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OSError: AF_UNIX path too long regression in forkserver #149527
Description
Bug report
Bug description:
Since fd81246 (in 3.14 as e590f00), we're seeing Gentoo Portage randomly fail with:
Traceback (most recent call last):
File "/usr/lib/portage/python3.14/ebuild-ipc.py", line 303, in <module>
sys.exit(ebuild_ipc_main(sys.argv[1:]))
~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
File "/usr/lib/portage/python3.14/ebuild-ipc.py", line 299, in ebuild_ipc_main
return ebuild_ipc.communicate(args)
~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/usr/lib/portage/python3.14/ebuild-ipc.py", line 151, in communicate
lock_obj = portage.locks.lockfile(self.ipc_lock_file, unlinkfile=True)
File "/usr/lib/python3.14/site-packages/portage/locks.py", line 184, in lockfile
lock = _lockfile_iteration(
mypath,
...<3 lines>...
flags=flags,
)
File "/usr/lib/python3.14/site-packages/portage/locks.py", line 314, in _lockfile_iteration
locking_method = _get_lock_fn()
File "/usr/lib/python3.14/site-packages/portage/locks.py", line 96, in _get_lock_fn
if _test_lock_fn(_lockf_test_lock_fn):
~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.14/site-packages/portage/locks.py", line 128, in _test_lock_fn
proc.start()
~~~~~~~~~~^^
File "/usr/lib/python3.14/multiprocessing/process.py", line 121, in start
self._popen = self._Popen(self)
~~~~~~~~~~~^^^^^^
File "/usr/lib/python3.14/multiprocessing/context.py", line 230, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
File "/usr/lib/python3.14/multiprocessing/context.py", line 306, in _Popen
return Popen(process_obj)
File "/usr/lib/python3.14/multiprocessing/popen_forkserver.py", line 35, in __init__
super().__init__(process_obj)
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
File "/usr/lib/python3.14/multiprocessing/popen_fork.py", line 20, in __init__
self._launch(process_obj)
~~~~~~~~~~~~^^^^^^^^^^^^^
File "/usr/lib/python3.14/multiprocessing/popen_forkserver.py", line 51, in _launch
self.sentinel, w = forkserver.connect_to_new_process(self._fds)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^
File "/usr/lib/python3.14/multiprocessing/forkserver.py", line 89, in connect_to_new_process
self.ensure_running()
~~~~~~~~~~~~~~~~~~~^^
File "/usr/lib/python3.14/multiprocessing/forkserver.py", line 167, in ensure_running
listener.bind(address)
~~~~~~~~~~~~~^^^^^^^^^
OSError: AF_UNIX path too longApparently in this case the resulting path was:
/tmp/mgorny-dev-scripts/portage/dev-python/trove-classifiers-2026.5.7.17/temp/pymp-o2g23iqr/sock-d559f6e62fa1
Note that tempfile.mktemp() used to append 8 ASCII characters, while this logic appends 12 hex digits, so the logic introduced in 1a07a01 would be off by 4 now.
CPython versions tested on:
3.14, CPython main branch
Operating systems tested on:
Linux
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picnixz commented on May 8, 2026
Ah so the computation was not updated. To avoid future issues I am going to hardcode the number of random bytes we use and add a comment. I will address this tomorrow
cc @gpshead
picnixz commented on May 9, 2026
So I fixed the issue but note that in your case the temporary directory will be switched to /tmp/ instead of $TMPDIR because the path is too long. It will be /tmp/pymp-XXXXXXXX/sock-XXXXXXXXXXXX.
picnixz commented on May 9, 2026
Note: I centralized the constants that we use in multiprocessing.util so that we just need to update them to bump security stuff instead of changing them one by one (and the comments). I can hardcode them but we won't get bitten by such changes in the future (at least we know what will needs to be changed!)
mgorny commented on May 9, 2026
Thanks!
python3: bump to 3.14.5
gh-149527: fix creation of temporary socket files post GH-148578 (#14…
[3.15] gh-149527: fix creation of temporary socket files post GH-148578…
[3.14] gh-149527: fix creation of temporary socket files post GH-148578…
picnixz commented on Oct 22, 2026
3.13 is security-only so it won't be backported. I'm sorry for taking that long though but I hope it fix your issues!