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sys._setprofileallthreads race condition #137400

Description

@colesbury

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()

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    3.13bugs and security fixes3.14bugs and security fixes3.15pre-release feature fixes, bugs and security fixesinterpreter-core(Objects, Python, Grammar, and Parser dirs)topic-free-threadingtype-bugAn unexpected behavior, bug, or error

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