8054808: Bitmap verification sometimes fails after Full GC aborts concurrent mark.

Summary: The verification code that checked whether no bitmap mark had been found re-read HeapRegion::end() after the check on the bitmap. Concurrent humongous object allocation could have changed HeapRegion::end() in the meantime. Fix this by using the actual end of the region instead of HeapRegion::end() for comparison.
Reviewed-by: brutisso, jmasa

src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -887,7 +887,16 @@ class CheckBitmapClearHRClosure : public HeapRegionClosure {
   }
 
   virtual bool doHeapRegion(HeapRegion* r) {
-    return _bitmap->getNextMarkedWordAddress(r->bottom(), r->end()) != r->end();
+    // This closure can be called concurrently to the mutator, so we must make sure
+    // that the result of the getNextMarkedWordAddress() call is compared to the
+    // value passed to it as limit to detect any found bits.
+    // We can use the region's orig_end() for the limit and the comparison value
+    // as it always contains the "real" end of the region that never changes and
+    // has no side effects.
+    // Due to the latter, there can also be no problem with the compiler generating
+    // reloads of the orig_end() call.
+    HeapWord* end = r->orig_end();
+    return _bitmap->getNextMarkedWordAddress(r->bottom(), end) != end;
   }
 };
 

src/share/vm/gc_implementation/g1/heapRegion.hpp

@@ -570,7 +570,7 @@ class HeapRegion: public G1OffsetTableContigSpace {
   void set_next_dirty_cards_region(HeapRegion* hr) { _next_dirty_cards_region = hr; }
   bool is_on_dirty_cards_region_list() const { return get_next_dirty_cards_region() != NULL; }
 
-  HeapWord* orig_end() { return _orig_end; }
+  HeapWord* orig_end() const { return _orig_end; }
 
   // Reset HR stuff to default values.
   void hr_clear(bool par, bool clear_space, bool locked = false);