Raising in an atexit function in dev mode crashes

[pablogsal]

BPO	46025
Nosy	@vstinner, @pablogsal, @miss-islington
PRs	bpo-46025: Fix a crash in the atexit module for auto-unregistering functions #30002 [3.10] bpo-46025: Fix a crash in the atexit module for auto-unregistering functions (GH-30002) #30005

^{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 2021-12-09.15:15:34.300>
created_at = <Date 2021-12-09.11:20:52.793>
labels = ['3.10', '3.11']
title = 'Raising in an atexit function in dev mode crashes'
updated_at = <Date 2021-12-09.17:06:29.881>
user = 'https://github.com/pablogsal'

bugs.python.org fields:

activity = <Date 2021-12-09.17:06:29.881>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2021-12-09.15:15:34.300>
closer = 'pablogsal'
components = []
creation = <Date 2021-12-09.11:20:52.793>
creator = 'pablogsal'
dependencies = []
files = []
hgrepos = []
issue_num = 46025
keywords = ['patch', '3.10regression', '3.11regression']
message_count = 6.0
messages = ['408106', '408123', '408132', '408143', '408144', '408147']
nosy_count = 3.0
nosy_names = ['vstinner', 'pablogsal', 'miss-islington']
pr_nums = ['30002', '30005']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46025'
versions = ['Python 3.10', 'Python 3.11']

[pablogsal]

Issue found by Matt Wozniski:

Running this with python3.10 -X dev segfaults:

import atexit
def func():
    atexit.unregister(func)
    1/0
atexit.register(func)

[pablogsal]

New changeset f0d290d by Pablo Galindo Salgado in branch 'main':
bpo-46025: Fix a crash in the atexit module for auto-unregistering functions (GH-30002)
f0d290d

[pablogsal]

New changeset 934a24c by Miss Islington (bot) in branch '3.10':
bpo-46025: Fix a crash in the atexit module for auto-unregistering functions (GH-30002) (GH-30005)
934a24c

[vstinner]

Interesting bug report! Thanks for the fix ;-)

[vstinner]

For me, the question is why would anyone call atexit.unregister() inside an atexit callback. Is it useful?

atexit._run_exitfuncs() removes all registered callbacks.

Py_Finalize() calls _PyAtExit_Call() which also removes all registered callbacks.

[pablogsal]

For me, the question is why would anyone call atexit.unregister() inside an atexit callback. Is it useful?

Is not useful, is just an edge case