gh-127266: avoid data races when updating type slots (gh-131174)

In the free-threaded build, avoid data races caused by updating type slots
or type flags after the type was initially created.  For those (typically
rare) cases, use the stop-the-world mechanism.  Remove the use of atomics
when reading or writing type flags.  The use of atomics is not sufficient to
avoid races (since flags are sometimes read without a lock and without
atomics) and are no longer required.

1 files changed, 3 insertions, 0 deletions

diff --git a/Include/internal/pycore_interp_structs.h b/Include/internal/pycore_interp_structs.h
index af6ee3ab489..f193fed1153 100644
--- a/Include/internal/pycore_interp_structs.h
+++ b/Include/internal/pycore_interp_structs.h
@@ -667,8 +667,11 @@ struct _Py_interp_cached_objects {
 
     /* object.__reduce__ */
     PyObject *objreduce;
+#ifndef Py_GIL_DISABLED
+    /* resolve_slotdups() */
     PyObject *type_slots_pname;
     pytype_slotdef *type_slots_ptrs[MAX_EQUIV];
+#endif
 
     /* TypeVar and related types */
     PyTypeObject *generic_type;