[sgen] Missing store/store fence.

[mono.git] / mono / sgen / sgen-minor-copy-object.h

diff --git a/mono/sgen/sgen-minor-copy-object.h b/mono/sgen/sgen-minor-copy-object.h
index a77d53b4744bed22af7beefdba02232bbb373c22..e6d6a40b467b15b08948ee8bcb4454308c036e4c 100644 (file)
--- a/mono/sgen/sgen-minor-copy-object.h
+++ b/mono/sgen/sgen-minor-copy-object.h
@@ -121,6 +121,8 @@ SERIAL_COPY_OBJECT_FROM_OBJ (GCObject **obj_slot, SgenGrayQueue *queue)
                SGEN_ASSERT (9, sgen_obj_get_descriptor (forwarded),  "forwarded object %p has no gc descriptor", forwarded);
                SGEN_LOG (9, " (already forwarded to %p)", forwarded);
                HEAVY_STAT (++stat_nursery_copy_object_failed_forwarded);
+               /* See comment on STORE_STORE_FENCE below. */
+               STORE_STORE_FENCE;
                SGEN_UPDATE_REFERENCE (obj_slot, forwarded);
 #ifndef SGEN_SIMPLE_NURSERY
                if (G_UNLIKELY (sgen_ptr_in_nursery (forwarded) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (forwarded)))
@@ -187,6 +189,17 @@ SERIAL_COPY_OBJECT_FROM_OBJ (GCObject **obj_slot, SgenGrayQueue *queue)
        HEAVY_STAT (++stat_objects_copied_nursery);
 
        copy = copy_object_no_checks (obj, queue);
+       /*
+        * If an object is evacuated to the major heap and a reference to it, from the major
+        * heap, updated, the concurrent major collector might follow that reference and
+        * scan the new major object.  To make sure the object contents are seen by the
+        * major collector we need this write barrier, so that the reference is seen after
+        * the object.
+        *
+        * FIXME: This is only required if there's a concurrent major collection running,
+        * but we can't conditionally compile on that at the moment.
+        */
+       STORE_STORE_FENCE;
        SGEN_UPDATE_REFERENCE (obj_slot, copy);
 #ifndef SGEN_SIMPLE_NURSERY
        if (G_UNLIKELY (sgen_ptr_in_nursery (copy) && !sgen_ptr_in_nursery (obj_slot) && !SGEN_OBJECT_IS_CEMENTED (copy)))