Fix refleak tests.

Revert back to Py_DECREF() instead of the Py_SET_REFCNT(dict, 0) and fix
check that this thread owns the only reference to the dict. That ensures
that the final Py_DECREF call immediately frees the dict instead of
possibly enqueuing it to be merged.

Objects/dictobject.c

@@ -5989,6 +5989,18 @@ _PyObject_MakeDictFromInstanceAttributes(PyObject *obj, PyDictValues *values)
  return make_dict_from_instance_attributes(interp, keys, values);
 }
 
+static bool
+has_unique_reference(PyObject *op)
+{
+#ifdef Py_GIL_DISABLED
+ return (_Py_IsOwnedByCurrentThread(op) &&
+ op->ob_ref_local == 1 &&
+ _Py_atomic_load_ssize_relaxed(&op->ob_ref_shared) == 0);
+#else
+ return Py_REFCNT(op) == 1;
+#endif
+}
+
 // Return true if the dict was dematerialized, false otherwise.
 bool
 _PyObject_MakeInstanceAttributesFromDict(PyObject *obj, PyDictOrValues *dorv)
@@ -6005,7 +6017,9 @@ _PyObject_MakeInstanceAttributesFromDict(PyObject *obj, PyDictOrValues *dorv)
  return false;
  }
  assert(_PyType_HasFeature(Py_TYPE(obj), Py_TPFLAGS_HEAPTYPE));
- if (dict->ma_keys != CACHED_KEYS(Py_TYPE(obj)) || Py_REFCNT(dict) != 1) {
+ if (dict->ma_keys != CACHED_KEYS(Py_TYPE(obj)) ||
+ !has_unique_reference((PyObject *)dict))
+ {
  return false;
  }
  assert(dict->ma_values);
@@ -6016,8 +6030,7 @@ _PyObject_MakeInstanceAttributesFromDict(PyObject *obj, PyDictOrValues *dorv)
  // Don't try this at home, kids:
  dict->ma_keys = NULL;
  dict->ma_values = NULL;
- Py_SET_REFCNT(dict, 0);
- _Py_Dealloc((PyObject *)dict);
+ Py_DECREF(dict);
  return true;
 }
 

Python/gc_free_threading.c

@@ -300,6 +300,9 @@ merge_queued_objects(_PyThreadStateImpl *tstate, struct collection_state *state)
  // non-GC objects here. Add one to the refcount so that we can
  // decref and deallocate the object once we start the world again.
  op->ob_ref_shared += (1 << _Py_REF_SHARED_SHIFT);
+#ifdef Py_REF_DEBUG
+ _Py_IncRefTotal(_PyInterpreterState_GET());
+#endif
  worklist_push(&state->objs_to_decref, op);
  }
  }