Issue #7466: segmentation fault when the garbage collector is called

in the middle of populating a tuple.  Patch by Florent Xicluna.

(note: no NEWS entry for trunk since the bug was introduced in 2.7/3.1)

Lib/test/test_tuple.py

@@ -146,6 +146,9 @@ class TupleTest(seq_tests.CommonTest):
             pass
         self.check_track_dynamic(MyTuple, True)
 
+    def test_bug7466(self):
+        # Trying to untrack an unfinished tuple could crash Python
+        self._not_tracked(tuple(gc.collect() for i in range(101)))
 
 def test_main():
     test_support.run_unittest(TupleTest)

Objects/tupleobject.c

@@ -875,7 +875,8 @@ _PyTuple_Resize(PyObject **pv, Py_ssize_t newsize)
 
 	/* XXX UNREF/NEWREF interface should be more symmetrical */
 	_Py_DEC_REFTOTAL;
-	_PyObject_GC_UNTRACK(v);
+	if (_PyObject_GC_IS_TRACKED(v))
+		_PyObject_GC_UNTRACK(v);
 	_Py_ForgetReference((PyObject *) v);
 	/* DECREF items deleted by shrinkage */
 	for (i = newsize; i < oldsize; i++) {