diff -r cbe83e9c2100 -r f1bb77833b59 src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp
--- a/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp	Thu Nov 08 11:22:28 2018 -0800
+++ b/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampler.cpp	Thu Nov 08 11:45:13 2018 -0800
@@ -359,9 +359,6 @@
 
   bool ret = false;
   thread->set_trace_flag();
-  if (!UseMembar) {
-    os::serialize_thread_states();
-  }
   if (JAVA_SAMPLE == type) {
     if (thread_state_in_java(thread)) {
       ret = sample_thread_in_java(thread, frames, max_frames);