gh-128130: Fix unhandled keyboard interrupt data race (gh-129975)

Use an atomic operation when setting
`_PyRuntime.signals.unhandled_keyboard_interrupt`. We now only clear the
variable at the start of `_PyRun_Main`, which is the same function where
we check it.

This avoids race conditions where previously another thread might call
`run_eval_code_obj()` and erroneously clear the unhandled keyboard
interrupt.

1 files changed, 8 insertions, 25 deletions

diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index ae0df9685ac..945e267ef72 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -589,8 +589,13 @@ parse_exit_code(PyObject *code, int *exitcode_p)
 }
 
 int
-_Py_HandleSystemExit(int *exitcode_p)
+_Py_HandleSystemExitAndKeyboardInterrupt(int *exitcode_p)
 {
+    if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
+        _Py_atomic_store_int(&_PyRuntime.signals.unhandled_keyboard_interrupt, 1);
+        return 0;
+    }
+
     int inspect = _Py_GetConfig()->inspect;
     if (inspect) {
         /* Don't exit if -i flag was given. This flag is set to 0
@@ -646,7 +651,7 @@ static void
 handle_system_exit(void)
 {
     int exitcode;
-    if (_Py_HandleSystemExit(&exitcode)) {
+    if (_Py_HandleSystemExitAndKeyboardInterrupt(&exitcode)) {
         Py_Exit(exitcode);
     }
 }
@@ -1105,8 +1110,6 @@ _PyErr_Display(PyObject *file, PyObject *unused, PyObject *value, PyObject *tb)
         }
     }
 
-    int unhandled_keyboard_interrupt = _PyRuntime.signals.unhandled_keyboard_interrupt;
-
     // Try first with the stdlib traceback module
     PyObject *print_exception_fn = PyImport_ImportModuleAttrString(
         "traceback",
@@ -1120,11 +1123,9 @@ _PyErr_Display(PyObject *file, PyObject *unused, PyObject *value, PyObject *tb)
     Py_XDECREF(print_exception_fn);
     if (result) {
         Py_DECREF(result);
-        _PyRuntime.signals.unhandled_keyboard_interrupt = unhandled_keyboard_interrupt;
         return;
     }
 fallback:
-    _PyRuntime.signals.unhandled_keyboard_interrupt = unhandled_keyboard_interrupt;
 #ifdef Py_DEBUG
      if (PyErr_Occurred()) {
          PyErr_FormatUnraisable(
@@ -1297,20 +1298,6 @@ flush_io(void)
 static PyObject *
 run_eval_code_obj(PyThreadState *tstate, PyCodeObject *co, PyObject *globals, PyObject *locals)
 {
-    PyObject *v;
-    /*
-     * We explicitly re-initialize _Py_UnhandledKeyboardInterrupt every eval
-     * _just in case_ someone is calling into an embedded Python where they
-     * don't care about an uncaught KeyboardInterrupt exception (why didn't they
-     * leave config.install_signal_handlers set to 0?!?) but then later call
-     * Py_Main() itself (which _checks_ this flag and dies with a signal after
-     * its interpreter exits).  We don't want a previous embedded interpreter's
-     * uncaught exception to trigger an unexplained signal exit from a future
-     * Py_Main() based one.
-     */
-    // XXX Isn't this dealt with by the move to _PyRuntimeState?
-    _PyRuntime.signals.unhandled_keyboard_interrupt = 0;
-
     /* Set globals['__builtins__'] if it doesn't exist */
     if (!globals || !PyDict_Check(globals)) {
         PyErr_SetString(PyExc_SystemError, "globals must be a real dict");
@@ -1328,11 +1315,7 @@ run_eval_code_obj(PyThreadState *tstate, PyCodeObject *co, PyObject *globals, Py
         }
     }
 
-    v = PyEval_EvalCode((PyObject*)co, globals, locals);
-    if (!v && _PyErr_Occurred(tstate) == PyExc_KeyboardInterrupt) {
-        _PyRuntime.signals.unhandled_keyboard_interrupt = 1;
-    }
-    return v;
+    return PyEval_EvalCode((PyObject*)co, globals, locals);
 }
 
 static PyObject *