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gh-149816: Fix a race condition in _PyBytes_FromList with free-threading#149909

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May 16, 2026
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gh-149816: Fix a race condition in _PyBytes_FromList with free-threading#149909
sobolevn merged 1 commit into
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sobolevn:issue-149816-128

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@sobolevn sobolevn commented May 16, 2026 •
edited by bedevere-app Bot
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_PyBytes_FromList is called from PyBytes_FromObject which does not own the passed object, so it is a borrowed reference.

Using _PyList_GetItemRef seems like the correct solution here.
However, I was not successful in actually triggering the failure without C-API direct usage.

@sobolevn sobolevn requested a review from kumaraditya303 May 16, 2026 08:07
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LGTM

@sobolevn sobolevn added needs backport to 3.14 bugs and security fixes needs backport to 3.15 pre-release feature fixes, bugs and security fixes labels May 16, 2026
@sobolevn sobolevn enabled auto-merge (squash) May 16, 2026 08:15
@sobolevn sobolevn merged commit 46afba7 into python:main May 16, 2026
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miss-islington-app Bot commented May 16, 2026

Thanks @sobolevn for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖

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miss-islington-app Bot commented May 16, 2026

Sorry, @sobolevn, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 46afba7b9324bc9492c3527d0fe47dd74f1f598c 3.14

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bedevere-app Bot commented May 16, 2026

GH-149911 is a backport of this pull request to the 3.15 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.15 pre-release feature fixes, bugs and security fixes label May 16, 2026
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bedevere-app Bot commented May 16, 2026

GH-149912 is a backport of this pull request to the 3.14 branch.

@bedevere-app bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label May 16, 2026
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eendebakpt commented May 16, 2026

@sobolevn @kumaraditya303 The same issue was addressed in #132590, which takes a different approach. Using Py_BEGIN_CRITICAL_SECTION_SEQUENCE_FAST we can unify the tuple and list cases and improve performance. It also adds a FT test. Could you have a look at that PR please?

sobolevn added a commit that referenced this pull request May 16, 2026
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[3.15] gh-149816: Fix a race condition in _PyBytes_FromList with fr…
ec3aa6a 
…ee-threading (GH-149909) (#149911)

gh-149816: Fix a race condition in `_PyBytes_FromList` with free-threading (GH-149909)
(cherry picked from commit 46afba7)

Co-authored-by: sobolevn <mail@sobolevn.me>
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