--- old/src/share/vm/memory/universe.cpp	2016-05-10 22:20:04.666699050 +0900
+++ new/src/share/vm/memory/universe.cpp	2016-05-10 22:20:04.528699937 +0900
@@ -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();