diff -r 10621b0e8e38 -r 4b469f5f4bf2 src/hotspot/share/oops/instanceKlass.cpp
--- a/src/hotspot/share/oops/instanceKlass.cpp	Wed Jan 09 15:53:56 2019 +0100
+++ b/src/hotspot/share/oops/instanceKlass.cpp	Thu Jan 10 18:10:15 2019 +0100
@@ -2186,6 +2186,7 @@
   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);
     }
   }