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GeezerVison is showing github.com — gh-159739: Preserve ContextVar cache updates from finalizers by jelle-openai · Pull Request #160197 · python/cpython

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@jelle-openai

@jelle-openai jelle-openai commented Oct 22, 2026 •
edited by bedevere-app Bot
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Resetting a ContextVar can finalize the replaced value, whose finalizer may set the variable again. Updating the lookup cache after releasing the old context root overwrites that newer cached value, so get() can return a stale value or use a freed object. Update the cache before the old root can be released. Backport to 3.15 and 3.14.

  • Issue: Fix minor safety issues #159739

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@jelle-openai
pythongh-159739: Preserve ContextVar cache updates from finalizers
125f64c 
Resetting a ContextVar can finalize the replaced value, whose finalizer may set the variable again. Updating the lookup cache after releasing the old context root overwrites that newer cached value, so get() can return a stale value or use a freed object. Update the cache before the old root can be released. Backport to 3.15 and 3.14.
@jelle-openai
jelle-openai requested a review from 1st1 as a code owner October 22, 2026 04:43
@bedevere-app bedevere-app Bot added the awaiting review label Oct 22, 2026
@bedevere-app bedevere-app Bot mentioned this pull request Oct 22, 2026
Fix minor safety issues #159739
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@JelleZijlstra
JelleZijlstra merged commit f4f8b93 into python:main Oct 22, 2026
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@JelleZijlstra JelleZijlstra added needs backport to 3.14 bugs and security fixes needs backport to 3.15 bugs and security fixes labels Oct 22, 2026
@bedevere-app bedevere-app Bot removed the awaiting review label Oct 22, 2026
@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖
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@miss-islington-app

miss-islington-app Bot commented Oct 22, 2026

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Thanks @jelle-openai for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖
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@bedevere-app

bedevere-app Bot commented Oct 22, 2026

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GH-160329 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 22, 2026
@bedevere-app

bedevere-app Bot commented Oct 22, 2026

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GH-160330 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 22, 2026
JelleZijlstra pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @jelle-openai
[3.14] gh-159739: Preserve ContextVar cache updates from finalizers (G…
a99e929 
…H-160197) (#160329)

Resetting a ContextVar can finalize the replaced value, whose finalizer may set the variable again. Updating the lookup cache after releasing the old context root overwrites that newer cached value, so get() can return a stale value or use a freed object. Update the cache before the old root can be released. Backport to 3.15 and 3.14.
(cherry picked from commit f4f8b93)

Co-authored-by: Jelle Zijlstra <[email protected]>
JelleZijlstra pushed a commit that referenced this pull request Oct 22, 2026
@miss-islington @jelle-openai
[3.15] gh-159739: Preserve ContextVar cache updates from finalizers (G…
1526be6 
…H-160197) (#160330)

Resetting a ContextVar can finalize the replaced value, whose finalizer may set the variable again. Updating the lookup cache after releasing the old context root overwrites that newer cached value, so get() can return a stale value or use a freed object. Update the cache before the old root can be released. Backport to 3.15 and 3.14.
(cherry picked from commit f4f8b93)

Co-authored-by: Jelle Zijlstra <[email protected]>
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@jelle-openai @JelleZijlstra
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