[Python-checkins] gh-132685: fix thread safety of `PyMember_GetOne` with `_Py_T_OBJECT` (#132690)

[kumaraditya303]

https://github.com/python/cpython/commit/7fd708b727fe19403726da6cb912b81768a96946
commit: 7fd708b727fe19403726da6cb912b81768a96946
branch: main
author: Kumar Aditya <kumaradi...@python.org>
committer: kumaraditya303 <kumaradi...@python.org>
date: 2025-04-18T21:03:42+05:30
summary:

gh-132685: fix thread safety of `PyMember_GetOne` with `_Py_T_OBJECT` (#132690)

files:
M Python/structmember.c

diff --git a/Python/structmember.c b/Python/structmember.c
index d36e049d6b5d20..574acf296157f3 100644
--- a/Python/structmember.c
+++ b/Python/structmember.c
@@ -85,10 +85,22 @@ PyMember_GetOne(const char *obj_addr, PyMemberDef *l)
         break;
     }
     case _Py_T_OBJECT:
-        v = *(PyObject **)addr;
-        if (v == NULL)
+        v = FT_ATOMIC_LOAD_PTR(*(PyObject **) addr);
+        if (v != NULL) {
+#ifdef Py_GIL_DISABLED
+            if (!_Py_TryIncrefCompare((PyObject **) addr, v)) {
+                Py_BEGIN_CRITICAL_SECTION((PyObject *) obj_addr);
+                v = FT_ATOMIC_LOAD_PTR(*(PyObject **) addr);
+                Py_XINCREF(v);
+                Py_END_CRITICAL_SECTION();
+            }
+#else
+            Py_INCREF(v);
+#endif
+        }
+        if (v == NULL) {
             v = Py_None;
-        Py_INCREF(v);
+        }
         break;
     case Py_T_OBJECT_EX:
         v = member_get_object(addr, obj_addr, l);

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