https://github.com/python/cpython/commit/485b16b4f7b28cefdfb524c2869d473078e349bf
commit: 485b16b4f7b28cefdfb524c2869d473078e349bf
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2025-08-05T09:32:22-04:00
summary:
gh-137238: Fix data race in `_Py_slot_tp_getattr_hook` (gh-137240)
Replacing the slot isn't thread-safe if the GIL is disabled. Don't
require that the slot has been replaced when specializing.
files:
M Objects/typeobject.c
M Python/specialize.c
M Tools/tsan/suppressions_free_threading.txt
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 6e67b6e01cb8b8..14bc5a4bc49f84 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -10585,7 +10585,10 @@ _Py_slot_tp_getattr_hook(PyObject *self, PyObject
*name)
getattr = _PyType_LookupRef(tp, &_Py_ID(__getattr__));
if (getattr == NULL) {
/* No __getattr__ hook: use a simpler dispatcher */
+#ifndef Py_GIL_DISABLED
+ // Replacing the slot is only thread-safe if there is a GIL.
tp->tp_getattro = _Py_slot_tp_getattro;
+#endif
return _Py_slot_tp_getattro(self, name);
}
/* speed hack: we could use lookup_maybe, but that would resolve the
diff --git a/Python/specialize.c b/Python/specialize.c
index fe8d04cf3442f1..38df5741f32520 100644
--- a/Python/specialize.c
+++ b/Python/specialize.c
@@ -935,8 +935,7 @@ analyze_descriptor_load(PyTypeObject *type, PyObject *name,
PyObject **descr, un
PyObject *getattr = _PyType_Lookup(type, &_Py_ID(__getattr__));
has_getattr = getattr != NULL;
if (has_custom_getattribute) {
- if (getattro_slot == _Py_slot_tp_getattro &&
- !has_getattr &&
+ if (!has_getattr &&
Py_IS_TYPE(getattribute, &PyFunction_Type)) {
*descr = getattribute;
*tp_version = ga_version;
@@ -1259,12 +1258,6 @@ do_specialize_instance_load_attr(PyObject* owner,
_Py_CODEUNIT* instr, PyObject*
return -1;
case GETATTRIBUTE_IS_PYTHON_FUNCTION:
{
- #ifndef Py_GIL_DISABLED
- // In free-threaded builds it's possible for tp_getattro to change
- // after the call to analyze_descriptor. That is fine: the version
- // guard will fail.
- assert(type->tp_getattro == _Py_slot_tp_getattro);
- #endif
assert(Py_IS_TYPE(descr, &PyFunction_Type));
_PyLoadMethodCache *lm_cache = (_PyLoadMethodCache *)(instr + 1);
if (!function_check_args(descr, 2, LOAD_ATTR)) {
diff --git a/Tools/tsan/suppressions_free_threading.txt
b/Tools/tsan/suppressions_free_threading.txt
index 52d7c25a5bb37a..6bd31e8e6ecb9d 100644
--- a/Tools/tsan/suppressions_free_threading.txt
+++ b/Tools/tsan/suppressions_free_threading.txt
@@ -43,6 +43,5 @@ race:list_inplace_repeat_lock_held
race:PyObject_Realloc
# gh-133467. Some of these could be hard to trigger.
-race_top:_Py_slot_tp_getattr_hook
race_top:set_tp_bases
race_top:type_set_bases_unlocked
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