8380390: Shenandoah: Missing store barrier when resetting bitmaps

Reviewed-by: ruili, xpeng, kdnilsen

Author: William Kemper

src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.hpp

@@ -280,6 +280,7 @@ class ShenandoahHeapRegion {
   // clears the self_fwd bits. Safety-net reset on region recycle.
   ShenandoahSharedFlag _has_self_forwards;
 
+  // This is only read/written by a gc worker to avoid unnecessary bitmap resets
   bool _needs_bitmap_reset;
 
 public:

src/hotspot/share/gc/shenandoah/shenandoahMarkingContext.cpp

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2018, 2021, Red Hat, Inc. All rights reserved.
+ * Copyright (c) 2018, 2026, Red Hat, Inc. All rights reserved.
  * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
- * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2026, 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
@@ -27,6 +27,7 @@
 #include "gc/shared/markBitMap.inline.hpp"
 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
 #include "gc/shenandoah/shenandoahMarkingContext.hpp"
+#include "runtime/orderAccess.hpp"
 
 ShenandoahMarkingContext::ShenandoahMarkingContext(MemRegion heap_region, MemRegion bitmap_region, size_t num_regions) :
   _mark_bit_map(heap_region, bitmap_region),
@@ -90,6 +91,7 @@ void ShenandoahMarkingContext::clear_bitmap(ShenandoahHeapRegion* r) {
 
   if (top_bitmap > bottom) {
     _mark_bit_map.clear_range_large(MemRegion(bottom, top_bitmap));
+    OrderAccess::storestore();
     _top_bitmaps[r->index()] = bottom;
   }