--- a/src/hotspot/share/oops/instanceKlass.cpp	Mon Jan 14 11:22:32 2019 -0800
+++ b/src/hotspot/share/oops/instanceKlass.cpp	Mon Jan 14 23:05:26 2019 +0100
@@ -2178,6 +2178,7 @@
   for (int m = 0; m < methods()->length(); m++) {
     MethodData* mdo = methods()->at(m)->method_data();
     if (mdo != NULL) {
+      MutexLockerEx ml(SafepointSynchronize::is_at_safepoint() ? NULL : mdo->extra_data_lock());
       mdo->clean_method_data(/*always_clean*/false);
     }
   }