Bug report

There's a race on tstate->c_profilefunc if profiling is disable concurrently via sys._setprofileallthreads or threading.setprofile_all_threads or PyEval_SetProfileAllThreads.

	static PyObject *
	call_profile_func(_PyLegacyEventHandler self, PyObject arg)
	{
	PyThreadState *tstate = _PyThreadState_GET();
	if (tstate->c_profilefunc == NULL) {
	Py_RETURN_NONE;
	}
	PyFrameObject *frame = PyEval_GetFrame();
	if (frame == NULL) {
	PyErr_SetString(PyExc_SystemError,
	"Missing frame when calling profile function.");
	return NULL;
	}
	Py_INCREF(frame);
	int err = tstate->c_profilefunc(tstate->c_profileobj, frame, self->event, arg);
	Py_DECREF(frame);
	if (err) {
	return NULL;
	}
	Py_RETURN_NONE;
	}

Repro

import sys
import threading
done = threading.Event()
def foo():
    pass
def my_profile(frame, event, arg):
    return None
def bg_thread():
    while not done.is_set():
        foo()
        foo()
        foo()
        foo()
        foo()
        foo()
        foo()
        foo()
        foo()
        foo()
def main():
    bg_threads = []
    for i in range(10):
        t = threading.Thread(target=bg_thread)
        t.start()
        bg_threads.append(t)
    for i in range(100):
        print(f"Iteration {i}")
        sys._setprofileallthreads(my_profile)
        sys._setprofileallthreads(None)
    done.set()
    for t in bg_threads:
        t.join()
if __name__ == "__main__":
    main()

Bug report

Repro

Linked PRs