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gh-132869: Fix crash due to memory ordering problem in dictobject und… #133593

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gh-132869: Fix crash due to memory ordering problem in dictobject und… #133593

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-05-08-12-07-56.gh-issue-132869.SpSN9s.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Fixed a crash from concurrent reads and writes to a dictionary under
free-threading.
13 changes: 6 additions & 7 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -168,8 +168,8 @@ ASSERT_DICT_LOCKED(PyObject *op)

#define IS_DICT_SHARED(mp) _PyObject_GC_IS_SHARED(mp)
#define SET_DICT_SHARED(mp) _PyObject_GC_SET_SHARED(mp)
#define LOAD_INDEX(keys, size, idx) _Py_atomic_load_int##size##_relaxed(&((const int##size##_t*)keys->dk_indices)[idx]);
#define STORE_INDEX(keys, size, idx, value) _Py_atomic_store_int##size##_relaxed(&((int##size##_t*)keys->dk_indices)[idx], (int##size##_t)value);
#define LOAD_INDEX(keys, size, idx) _Py_atomic_load_int##size(&((const int##size##_t*)keys->dk_indices)[idx]);
#define STORE_INDEX(keys, size, idx, value) _Py_atomic_store_int##size(&((int##size##_t*)keys->dk_indices)[idx], (int##size##_t)value);
#define ASSERT_OWNED_OR_SHARED(mp) \
assert(_Py_IsOwnedByCurrentThread((PyObject *)mp) || IS_DICT_SHARED(mp));

Expand Down Expand Up @@ -1734,8 +1734,6 @@ insert_combined_dict(PyInterpreterState *interp, PyDictObject *mp,
FT_ATOMIC_STORE_UINT32_RELAXED(mp->ma_keys->dk_version, 0);

Py_ssize_t hashpos = find_empty_slot(mp->ma_keys, hash);
dictkeys_set_index(mp->ma_keys, hashpos, mp->ma_keys->dk_nentries);

if (DK_IS_UNICODE(mp->ma_keys)) {
PyDictUnicodeEntry *ep;
ep = &DK_UNICODE_ENTRIES(mp->ma_keys)[mp->ma_keys->dk_nentries];
Expand All @@ -1749,6 +1747,7 @@ insert_combined_dict(PyInterpreterState *interp, PyDictObject *mp,
STORE_VALUE(ep, value);
STORE_HASH(ep, hash);
}
dictkeys_set_index(mp->ma_keys, hashpos, mp->ma_keys->dk_nentries);
STORE_KEYS_USABLE(mp->ma_keys, mp->ma_keys->dk_usable - 1);
STORE_KEYS_NENTRIES(mp->ma_keys, mp->ma_keys->dk_nentries + 1);
assert(mp->ma_keys->dk_usable >= 0);
Expand Down Expand Up @@ -1776,9 +1775,9 @@ insert_split_key(PyDictKeysObject *keys, PyObject *key, Py_hash_t hash)
FT_ATOMIC_STORE_UINT32_RELAXED(keys->dk_version, 0);
Py_ssize_t hashpos = find_empty_slot(keys, hash);
ix = keys->dk_nentries;
dictkeys_set_index(keys, hashpos, ix);
PyDictUnicodeEntry *ep = &DK_UNICODE_ENTRIES(keys)[ix];
STORE_SHARED_KEY(ep->me_key, Py_NewRef(key));
dictkeys_set_index(keys, hashpos, ix);
split_keys_entry_added(keys);
}
assert (ix < SHARED_KEYS_MAX_SIZE);
Expand Down Expand Up @@ -1906,7 +1905,6 @@ insert_to_emptydict(PyInterpreterState *interp, PyDictObject *mp,
assert(mp->ma_values == NULL);

size_t hashpos = (size_t)hash & (PyDict_MINSIZE-1);
dictkeys_set_index(newkeys, hashpos, 0);
if (unicode) {
PyDictUnicodeEntry *ep = DK_UNICODE_ENTRIES(newkeys);
ep->me_key = key;
Expand All @@ -1918,6 +1916,7 @@ insert_to_emptydict(PyInterpreterState *interp, PyDictObject *mp,
ep->me_hash = hash;
STORE_VALUE(ep, value);
}
dictkeys_set_index(newkeys, hashpos, 0);
STORE_USED(mp, mp->ma_used + 1);
newkeys->dk_usable--;
newkeys->dk_nentries++;
Expand Down Expand Up @@ -2736,7 +2735,6 @@ delitem_common(PyDictObject *mp, Py_hash_t hash, Py_ssize_t ix,
}
else {
FT_ATOMIC_STORE_UINT32_RELAXED(mp->ma_keys->dk_version, 0);
dictkeys_set_index(mp->ma_keys, hashpos, DKIX_DUMMY);
if (DK_IS_UNICODE(mp->ma_keys)) {
PyDictUnicodeEntry *ep = &DK_UNICODE_ENTRIES(mp->ma_keys)[ix];
old_key = ep->me_key;
Expand All @@ -2750,6 +2748,7 @@ delitem_common(PyDictObject *mp, Py_hash_t hash, Py_ssize_t ix,
STORE_VALUE(ep, NULL);
STORE_HASH(ep, 0);
}
dictkeys_set_index(mp->ma_keys, hashpos, DKIX_DUMMY);
Py_DECREF(old_key);
}
Py_DECREF(old_value);
Expand Down
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