fix bug causing assertion failure because find_name_in_mro can release the type lock

kumaraditya303 · kumaraditya303 · commit b09600980376 · 2026-06-04T17:39:27.000+05:30
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -6194,7 +6194,9 @@ _PyType_LookupStackRefAndVersion(PyTypeObject *type, PyObject *name, _PyStackRef
             version_tag = type->tp_version_tag;
         }
         res = find_name_in_mro(type, name, out);
-        if (res >= 0 && version_tag != 0) {
+        // find_name_in_mro can release the type lock and another thread can
+        // modify the type, so we need to check version tag again before caching the result.
+        if (res >= 0 && version_tag != 0 && version_tag == type->tp_version_tag) {
             _PyTypeCache_Insert(type, name, PyStackRef_AsPyObjectBorrow(*out));
         }
         END_TYPE_LOCK();

Original file line number	Diff line number	Diff line change
`@@ -6194,7 +6194,9 @@ _PyType_LookupStackRefAndVersion(PyTypeObject type, PyObject name, _PyStackRef`
`6194`	`6194`	`version_tag = type->tp_version_tag;`
`6195`	`6195`	`}`
`6196`	`6196`	`res = find_name_in_mro(type, name, out);`
`6197`		`- if (res >= 0 && version_tag != 0) {`
	`6197`	`+ // find_name_in_mro can release the type lock and another thread can`
	`6198`	`+ // modify the type, so we need to check version tag again before caching the result.`
	`6199`	`+ if (res >= 0 && version_tag != 0 && version_tag == type->tp_version_tag) {`
`6198`	`6200`	`_PyTypeCache_Insert(type, name, PyStackRef_AsPyObjectBorrow(*out));`
`6199`	`6201`	`}`
`6200`	`6202`	`END_TYPE_LOCK();`