8058209: Race in G1 card scanning could allow scanning of memory covered by PLABs
Summary: Read _top before _gc_time_stamp in saved_mark_word() with LoadLoad order to ensure we get a consistent view
Reviewed-by: brutisso, dcubed, dholmes, stefank
--- a/hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp Fri Nov 14 09:47:09 2014 +0100
+++ b/hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp Fri Nov 14 14:23:25 2014 +0100
@@ -1004,10 +1004,13 @@
HeapWord* G1OffsetTableContigSpace::saved_mark_word() const {
G1CollectedHeap* g1h = G1CollectedHeap::heap();
assert( _gc_time_stamp <= g1h->get_gc_time_stamp(), "invariant" );
- if (_gc_time_stamp < g1h->get_gc_time_stamp())
- return top();
- else
+ HeapWord* local_top = top();
+ OrderAccess::loadload();
+ if (_gc_time_stamp < g1h->get_gc_time_stamp()) {
+ return local_top;
+ } else {
return Space::saved_mark_word();
+ }
}
void G1OffsetTableContigSpace::record_top_and_timestamp() {