--- old/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	2011-05-16 15:43:04.077606764 -0700
+++ new/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp	2011-05-16 15:43:02.602154599 -0700
@@ -3323,8 +3323,9 @@
       // progress, this will be zero.
       _cm->set_oops_do_bound();
 
-      if (mark_in_progress())
+      if (mark_in_progress()) {
         concurrent_mark()->newCSet();
+      }
 
 #if YOUNG_LIST_VERBOSE
       gclog_or_tty->print_cr("\nBefore choosing collection set.\nYoung_list:");
@@ -3334,6 +3335,16 @@
 
       g1_policy()->choose_collection_set(target_pause_time_ms);
 
+      // We have chosen the complete collection set. If marking is
+      // active then, we clear the region fields of any of the
+      // concurrent marking tasks whose region fields point into
+      // the collection set as these values will become stale. This
+      // will cause the owning marking threads to claim a new region
+      // when marking restarts.
+      if (mark_in_progress()) {
+        concurrent_mark()->reset_active_task_region_fields_in_cset();
+      }
+
       // Nothing to do if we were unable to choose a collection set.
 #if G1_REM_SET_LOGGING
       gclog_or_tty->print_cr("\nAfter pause, heap:");