python
diff --git a/‎Lib/test/test_weakref.py
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+8Lines changed: 8 additions & 0 deletions b/‎Lib/test/test_weakref.py
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+8Lines changed: 8 additions & 0 deletions
diff --git a/‎Misc/NEWS.d/next/Core and Builtins/2017-07-15-13-55-22.bpo-26617.Gh5LvN.rst
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+1Lines changed: 1 addition & 0 deletions b/‎Misc/NEWS.d/next/Core and Builtins/2017-07-15-13-55-22.bpo-26617.Gh5LvN.rst
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+1Lines changed: 1 addition & 0 deletions
diff --git a/‎Objects/typeobject.c
Copy file name to clipboardExpand all lines: Objects/typeobject.c
+13-12Lines changed: 13 additions & 12 deletions b/‎Objects/typeobject.c
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+13-12Lines changed: 13 additions & 12 deletions
@@ -827,6 +827,14 @@ def test_set_callback_attribute(self):
         with self.assertRaises(AttributeError):
             ref1.__callback__ = lambda ref: None
 
+    def test_callback_gcs(self):
+        class ObjectWithDel(Object):
+            def __del__(self): pass
+        x = ObjectWithDel(1)
+        ref1 = weakref.ref(x, lambda ref: support.gc_collect())
+        del x
+        support.gc_collect()
+
 
 class SubclassableWeakrefTestCase(TestBase):
 
 
@@ -0,0 +1 @@
+Fix crash when GC runs during weakref callbacks.
@@ -1116,11 +1116,6 @@ subtype_dealloc(PyObject *self)
     Py_TRASHCAN_SAFE_BEGIN(self);
     --_PyTrash_delete_nesting;
     -- tstate->trash_delete_nesting;
-    /* DO NOT restore GC tracking at this point.  weakref callbacks
-     * (if any, and whether directly here or indirectly in something we
-     * call) may trigger GC, and if self is tracked at that point, it
-     * will look like trash to GC and GC will try to delete self again.
-     */
 
     /* Find the nearest base with a different tp_dealloc */
     base = type;
@@ -1131,30 +1126,36 @@ subtype_dealloc(PyObject *self)
 
     has_finalizer = type->tp_finalize || type->tp_del;
 
-    /* Maybe call finalizer; exit early if resurrected */
-    if (has_finalizer)
-        _PyObject_GC_TRACK(self);
-
     if (type->tp_finalize) {
+        _PyObject_GC_TRACK(self);
         if (PyObject_CallFinalizerFromDealloc(self) < 0) {
             /* Resurrected */
             goto endlabel;
         }
+        _PyObject_GC_UNTRACK(self);
     }
-    /* If we added a weaklist, we clear it.      Do this *before* calling
-       tp_del, clearing slots, or clearing the instance dict. */
+    /*
+      If we added a weaklist, we clear it. Do this *before* calling tp_del,
+      clearing slots, or clearing the instance dict.
+
+      GC tracking must be off at this point. weakref callbacks (if any, and
+      whether directly here or indirectly in something we call) may trigger GC,
+      and if self is tracked at that point, it will look like trash to GC and GC
+      will try to delete self again.
+    */
     if (type->tp_weaklistoffset && !base->tp_weaklistoffset)
         PyObject_ClearWeakRefs(self);
 
     if (type->tp_del) {
+        _PyObject_GC_TRACK(self);
         type->tp_del(self);
         if (self->ob_refcnt > 0) {
             /* Resurrected */
             goto endlabel;
         }
+        _PyObject_GC_UNTRACK(self);
     }
     if (has_finalizer) {
-        _PyObject_GC_UNTRACK(self);
         /* New weakrefs could be created during the finalizer call.
            If this occurs, clear them out without calling their
            finalizers since they might rely on part of the object
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix crash when GC runs during weakref callbacks.`