gh-129983: fix data race in compile_template in sre.c

Misc/NEWS.d/next/Core_and_Builtins/2025-02-11-20-38-37.gh-issue-129983._1Fujo.rst

@@ -0,0 +1 @@
+Fix data race in compile_template in :file:`sre.c`.

Modules/_sre/sre.c

@@ -1167,13 +1167,21 @@ compile_template(_sremodulestate *module_state,
  PatternObject *pattern, PyObject *template)
 {
  /* delegate to Python code */
- PyObject *func = module_state->compile_template;
+ PyObject *func = FT_ATOMIC_LOAD_PTR(module_state->compile_template);
  if (func == NULL) {
  func = PyImport_ImportModuleAttrString("re", "_compile_template");
  if (func == NULL) {
  return NULL;
  }
+#ifdef Py_GIL_DISABLED
+ PyObject *other_func = NULL;
+ if (!_Py_atomic_compare_exchange_ptr(&module_state->compile_template, &other_func, func)) {
+ Py_DECREF(func);
+ func = other_func;
+ }
+#else
  Py_XSETREF(module_state->compile_template, func);
+#endif
  }
 
  PyObject *args[] = {(PyObject *)pattern, template};