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GeezerVison is showing github.com — gh-154431: Use existing `runtime->audit_hooks.mutex` instead of a new one by sobolevn · Pull Request #154494 · python/cpython

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@sobolevn

@sobolevn sobolevn commented Jul 22, 2026 •
edited by bedevere-app Bot
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  • Issue: Data race: sys.addaudithook() lazily creates interp->audit_hooks with no lock #154431

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@sobolevn
pythongh-154431: Use existing runtime->audit_hooks.mutex instead of…
8adcde5 
… a new one
@sobolevn
sobolevn requested a review from ambv July 22, 2026 16:30
@sobolevn
sobolevn requested review from FFY00, ZeroIntensity and ericsnowcurrently as code owners July 22, 2026 16:30
@bedevere-app bedevere-app Bot mentioned this pull request Jul 22, 2026
Data race: sys.addaudithook() lazily creates interp->audit_hooks with no lock #154431
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@bedevere-app bedevere-app Bot added the awaiting core review label Jul 22, 2026
ZeroIntensity
ZeroIntensity reviewed Jul 22, 2026
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@ZeroIntensity ZeroIntensity left a comment

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This will just increase contention in sys.addaudithook, won't it?

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@sobolevn

sobolevn commented Jul 22, 2026

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I don't think that we actually concurrenly add hooks with both PySys_AddAuditHook and sys.audithook, so realistically - it should not matter.
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@sobolevn sobolevn added skip news needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Jul 22, 2026
@ZeroIntensity

ZeroIntensity commented Jul 22, 2026

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Agreed, but why make this change at all? We're just increasing pressure on a lock for no reason. PyMutex is just a single byte; due to alignment, I would be surprised if you see any change in memory overhead.
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@sobolevn

sobolevn commented Jul 22, 2026

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Because we can't backport the fix with interpreter state changed due to ABI change.
And we want to fix the data race on 3.14 :(
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weixlu
weixlu reviewed Jul 23, 2026
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Comment thread Python/sysmodule.c

PyInterpreterState *interp = tstate->interp;
PyMutex mutex = interp->audit_hooks_mutex;
PyMutex mutex = interp->runtime->audit_hooks.mutex;

@weixlu weixlu Jul 23, 2026

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Hi, I noticed the mutex here is copied by value onto the stack, then being locked. I'm worried this subtly changes the semantics into locking a stack-local object instead. The typical usage may be to lock the address directly, i.e. PyMutex_Lock(&interp->runtime->audit_hooks.mutex);

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@weixlu weixlu Jul 23, 2026

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Here is a demo shows locking a stack-local mutex won't affect the real mutex.

#include <Python.h>
#include <stdio.h>

static PyMutex shared = {0};

int main(void)
{
    PyMutex mutex = shared;
    PyMutex_Lock(&mutex);
    printf("locked the COPY:  shared=%d copy=%d\n", PyMutex_IsLocked(&shared), PyMutex_IsLocked(&mutex));
    PyMutex_Unlock(&mutex);

    PyMutex_Lock(&shared);
    printf("locked the FIELD: shared=%d\n", PyMutex_IsLocked(&shared));
    PyMutex_Unlock(&shared);
    return 0;
}

Run gcc mutex_copy_demo.c -I Include -I . libpython3.16.a -lpthread -lm -ldl -lutil -o demo && ./demo then it print

locked the COPY:  shared=0 copy=1
locked the FIELD: shared=1

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@sobolevn sobolevn mentioned this pull request Jul 23, 2026
gh-154431: Fix data race in sys.audithook #154462
Merged
@ZeroIntensity ZeroIntensity mentioned this pull request Jul 23, 2026
gh-154431: Eagerly initialize the audit hooks list #154554
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@encukou

encukou commented Jul 27, 2026

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!buildbot CentOS9.NoGIL.Refleaks
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@bedevere-bot

bedevere-bot commented Jul 27, 2026

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🤖 New build scheduled with the buildbot fleet by @encukou for commit 8adcde5 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F154494%2Fmerge

The command will test the builders whose names match following regular expression: CentOS9.NoGIL.Refleaks

The builders matched are:

  • AMD64 CentOS9 NoGIL Refleaks PR
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@github-actions

github-actions Bot commented Oct 28, 2026

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This PR is stale because it has been open for 90 days with no activity.
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@github-actions github-actions Bot added the stale Stale PR or inactive for long period of time. label Oct 28, 2026
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Reviewers

@ZeroIntensity ZeroIntensity ZeroIntensity left review comments
@ambv ambv Awaiting requested review from ambv
@ericsnowcurrently ericsnowcurrently Awaiting requested review from ericsnowcurrently ericsnowcurrently is a code owner
@FFY00 FFY00 Awaiting requested review from FFY00 FFY00 is a code owner
+1 more reviewer
@weixlu weixlu weixlu left review comments
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@sobolevn @ZeroIntensity @encukou @bedevere-bot @weixlu
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