nonmoving: Handle new closures in nonmovingIsNowAlive

We must conservatively assume that new closures are reachable since we
are not guaranteed to mark such blocks.

2 files changed, 18 insertions, 8 deletions

diff --git a/rts/sm/NonMoving.h b/rts/sm/NonMoving.h
index 1f82a77a93..5be85788d7 100644
--- a/rts/sm/NonMoving.h
+++ b/rts/sm/NonMoving.h
@@ -300,19 +300,17 @@ INLINE_HEADER void nonmovingSetClosureMark(StgPtr p)
     nonmovingSetMark(nonmovingGetSegment(p), nonmovingGetBlockIdx(p));
 }
 
-/* Was the given closure marked this major GC cycle? */
-INLINE_HEADER bool nonmovingClosureMarkedThisCycle(StgPtr p)
+INLINE_HEADER uint8_t nonmovingGetClosureMark(StgPtr p)
 {
     struct NonmovingSegment *seg = nonmovingGetSegment(p);
     nonmoving_block_idx blk_idx = nonmovingGetBlockIdx(p);
-    return nonmovingGetMark(seg, blk_idx) == nonmovingMarkEpoch;
+    return nonmovingGetMark(seg, blk_idx);
 }
 
-INLINE_HEADER bool nonmovingClosureMarked(StgPtr p)
+/* Was the given closure marked this major GC cycle? */
+INLINE_HEADER bool nonmovingClosureMarkedThisCycle(StgPtr p)
 {
-    struct NonmovingSegment *seg = nonmovingGetSegment(p);
-    nonmoving_block_idx blk_idx = nonmovingGetBlockIdx(p);
-    return nonmovingGetMark(seg, blk_idx) != 0;
+    return nonmovingGetClosureMark(p) == nonmovingMarkEpoch;
 }
 
 // Can be called during a major collection to determine whether a particular
diff --git a/rts/sm/NonMovingMark.c b/rts/sm/NonMovingMark.c
index f91bcbd58d..56cb73b5e4 100644
--- a/rts/sm/NonMovingMark.c
+++ b/rts/sm/NonMovingMark.c
@@ -1896,7 +1896,19 @@ static bool nonmovingIsNowAlive (StgClosure *p)
             || (bd->flags & BF_MARKED) != 0;
                    // The object was marked
     } else {
-        return nonmovingClosureMarkedThisCycle((P_)p);
+        struct NonmovingSegment *seg = nonmovingGetSegment((StgPtr) p);
+        StgClosure *snapshot_loc =
+          (StgClosure *) nonmovingSegmentGetBlock(seg, nonmovingSegmentInfo(seg)->next_free_snap);
+        if (p >= snapshot_loc && nonmovingGetClosureMark((StgPtr) p) == 0) {
+            /*
+             * In this case we are looking at a block that wasn't allocated
+             * at the time that the snapshot was taken. As we do not mark such
+             * blocks, we must assume that it is reachable.
+             */
+            return true;
+        } else {
+            return nonmovingClosureMarkedThisCycle((P_)p);
+        }
     }
 }