Restore the original guard for list_get_item_ref's fast path, since it's

actually correct and the real problem was an incorrect assert. The fast path still contains notionally unsafe uses of memcpy/memmove, so add list_get_item_ref back to the TSan suppressions file.
Yhg1s · Feb 19, 2025 · Jan 8, 2025 · Jan 8, 2025 · Jan 9, 2025 · Jan 9, 2025
commit 661dc7bf4448fcb1ec6b437bc6559fef608fcab7
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -344,7 +344,7 @@ list_item_impl(PyListObject *self, Py_ssize_t idx)
 static inline PyObject*
 list_get_item_ref(PyListObject *op, Py_ssize_t i)
 {
-    if (!_Py_IsOwnedByCurrentThread((PyObject *)op)) {
+    if (!_Py_IsOwnedByCurrentThread((PyObject *)op) && !_PyObject_GC_IS_SHARED(op)) {
         return list_item_impl(op, i);
     }
     // Need atomic operation for the getting size.
@@ -357,7 +357,7 @@ list_get_item_ref(PyListObject *op, Py_ssize_t i)
         return NULL;
     }
     Py_ssize_t cap = list_capacity(ob_item);
-    assert(cap != -1 && cap >= size);
+    assert(cap != -1);
     if (!valid_index(i, cap)) {
         return NULL;
     }
@@ -937,7 +937,7 @@ list_ass_slice_lock_held(PyListObject *a, Py_ssize_t ilow, Py_ssize_t ihigh, PyO
     }
     for (k = 0; k < n; k++, ilow++) {
         PyObject *w = vitem[k];
-        item[ilow] = Py_XNewRef(w);
+        FT_ATOMIC_STORE_PTR_RELAXED(item[ilow], Py_XNewRef(w));
     }
     for (k = norig - 1; k >= 0; --k)
         Py_XDECREF(recycle[k]);

diff --git a/Tools/tsan/suppressions_free_threading.txt b/Tools/tsan/suppressions_free_threading.txt
@@ -29,6 +29,7 @@ race_top:add_threadstate
 race_top:dump_traceback
 race_top:fatal_error
 race_top:_multiprocessing_SemLock_release_impl
+race_top:list_get_item_ref
 race_top:_PyFrame_GetCode
 race_top:_PyFrame_Initialize
 race_top:PyInterpreterState_ThreadHead