--- a/src/hotspot/share/utilities/vmError.cpp	Fri Jun 22 18:49:45 2018 +0300
+++ b/src/hotspot/share/utilities/vmError.cpp	Fri Jun 22 12:15:16 2018 -0400
@@ -1698,6 +1698,13 @@
   // Case 15 is tested by test/hotspot/jtreg/runtime/ErrorHandling/SecondaryErrorTest.java.
   // Case 16 is tested by test/hotspot/jtreg/runtime/ErrorHandling/ThreadsListHandleInErrorHandlingTest.java.
   // Case 17 is tested by test/hotspot/jtreg/runtime/ErrorHandling/NestedThreadsListHandleInErrorHandlingTest.java.
+
+  // We grab Threads_lock to keep ThreadsSMRSupport::print_info_on()
+  // from racing with Threads::add() or Threads::remove() as we
+  // generate the hs_err_pid file. This makes our ErrorHandling tests
+  // more stable.
+  MutexLockerEx ml(Threads_lock, Mutex::_no_safepoint_check_flag);
+
   switch (how) {
     case  1: vmassert(str == NULL, "expected null"); break;
     case  2: vmassert(num == 1023 && *str == 'X',