[3.13] gh-125221: Fix free-threading data race in object.__reduce_ex__ (GH-125267) (#125305)

miss-islington · colesbury · web-flow · commit b3badabcd9bc · 2024-10-11T08:26:23.000Z
gh-125221: Fix free-threading data race in `object.__reduce_ex__` (GH-125267) (cherry picked from commit b12e992) Co-authored-by: Sam Gross <colesbury@gmail.com>
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-10-10-14-47-13.gh-issue-125221.nfSQzT.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-10-10-14-47-13.gh-issue-125221.nfSQzT.rst
@@ -0,0 +1,2 @@
+Fix possible race condition when calling :meth:`~object.__reduce_ex__` for the
+first time in the free threading build.
diff --git a/Objects/object.c b/Objects/object.c
@@ -2353,6 +2353,14 @@ _PyTypes_InitTypes(PyInterpreterState *interp)
         }
     }
 
+    // Cache __reduce__ from PyBaseObject_Type object
+    PyObject *baseobj_dict = _PyType_GetDict(&PyBaseObject_Type);
+    PyObject *baseobj_reduce = PyDict_GetItemWithError(baseobj_dict, &_Py_ID(__reduce__));
+    if (baseobj_reduce == NULL && PyErr_Occurred()) {
+        return _PyStatus_ERR("Can't get __reduce__ from base object");
+    }
+    _Py_INTERP_CACHED_OBJECT(interp, objreduce) = baseobj_reduce;
+
     // Must be after static types are initialized
     if (_Py_initialize_generic(interp) < 0) {
         return _PyStatus_ERR("Can't initialize generic types");
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -7050,18 +7050,7 @@ static PyObject *
 object___reduce_ex___impl(PyObject *self, int protocol)
 /*[clinic end generated code: output=2e157766f6b50094 input=f326b43fb8a4c5ff]*/
 {
-#define objreduce \
-    (_Py_INTERP_CACHED_OBJECT(_PyInterpreterState_GET(), objreduce))
-    PyObject *reduce, *res;
-
-    if (objreduce == NULL) {
-        PyObject *dict = lookup_tp_dict(&PyBaseObject_Type);
-        objreduce = PyDict_GetItemWithError(dict, &_Py_ID(__reduce__));
-        if (objreduce == NULL && PyErr_Occurred()) {
-            return NULL;
-        }
-    }
-
+    PyObject *reduce;
     if (PyObject_GetOptionalAttr(self, &_Py_ID(__reduce__), &reduce) < 0) {
         return NULL;
     }
@@ -7075,10 +7064,12 @@ object___reduce_ex___impl(PyObject *self, int protocol)
             Py_DECREF(reduce);
             return NULL;
         }
-        override = (clsreduce != objreduce);
+
+        PyInterpreterState *interp = _PyInterpreterState_GET();
+        override = (clsreduce != _Py_INTERP_CACHED_OBJECT(interp, objreduce));
         Py_DECREF(clsreduce);
         if (override) {
-            res = _PyObject_CallNoArgs(reduce);
+            PyObject *res = _PyObject_CallNoArgs(reduce);
             Py_DECREF(reduce);
             return res;
         }
@@ -7087,7 +7078,6 @@ object___reduce_ex___impl(PyObject *self, int protocol)
     }
 
     return _common_reduce(self, protocol);
-#undef objreduce
 }
 
 static PyObject *

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Fix possible race condition when calling :meth:`~object.__reduce_ex__` for the
	`2`	`+first time in the free threading build.`
Original file line number	Diff line number	Diff line change
`@@ -2353,6 +2353,14 @@ _PyTypes_InitTypes(PyInterpreterState *interp)`
`2353`	`2353`	`}`
`2354`	`2354`	`}`
`2355`	`2355`
	`2356`	`+ // Cache __reduce__ from PyBaseObject_Type object`
	`2357`	`+ PyObject *baseobj_dict = _PyType_GetDict(&PyBaseObject_Type);`
	`2358`	`+ PyObject *baseobj_reduce = PyDict_GetItemWithError(baseobj_dict, &_Py_ID(__reduce__));`
	`2359`	`+ if (baseobj_reduce == NULL && PyErr_Occurred()) {`
	`2360`	`+ return _PyStatus_ERR("Can't get __reduce__ from base object");`
	`2361`	`+ }`
	`2362`	`+ _Py_INTERP_CACHED_OBJECT(interp, objreduce) = baseobj_reduce;`
	`2363`	`+`
`2356`	`2364`	`// Must be after static types are initialized`
`2357`	`2365`	`if (_Py_initialize_generic(interp) < 0) {`
`2358`	`2366`	`return _PyStatus_ERR("Can't initialize generic types");`