--- old/src/share/vm/gc/g1/concurrentMarkThread.cpp	2016-02-08 15:06:01.340847826 +0100
+++ new/src/share/vm/gc/g1/concurrentMarkThread.cpp	2016-02-08 15:06:01.228847821 +0100
@@ -141,9 +141,11 @@
       // without the root regions have been scanned which would be a
       // correctness issue.
 
-      assert(!cm()->has_aborted(), "Aborting before root region scanning is finished not supported.");
-      GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
-      _cm->scanRootRegions();
+      if (_cm->root_regions()->scan_in_progress()) {
+        assert(!cm()->has_aborted(), "Aborting before root region scanning is finished not supported.");
+        GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
+        _cm->scanRootRegions();
+      }
 
       // It would be nice to use the GCTraceConcTime class here but
       // the "end" logging is inside the loop and not at the end of
--- old/src/share/vm/gc/g1/g1ConcurrentMark.cpp	2016-02-08 15:06:01.544847834 +0100
+++ new/src/share/vm/gc/g1/g1ConcurrentMark.cpp	2016-02-08 15:06:01.432847830 +0100
@@ -372,12 +372,16 @@
   return res;
 }
 
-void G1CMRootRegions::cancel_scan() {
+void G1CMRootRegions::notify_scan_done() {
   MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
   _scan_in_progress = false;
   RootRegionScan_lock->notify_all();
 }
 
+void G1CMRootRegions::cancel_scan() {
+  notify_scan_done();
+}
+
 void G1CMRootRegions::scan_finished() {
   assert(scan_in_progress(), "pre-condition");
 
@@ -387,11 +391,7 @@
   }
   _next_survivor = NULL;
 
-  {
-    MutexLockerEx x(RootRegionScan_lock, Mutex::_no_safepoint_check_flag);
-    _scan_in_progress = false;
-    RootRegionScan_lock->notify_all();
-  }
+  notify_scan_done();
 }
 
 bool G1CMRootRegions::wait_until_scan_finished() {
--- old/src/share/vm/gc/g1/g1ConcurrentMark.hpp	2016-02-08 15:06:01.784847844 +0100
+++ new/src/share/vm/gc/g1/g1ConcurrentMark.hpp	2016-02-08 15:06:01.676847840 +0100
@@ -229,6 +229,8 @@
   volatile bool        _should_abort;
   HeapRegion* volatile _next_survivor;
 
+  void notify_scan_done();
+
 public:
   G1CMRootRegions();
   // We actually do most of the initialization in this method.