diff -r 9dc92e89243a -r 4aea554692aa src/hotspot/share/runtime/mutexLocker.cpp
--- a/src/hotspot/share/runtime/mutexLocker.cpp	Fri Aug 09 10:06:44 2019 +0200
+++ b/src/hotspot/share/runtime/mutexLocker.cpp	Fri Aug 09 11:04:08 2019 +0200
@@ -287,7 +287,7 @@
   // CMS_bitMap_lock                          leaf 1
   // CMS_freeList_lock                        leaf 2
 
-  def(Threads_lock                 , PaddedMonitor, barrier,     true,  Monitor::_safepoint_check_sometimes);  // Used for safepoint protocol.
+  def(Threads_lock                 , PaddedMonitor, barrier,     true,  Monitor::_safepoint_check_always);  // Used for safepoint protocol.
   def(NonJavaThreadsList_lock      , PaddedMutex,   leaf,        true,  Monitor::_safepoint_check_never);
   def(NonJavaThreadsListSync_lock  , PaddedMutex,   leaf,        true,  Monitor::_safepoint_check_never);