[issue31166] null pointer deref and segfault in _PyObject_Alloc (obmalloc.c:1258)

[INADA Naoki]

INADA Naoki added the comment:

As Benjamin commented, this is caused by mutating internal dict.

PyType_Lookup() use "method cache", based on "tp_version_tag" in the type object.
When you modify internal dict directly, namespace is changed without
invalidating tp_version_tag.
So cached pointer is used, and it's already deallocated.

I don't know we should fix it or not.
I don't have any idea fix this without any performance penalty.

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<http://bugs.python.org/issue31166>
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