--- a/hotspot/src/share/vm/memory/universe.cpp	Mon Jun 20 22:02:20 2016 -0700
+++ b/hotspot/src/share/vm/memory/universe.cpp	Tue Jun 21 09:19:53 2016 +0200
@@ -1070,13 +1070,13 @@
 }
 
 void Universe::print_on(outputStream* st) {
+  GCMutexLocker hl(Heap_lock); // Heap_lock might be locked by caller thread.
   st->print_cr("Heap");
   heap()->print_on(st);
 }
 
 void Universe::print_heap_at_SIGBREAK() {
   if (PrintHeapAtSIGBREAK) {
-    MutexLocker hl(Heap_lock);
     print_on(tty);
     tty->cr();
     tty->flush();