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[3.13] gh-117657: Fix data races when writing / reading ob_gc_bits (GH-118292) (#118796)

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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.
(cherry picked from commit cb6f75a32c)

Co-authored-by: mpage <mpage@meta.com>
This commit is contained in:
Miss Islington (bot) 2024-05-08 23:31:37 +02:00 • committed by GitHub
parent 8f31af68d0
commit 7b9ca26812
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4 changed files with 45 additions and 16 deletions
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Objects/object.c
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@ -2431,6 +2431,7 @@ _PyObject_SetDeferredRefcount(PyObject *op)
assert(PyType_IS_GC(Py_TYPE(op)));
assert(_Py_IsOwnedByCurrentThread(op));
assert(op->ob_ref_shared == 0);
_PyObject_SET_GC_BITS(op, _PyGC_BITS_DEFERRED);
PyInterpreterState *interp = _PyInterpreterState_GET();
if (interp->gc.immortalize.enabled) {
// gh-117696: immortalize objects instead of using deferred reference
@ -2438,7 +2439,6 @@ _PyObject_SetDeferredRefcount(PyObject *op)
_Py_SetImmortal(op);
return;
}
op->ob_gc_bits |= _PyGC_BITS_DEFERRED;
op->ob_ref_local += 1;
op->ob_ref_shared = _Py_REF_QUEUED;
#endif