--- old/src/hotspot/share/trace/tracingExport.cpp	2018-04-03 17:00:16.000000000 -0400
+++ new/src/hotspot/share/trace/tracingExport.cpp	2018-04-03 17:00:15.000000000 -0400
@@ -26,13 +26,15 @@
 #include "runtime/orderAccess.inline.hpp"
 #include "trace/tracingExport.hpp"
 
-// Allow lock-free access to _sampler_thread.
+// Allow lock-free reads of _sampler_thread.
 Thread* volatile TracingExport::_sampler_thread = NULL;
 
-Thread* TracingExport::get_sampler_thread() {
+Thread* TracingExport::sampler_thread_acquire() {
   return (Thread*)OrderAccess::load_acquire(&_sampler_thread);
 }
 
-void TracingExport::set_sampler_thread(Thread* thread) {
-  OrderAccess::release_store_fence(&_sampler_thread, thread);
+void TracingExport::set_sampler_thread_with_lock(Thread* thread) {
+  // Grab Threads_lock to avoid conflicts with Thread-SMR scans.
+  MutexLocker ml(Threads_lock);
+  _sampler_thread = thread;
 }