Fix missing write barrier on namespace classext

Found by wbcheck

It seems like here the classext was associated with the class, but it
already had Ruby objects attached.

rb_gc_writebarrier_remember works around that issue, but I suspect if we
enabled autocompaction the values copied into the classext before it was
attached could be broken.

1 files changed, 6 insertions, 0 deletions

diff --git a/class.c b/class.c
index 34bc7d1005..2f94b80147 100644
--- a/class.c
+++ b/class.c
@@ -183,6 +183,12 @@ rb_class_set_box_classext(VALUE obj, const rb_box_t *box, rb_classext_t *ext)
     };
 
     st_update(RCLASS_CLASSEXT_TBL(obj), (st_data_t)box->box_object, rb_class_set_box_classext_update, (st_data_t)&args);
+
+    // FIXME: This is done here because this is the first time the objects in
+    // the classext are exposed via this class. It's likely that if GC
+    // compaction occurred between the VALUEs being copied in and this
+    // writebarrier trigger the values will be stale.
+    rb_gc_writebarrier_remember(obj);
 }
 
 RUBY_EXTERN rb_serial_t ruby_vm_global_cvar_state;