--- a/hotspot/src/share/vm/gc/g1/concurrentMark.cpp	Wed Jun 24 10:28:00 2015 +0200
+++ b/hotspot/src/share/vm/gc/g1/concurrentMark.cpp	Tue Jun 23 13:26:05 2015 +0200
@@ -1179,6 +1179,8 @@
 };
 
 void ConcurrentMark::scanRootRegions() {
+  double scan_start = os::elapsedTime();
+
   // Start of concurrent marking.
   ClassLoaderDataGraph::clear_claimed_marks();
 
@@ -1186,6 +1188,11 @@
   // at least one root region to scan. So, if it's false, we
   // should not attempt to do any further work.
   if (root_regions()->scan_in_progress()) {
+    if (G1Log::fine()) {
+      gclog_or_tty->gclog_stamp(concurrent_gc_id());
+      gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
+    }
+
     _parallel_marking_threads = calc_parallel_marking_threads();
     assert(parallel_marking_threads() <= max_parallel_marking_threads(),
            "Maximum number of marking threads exceeded");
@@ -1195,6 +1202,11 @@
     _parallel_workers->set_active_workers(active_workers);
     _parallel_workers->run_task(&task);
 
+    if (G1Log::fine()) {
+      gclog_or_tty->gclog_stamp(concurrent_gc_id());
+      gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]", os::elapsedTime() - scan_start);
+    }
+
     // It's possible that has_aborted() is true here without actually
     // aborting the survivor scan earlier. This is OK as it's
     // mainly used for sanity checking.
@@ -2993,6 +3005,11 @@
 
 // abandon current marking iteration due to a Full GC
 void ConcurrentMark::abort() {
+  if (!cmThread()->during_cycle() || _has_aborted) {
+    // We haven't started a concurrent cycle or we have already aborted it. No need to do anything.
+    return;
+  }
+
   // Clear all marks in the next bitmap for the next marking cycle. This will allow us to skip the next
   // concurrent bitmap clearing.
   _nextMarkBitMap->clearAll();
@@ -3010,12 +3027,8 @@
   }
   _first_overflow_barrier_sync.abort();
   _second_overflow_barrier_sync.abort();
-  const GCId& gc_id = _g1h->gc_tracer_cm()->gc_id();
-  if (!gc_id.is_undefined()) {
-    // We can do multiple full GCs before ConcurrentMarkThread::run() gets a chance
-    // to detect that it was aborted. Only keep track of the first GC id that we aborted.
-    _aborted_gc_id = gc_id;
-   }
+  _aborted_gc_id = _g1h->gc_tracer_cm()->gc_id();
+  assert(!_aborted_gc_id.is_undefined(), "ConcurrentMark::abort() executed more than once?");
   _has_aborted = true;
 
   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();

--- a/hotspot/src/share/vm/gc/g1/concurrentMarkThread.cpp	Wed Jun 24 10:28:00 2015 +0200
+++ b/hotspot/src/share/vm/gc/g1/concurrentMarkThread.cpp	Tue Jun 23 13:26:05 2015 +0200
@@ -78,7 +78,19 @@
   }
 };
 
-
+// We want to avoid that the logging from the concurrent thread is mixed
+// with the logging from a STW GC. So, if necessary join the STS to ensure
+// that the logging is done either before or after the STW logging.
+void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) {
+  if (doit) {
+    SuspendibleThreadSetJoiner sts_joiner(join_sts);
+    va_list args;
+    va_start(args, fmt);
+    gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
+    gclog_or_tty->vprint_cr(fmt, args);
+    va_end(args);
+  }
+}
 
 void ConcurrentMarkThread::run() {
   initialize_in_thread();
@@ -110,28 +122,12 @@
       // without the root regions have been scanned which would be a
       // correctness issue.
 
-      double scan_start = os::elapsedTime();
       if (!cm()->has_aborted()) {
-        if (G1Log::fine()) {
-          gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-          gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
-        }
-
         _cm->scanRootRegions();
-
-        double scan_end = os::elapsedTime();
-        if (G1Log::fine()) {
-          gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-          gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
-                                 scan_end - scan_start);
-        }
       }
 
       double mark_start_sec = os::elapsedTime();
-      if (G1Log::fine()) {
-        gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-        gclog_or_tty->print_cr("[GC concurrent-mark-start]");
-      }
+      cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]");
 
       int iter = 0;
       do {
@@ -151,25 +147,15 @@
             os::sleep(current_thread, sleep_time_ms, false);
           }
 
-          if (G1Log::fine()) {
-            gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-            gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
-                                      mark_end_sec - mark_start_sec);
-          }
+          cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec);
 
           CMCheckpointRootsFinalClosure final_cl(_cm);
           VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
           VMThread::execute(&op);
         }
         if (cm()->restart_for_overflow()) {
-          if (G1TraceMarkStackOverflow) {
-            gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
-                                   "in remark (restart #%d).", iter);
-          }
-          if (G1Log::fine()) {
-            gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-            gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
-          }
+          cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
+          cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]");
         }
       } while (cm()->restart_for_overflow());
 
@@ -209,10 +195,7 @@
         // reclaimed by cleanup.
 
         double cleanup_start_sec = os::elapsedTime();
-        if (G1Log::fine()) {
-          gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-          gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
-        }
+        cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-start]");
 
         // Now do the concurrent cleanup operation.
         _cm->completeCleanup();
@@ -229,11 +212,7 @@
         g1h->reset_free_regions_coming();
 
         double cleanup_end_sec = os::elapsedTime();
-        if (G1Log::fine()) {
-          gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-          gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
-                                 cleanup_end_sec - cleanup_start_sec);
-        }
+        cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec);
       }
       guarantee(cm()->cleanup_list_is_empty(),
                 "at this point there should be no regions on the cleanup list");
@@ -266,13 +245,8 @@
         SuspendibleThreadSetJoiner sts_join;
         if (!cm()->has_aborted()) {
           g1_policy->record_concurrent_mark_cleanup_completed();
-        }
-      }
-
-      if (cm()->has_aborted()) {
-        if (G1Log::fine()) {
-          gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
-          gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
+        } else {
+          cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]");
         }
       }
 

--- a/hotspot/src/share/vm/gc/g1/concurrentMarkThread.hpp	Wed Jun 24 10:28:00 2015 +0200
+++ b/hotspot/src/share/vm/gc/g1/concurrentMarkThread.hpp	Tue Jun 23 13:26:05 2015 +0200
@@ -40,6 +40,7 @@
   double _vtime_accum;  // Accumulated virtual time.
 
   double _vtime_mark_accum;
+  void cm_log(bool doit, bool join_sts, const char* fmt, ...) ATTRIBUTE_PRINTF(4, 5);
 
  public:
   virtual void run();

--- a/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Wed Jun 24 10:28:00 2015 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1CollectedHeap.cpp	Tue Jun 23 13:26:05 2015 +0200
@@ -3867,6 +3867,21 @@
   gclog_or_tty->flush();
 }
 
+void G1CollectedHeap::wait_for_root_region_scanning() {
+  double scan_wait_start = os::elapsedTime();
+  // We have to wait until the CM threads finish scanning the
+  // root regions as it's the only way to ensure that all the
+  // objects on them have been correctly scanned before we start
+  // moving them during the GC.
+  bool waited = _cm->root_regions()->wait_until_scan_finished();
+  double wait_time_ms = 0.0;
+  if (waited) {
+    double scan_wait_end = os::elapsedTime();
+    wait_time_ms = (scan_wait_end - scan_wait_start) * 1000.0;
+  }
+  g1_policy()->phase_times()->record_root_region_scan_wait_time(wait_time_ms);
+}
+
 bool
 G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
   assert_at_safepoint(true /* should_be_vm_thread */);
@@ -3883,6 +3898,8 @@
   SvcGCMarker sgcm(SvcGCMarker::MINOR);
   ResourceMark rm;
 
+  wait_for_root_region_scanning();
+
   G1Log::update_level();
   print_heap_before_gc();
   trace_heap_before_gc(_gc_tracer_stw);
@@ -4004,19 +4021,6 @@
 
         g1_policy()->record_collection_pause_start(sample_start_time_sec);
 
-        double scan_wait_start = os::elapsedTime();
-        // We have to wait until the CM threads finish scanning the
-        // root regions as it's the only way to ensure that all the
-        // objects on them have been correctly scanned before we start
-        // moving them during the GC.
-        bool waited = _cm->root_regions()->wait_until_scan_finished();
-        double wait_time_ms = 0.0;
-        if (waited) {
-          double scan_wait_end = os::elapsedTime();
-          wait_time_ms = (scan_wait_end - scan_wait_start) * 1000.0;
-        }
-        g1_policy()->phase_times()->record_root_region_scan_wait_time(wait_time_ms);
-
 #if YOUNG_LIST_VERBOSE
         gclog_or_tty->print_cr("\nAfter recording pause start.\nYoung_list:");
         _young_list->print();

--- a/hotspot/src/share/vm/gc/g1/g1CollectedHeap.hpp	Wed Jun 24 10:28:00 2015 +0200
+++ b/hotspot/src/share/vm/gc/g1/g1CollectedHeap.hpp	Tue Jun 23 13:26:05 2015 +0200
@@ -805,6 +805,8 @@
                                 bool*          succeeded,
                                 GCCause::Cause gc_cause);
 
+  void wait_for_root_region_scanning();
+
   // The guts of the incremental collection pause, executed by the vm
   // thread. It returns false if it is unable to do the collection due
   // to the GC locker being active, true otherwise