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gh-143100: Fix memcpy data race in setobject.c by colesbury · Pull Request #143127 · python/cpython · GitHub

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gh-143100: Fix memcpy data race in setobject.c #143127

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Merged
colesbury merged 1 commit into from
Dec 24, 2025
+16 −3
Conversation 1 Commits 1 Checks 52 Files changed 2
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gh-143100: Fix memcpy data race in setobject.c #143127

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16 changes: 16 additions & 0 deletions Objects/setobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1420,6 +1420,17 @@ set_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
return make_new_set(type, NULL);
}

#ifdef Py_GIL_DISABLED
static void
copy_small_table(setentry *dest, setentry *src)
{
for (Py_ssize_t i = 0; i < PySet_MINSIZE; i++) {
_Py_atomic_store_ptr_release(&dest[i].key, src[i].key);
_Py_atomic_store_ssize_relaxed(&dest[i].hash, src[i].hash);
}
}
#endif

/* set_swap_bodies() switches the contents of any two sets by moving their
internal data pointers and, if needed, copying the internal smalltables.
Semantically equivalent to:
Expand Down Expand Up @@ -1462,8 +1473,13 @@ set_swap_bodies(PySetObject *a, PySetObject *b)

if (a_table == a->smalltable || b_table == b->smalltable) {
memcpy(tab, a->smalltable, sizeof(tab));
#ifndef Py_GIL_DISABLED
memcpy(a->smalltable, b->smalltable, sizeof(tab));
memcpy(b->smalltable, tab, sizeof(tab));
#else
copy_small_table(a->smalltable, b->smalltable);
copy_small_table(b->smalltable, tab);
#endif
}

if (PyType_IsSubtype(Py_TYPE(a), &PyFrozenSet_Type) &&
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3 changes: 0 additions & 3 deletions Tools/tsan/suppressions_free_threading.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,3 @@ thread:pthread_create
# PyObject_Realloc internally does memcpy which isn't atomic so can race
# with non-locking reads. See #132070
race:PyObject_Realloc

# gh-143100: set_swap_bodies in setobject.c calls memcpy, which isn't atomic
race:set_swap_bodies
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