[issue32584] Uninitialized free_extra in code_dealloc

[Jeethu Rao]

New submission from Jeethu Rao <jeethu at 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

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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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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32584>
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