6988458: G1: assert(mr.end() <= _cm->finger()) failed: otherwise the region...

6988458: G1: assert(mr.end() <= _cm->finger()) failed: otherwise the region shouldn't be on the stack
Summary: The changes from 6941395 did not clear the CMTask::_aborted_region fields when concurrent marking aborted because of overflow. As a result, the next time around we could see a memory region whose start address was above the global finger and the assertion tripped. Moved the clearing of the aborted regions to ConcurrentMark::clear_marking_state, which is executed on all of the exit paths.
Reviewed-by: tonyp, ysr, jmasa

hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -2418,6 +2418,8 @@ void ConcurrentMark::clear_marking_state() {
   for (int i = 0; i < (int)_max_task_num; ++i) {
     OopTaskQueue* queue = _task_queues->queue(i);
     queue->set_empty();
+    // Clear any partial regions from the CMTasks
+    _tasks[i]->clear_aborted_region();
   }
 }
 
@@ -2706,7 +2708,6 @@ void ConcurrentMark::abort() {
   clear_marking_state();
   for (int i = 0; i < (int)_max_task_num; ++i) {
     _tasks[i]->clear_region_fields();
-    _tasks[i]->clear_aborted_region();
   }
   _has_aborted = true;
 
@@ -2985,7 +2986,7 @@ void CMTask::reset(CMBitMap* nextMarkBitMap) {
 
   _nextMarkBitMap                = nextMarkBitMap;
   clear_region_fields();
-  clear_aborted_region();
+  assert(_aborted_region.is_empty(), "should have been cleared");
 
   _calls                         = 0;
   _elapsed_time_ms               = 0.0;