7086533: G1: assert(!_g1->is_obj_dead(obj)): We should not be preserving dead...

7086533: G1: assert(!_g1->is_obj_dead(obj)): We should not be preserving dead objs: g1CollectedHeap.cpp:3835
Summary: Some objects may not be marked in the event of an evacuation failure in a partially young GC, during a marking cycle. Avoid this situation by not allowing partially young GCs during a marking cycle.
Reviewed-by: tonyp, ysr, brutisso

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -3365,6 +3365,14 @@ G1CollectedHeap::do_collection_pause_at_safepoint(double target_pause_time_ms) {
     // for the duration of this pause.
     g1_policy()->decide_on_conc_mark_initiation();
 
+    // We do not allow initial-mark to be piggy-backed on a
+    // partially-young GC.
+    assert(!g1_policy()->during_initial_mark_pause() ||
+            g1_policy()->full_young_gcs(), "sanity");
+
+    // We also do not allow partially-young GCs during marking.
+    assert(!mark_in_progress() || g1_policy()->full_young_gcs(), "sanity");
+
     char verbose_str[128];
     sprintf(verbose_str, "GC pause ");
     if (g1_policy()->full_young_gcs()) {

src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp

@@ -1525,11 +1525,17 @@ void G1CollectorPolicy::record_collection_pause_end() {
   }
 
   if (_last_full_young_gc) {
+    if (!last_pause_included_initial_mark) {
       ergo_verbose2(ErgoPartiallyYoungGCs,
                     "start partially-young GCs",
                     ergo_format_byte_perc("known garbage"),
                     _known_garbage_bytes, _known_garbage_ratio * 100.0);
       set_full_young_gcs(false);
+    } else {
+      ergo_verbose0(ErgoPartiallyYoungGCs,
+                    "do not start partially-young GCs",
+                    ergo_format_reason("concurrent cycle is about to start"));
+    }
     _last_full_young_gc = false;
   }
 
@@ -2491,6 +2497,13 @@ G1CollectorPolicy::decide_on_conc_mark_initiation() {
       // initiate a new cycle.
 
       set_during_initial_mark_pause();
+      // We do not allow non-full young GCs during marking.
+      if (!full_young_gcs()) {
+        set_full_young_gcs(true);
+        ergo_verbose0(ErgoPartiallyYoungGCs,
+                      "end partially-young GCs",
+                      ergo_format_reason("concurrent cycle is about to start"));
+      }
 
       // And we can now clear initiate_conc_mark_if_possible() as
       // we've already acted on it.