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bpo-46025: Fix a crash in the atexit module for auto-unregistering functions #30002

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Merged
pablogsal merged 3 commits into from
Dec 9, 2021
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bpo-46025: Fix a crash in the atexit module for auto-unregistering functions #30002

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002b033
bpo-46025: Fix a crash in the atexit module for auto-unregistering fu…
pablogsal Dec 9, 2021
ebc949b
Update Modules/atexitmodule.c
pablogsal Dec 9, 2021
ec3741e
Update Modules/atexitmodule.c
pablogsal Dec 9, 2021
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15 changes: 15 additions & 0 deletions Lib/test/_test_atexit.py
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Original file line number Diff line number Diff line change
Expand Up @@ -116,6 +116,21 @@ def test_bound_methods(self):
atexit._run_exitfuncs()
self.assertEqual(l, [5])

def test_atexit_with_unregistered_function(self):
# See bpo-46025 for more info
def func():
atexit.unregister(func)
1/0
atexit.register(func)
try:
with support.catch_unraisable_exception() as cm:
atexit._run_exitfuncs()
self.assertEqual(cm.unraisable.object, func)
self.assertEqual(cm.unraisable.exc_type, ZeroDivisionError)
self.assertEqual(type(cm.unraisable.exc_value), ZeroDivisionError)

@vstinner vstinner Dec 9, 2021

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Not sure if checking exc_value is needed, but it's ok to test it :-)

@pablogsal pablogsal Dec 9, 2021

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This makes it a military-grade test :)

finally:
atexit.unregister(func)


if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-12-09-11-41-35.bpo-46025.pkEvW9.rst
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@@ -0,0 +1,2 @@
Fix a crash in the :mod:`atexit` module involving functions that unregister
themselves before raising exceptions. Patch by Pablo Galindo.
5 changes: 4 additions & 1 deletion Modules/atexitmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,13 +93,16 @@ atexit_callfuncs(struct atexit_state *state)
continue;
}

// bpo-46025: Increment the refcount of cb->func as the call itself may unregister it
PyObject* the_func = Py_NewRef(cb->func);
PyObject *res = PyObject_Call(cb->func, cb->args, cb->kwargs);
if (res == NULL) {
_PyErr_WriteUnraisableMsg("in atexit callback", cb->func);
_PyErr_WriteUnraisableMsg("in atexit callback", the_func);
}
else {
Py_DECREF(res);
}
Py_DECREF(the_func);
}

atexit_cleanup(state);
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