8036673: G1: Abort weak reference processing if mark stack overflows

Reviewed-by: brutisso, tschatzl

src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -2529,6 +2529,11 @@ void ConcurrentMark::weakRefsWork(bool clear_all_soft_refs) {
     assert(!rp->discovery_enabled(), "Post condition");
   }
 
+  if (has_overflown()) {
+    // We can not trust g1_is_alive if the marking stack overflowed
+    return;
+  }
+
   g1h->unlink_string_and_symbol_table(&g1_is_alive,
                                       /* process_strings */ false, // currently strings are always roots
                                       /* process_symbols */ true);