From 87d7a19ef0a751925be1f703858831c5e0c4fb57 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 21 May 2025 11:36:39 +0200
Subject: [PATCH] [3.14] gh-133980: use atomic store in
 `PyObject_GenericSetDict` (GH-133988) (#134354)

gh-133980: use atomic store in `PyObject_GenericSetDict` (GH-133988)
(cherry picked from commit ec39fd2c20323ee9814a1137b1a0819e92efae4e)

Co-authored-by: Kumar Aditya <kumaraditya@python.org>
---
 Lib/test/test_free_threading/test_dict.py | 16 ++++++++++++++++
 Objects/object.c                          |  8 +++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_free_threading/test_dict.py b/Lib/test/test_free_threading/test_dict.py
index 476cc3178d8..5d5d4e226ca 100644
--- a/Lib/test/test_free_threading/test_dict.py
+++ b/Lib/test/test_free_threading/test_dict.py
@@ -228,6 +228,22 @@ class TestDict(TestCase):
 
             self.assertEqual(count, 0)
 
+    def test_racing_object_get_set_dict(self):
+        e = Exception()
+
+        def writer():
+            for i in range(10000):
+                e.__dict__ = {1:2}
+
+        def reader():
+            for i in range(10000):
+                e.__dict__
+
+        t1 = Thread(target=writer)
+        t2 = Thread(target=reader)
+
+        with threading_helper.start_threads([t1, t2]):
+            pass
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Objects/object.c b/Objects/object.c
index 723b0427e69..af1aa217f75 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1931,7 +1931,13 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
         return -1;
     }
     Py_BEGIN_CRITICAL_SECTION(obj);
-    Py_XSETREF(*dictptr, Py_NewRef(value));
+    PyObject *olddict = *dictptr;
+    FT_ATOMIC_STORE_PTR_RELEASE(*dictptr, Py_NewRef(value));
+#ifdef Py_GIL_DISABLED
+    _PyObject_XDecRefDelayed(olddict);
+#else
+    Py_XDECREF(olddict);
+#endif
     Py_END_CRITICAL_SECTION();
     return 0;
 }