It looks like a dirty hack, it probably is, but this fixes the GC

src/common/runtime.cpp

@@ -31,10 +31,13 @@
 
 // SDL
 #include <SDL_mutex.h>
+#include <SDL_thread.h>
 
 namespace love
 {
 	static SDL_mutex *gcmutex = 0;
+	void *_gcmutex = 0;
+	unsigned int _gcthread = 0;
 	/**
 	* Called when an object is collected. The object is released
 	* once in this function, possibly deleting it.
@@ -42,13 +45,19 @@ namespace love
 	static int w__gc(lua_State * L)
 	{
 		if (!gcmutex)
+		{
 			gcmutex = SDL_CreateMutex();
+			_gcmutex = (void*) gcmutex;
+		}
 		Proxy * p = (Proxy *)lua_touserdata(L, 1);
 		Object * t = (Object *)p->data;
-		SDL_mutexP(gcmutex);
 		if(p->own)
+		{
+			SDL_mutexP(gcmutex);
+			_gcthread = (unsigned int) SDL_ThreadID();
 			t->release();
-		SDL_mutexV(gcmutex);
+			SDL_mutexV(gcmutex);
+		}
 		return 0;
 	}
 

src/common/runtime.h

@@ -37,6 +37,10 @@ namespace love
 	class Module;
 	class Reference;
 
+	// Exposed mutex of the GC
+	extern void *_gcmutex;
+	extern unsigned int _gcthread;
+
 	/**
 	* Registries represent special tables which can be accessed with
 	* luax_getregistry.

src/modules/thread/sdl/Thread.cpp

@@ -194,7 +194,15 @@ namespace sdl
 			delete[] data;
 		delete comm;
 		if (handle)
+		{
+			bool inGC = (_gcthread == SDL_GetThreadID(handle));
+			bool collectSelf = (inGC && _gcthread == SDL_ThreadID());
+			inGC = inGC && !collectSelf;
+			if (inGC) SDL_mutexP((SDL_mutex *) _gcmutex);
+			if (collectSelf) SDL_mutexV((SDL_mutex *) _gcmutex);
 			SDL_KillThread(handle);
+			if (inGC) SDL_mutexV((SDL_mutex *) _gcmutex);
+		}
 		module->unregister(name);
 		SDL_DestroyMutex(mutex);
 		SDL_DestroyCond(cond);
@@ -211,8 +219,10 @@ namespace sdl
 	{
 		if (handle)
 		{
+			SDL_mutexP((SDL_mutex *) _gcmutex);
 			SDL_KillThread(handle);
 			handle = 0;
+			SDL_mutexV((SDL_mutex *) _gcmutex);
 		}
 	}