gh-153908: Fix data race in itertools.count.__repr__ (GH-153917)

Author: johng

Misc/NEWS.d/next/Library/2026-07-18-11-16-41.gh-issue-153908.82FiGk.rst

@@ -0,0 +1 @@
+Fix data race when calling :func:`repr` on :class:`itertools.count` under the :term:`free-threaded build`.

Modules/itertoolsmodule.c

@@ -3675,9 +3675,11 @@ static PyObject *
 count_repr(PyObject *op)
 {
     countobject *lz = countobject_CAST(op);
-    if (lz->long_cnt == NULL)
+    if (lz->long_cnt == NULL) {
+        Py_ssize_t cnt = FT_ATOMIC_LOAD_SSIZE_RELAXED(lz->cnt);
         return PyUnicode_FromFormat("%s(%zd)",
-                                    _PyType_Name(Py_TYPE(lz)), lz->cnt);
+                                    _PyType_Name(Py_TYPE(lz)), cnt);
+    }
 
     if (PyLong_Check(lz->long_step)) {
         long step = PyLong_AsLong(lz->long_step);