--- old/src/share/vm/gc/g1/heapRegion.cpp	2016-09-25 19:17:50.266994033 -0400
+++ new/src/share/vm/gc/g1/heapRegion.cpp	2016-09-25 19:17:50.162993517 -0400
@@ -352,19 +352,10 @@
   _prev_marked_bytes = marked_bytes;
 }
 
-HeapWord*
-HeapRegion::
-oops_on_card_seq_iterate_careful(MemRegion mr,
-                                 FilterOutOfRegionClosure* cl,
-                                 bool filter_young,
-                                 jbyte* card_ptr) {
-  // Currently, we should only have to clean the card if filter_young
-  // is true and vice versa.
-  if (filter_young) {
-    assert(card_ptr != NULL, "pre-condition");
-  } else {
-    assert(card_ptr == NULL, "pre-condition");
-  }
+bool HeapRegion::oops_on_card_seq_iterate_careful(MemRegion mr,
+                                                  FilterOutOfRegionClosure* cl,
+                                                  jbyte* card_ptr) {
+  assert(card_ptr != NULL, "pre-condition");
   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 
   // If we're within a stop-world GC, then we might look at a card in a
@@ -375,7 +366,7 @@
   } else {
     mr = mr.intersection(used_region());
   }
-  if (mr.is_empty()) return NULL;
+  if (mr.is_empty()) return true;
   // Otherwise, find the obj that extends onto mr.start().
 
   // The intersection of the incoming mr (for the card) and the
@@ -384,27 +375,21 @@
   // G1CollectedHeap.cpp that allocates a new region sets the
   // is_young tag on the region before allocating. Thus we
   // safely know if this region is young.
-  if (is_young() && filter_young) {
-    return NULL;
+  if (is_young()) {
+    return true;
   }
 
-  assert(!is_young(), "check value of filter_young");
-
   // We can only clean the card here, after we make the decision that
-  // the card is not young. And we only clean the card if we have been
-  // asked to (i.e., card_ptr != NULL).
-  if (card_ptr != NULL) {
-    *card_ptr = CardTableModRefBS::clean_card_val();
-    // We must complete this write before we do any of the reads below.
-    OrderAccess::storeload();
-  }
+  // the card is not young.
+  *card_ptr = CardTableModRefBS::clean_card_val();
+  // We must complete this write before we do any of the reads below.
+  OrderAccess::storeload();
 
   // Cache the boundaries of the memory region in some const locals
   HeapWord* const start = mr.start();
   HeapWord* const end = mr.end();
 
-  // We used to use "block_start_careful" here.  But we're actually happy
-  // to update the BOT while we do this...
+  // Update BOT as needed while finding start of (potential) object.
   HeapWord* cur = block_start(start);
   assert(cur <= start, "Postcondition");
 
@@ -416,7 +401,9 @@
     obj = oop(cur);
     if (obj->klass_or_null() == NULL) {
       // Ran into an unparseable point.
-      return cur;
+      assert(!g1h->is_gc_active(),
+             "Unparsable heap during GC at " PTR_FORMAT, p2i(cur));
+      return false;
     }
     // Otherwise...
     next = cur + block_size(cur);
@@ -433,7 +420,9 @@
     assert((cur + block_size(cur)) > (HeapWord*)obj, "Loop invariant");
     if (obj->klass_or_null() == NULL) {
       // Ran into an unparseable point.
-      return cur;
+      assert(!g1h->is_gc_active(),
+             "Unparsable heap during GC at " PTR_FORMAT, p2i(cur));
+      return false;
     }
 
     // Advance the current pointer. "obj" still points to the object to iterate.
@@ -452,7 +441,7 @@
     }
   } while (cur < end);
 
-  return NULL;
+  return true;
 }
 
 // Code roots support