From: Brandt Bucher <brandtbucher@microsoft.com>
Date: Mon, 12 May 2025 20:00:01 +0000 (-0700)
Subject: [3.13] GH-133543: Maintain tracking for materialized instance dictionaries (GH-133617)
X-Git-Tag: v3.13.4~118
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=50b45c4f457a7b77ec526fae4d2894c3e4f38e2e;p=thirdparty%2FPython%2Fcpython.git

[3.13] GH-133543: Maintain tracking for materialized instance dictionaries (GH-133617)
---

diff --git a/Lib/test/test_dict.py b/Lib/test/test_dict.py
index 40b0c210ab34..4729132c5a5f 100644
--- a/Lib/test/test_dict.py
+++ b/Lib/test/test_dict.py
@@ -1006,6 +1006,18 @@ class DictTest(unittest.TestCase):
             pass
         self._tracked(MyDict())
 
+    @support.cpython_only
+    def test_track_lazy_instance_dicts(self):
+        class C:
+            pass
+        o = C()
+        d = o.__dict__
+        self._not_tracked(d)
+        o.untracked = 42
+        self._not_tracked(d)
+        o.tracked = []
+        self._tracked(d)
+
     def make_shared_key_dict(self, n):
         class C:
             pass
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-05-07-10-48-31.gh-issue-133543.4jcszP.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-07-10-48-31.gh-issue-133543.4jcszP.rst
new file mode 100644
index 000000000000..046085892d45
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-05-07-10-48-31.gh-issue-133543.4jcszP.rst
@@ -0,0 +1,2 @@
+Fix a possible memory leak that could occur when directly accessing instance
+dictionaries (``__dict__``) that later become part of a reference cycle.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index e89ed467bf7c..501f3d2d2bca 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -6839,6 +6839,9 @@ store_instance_attr_lock_held(PyObject *obj, PyDictValues *values,
                                    value == NULL ? PyDict_EVENT_DELETED :
                                    PyDict_EVENT_MODIFIED);
         _PyDict_NotifyEvent(interp, event, dict, name, value);
+        if (value) {
+            MAINTAIN_TRACKING(dict, name, value);
+        }
     }
 
     FT_ATOMIC_STORE_PTR_RELEASE(values->values[ix], Py_XNewRef(value));