Bug: finalizer calling exit can corrupt finalization order

'os.exit' can call lua_close again, separating new finalizers
created after all previous finalizers were already separated.

lgc.c

@@ -907,7 +907,7 @@ static void GCTM (lua_State *L) {
     int status;
     lu_byte oldah = L->allowhook;
     int oldgcstp  = g->gcstp;
-    g->gcstp = GCSTPGC;  /* avoid GC steps */
+    g->gcstp |= GCSTPGC;  /* avoid GC steps */
     L->allowhook = 0;  /* stop debug hooks during GC metamethod */
     setobj2s(L, L->top++, tm);  /* push finalizer... */
     setobj2s(L, L->top++, &v);  /* ... and its argument */
@@ -1011,7 +1011,8 @@ static void correctpointers (global_State *g, GCObject *o) {
 void luaC_checkfinalizer (lua_State *L, GCObject *o, Table *mt) {
   global_State *g = G(L);
   if (tofinalize(o) ||                 /* obj. is already marked... */
-      gfasttm(g, mt, TM_GC) == NULL)   /* or has no finalizer? */
+      gfasttm(g, mt, TM_GC) == NULL ||    /* or has no finalizer... */
+      (g->gcstp & GCSTPCLS))                   /* or closing state? */
     return;  /* nothing to be done */
   else {  /* move 'o' to 'finobj' list */
     GCObject **p;
@@ -1502,14 +1503,13 @@ static void deletelist (lua_State *L, GCObject *p, GCObject *limit) {
 */
 void luaC_freeallobjects (lua_State *L) {
   global_State *g = G(L);
-  g->gcstp = GCSTPGC;
+  g->gcstp = GCSTPCLS;  /* no extra finalizers after here */
   luaC_changemode(L, KGC_INC);
   separatetobefnz(g, 1);  /* separate all objects with finalizers */
   lua_assert(g->finobj == NULL);
-  g->gcstp = 0;
   callallpendingfinalizers(L);
   deletelist(L, g->allgc, obj2gco(g->mainthread));
-  deletelist(L, g->finobj, NULL);
+  lua_assert(g->finobj == NULL);  /* no new finalizers */
   deletelist(L, g->fixedgc, NULL);  /* collect fixed objects */
   lua_assert(g->strt.nuse == 0);
 }

lgc.h

@@ -154,6 +154,7 @@
 */
 #define GCSTPUSR	1  /* bit true when GC stopped by user */
 #define GCSTPGC		2  /* bit true when GC stopped by itself */
+#define GCSTPCLS	4  /* bit true when closing Lua state */
 #define gcrunning(g)	((g)->gcstp == 0)
 
 

testes/main.lua

@@ -261,6 +261,34 @@ u2 = setmetatable({}, {__gc = function () error("ZYX") end})
 RUN('lua -W %s 2> %s', prog, out)
 checkprogout("ZYX)\nXYZ)\n")
 
+-- bug since 5.2: finalizer called when closing a state could
+-- subvert finalization order
+prepfile[[
+-- should be called last
+print("creating 1")
+setmetatable({}, {__gc = function () print(1) end})
+
+print("creating 2")
+setmetatable({}, {__gc = function ()
+  print("2")
+  print("creating 3")
+  -- this finalizer should not be called, as object will be
+  -- created after 'lua_close' has been called
+  setmetatable({}, {__gc = function () print(3) end})
+  print(collectgarbage())    -- cannot call collector here
+  os.exit(0, true)
+end})
+]]
+RUN('lua -W %s > %s', prog, out)
+checkout[[
+creating 1
+creating 2
+2
+creating 3
+nil
+1
+]]
+
 
 -- test many arguments
 prepfile[[print(({...})[30])]]