8260704: ParallelGC: oldgen expansion needs release-store for _end

Move JDK-8257999 barrier to correct location.

Reviewed-by: yan
Backport-of: afd5eefdae388a53a0d6bffc2cf94b878ac1881e

src/hotspot/share/gc/parallel/mutableSpace.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2021, 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
@@ -123,7 +123,11 @@ void MutableSpace::initialize(MemRegion mr,
   }
 
   set_bottom(mr.start());
-  set_end(mr.end());
+  // When expanding concurrently with callers of cas_allocate, setting end
+  // makes the new space available for allocation by other threads.  So this
+  // assignment must follow all other configuration and initialization that
+  // might be done for expansion.
+  Atomic::release_store(end_addr(), mr.end());
 
   if (clear_space) {
     clear(mangle_space);

src/hotspot/share/gc/parallel/psOldGen.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2021, 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
@@ -36,7 +36,6 @@
 #include "logging/log.hpp"
 #include "oops/oop.inline.hpp"
 #include "runtime/java.hpp"
-#include "runtime/orderAccess.hpp"
 #include "utilities/align.hpp"
 
 PSOldGen::PSOldGen(ReservedSpace rs, size_t initial_size, size_t min_size,
@@ -352,9 +351,9 @@ void PSOldGen::post_resize() {
   start_array()->set_covered_region(new_memregion);
   ParallelScavengeHeap::heap()->card_table()->resize_covered_region(new_memregion);
 
-  // Ensure the space bounds are updated and made visible to other
-  // threads after the other data structures have been resized.
-  OrderAccess::storestore();
+  // The update of the space's end is done by this call.  As that
+  // makes the new space available for concurrent allocation, this
+  // must be the last step when expanding.
   object_space()->initialize(new_memregion,
                              SpaceDecorator::DontClear,
                              SpaceDecorator::DontMangle);