[3.14] pythongh-143880: Fix data race in functools.partial in free threading build (python#143882)

colesbury · web-flow · commit 0042384bd56c · 2026-01-16T22:25:40.000+05:30
pythongh-143880: Fix data race in `functools.partial` in free threading build The assignment to `pto->vectorcall` isn't thread-safe in the free threading build. Note that this is already fixed in the main branch.
diff --git a/Misc/NEWS.d/next/Library/2026-01-15-13-03-22.gh-issue-143880.sWoLsf.rst b/Misc/NEWS.d/next/Library/2026-01-15-13-03-22.gh-issue-143880.sWoLsf.rst
@@ -0,0 +1 @@
+Fix data race in :func:`functools.partial` in the :term:`free threading` build.
diff --git a/Modules/_functoolsmodule.c b/Modules/_functoolsmodule.c
@@ -375,7 +375,9 @@ partial_vectorcall_fallback(PyThreadState *tstate, partialobject *pto,
                             PyObject *const *args, size_t nargsf,
                             PyObject *kwnames)
 {
+#ifndef Py_GIL_DISABLED
     pto->vectorcall = NULL;
+#endif
     Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
     return _PyObject_MakeTpCall(tstate, (PyObject *)pto, args, nargs, kwnames);
 }

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	+Fix data race in :func:`functools.partial` in the :term:`free threading` build.
Original file line number	Diff line number	Diff line change
`@@ -375,7 +375,9 @@ partial_vectorcall_fallback(PyThreadState tstate, partialobject pto,`
`375`	`375`	`PyObject const args, size_t nargsf,`
`376`	`376`	`PyObject *kwnames)`
`377`	`377`	`{`
	`378`	`+#ifndef Py_GIL_DISABLED`
`378`	`379`	`pto->vectorcall = NULL;`
	`380`	`+#endif`
`379`	`381`	`Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);`
`380`	`382`	`return _PyObject_MakeTpCall(tstate, (PyObject *)pto, args, nargs, kwnames);`
`381`	`383`	`}`