[3.14] gh-143547: Fix PyErr_FormatUnraisable() fallback (#143557) (#143603)

gh-143547: Fix PyErr_FormatUnraisable() fallback (#143557)

Hold a strong reference to 'hook' while calling the default
unraisable took to log hook failure.

(cherry picked from commit 39a2bcf949095bd603f7b73f15b5b478dbb49ba9)

diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index e2117b9588dba26b066c5050a76f2519663373d8..4aeeac56b1aae39b41208f00efbc57396046305b 100644 (file)
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -1480,6 +1480,7 @@ class UnraisableHookTest(unittest.TestCase):
     def test_custom_unraisablehook_fail(self):
         _testcapi = import_helper.import_module('_testcapi')
         from _testcapi import err_writeunraisable
+
         def hook_func(*args):
             raise Exception("hook_func failed")
 

diff --git a/Misc/NEWS.d/next/Library/2026-01-08-14-53-46.gh-issue-143547.wHBVlr.rst b/Misc/NEWS.d/next/Library/2026-01-08-14-53-46.gh-issue-143547.wHBVlr.rst
new file mode 100644 (file)
index 0000000..934570b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-08-14-53-46.gh-issue-143547.wHBVlr.rst
@@ -0,0 +1,3 @@
+Fix :func:`sys.unraisablehook` when the hook raises an exception and changes
+:func:`sys.unraisablehook`: hold a strong reference to the old hook. Patch
+by Victor Stinner.

diff --git a/Python/errors.c b/Python/errors.c
index 89ea79f8c914fb88dbbf17e00aaa95c1ce580b3b..3fd97ea36b336833f7a5d621984593320dc5dd06 100644 (file)
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -1632,6 +1632,7 @@ format_unraisable_v(const char *format, va_list va, PyObject *obj)
     _Py_EnsureTstateNotNULL(tstate);
 
     PyObject *err_msg = NULL;
+    PyObject *hook = NULL;
     PyObject *exc_type, *exc_value, *exc_tb;
     _PyErr_Fetch(tstate, &exc_type, &exc_value, &exc_tb);
 
@@ -1676,7 +1677,6 @@ format_unraisable_v(const char *format, va_list va, PyObject *obj)
         goto error;
     }
 
-    PyObject *hook;
     if (_PySys_GetOptionalAttr(&_Py_ID(unraisablehook), &hook) < 0) {
         Py_DECREF(hook_args);
         err_msg_str = NULL;
@@ -1689,7 +1689,6 @@ format_unraisable_v(const char *format, va_list va, PyObject *obj)
     }
 
     if (_PySys_Audit(tstate, "sys.unraisablehook", "OO", hook, hook_args) < 0) {
-        Py_DECREF(hook);
         Py_DECREF(hook_args);
         err_msg_str = "Exception ignored in audit hook";
         obj = NULL;
@@ -1697,13 +1696,11 @@ format_unraisable_v(const char *format, va_list va, PyObject *obj)
     }
 
     if (hook == Py_None) {
-        Py_DECREF(hook);
         Py_DECREF(hook_args);
         goto default_hook;
     }
 
     PyObject *res = PyObject_CallOneArg(hook, hook_args);
-    Py_DECREF(hook);
     Py_DECREF(hook_args);
     if (res != NULL) {
         Py_DECREF(res);
@@ -1733,6 +1730,7 @@ done:
     Py_XDECREF(exc_value);
     Py_XDECREF(exc_tb);
     Py_XDECREF(err_msg);
+    Py_XDECREF(hook);
     _PyErr_Clear(tstate); /* Just in case */
 }