8000 gh-130019: Fix data race in _PyType_AllocNoTrack by colesbury · Pull Request #130058 · python/cpython · GitHub
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gh-130019: Fix data race in _PyType_AllocNoTrack #130058

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Merged
merged 2 commits into from
Feb 13, 2025
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gh-130019: Fix data race in _PyType_AllocNoTrack #130058

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78e40c8
gh-130019: Fix data race in _PyType_AllocNoTrack
colesbury Feb 12, 2025
7131774
Update Objects/typeobject.c
colesbury Feb 13, 2025
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gh-130019: Fix data race in _PyType_AllocNoTrack 
The reference count fields, such as `ob_tid` and `ob_ref_shared`, may be
accessed concurrently in the free threading build by a `_Py_TryXGetRef`
or similar operation. The PyObject header fields will be initialized by
`_PyObject_Init`, so only call `memset()` to zero-initialize the remainder
of the allocation.
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@colesbury
colesbury committed Feb 12, 2025
commit 78e40c86a1ae8da39766cfe25423ccc753183750
4 changes: 3 additions & 1 deletion Objects/typeobject.c
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Expand Up @@ -2251,7 +2251,9 @@ _PyType_AllocNoTrack(PyTypeObject *type, Py_ssize_t nitems)
if (PyType_IS_GC(type)) {
_PyObject_GC_Link(obj);
}
memset(obj, '\0', size);
// Zero out the object after the PyObject header. The header fields are
// initialized by _PyObject_Init[Var]().
memset((char *)obj + sizeof(PyObject), '\0', size - sizeof(PyObject));

if (type->tp_itemsize == 0) {
_PyObject_Init(obj, type);
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5 changes: 3 additions & 2 deletions Python/gc.c
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Expand Up @@ -2309,11 +2309,12 @@ PyObject *
PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
{
size_t presize = _PyType_PreHeaderSize(tp);
PyObject *op = gc_alloc(tp, _PyObject_SIZE(tp) + extra_size, presize);
size_t size = _PyObject_SIZE(tp) + extra_size;
PyObject *op = gc_alloc(tp, size, presize);
if (op == NULL) {
return NULL;
}
memset(op, 0, _PyObject_SIZE(tp) + extra_size);
memset((char *)op + sizeof(PyObject), 0, size - sizeof(PyObject));
_PyObject_Init(op, tp);
return op;
}
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5 changes: 3 additions & 2 deletions Python/gc_free_threading.c
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Expand Up @@ -2593,11 +2593,12 @@ PyObject *
PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
{
size_t presize = _PyType_PreHeaderSize(tp);
PyObject *op = gc_alloc(tp, _PyObject_SIZE(tp) + extra_size, presize);
size_t size = _PyObject_SIZE(tp) + extra_size;
PyObject *op = gc_alloc(tp, size, presize);
if (op == NULL) {
return NULL;
}
memset(op, 0, _PyObject_SIZE(tp) + extra_size);
memset((char *)op + sizeof(PyObject), 0, size - sizeof(PyObject));
_PyObject_Init(op, tp);
return op;
}
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