--- a/hotspot/src/share/vm/gc_implementation/g1/g1RootProcessor.cpp	Tue Mar 17 11:19:05 2015 -0700
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1RootProcessor.cpp	Thu Apr 02 06:42:24 2015 +0200
@@ -253,7 +253,8 @@
 
   {
     G1GCParPhaseTimesTracker x(phase_times, G1GCPhaseTimes::ThreadRoots, worker_i);
-    Threads::possibly_parallel_oops_do(strong_roots, thread_stack_clds, strong_code);
+    bool is_par = _g1h->n_par_threads() > 0;
+    Threads::possibly_parallel_oops_do(is_par, strong_roots, thread_stack_clds, strong_code);
   }
 }