New submission from Jeethu Rao <jee...@jeethurao.com>:

In one of patches I'm building, (yet another attempt at caching 
LOAD_GLOBALS)[1], I'm using the private APIs from PEP 523 to store an array 
with every code object. I'm calling _PyEval_RequestCodeExtraIndex with 
PyMem_Free for the freefunc argument. While running  the cpython testsuite, I 
found that test_embed case crashes with a segfault. The gdb backtrace[2] seems 
to indicate that PyInterpreterState::co_extra_freefuncs is uninitialized, while 
it should be a pointer to the PyMem_Free function. 

One way to work around this is to set the array as a member on the PyCodeObject 
struct and use it directly. And I've verified that it works. Am I using the PEP 
523 private api correctly? Also, on Linux, this consistently crashes while on 
OSX, it occasionally doesn't crash which makes me wonder if it's some kind of a 
race condition involving Sub-interpreters. The attached gist[2] has steps for 
repro.

[1]: 
https://github.com/python/cpython/compare/master...jeethu:py3.7_load_global_cache
[2]: https://gist.github.com/jeethu/6d92185ca97dd692e7fadcd105e0ef70

----------
components: Interpreter Core
messages: 310191
nosy: jeethu
priority: normal
severity: normal
status: open
title: Uninitialized free_extra in code_dealloc
type: crash
versions: Python 3.7

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<https://bugs.python.org/issue32584>
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