Xavier de Gaye added the comment:
When tstate->overflowed is already set to 1 before entering
PyErr_NormalizeException() to normalize an exception, the following cases may
occur:
1) Normalizing a built-in exception => instantiation ok.
2) Normalizing a python exception that fails with a built-in exception =>
next recursion of PyErr_NormalizeException() ok.
3) Normalizing a python exception that fails with a python exception that
fails with a python exception and so on infinitely...
=> PyObject_Call() never returns and the interpreter aborts with a fatal
error when the high warter mark is exceeded, the infinite recursion is in
PyObject_Call().
4) Normalizing a python exception defined in an extension module and the
instantiation returns NULL and sets the same exception:
a) Without any patch, we get a segfault caused by another bug in
PyErr_NormalizeException() at Py_DECREF(*val), just before setting val to
PyExc_RecursionErrorInst.
This is fixed by changing Py_DECREF(*val) to Py_XDECREF(*val).
With the above fix, we get the same abort as the one caused by
runtimerror_singleton_2.py, so this is another reproducer of the current issue.
b) The test is ok with patch warn_5.patch, and the above fix.
c) With patch remove_singleton.patch the interpreter aborts with a fatal
error when the high warter mark is exceeded, the infinite recursion is in
PyErr_NormalizeException().
Cases 3) and 4) can be tested with runtimerror_singleton_3.py (install mymodule
with setup.py for all three test cases in 4).
remove_singleton.patch introduces a regression in case c), but IMHO the abort
in case c) is consistent with the abort in case 3), they
are both related to a more general problem involving the low/high water mark
heuristic and described by Antoine in [1].
[1] http://thread.gmane.org/gmane.comp.python.devel/97016
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Added file: http://bugs.python.org/file37332/runtimerror_singleton_3.py
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