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GeezerVison is showing github.com — gh-159864: Fix syslog.openlog() crash with concurrent sys.argv changes by espressolee · Pull Request #159884 · python/cpython

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@espressolee

@espressolee espressolee commented Oct 20, 2026 •
edited by ZeroIntensity
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syslog_get_argv() took sys.argv[0] with PyList_GetItem() and only increfed it afterwards, so on the free-threaded build another thread replacing sys.argv[0] could free it in between. Use PyList_GetItemRef() instead.

Adds a regression test to test_free_threading.test_syslog that races syslog.openlog() (without ident) against sys.argv[0] assignment.

Thanks to @lazerg for confirming the crash on main and identifying the fix.

Fixes #159864.

  • Issue: Free-threaded: concurrent syslog.openlog() and sys.argv[0] assignment crash the interpreter #159864

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@espressolee @lazerg
pythongh-159864: Fix syslog.openlog() crash with concurrent sys.argv …
38a30c5 
…changes

syslog_get_argv() took sys.argv[0] with PyList_GetItem() and increfed it
only afterwards, so on the free-threaded build a concurrent replacement of
sys.argv[0] could free it in between. Use PyList_GetItemRef() instead.

Co-authored-by: Lazizbek Ergashev <[email protected]>
@python-cla-bot

python-cla-bot Bot commented Oct 20, 2026 •
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All commit authors signed the Contributor License Agreement.

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@bedevere-app bedevere-app Bot mentioned this pull request Oct 20, 2026
Free-threaded: concurrent syslog.openlog() and sys.argv[0] assignment crash the interpreter #159864
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@bedevere-app bedevere-app Bot added the awaiting review label Oct 20, 2026
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chatgpt-codex-connector Bot commented Oct 20, 2026 •
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Codex Review Summary

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Review Status Commit Review trigger
📝 Code Review ✅ Completed 2026-10-20T13:43:10.293424Z 38a30c5 PR opened
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aisk
aisk approved these changes Oct 20, 2026
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@bedevere-app bedevere-app Bot added awaiting core review and removed awaiting review labels Oct 20, 2026
@aisk aisk added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 20, 2026
ZeroIntensity
ZeroIntensity approved these changes Oct 20, 2026
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Oct 20, 2026
@ZeroIntensity
ZeroIntensity merged commit e5e0748 into python:main Oct 20, 2026
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@miss-islington-app

miss-islington-app Bot commented Oct 20, 2026

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Thanks @espressolee for the PR, and @ZeroIntensity for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖
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@bedevere-app bedevere-app Bot removed the awaiting merge label Oct 20, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 20, 2026

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Sorry, @espressolee and @ZeroIntensity, I could not cleanly backport this to 3.14 due to a conflict.

Please backport manually with cherry_picker, see the devguide for more information.

cherry_picker e5e0748abd27e39655cb8dc313a82cad6563c54f 3.14
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@bedevere-app

bedevere-app Bot commented Oct 20, 2026

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GH-159952 is a backport of this pull request to the 3.15 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label Oct 20, 2026
@miss-islington-app miss-islington-app Bot assigned ZeroIntensity Oct 20, 2026
@bedevere-app

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GH-159954 is a backport of this pull request to the 3.14 branch.
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@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label Oct 20, 2026
@ZeroIntensity

ZeroIntensity commented Oct 20, 2026

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Congrats on your first contribution :)
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ZeroIntensity pushed a commit that referenced this pull request Oct 20, 2026
@miss-islington @espressolee @lazerg
[3.15] gh-159864: Fix syslog.openlog() crash with concurrent sys.argv…
a11aa06 
… changes (GH-159884) (GH-159952)

syslog_get_argv() took sys.argv[0] with PyList_GetItem() and increfed it
only afterwards, so on the free-threaded build a concurrent replacement of
sys.argv[0] could free it in between. Use PyList_GetItemRef() instead.
(cherry picked from commit e5e0748)

Co-authored-by: Junhyung Lee <[email protected]>
Co-authored-by: Lazizbek Ergashev <[email protected]>
ZeroIntensity added a commit that referenced this pull request Oct 21, 2026
@ZeroIntensity @espressolee @lazerg
[3.14] gh-159864: Fix syslog.openlog() crash with concurrent sys.argv…
ed5bcda 
… changes (GH-159884) (GH-159954)

syslog_get_argv() took sys.argv[0] with PyList_GetItem() and increfed it
only afterwards, so on the free-threaded build a concurrent replacement of
sys.argv[0] could free it in between. Use PyList_GetItemRef() instead.
(cherry picked from commit e5e0748)

Co-authored-by: Junhyung Lee <[email protected]>
Co-authored-by: Lazizbek Ergashev <[email protected]>
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@aisk aisk aisk approved these changes
@ZeroIntensity ZeroIntensity ZeroIntensity approved these changes

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@espressolee @ZeroIntensity @aisk
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