https://github.com/python/cpython/commit/19c72d23fd99292dd33d9cae85661df848f6cf43
commit: 19c72d23fd99292dd33d9cae85661df848f6cf43
branch: main
author: Neil Schemenauer <[email protected]>
committer: nascheme <[email protected]>
date: 2025-12-14T20:27:37-08:00
summary:
gh-132657: Use stronger memory ordering for so->mask. (gh-142735)
We need to use release/acquire ordering for the 'mask' member of the set
structure. Without this, `set_lookkey_threadsafe()` could be looking at
the old value of `table` but the new value of `mask`.
files:
M Objects/setobject.c
diff --git a/Objects/setobject.c b/Objects/setobject.c
index 2c585da1c43a78..5f868c858273ee 100644
--- a/Objects/setobject.c
+++ b/Objects/setobject.c
@@ -445,7 +445,7 @@ set_lookkey_threadsafe(PySetObject *so, PyObject *key,
Py_hash_t hash)
}
ensure_shared_on_read(so);
setentry *table = FT_ATOMIC_LOAD_PTR_ACQUIRE(so->table);
- size_t mask = FT_ATOMIC_LOAD_SSIZE_RELAXED(so->mask);
+ size_t mask = FT_ATOMIC_LOAD_SSIZE_ACQUIRE(so->mask);
if (table == NULL || table != FT_ATOMIC_LOAD_PTR_ACQUIRE(so->table)) {
return set_lookkey(so, key, hash, &entry);
}
@@ -532,7 +532,7 @@ set_table_resize(PySetObject *so, Py_ssize_t minused)
assert(newtable != oldtable);
set_zero_table(newtable, newsize);
FT_ATOMIC_STORE_PTR_RELEASE(so->table, NULL);
- FT_ATOMIC_STORE_SSIZE_RELAXED(so->mask, newsize - 1);
+ FT_ATOMIC_STORE_SSIZE_RELEASE(so->mask, newsize - 1);
/* Copy the data over; this is refcount-neutral for active entries;
dummy entries aren't copied over, of course */
@@ -634,7 +634,7 @@ set_empty_to_minsize(PySetObject *so)
set_zero_table(so->smalltable, PySet_MINSIZE);
so->fill = 0;
FT_ATOMIC_STORE_SSIZE_RELAXED(so->used, 0);
- FT_ATOMIC_STORE_SSIZE_RELAXED(so->mask, PySet_MINSIZE - 1);
+ FT_ATOMIC_STORE_SSIZE_RELEASE(so->mask, PySet_MINSIZE - 1);
FT_ATOMIC_STORE_SSIZE_RELAXED(so->hash, -1);
FT_ATOMIC_STORE_PTR_RELEASE(so->table, so->smalltable);
}
@@ -1449,8 +1449,8 @@ set_swap_bodies(PySetObject *a, PySetObject *b)
FT_ATOMIC_STORE_SSIZE_RELAXED(a->used, b->used);
FT_ATOMIC_STORE_SSIZE_RELAXED(b->used, t);
t = a->mask;
- FT_ATOMIC_STORE_SSIZE_RELAXED(a->mask, b->mask);
- FT_ATOMIC_STORE_SSIZE_RELAXED(b->mask, t);
+ FT_ATOMIC_STORE_SSIZE_RELEASE(a->mask, b->mask);
+ FT_ATOMIC_STORE_SSIZE_RELEASE(b->mask, t);
u = a_table;
if (a_table == a->smalltable)
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