--- a/src/hotspot/share/services/heapDumper.cpp	Fri Aug 31 12:41:00 2018 +0200
+++ b/src/hotspot/share/services/heapDumper.cpp	Fri Aug 31 07:03:46 2018 -0400
@@ -1464,6 +1464,7 @@
   bool skip_operation() const;
 
   // writes a HPROF_LOAD_CLASS record
+  class ClassesDo;
   static void do_load_class(Klass* k);
 
   // writes a HPROF_GC_CLASS_DUMP record for the given class
@@ -1821,7 +1822,10 @@
   SymbolTable::symbols_do(&sym_dumper);
 
   // write HPROF_LOAD_CLASS records
-  ClassLoaderDataGraph::classes_do(&do_load_class);
+  {
+    LockedClassesDo locked_load_classes(&do_load_class);
+    ClassLoaderDataGraph::classes_do(&locked_load_classes);
+  }
   Universe::basic_type_classes_do(&do_load_class);
 
   // write HPROF_FRAME and HPROF_TRACE records
@@ -1832,7 +1836,10 @@
   DumperSupport::write_dump_header(writer());
 
   // Writes HPROF_GC_CLASS_DUMP records
-  ClassLoaderDataGraph::classes_do(&do_class_dump);
+  {
+    LockedClassesDo locked_dump_class(&do_class_dump);
+    ClassLoaderDataGraph::classes_do(&locked_dump_class);
+  }
   Universe::basic_type_classes_do(&do_basic_type_array_class_dump);
   check_segment_length();