Merge from 3.6.

Lib/test/test_xml_etree_c.py

@@ -11,6 +11,7 @@ cET_alias = import_fresh_module('xml.etree.cElementTree',
                                 fresh=['_elementtree', 'xml.etree'])
 
 
+@unittest.skipUnless(cET, 'requires _elementtree')
 class MiscTests(unittest.TestCase):
     # Issue #8651.
     @support.bigmemtest(size=support._2G + 100, memuse=1, dry_run=False)
@@ -54,6 +55,15 @@ class MiscTests(unittest.TestCase):
             del element.attrib
         self.assertEqual(element.attrib, {'A': 'B', 'C': 'D'})
 
+    def test_trashcan(self):
+        # If this test fails, it will most likely die via segfault.
+        e = root = cET.Element('root')
+        for i in range(200000):
+            e = cET.SubElement(e, 'x')
+        del e
+        del root
+        support.gc_collect()
+
 
 @unittest.skipUnless(cET, 'requires _elementtree')
 class TestAliasWorking(unittest.TestCase):

Misc/NEWS

@@ -205,6 +205,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #28871: Fixed a crash when deallocate deep ElementTree.
+
 - Issue #19542: Fix bugs in WeakValueDictionary.setdefault() and
   WeakValueDictionary.pop() when a GC collection happens in another
   thread.

Modules/_elementtree.c

@@ -626,6 +626,7 @@ static void
 element_dealloc(ElementObject* self)
 {
     PyObject_GC_UnTrack(self);
+    Py_TRASHCAN_SAFE_BEGIN(self)
 
     if (self->weakreflist != NULL)
         PyObject_ClearWeakRefs((PyObject *) self);
@@ -636,6 +637,7 @@ element_dealloc(ElementObject* self)
 
     RELEASE(sizeof(ElementObject), "destroy element");
     Py_TYPE(self)->tp_free((PyObject *)self);
+    Py_TRASHCAN_SAFE_END(self)
 }
 
 /* -------------------------------------------------------------------- */