+
+			prev->next = ptr->next;
+			FreeTsEvent(ptr);
+			ptr = prev->next;
+		}
+		else
+		{
+			prev = ptr;
+			ptr = ptr->next;
+		}
+	}
+
+	return result;
+}
+
 // Warning: not included in save state.
 void RegisterAdvanceCallback(void (*callback)(int cyclesExecuted))
 {

Core/CoreTiming.h

@@ -94,6 +94,7 @@ namespace CoreTiming
 	void ScheduleEvent_Threadsafe(s64 cyclesIntoFuture, int event_type, u64 userdata=0);
 	void ScheduleEvent_Threadsafe_Immediate(int event_type, u64 userdata=0);
 	s64 UnscheduleEvent(int event_type, u64 userdata);
+	s64 UnscheduleThreadsafeEvent(int event_type, u64 userdata);
 
 	void RemoveEvent(int event_type);
 	void RemoveThreadsafeEvent(int event_type);

Core/HLE/sceGe.cpp

@@ -195,6 +195,8 @@ void __GeShutdown()
 bool __GeTriggerSync(WaitType waitType, int id, u64 atTicks)
 {
 	u64 userdata = (u64)id << 32 | (u64) waitType;
+	if (waitType == WAITTYPE_GEDRAWSYNC)
+		CoreTiming::UnscheduleThreadsafeEvent(geSyncEvent, userdata);
 	CoreTiming::ScheduleEvent_Threadsafe(atTicks - CoreTiming::GetTicks(), geSyncEvent, userdata);
 	return true;
 }