--- a/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp	Tue Apr 26 11:46:34 2011 -0700
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp	Tue Apr 26 21:17:24 2011 -0700
@@ -1963,10 +1963,21 @@
 // Iteration support, mostly delegated from a CMS generation
 
 void CompactibleFreeListSpace::save_marks() {
-  // mark the "end" of the used space at the time of this call;
+  assert(Thread::current()->is_VM_thread(),
+         "Global variable should only be set when single-threaded");
+  // Mark the "end" of the used space at the time of this call;
   // note, however, that promoted objects from this point
   // on are tracked in the _promoInfo below.
   set_saved_mark_word(unallocated_block());
+#ifdef ASSERT
+  // Check the sanity of save_marks() etc.
+  MemRegion ur    = used_region();
+  MemRegion urasm = used_region_at_save_marks();
+  assert(ur.contains(urasm),
+         err_msg(" Error at save_marks(): [" PTR_FORMAT "," PTR_FORMAT ")"
+                 " should contain [" PTR_FORMAT "," PTR_FORMAT ")",
+                 ur.start(), ur.end(), urasm.start(), urasm.end()));
+#endif
   // inform allocator that promotions should be tracked.
   assert(_promoInfo.noPromotions(), "_promoInfo inconsistency");
   _promoInfo.startTrackingPromotions();