Crash in Objects/typeobject.c

[felixxm]

BPO	44232
Nosy	@vstinner, @pablogsal, @miss-islington, @felixxm, @Fidget-Spinner
PRs	bpo-44232: Fix type_new crash caused by AssertionError #26358 bpo-44232: Fix type_new() error reporting #26359 [3.10] bpo-44232: Fix type_new() error reporting (GH-26359) #26365

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-05-26.10:23:18.580>
created_at = <Date 2021-05-25.11:39:15.184>
labels = ['interpreter-core', '3.10', 'type-crash', '3.11']
title = 'Crash in Objects/typeobject.c'
updated_at = <Date 2021-05-26.10:23:18.579>
user = 'https://github.com/felixxm'

bugs.python.org fields:

activity = <Date 2021-05-26.10:23:18.579>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2021-05-26.10:23:18.580>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2021-05-25.11:39:15.184>
creator = 'felixxm'
dependencies = []
files = []
hgrepos = []
issue_num = 44232
keywords = ['patch']
message_count = 7.0
messages = ['394330', '394350', '394371', '394375', '394393', '394426', '394428']
nosy_count = 5.0
nosy_names = ['vstinner', 'pablogsal', 'miss-islington', 'felixxm', 'kj']
pr_nums = ['26358', '26359', '26365']
priority = None
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue44232'
versions = ['Python 3.10', 'Python 3.11']

[felixxm]

We noticed a behavior change in [1]. One of our tests apps.tests.AppsTests.test_model_clash()[2] crashes with:

python: Objects/typeobject.c:3219: type_new: Assertion `type != NULL' failed.
Fatal Python error: Aborted

Current thread 0x00007ffa6951a280 (most recent call first):
File "django/tests/apps/tests.py", line 301 in test_model_clash
File "cpython/Lib/unittest/case.py", line 549 in _callTestMethod
File "cpython/Lib/unittest/case.py", line 592 in run
File "cpython/Lib/unittest/case.py", line 652 in __call__
File "django/django/test/testcases.py", line 283 in _setup_and_call
File "django/django/test/testcases.py", line 247 in __call__
File "cpython/Lib/unittest/suite.py", line 122 in run
File "cpython/Lib/unittest/suite.py", line 84 in __call__
File "cpython/Lib/unittest/runner.py", line 176 in run
File "django/django/test/runner.py", line 705 in run_suite
File "django/django/test/runner.py", line 772 in run_tests
File "django/tests/./runtests.py", line 332 in django_tests
File "django/tests/./runtests.py", line 596 in <module>
Aborted (core dumped)

This can be an issue is our test which is quite tricky. I will try to investigate it.

[1] ecf14e6
[2] https://github.com/django/django/blob/7e51893911237dfca9294e3ca12163ff813fb656/tests/apps/tests.py#L274-L309

[Fidget-Spinner]

Can you please try removing the assert(type != NULL); line at https://github.com/python/cpython/blob/main/Objects/typeobject.c#L3313 and see if it works for you? I suspect that winner->tp_new() may sometimes fail and should return NULL to indicate that in those cases, so the assert may not always hold.

[Fidget-Spinner]

Alright, I got a minimum reproducible example:

class XBase(type):
    def __new__(cls, name, bases, attrs, **kwargs):
        attrs.pop('__module__')
        return super().__new__(cls, name, bases, attrs, **kwargs)

class X(metaclass=XBase): ...

type('A', (X, ), {})

This triggers it, sending patch soon.

[vstinner]

We noticed a behavior change in [1].

Hey, well done bisection, you're right, it's a regression of my large type_new() refactoring in bpo-43770.

I wrote PR 26359 to fix it.

[vstinner]

New changeset bd199e7 by Victor Stinner in branch 'main':
bpo-44232: Fix type_new() error reporting (GH-26359)
bd199e7

[vstinner]

New changeset 7b3b698 by Miss Islington (bot) in branch '3.10':
bpo-44232: Fix type_new() error reporting (GH-26359) (GH-26365)
7b3b698

[vstinner]

Ok, it's now fixed in 3.10 and main branches. Thanks for the bug report, and thanks Ken Jin for your PR ;-)