--- a/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Thu Aug 07 22:28:53 2014 +0200
+++ b/src/share/vm/gc_implementation/g1/concurrentMark.cpp	Tue Aug 12 15:17:46 2014 +0000
@@ -1310,6 +1310,7 @@
     Universe::verify(VerifyOption_G1UsePrevMarking,
                      " VerifyDuringGC:(before)");
   }
+  g1h->check_bitmaps("Remark Start");
 
   G1CollectorPolicy* g1p = g1h->g1_policy();
   g1p->record_concurrent_mark_remark_start();
@@ -1358,6 +1359,7 @@
       Universe::verify(VerifyOption_G1UseNextMarking,
                        " VerifyDuringGC:(after)");
     }
+    g1h->check_bitmaps("Remark End");
     assert(!restart_for_overflow(), "sanity");
     // Completely reset the marking state since marking completed
     set_non_marking_state();
@@ -2007,6 +2009,7 @@
     Universe::verify(VerifyOption_G1UsePrevMarking,
                      " VerifyDuringGC:(before)");
   }
+  g1h->check_bitmaps("Cleanup Start");
 
   G1CollectorPolicy* g1p = G1CollectedHeap::heap()->g1_policy();
   g1p->record_concurrent_mark_cleanup_start();
@@ -2153,6 +2156,7 @@
     Universe::verify(VerifyOption_G1UsePrevMarking,
                      " VerifyDuringGC:(after)");
   }
+  g1h->check_bitmaps("Cleanup End");
 
   g1h->verify_region_sets_optional();
 
@@ -3367,6 +3371,11 @@
   // Clear all marks in the next bitmap for the next marking cycle. This will allow us to skip the next
   // concurrent bitmap clearing.
   _nextMarkBitMap->clearAll();
+
+  // Note we cannot clear the previous marking bitmap here
+  // since VerifyDuringGC verifies the objects marked during
+  // a full GC against the previous bitmap.
+
   // Clear the liveness counting data
   clear_all_count_data();
   // Empty mark stack

--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Thu Aug 07 22:28:53 2014 +0200
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	Tue Aug 12 15:17:46 2014 +0000
@@ -771,6 +771,7 @@
   // match new_top.
   assert(hr == NULL ||
          (hr->end() == new_end && hr->top() == new_top), "sanity");
+  check_bitmaps("Humongous Region Allocation", first_hr);
 
   assert(first_hr->used() == word_size * HeapWordSize, "invariant");
   _summary_bytes_used += first_hr->used();
@@ -1329,6 +1330,7 @@
 
       verify_before_gc();
 
+      check_bitmaps("Full GC Start");
       pre_full_gc_dump(gc_timer);
 
       COMPILER2_PRESENT(DerivedPointerTable::clear());
@@ -1502,6 +1504,18 @@
 
       verify_after_gc();
 
+      // Clear the previous marking bitmap, if needed for bitmap verification.
+      // Note we cannot do this when we clear the next marking bitmap in
+      // ConcurrentMark::abort() above since VerifyDuringGC verifies the
+      // objects marked during a full GC against the previous bitmap.
+      // But we need to clear it before calling check_bitmaps below since
+      // the full GC has compacted objects and updated TAMS but not updated
+      // the prev bitmap.
+      if (G1VerifyBitmaps) {
+        ((CMBitMap*) concurrent_mark()->prevMarkBitMap())->clearAll();
+      }
+      check_bitmaps("Full GC End");
+
       // Start a new incremental collection set for the next pause
       assert(g1_policy()->collection_set() == NULL, "must be");
       g1_policy()->start_incremental_cset_building();
@@ -4048,6 +4062,7 @@
       increment_gc_time_stamp();
 
       verify_before_gc();
+      check_bitmaps("GC Start");
 
       COMPILER2_PRESENT(DerivedPointerTable::clear());
 
@@ -4298,6 +4313,7 @@
         increment_gc_time_stamp();
 
         verify_after_gc();
+        check_bitmaps("GC End");
 
         assert(!ref_processor_stw()->discovery_enabled(), "Postcondition");
         ref_processor_stw()->verify_no_references_recorded();
@@ -6162,6 +6178,11 @@
   assert(!hr->is_empty(), "the region should not be empty");
   assert(free_list != NULL, "pre-condition");
 
+  if (G1VerifyBitmaps) {
+    MemRegion mr(hr->bottom(), hr->end());
+    concurrent_mark()->clearRangePrevBitmap(mr);
+  }
+
   // Clear the card counts for this region.
   // Note: we only need to do this if the region is not young
   // (since we don't refine cards in young regions).
@@ -6296,7 +6317,87 @@
 void G1CollectedHeap::verify_dirty_young_regions() {
   verify_dirty_young_list(_young_list->first_region());
 }
-#endif
+
+bool G1CollectedHeap::verify_no_bits_over_tams(const char* bitmap_name, CMBitMapRO* bitmap,
+                                               HeapWord* tams, HeapWord* end) {
+  guarantee(tams <= end,
+            err_msg("tams: "PTR_FORMAT" end: "PTR_FORMAT, tams, end));
+  HeapWord* result = bitmap->getNextMarkedWordAddress(tams, end);
+  if (result < end) {
+    gclog_or_tty->cr();
+    gclog_or_tty->print_cr("## wrong marked address on %s bitmap: "PTR_FORMAT,
+                           bitmap_name, result);
+    gclog_or_tty->print_cr("## %s tams: "PTR_FORMAT" end: "PTR_FORMAT,
+                           bitmap_name, tams, end);
+    return false;
+  }
+  return true;
+}
+
+bool G1CollectedHeap::verify_bitmaps(const char* caller, HeapRegion* hr) {
+  CMBitMapRO* prev_bitmap = concurrent_mark()->prevMarkBitMap();
+  CMBitMapRO* next_bitmap = (CMBitMapRO*) concurrent_mark()->nextMarkBitMap();
+
+  HeapWord* bottom = hr->bottom();
+  HeapWord* ptams  = hr->prev_top_at_mark_start();
+  HeapWord* ntams  = hr->next_top_at_mark_start();
+  HeapWord* end    = hr->end();
+
+  bool res_p = verify_no_bits_over_tams("prev", prev_bitmap, ptams, end);
+
+  bool res_n = true;
+  // We reset mark_in_progress() before we reset _cmThread->in_progress() and in this window
+  // we do the clearing of the next bitmap concurrently. Thus, we can not verify the bitmap
+  // if we happen to be in that state.
+  if (mark_in_progress() || !_cmThread->in_progress()) {
+    res_n = verify_no_bits_over_tams("next", next_bitmap, ntams, end);
+  }
+  if (!res_p || !res_n) {
+    gclog_or_tty->print_cr("#### Bitmap verification failed for "HR_FORMAT,
+                           HR_FORMAT_PARAMS(hr));
+    gclog_or_tty->print_cr("#### Caller: %s", caller);
+    return false;
+  }
+  return true;
+}
+
+void G1CollectedHeap::check_bitmaps(const char* caller, HeapRegion* hr) {
+  if (!G1VerifyBitmaps) return;
+
+  guarantee(verify_bitmaps(caller, hr), "bitmap verification");
+}
+
+class G1VerifyBitmapClosure : public HeapRegionClosure {
+private:
+  const char* _caller;
+  G1CollectedHeap* _g1h;
+  bool _failures;
+
+public:
+  G1VerifyBitmapClosure(const char* caller, G1CollectedHeap* g1h) :
+    _caller(caller), _g1h(g1h), _failures(false) { }
+
+  bool failures() { return _failures; }
+
+  virtual bool doHeapRegion(HeapRegion* hr) {
+    if (hr->continuesHumongous()) return false;
+
+    bool result = _g1h->verify_bitmaps(_caller, hr);
+    if (!result) {
+      _failures = true;
+    }
+    return false;
+  }
+};
+
+void G1CollectedHeap::check_bitmaps(const char* caller) {
+  if (!G1VerifyBitmaps) return;
+
+  G1VerifyBitmapClosure cl(caller, this);
+  heap_region_iterate(&cl);
+  guarantee(!cl.failures(), "bitmap verification");
+}
+#endif // PRODUCT
 
 void G1CollectedHeap::cleanUpCardTable() {
   G1SATBCardTableModRefBS* ct_bs = g1_barrier_set();
@@ -6833,6 +6934,7 @@
     if (new_alloc_region != NULL) {
       set_region_short_lived_locked(new_alloc_region);
       _hr_printer.alloc(new_alloc_region, G1HRPrinter::Eden, young_list_full);
+      check_bitmaps("Mutator Region Allocation", new_alloc_region);
       return new_alloc_region;
     }
   }
@@ -6899,8 +7001,10 @@
       if (survivor) {
         new_alloc_region->set_survivor();
         _hr_printer.alloc(new_alloc_region, G1HRPrinter::Survivor);
+        check_bitmaps("Survivor Region Allocation", new_alloc_region);
       } else {
         _hr_printer.alloc(new_alloc_region, G1HRPrinter::Old);
+        check_bitmaps("Old Region Allocation", new_alloc_region);
       }
       bool during_im = g1_policy()->during_initial_mark_pause();
       new_alloc_region->note_start_of_copying(during_im);

--- a/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Thu Aug 07 22:28:53 2014 +0200
+++ b/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp	Tue Aug 12 15:17:46 2014 +0000
@@ -1213,6 +1213,30 @@
   void verify_dirty_young_list(HeapRegion* head) PRODUCT_RETURN;
   void verify_dirty_young_regions() PRODUCT_RETURN;
 
+#ifndef PRODUCT
+  // Make sure that the given bitmap has no marked objects in the
+  // range [from,limit). If it does, print an error message and return
+  // false. Otherwise, just return true. bitmap_name should be "prev"
+  // or "next".
+  bool verify_no_bits_over_tams(const char* bitmap_name, CMBitMapRO* bitmap,
+                                HeapWord* from, HeapWord* limit);
+
+  // Verify that the prev / next bitmap range [tams,end) for the given
+  // region has no marks. Return true if all is well, false if errors
+  // are detected.
+  bool verify_bitmaps(const char* caller, HeapRegion* hr);
+#endif // PRODUCT
+
+  // If G1VerifyBitmaps is set, verify that the marking bitmaps for
+  // the given region do not have any spurious marks. If errors are
+  // detected, print appropriate error messages and crash.
+  void check_bitmaps(const char* caller, HeapRegion* hr) PRODUCT_RETURN;
+
+  // If G1VerifyBitmaps is set, verify that the marking bitmaps do not
+  // have any spurious marks. If errors are detected, print
+  // appropriate error messages and crash.
+  void check_bitmaps(const char* caller) PRODUCT_RETURN;
+
   // verify_region_sets() performs verification over the region
   // lists. It will be compiled in the product code to be used when
   // necessary (i.e., during heap verification).

--- a/src/share/vm/gc_implementation/g1/g1EvacFailure.hpp	Thu Aug 07 22:28:53 2014 +0200
+++ b/src/share/vm/gc_implementation/g1/g1EvacFailure.hpp	Tue Aug 12 15:17:46 2014 +0000
@@ -202,6 +202,7 @@
 
         hr->note_self_forwarding_removal_start(during_initial_mark,
                                                during_conc_mark);
+        _g1h->check_bitmaps("Self-Forwarding Ptr Removal", hr);
 
         // In the common case (i.e. when there is no evacuation
         // failure) we make sure that the following is done when

--- a/src/share/vm/gc_implementation/g1/g1_globals.hpp	Thu Aug 07 22:28:53 2014 +0200
+++ b/src/share/vm/gc_implementation/g1/g1_globals.hpp	Tue Aug 12 15:17:46 2014 +0000
@@ -332,11 +332,14 @@
           "evacuation pauses")                                              \
                                                                             \
   diagnostic(bool, G1VerifyRSetsDuringFullGC, false,                        \
-             "If true, perform verification of each heap region's "         \
-             "remembered set when verifying the heap during a full GC.")    \
+          "If true, perform verification of each heap region's "            \
+          "remembered set when verifying the heap during a full GC.")       \
                                                                             \
   diagnostic(bool, G1VerifyHeapRegionCodeRoots, false,                      \
-             "Verify the code root lists attached to each heap region.")
+          "Verify the code root lists attached to each heap region.")       \
+                                                                            \
+  develop(bool, G1VerifyBitmaps, false,                                     \
+          "Verifies the consistency of the marking bitmaps")
 
 G1_FLAGS(DECLARE_DEVELOPER_FLAG, DECLARE_PD_DEVELOPER_FLAG, DECLARE_PRODUCT_FLAG, DECLARE_PD_PRODUCT_FLAG, DECLARE_DIAGNOSTIC_FLAG, DECLARE_EXPERIMENTAL_FLAG, DECLARE_NOTPRODUCT_FLAG, DECLARE_MANAGEABLE_FLAG, DECLARE_PRODUCT_RW_FLAG)