Ah! I found a way to reproduce the crash:

diff --git a/Lib/test/test_slice.py b/Lib/test/test_slice.py
index 4ae4142c60..b18f8f1c8c 100644
--- a/Lib/test/test_slice.py
+++ b/Lib/test/test_slice.py
@@ -1,4 +1,8 @@
 # tests for slice objects; in particular the indices method.
+import gc, random
+n = random.randint(1, 700)
+print("set_threshold(%s)" % n)
+gc.set_threshold(n)
 
 import itertools
 import operator


$ ./python -m test -F -j0 test_slice test_slice test_slice test_slice test_slice test_slice test_slice test_slice


I went up to January 1st, 2018 (commit e8ed96550c6aa9a1e39c36e67e892994e25e2c41): the test already crashed with my patch, so it's not a regression. I reset the priority.