gh-117657: Fix data races when writing / reading ob_gc_bits #118292
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Use relaxed atomics when reading / writing to the field. There are still a few places in the GC where we do not use atomics. Those should be safe as the world is stopped. Sample races reported by TSAN: * [Race between `_PyObject_GC_IS_SHARED()` and `_PyObject_GC_SET_SHARED()`](https://gist.github.com/mpage/ebfd022773f39c33bec68c0993a2249e) * [Race between `_PyObject_GC_TRACK()` and `_PyObject_GC_IS_SHARED()`](https://gist.github.com/mpage/b53b5c22a2f923bf1571b887bb31ef88)
colesbury reviewed Apr 25, 2024
colesbury approved these changes May 8, 2024
| Thanks @mpage for the PR, and @colesbury for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13. |
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request May 8, 2024
…ythonGH-118292) Use relaxed atomics when reading / writing to the field. There are still a few places in the GC where we do not use atomics. Those should be safe as the world is stopped. (cherry picked from commit cb6f75a) Co-authored-by: mpage <mpage@meta.com>
| GH-118796 is a backport of this pull request to the 3.13 branch. |
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Use relaxed atomics when reading / writing to the field. There are still a few places in the GC where we do not use atomics. Those should be safe as the world is stopped.
Sample races reported by TSAN:
_PyObject_GC_IS_SHARED()and_PyObject_GC_SET_SHARED()_PyObject_GC_TRACK()and_PyObject_GC_IS_SHARED()