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GeezerVison is showing github.com — gh-120321: Fix TSan reported race in gen_clear_frame by colesbury · Pull Request #142995 · python/cpython

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@colesbury

@colesbury colesbury commented Dec 19, 2025 •
edited by bedevere-app Bot
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TSan treats compare-exchanges that fail as if they are writes so there is a false positive with the read of gi_frame_state in gen_close.

  • Issue: SIGSEGV with generators in free-threaded build #120321

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@colesbury
pythongh-120321: Fix TSan reported race in gen_clear_frame
807c03f 
TSan treats compare-exchanges that fail as if they are writes
so there is a false positive with the read of gi_frame_state in
gen_close.
@colesbury
colesbury requested a review from mpage December 19, 2025 22:06
@colesbury
colesbury requested a review from markshannon as a code owner December 19, 2025 22:06
@colesbury colesbury added skip news topic-free-threading labels Dec 19, 2025
@bedevere-app bedevere-app Bot mentioned this pull request Dec 19, 2025
SIGSEGV with generators in free-threaded build #120321
Closed
@bedevere-app bedevere-app Bot added the awaiting core review label Dec 19, 2025
@colesbury

colesbury commented Dec 19, 2025

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I keep making this same mistake. This Should fix https://github.com/python/cpython/actions/runs/20383044472/job/58577900039?pr=142957:

WARNING: ThreadSanitizer: data race (pid=21767)
  Read of size 1 at 0x7f9ccb6ceb63 by thread T475:
    #0 gen_clear_frame /home/runner/work/cpython/cpython/Objects/genobject.c:156:5 (python+0x2afcde) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #1 gen_close /home/runner/work/cpython/cpython/Objects/genobject.c (python+0x2ac1d1) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #2 method_vectorcall_NOARGS /home/runner/work/cpython/cpython/Objects/descrobject.c:448:24 (python+0x289784) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #3 _PyObject_VectorcallTstate /home/runner/work/cpython/cpython/./Include/internal/pycore_call.h:136:11 (python+0x26a6ab) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
...

  Previous atomic write of size 1 at 0x7f9ccb6ceb63 by thread T472:
    #0 _Py_atomic_compare_exchange_int8 /home/runner/work/cpython/cpython/./Include/cpython/pyatomic_gcc.h:75:10 (python+0x2b0751) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #1 gen_send_ex /home/runner/work/cpython/cpython/Objects/genobject.c:327:15 (python+0x2b0751)
    #2 gen_iternext /home/runner/work/cpython/cpython/Objects/genobject.c:720:9 (python+0x2acf7c) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #3 _PyForIter_VirtualIteratorNext /home/runner/work/cpython/cpython/Python/ceval.c:4056:24 (python+0x520502) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
    #4 _PyEval_EvalFrameDefault /home/runner/work/cpython/cpython/Python/generated_cases.c.h:5500:36 (python+0x4f33f8) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)
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mpage
mpage approved these changes Dec 19, 2025
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Dec 19, 2025
@colesbury
colesbury merged commit 4ea3c1a into python:main Dec 19, 2025
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@colesbury
colesbury deleted the gh-120321-gen-atomic-close branch December 19, 2025 22:33
@bedevere-app bedevere-app Bot removed the awaiting merge label Dec 19, 2025
cocolato pushed a commit to cocolato/cpython that referenced this pull request Dec 22, 2025
@colesbury @cocolato
pythongh-120321: Fix TSan reported race in gen_clear_frame (pythongh-…
91f4bbd 
…142995)

TSan treats compare-exchanges that fail as if they are writes
so there is a false positive with the read of gi_frame_state in
gen_close.
@colesbury colesbury mentioned this pull request Dec 24, 2025
gh-120321: Fix TSan reported races on gi_frame_state #143128
Merged
@kumaraditya303 kumaraditya303 mentioned this pull request Jan 17, 2026
gh-143939: Fix assignment to _PyThreadStateImpl.generator_return_kind #143951
Merged
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@mpage mpage mpage approved these changes
@markshannon markshannon Awaiting requested review from markshannon markshannon is a code owner

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@colesbury @mpage
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