Clear weakref sentinel in the right place

Author: sergey-miryanov

Objects/weakrefobject.c

@@ -1280,6 +1280,12 @@ void
 _PyWeakref_ClearSubclassSentinel(PyInterpreterState *interp)
 {
     if (interp == interp->runtime->interpreters.main) {
+        PyObject *func = _Py_INTERP_SINGLETON(interp, subclasses_weakref_sentinel);
+
+        assert(PyObject_GC_IsTracked(func) == 0);
+        _Py_SetMortal(_Py_INTERP_SINGLETON(interp, subclasses_weakref_sentinel), 1);
+        PyObject_GC_Track(func);
+
         Py_CLEAR(_Py_INTERP_SINGLETON(interp, subclasses_weakref_sentinel));
     }
 }

Python/pylifecycle.c

@@ -1876,6 +1876,10 @@ finalize_interp_types(PyInterpreterState *interp)
     _PyObject_FinalizeUniqueIdPool(interp);
 #endif
 
+    // We clear subclass sentinel here because some weakrefs may
+    // hold reference to it (for example, type's subclasses)
+    _PyWeakref_ClearSubclassSentinel(interp);
+
     _PyCode_Fini(interp);
 
     // Call _PyUnicode_ClearInterned() before _PyDict_Fini() since it uses

Python/pystate.c

@@ -761,8 +761,6 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
 
     Py_CLEAR(interp->audit_hooks);
 
-    _PyWeakref_ClearSubclassSentinel(interp);
-
     // At this time, all the threads should be cleared so we don't need atomic
     // operations for instrumentation_version or eval_breaker.
     interp->ceval.instrumentation_version = 0;