--- old/src/hotspot/share/oops/instanceKlass.cpp	2020-03-11 01:12:49.481351211 -0400
+++ new/src/hotspot/share/oops/instanceKlass.cpp	2020-03-11 01:12:48.336338482 -0400
@@ -226,6 +226,10 @@
 // from higher-level access checking code, and reported as part of access checking
 // exceptions.
 // VirtualMachineErrors are propagated with a NULL return.
+// Under any conditions where the _nest_host can be set to non-NULL the resulting value
+// of it and, if applicable, _nest_host_res_error, are idempotent. But as we can be
+// executing this code concurrently we need to ensure ordering is maintained so that
+// errors messages can safely be read.
 InstanceKlass* InstanceKlass::nest_host(TRAPS) {
   InstanceKlass* nest_host_k = _nest_host;
   if (nest_host_k != NULL) {
@@ -234,10 +238,7 @@
 
   const bool doLog = log_is_enabled(Trace, class, nestmates);
 
-  // need to resolve and save our nest-host class. This could be attempted
-  // concurrently but as the result is idempotent and we don't use the class
-  // then we do not need any synchronization beyond what is implicitly used
-  // during class loading.
+  // need to resolve and save our nest-host class.
   if (_nest_host_index != 0) { // we have a real nest_host
     // Before trying to resolve check if we're in a suitable context
     if (!THREAD->can_call_java() && !_constants->tag_at(_nest_host_index).is_klass()) {
@@ -268,6 +269,8 @@
                this->external_name(), target_host_class);
       java_lang_Throwable::print(PENDING_EXCEPTION, &ss);
       _nest_host_res_error = ss.as_string(true /* on C-heap */);
+      // ensure we see _nest_host_res_error is set if _nest_host is non-NULL
+      OrderAccess::storestore();
       CLEAR_PENDING_EXCEPTION;
       if (doLog) {
         log_trace(class, nestmates)("%s", _nest_host_res_error);
@@ -325,6 +328,8 @@
                  k->class_loader_data()->loader_name_and_id(),
                  error);
         _nest_host_res_error = ss.as_string(true /* on C-heap */);
+        // ensure we see _nest_host_res_error is set if _nest_host is non-NULL
+        OrderAccess::storestore();
 
         if (doLog) {
           log_trace(class, nestmates)("%s", _nest_host_res_error);
@@ -340,7 +345,8 @@
   }
 
   // Either not in an explicit nest, or else an error occurred, so
-  // the nest-host is set to `this`.
+  // the nest-host is set to `this`. Any thread that sees this assignment
+  // will also see any setting of _nest_host_res_error, if applicable.
   return (_nest_host = this);
 }