# HG changeset patch
# Parent  b6e33798f82a2c025ad9cd55b0d656f3c78a3684
Issue #25395: Fix crashes with highly nested OrderedDict

diff -r b6e33798f82a Lib/test/test_collections.py
--- a/Lib/test/test_collections.py	Sun Oct 18 09:53:17 2015 +0300
+++ b/Lib/test/test_collections.py	Sun Oct 18 09:01:27 2015 +0000
@@ -2025,6 +2025,14 @@
         items = [('a', 1), ('c', 3), ('b', 2)]
         self.assertEqual(list(MyOD(items).items()), items)
 
+    def test_highly_nested(self):
+        # Issue 25395: crashes during garbage collection
+        obj = None
+        for _ in range(1000):
+            obj = self.module.OrderedDict([(None, obj)])
+        del obj
+        support.gc_collect()
+
 
 class PurePythonOrderedDictTests(OrderedDictTests, unittest.TestCase):
 
diff -r b6e33798f82a Misc/NEWS
--- a/Misc/NEWS	Sun Oct 18 09:53:17 2015 +0300
+++ b/Misc/NEWS	Sun Oct 18 09:01:27 2015 +0000
@@ -11,6 +11,9 @@
 Core and Builtins
 -----------------
 
+- Issue #25395: Fix crash when highly nested OrderedDict structures were
+  garbage collected.
+
 - Issue #25274: sys.setrecursionlimit() now raises a RecursionError if the new
   recursion limit is too low depending at the current recursion depth. Modify
   also the "lower-water mark" formula to make it monotonic. This mark is used
diff -r b6e33798f82a Objects/odictobject.c
--- a/Objects/odictobject.c	Sun Oct 18 09:53:17 2015 +0300
+++ b/Objects/odictobject.c	Sun Oct 18 09:01:27 2015 +0000
@@ -1438,16 +1438,18 @@
 odict_dealloc(PyODictObject *self)
 {
     PyObject_GC_UnTrack(self);
-    Py_TRASHCAN_SAFE_BEGIN(self);
-    Py_XDECREF(self->od_inst_dict);
+    Py_TRASHCAN_SAFE_BEGIN(self)
+
+    Py_CLEAR(self->od_inst_dict);
     if (self->od_weakreflist != NULL)
         PyObject_ClearWeakRefs((PyObject *)self);
 
     _odict_clear_nodes(self);
-    Py_TRASHCAN_SAFE_END(self);
 
     /* must be last */
     PyDict_Type.tp_dealloc((PyObject *)self);
+
+    Py_TRASHCAN_SAFE_END(self)
 };
 
 /* tp_repr */