hotspot/src/share/vm/gc_implementation/g1/heapRegion.cpp

rev 6908 : 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

*** 1013,1026 ****
  }
  
  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
      return Space::saved_mark_word();
  }
  
  void G1OffsetTableContigSpace::record_top_and_timestamp() {
    G1CollectedHeap* g1h = G1CollectedHeap::heap();
    unsigned curr_gc_time_stamp = g1h->get_gc_time_stamp();
--- 1013,1029 ----
  }
  
  HeapWord* G1OffsetTableContigSpace::saved_mark_word() const {
    G1CollectedHeap* g1h = G1CollectedHeap::heap();
    assert( _gc_time_stamp <= g1h->get_gc_time_stamp(), "invariant" );
!   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() {
    G1CollectedHeap* g1h = G1CollectedHeap::heap();
    unsigned curr_gc_time_stamp = g1h->get_gc_time_stamp();