gray2black         78 lib/lua/lgc.c        gray2black(o);  /* udata are never gray */
gray2black         87 lib/lua/lgc.c          gray2black(o);  /* open upvalues are never black */
gray2black        280 lib/lua/lgc.c    gray2black(o);
gray2black        701 lib/lua/lgc.c        gray2black(o);  /* closed upvalues need barrier */