gh-129069: use atomic read in _Py_SIZE_impl()

part of TSAN-0013 in gh-153852

Author: xxyzz

Include/cpython/listobject.h

@@ -29,11 +29,7 @@ typedef struct {
 
 static inline Py_ssize_t PyList_GET_SIZE(PyObject *op) {
     PyListObject *list = _PyList_CAST(op);
-#ifdef Py_GIL_DISABLED
-    return _Py_atomic_load_ssize_relaxed(&(_PyVarObject_CAST(list)->ob_size));
-#else
     return Py_SIZE(list);
-#endif
 }
 #define PyList_GET_SIZE(op) PyList_GET_SIZE(_PyObject_CAST(op))
 

Include/object.h

@@ -240,7 +240,11 @@ _Py_SIZE_impl(PyObject *ob)
 {
     assert(Py_TYPE(ob) != &PyLong_Type);
     assert(Py_TYPE(ob) != &PyBool_Type);
-    return  _PyVarObject_CAST(ob)->ob_size;
+#ifdef Py_GIL_DISABLED
+    return _Py_atomic_load_ssize_relaxed(&(_PyVarObject_CAST(ob)->ob_size));
+#else
+    return _PyVarObject_CAST(ob)->ob_size;
+#endif
 }
 
 static inline int