--- old/src/hotspot/share/prims/jvmtiEventController.cpp	2019-07-05 16:18:40.000000000 -0400
+++ new/src/hotspot/share/prims/jvmtiEventController.cpp	2019-07-05 16:18:39.000000000 -0400
@@ -264,7 +264,7 @@
 
 
 VM_ChangeSingleStep::VM_ChangeSingleStep(bool on)
-  : _on(on != 0)
+  : _on(on)
 {
 }
 
@@ -331,14 +331,13 @@
 }
 
 
-// This change must always be occur when at a safepoint.
-// Being at a safepoint causes the interpreter to use the
-// safepoint dispatch table which we overload to find single
-// step points.  Just to be sure that it has been set, we
-// call notice_safepoints when turning on single stepping.
-// When we leave our current safepoint, should_post_single_step
-// will be checked by the interpreter, and the table kept
-// or changed accordingly.
+// When _on == true, we use the safepoint interpreter dispatch table
+// to allow us to find the single step points. Otherwise, we switch
+// back to the regular interpreter dispatch table.
+// Note: We call Interpreter::notice_safepoints() and ignore_safepoints()
+// in a VM_Operation to safely make the dispatch table switch. We
+// no longer rely on the safepoint mechanism to do any of this work
+// for us.
 void VM_ChangeSingleStep::doit() {
   log_debug(interpreter, safepoint)("changing single step to '%s'", _on ? "on" : "off");
   JvmtiEventControllerPrivate::set_should_post_single_step(_on);