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GeezerVison is showing github.com — gh-120321: Fix TSan reported races on gi_frame_state by colesbury · Pull Request #143128 · python/cpython

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@colesbury

@colesbury colesbury commented Dec 24, 2025 •
edited by bedevere-app Bot
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  • Issue: SIGSEGV with generators in free-threaded build #120321

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@colesbury
pythongh-120321: Fix TSan reported races on gi_frame_state
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@colesbury colesbury added skip news topic-free-threading labels Dec 24, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Dec 24, 2025
SIGSEGV with generators in free-threaded build #120321
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@colesbury

colesbury commented Dec 24, 2025

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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.
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@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
@colesbury
colesbury requested a review from markshannon as a code owner December 24, 2025 00:24
@bedevere-app bedevere-app Bot added the awaiting core review label Dec 24, 2025
@kumaraditya303

kumaraditya303 commented Dec 24, 2025

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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

colesbury 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.
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@kumaraditya303

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

colesbury commented Dec 24, 2025

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That will be fixed in #143112
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kumaraditya303
kumaraditya303 approved these changes Dec 24, 2025
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Dec 24, 2025
@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
@bedevere-app bedevere-app Bot removed the awaiting merge label Dec 24, 2025
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@kumaraditya303 kumaraditya303 kumaraditya303 approved these changes
@mpage mpage Awaiting requested review from mpage
@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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@colesbury @kumaraditya303
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