# HG changeset patch
# User aph
# Date 1560439071 -3600
#      Thu Jun 13 16:17:51 2019 +0100
# Node ID a2906ba6352430b23dcb3cd8bf018ed8b6121e9f
# Parent  8b8d83cf9097fd97b359d7a19583e81d822eebcd
8225716: G1 GC: Undefined behaviour in G1BlockOffsetTablePart::block_at_or_preceding
Reviewed-by: duke

diff --git a/src/hotspot/share/gc/g1/g1BlockOffsetTable.hpp b/src/hotspot/share/gc/g1/g1BlockOffsetTable.hpp
--- a/src/hotspot/share/gc/g1/g1BlockOffsetTable.hpp
+++ b/src/hotspot/share/gc/g1/g1BlockOffsetTable.hpp
@@ -65,7 +65,7 @@
   inline u_char offset_array(size_t index) const;
 
   void set_offset_array_raw(size_t index, u_char offset) {
-    _offset_array[index] = offset;
+    Atomic::store(offset, &_offset_array[index]);
   }
 
   inline void set_offset_array(size_t index, u_char offset);
diff --git a/src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp b/src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp
--- a/src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp
+++ b/src/hotspot/share/gc/g1/g1BlockOffsetTable.inline.hpp
@@ -51,7 +51,7 @@
 
 u_char G1BlockOffsetTable::offset_array(size_t index) const {
   check_index(index, "index out of range");
-  return _offset_array[index];
+  return Atomic::load(&_offset_array[index]);
 }
 
 void G1BlockOffsetTable::set_offset_array(size_t index, u_char offset) {