8291830: jvmti/RedefineClasses/StressRedefine failed: assert(!is_null(v)) failed: narrow klass value can never be zero

Reviewed-by: mdoerr
Backport-of: fb6fd03233b0eb001e2995d20a079b6af31d2b9b

Author: RealLucy

src/hotspot/share/oops/klass.cpp

@@ -25,7 +25,7 @@
 #include "precompiled.hpp"
 #include "classfile/classLoaderData.inline.hpp"
 #include "classfile/dictionary.hpp"
-#include "classfile/javaClasses.hpp"
+#include "classfile/javaClasses.inline.hpp"
 #include "classfile/systemDictionary.hpp"
 #include "classfile/vmSymbols.hpp"
 #include "gc/shared/collectedHeap.inline.hpp"
@@ -735,7 +735,7 @@ void Klass::verify_on(outputStream* st) {
   }
 
   if (java_mirror_no_keepalive() != NULL) {
-    guarantee(oopDesc::is_oop(java_mirror_no_keepalive()), "should be instance");
+    guarantee(java_lang_Class::is_instance(java_mirror_no_keepalive()), "should be instance");
   }
 }
 

src/hotspot/share/oops/klass.hpp

@@ -269,9 +269,8 @@ class Klass : public Metadata {
   // Both mirrors are on the ClassLoaderData::_handles list already so no
   // barriers are needed.
   void set_java_mirror_handle(OopHandle mirror) { _java_mirror = mirror; }
-  OopHandle java_mirror_handle() const          {
-    return _java_mirror;
-  }
+  OopHandle java_mirror_handle() const          { return _java_mirror;   }
+  void swap_java_mirror_handle(OopHandle& mirror) { _java_mirror.swap(mirror); }
 
   // modifier flags
   jint modifier_flags() const          { return _modifier_flags; }

src/hotspot/share/oops/oopHandle.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2017, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 2022, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -43,6 +43,10 @@ class OopHandle {
   OopHandle() : _obj(NULL) {}
   OopHandle(oop* w) : _obj(w) {}
 
+  void swap(OopHandle& copy) {
+    ::swap(_obj, copy._obj);
+  }
+
   inline oop resolve() const;
   inline oop peek() const;
 

src/hotspot/share/prims/jvmtiThreadState.hpp

@@ -411,14 +411,14 @@ class RedefineVerifyMark : public StackObj {
                      JvmtiThreadState *state) : _state(state), _scratch_class(scratch_class)
   {
     _state->set_class_versions_map(the_class, scratch_class);
-    _scratch_mirror = _scratch_class->java_mirror_handle();
-    _scratch_class->set_java_mirror_handle(the_class->java_mirror_handle());
+    _scratch_mirror = the_class->java_mirror_handle();  // this is a copy that is swapped
+    _scratch_class->swap_java_mirror_handle(_scratch_mirror);
   }
 
   ~RedefineVerifyMark() {
     // Restore the scratch class's mirror, so when scratch_class is removed
     // the correct mirror pointing to it can be cleared.
-    _scratch_class->set_java_mirror_handle(_scratch_mirror);
+    _scratch_class->swap_java_mirror_handle(_scratch_mirror);
     _state->clear_class_versions_map();
   }
 };