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GeezerVison is showing github.com — [gh-117657] _Py_MergeZeroLocalRefcount isn't loading ob_ref_shared with strong enough semantics by DinoV · Pull Request #118111 · python/cpython

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@DinoV

@DinoV DinoV commented Apr 19, 2024 •
edited by bedevere-app Bot
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In the nogil-integration branch there's some intermittent TSAN warnings like these:

https://gist.github.com/DinoV/52b7131cb149b9ebb2e965970c4ae9e8

It looks like we're racing on the loading of ob_ref_shared in _Py_MergeZeroLocalRefcount because we're doing a relaxed load, leading to the object potentially being freed while another thread holds a reference to it. This is occurring because with a lock-free read from the inline values there's no other synchronization points with the thread which owns the object.

This just changes the read to be acquire.

  • Issue: Make TSAN tests pass with the GIL disabled in free-threaded builds #117657

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@DinoV
Use acquire for load of ob_ref_shared
be49c36
@DinoV DinoV added skip news topic-free-threading labels Apr 19, 2024
@DinoV
DinoV requested a review from mpage April 19, 2024 19:26
@bedevere-app bedevere-app Bot mentioned this pull request Apr 19, 2024
Make TSAN tests pass with the GIL disabled in free-threaded builds #117657
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@bedevere-app bedevere-app Bot added the awaiting core review label Apr 19, 2024
@mpage

mpage commented Apr 19, 2024

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This looks right to me but it'd be good to have @colesbury take a look as well.
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mpage
mpage approved these changes Apr 19, 2024
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@mpage
mpage requested a review from colesbury April 19, 2024 19:36
colesbury
colesbury approved these changes Apr 19, 2024
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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting core review labels Apr 19, 2024
@DinoV
DinoV merged commit b45af00 into python:main Apr 19, 2024
@bedevere-app bedevere-app Bot removed the awaiting merge label Apr 19, 2024
@DinoV
DinoV deleted the nogil_tsan_decref branch May 31, 2024 18:22
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@mpage mpage mpage approved these changes
@colesbury colesbury colesbury approved these changes

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3 participants

@DinoV @mpage @colesbury
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