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gh-120321: Fix TSan reported races on gi_frame_state#143128

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colesbury merged 1 commit intopython:mainpython/cpython:mainfrom
colesbury:gh-120321-tsan-racescolesbury/cpython:gh-120321-tsan-racesCopy head branch name to clipboard
Dec 24, 2025
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gh-120321: Fix TSan reported races on gi_frame_state#143128
colesbury merged 1 commit intopython:mainpython/cpython:mainfrom
colesbury:gh-120321-tsan-racescolesbury/cpython:gh-120321-tsan-racesCopy head branch name to clipboard

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@colesbury colesbury commented Dec 24, 2025 •
edited by bedevere-app bot
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colesbury commented Dec 24, 2025

This is the same thing as #142995, but I missed a few cases. Again, I think these are false positives in the sense that TSan treats failed compare-exchanges as if they are modifications, when they don't perform any modification on failure.

@colesbury colesbury requested a review from mpage December 24, 2025 00:24
@colesbury colesbury marked this pull request as ready for review December 24, 2025 00:24
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kumaraditya303 commented Dec 24, 2025

In _PyGen_Finalize there are a few non-atomic reads of gi_frame_state, does that need fixing as well?

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colesbury commented Dec 24, 2025

No, _PyGen_Finalize is called when there are no other references to the generator (except cycles), so there's no concurrent compare-exchanges on gi_frame_state.

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kumaraditya303 commented Dec 24, 2025 •
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No, _PyGen_Finalize is called when there are no other references to the generator (except cycles), so there's no concurrent compare-exchanges on gi_frame_state.

It is possible that _PyGen_Finalize gets called from frame.clear though so IIUC it is not guaranteed to be called only when there are no other references to generator.

cpython/Objects/frameobject.c

Line 2025 in d4dc3dd

_PyGen_Finalize((PyObject *)gen);

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colesbury commented Dec 24, 2025

That will be fixed in #143112

@colesbury colesbury merged commit 594a463 into python:main Dec 24, 2025
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@colesbury colesbury deleted the gh-120321-tsan-races branch December 24, 2025 21:10
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@kumaraditya303 kumaraditya303 kumaraditya303 approved these changes

@mpage mpage Awaiting requested review from mpage

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