https://github.com/python/cpython/commit/1d4f9ab0c66378790a2482b76d84462ef0d23cf2
commit: 1d4f9ab0c66378790a2482b76d84462ef0d23cf2
branch: 3.14
author: sobolevn <[email protected]>
committer: sobolevn <[email protected]>
date: 2026-05-21T09:53:54Z
summary:
[3.14] gh-149816: Fix a race condition in `_PyBytes_FromList` with
free-threading (GH-149909) (#149912)
(cherry picked from commit 46afba7b9324bc9492c3527d0fe47dd74f1f598c)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2026-05-16-11-03-54.gh-issue-149816.X_gqMT.rst
M Objects/bytesobject.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2026-05-16-11-03-54.gh-issue-149816.X_gqMT.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-16-11-03-54.gh-issue-149816.X_gqMT.rst
new file mode 100644
index 00000000000000..d35f0857a1aefe
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-16-11-03-54.gh-issue-149816.X_gqMT.rst
@@ -0,0 +1 @@
+Fix a race condition in ``_PyBytes_FromList`` in free-threading mode.
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index eb13f16f67295c..765589d679cce3 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -10,6 +10,7 @@
#include "pycore_global_objects.h"// _Py_GET_GLOBAL_OBJECT()
#include "pycore_initconfig.h" // _PyStatus_OK()
#include "pycore_long.h" // _PyLong_DigitValue
+#include "pycore_list.h" // _PyList_GetItemRef
#include "pycore_object.h" // _PyObject_GC_TRACK
#include "pycore_pymem.h" // PYMEM_CLEANBYTE
#include "pycore_strhex.h" // _Py_strhex_with_sep()
@@ -2866,7 +2867,6 @@ _PyBytes_FromList(PyObject *x)
Py_ssize_t i, size = PyList_GET_SIZE(x);
Py_ssize_t value;
char *str;
- PyObject *item;
_PyBytesWriter writer;
_PyBytesWriter_Init(&writer);
@@ -2877,8 +2877,10 @@ _PyBytes_FromList(PyObject *x)
size = writer.allocated;
for (i = 0; i < PyList_GET_SIZE(x); i++) {
- item = PyList_GET_ITEM(x, i);
- Py_INCREF(item);
+ PyObject *item = _PyList_GetItemRef((PyListObject *)x, i);
+ if (item == NULL) {
+ goto error;
+ }
value = PyNumber_AsSsize_t(item, NULL);
Py_DECREF(item);
if (value == -1 && PyErr_Occurred())
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