--- old/src/share/vm/gc/g1/g1CollectedHeap.cpp	2016-04-11 17:32:15.650445032 +0200
+++ new/src/share/vm/gc/g1/g1CollectedHeap.cpp	2016-04-11 17:32:15.502439239 +0200
@@ -4462,7 +4462,11 @@
   // object discovered by the STW ref processor.
   double preserve_cm_referents_time = 0.0;
 
-  if (_ref_processor_cm->has_discovered_references()) {
+  // To avoid spawning task when there is no work to do, check that
+  // a concurrent cycle is active and that some references have been
+  // discovered.
+  if (concurrent_mark()->cmThread()->during_cycle() &&
+      ref_processor_cm()->has_discovered_references()) {
     double preserve_cm_referents_start = os::elapsedTime();
     uint no_of_gc_workers = workers()->active_workers();
     G1ParPreserveCMReferentsTask keep_cm_referents(this,