new flag in 'CallInfo.callstatus' to tell whether function is running

as a finalizer

lgc.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lgc.c,v 2.211 2015/12/10 18:12:30 roberto Exp roberto $
+** $Id: lgc.c,v 2.212 2016/03/31 19:02:03 roberto Exp roberto $
 ** Garbage Collector
 ** See Copyright Notice in lua.h
 */
@@ -818,7 +818,9 @@ static void GCTM (lua_State *L, int propagateerrors) {
     setobj2s(L, L->top, tm);  /* push finalizer... */
     setobj2s(L, L->top + 1, &v);  /* ... and its argument */
     L->top += 2;  /* and (next line) call the finalizer */
+    L->ci->callstatus |= CIST_FIN;  /* will run a finalizer */
     status = luaD_pcall(L, dothecall, NULL, savestack(L, L->top - 2), 0);
+    L->ci->callstatus &= ~CIST_FIN;  /* not running a finalizer anymore */
     L->allowhook = oldah;  /* restore hooks */
     g->gcrunning = running;  /* restore state */
     if (status != LUA_OK && propagateerrors) {  /* error while running __gc? */

lstate.h

@@ -1,5 +1,5 @@
 /*
-** $Id: lstate.h,v 2.130 2015/12/16 16:39:38 roberto Exp roberto $
+** $Id: lstate.h,v 2.131 2016/06/16 13:36:09 roberto Exp roberto $
 ** Global State
 ** See Copyright Notice in lua.h
 */
@@ -104,6 +104,7 @@ typedef struct CallInfo {
 #define CIST_TAIL	(1<<5)	/* call was tail called */
 #define CIST_HOOKYIELD	(1<<6)	/* last hook called yielded */
 #define CIST_LEQ	(1<<7)  /* using __lt for __le */
+#define CIST_FIN	(1<<8)  /* call is running a finalizer */
 
 #define isLua(ci)	((ci)->callstatus & CIST_LUA)