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GeezerVison is showing github.com — gh-117657: Quiet erroneous TSAN reports of data races in `_PySeqLock` by mpage · Pull Request #117955 · python/cpython

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@mpage

@mpage mpage commented Apr 17, 2024 •
edited by bedevere-app Bot
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TSAN reports a couple of data races between the compare/exchange in _PySeqLock_LockWrite:

cpython/Python/lock.c

Line 483 in a23fa33

else if (_Py_atomic_compare_exchange_uint32(&seqlock->sequence, &prev, prev + 1)) {

and the non-atomic loads in _PySeqLock_AbandonWrite (example race):

cpython/Python/lock.c

Lines 493 to 495 in a23fa33

void _PySeqLock_AbandonWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence - 1;

and _PySeqLock_UnlockWrite (example race):

cpython/Python/lock.c

Lines 500 to 502 in a23fa33

void _PySeqLock_UnlockWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence + 1;

This is another instance of TSAN incorrectly modeling failed compare/exchange as a write instead of a load.

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

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@mpage
Quiet erroneous TSAN reports of data races in _PySeqLock
a9907b8 
TSAN reports a couple of data races between the compare/exchange in
`_PySeqLock_LockWrite` and the non-atomic loads in `_PySeqLock_{Abandon,Unlock}Write`.
This is another instance of TSAN incorrectly modeling failed compare/exchange
as a write instead of a load.
@mpage mpage added the skip news label Apr 17, 2024
@mpage
mpage requested review from DinoV and colesbury April 17, 2024 04:40
@mpage
mpage marked this pull request as ready for review April 17, 2024 05:40
@bedevere-app bedevere-app Bot added the awaiting review label Apr 17, 2024
DinoV
DinoV approved these changes Apr 17, 2024
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LGTM!

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@bedevere-app bedevere-app Bot added awaiting merge and removed awaiting review labels Apr 17, 2024
@DinoV
Merge branch 'main' into pythongh-117657-seq-lock
778de8e
@ghost

ghost commented Apr 17, 2024 •
edited by ghost
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@bedevere-app bedevere-app Bot mentioned this pull request Apr 17, 2024
Make TSAN tests pass with the GIL disabled in free-threaded builds #117657
Closed
@DinoV
DinoV enabled auto-merge (squash) April 17, 2024 16:45
@DinoV
DinoV merged commit 0d29302 into python:main Apr 17, 2024
@bedevere-app bedevere-app Bot removed the awaiting merge label Apr 17, 2024
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@DinoV DinoV DinoV approved these changes
@colesbury colesbury Awaiting requested review from colesbury

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@mpage @DinoV
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