gh-154014: Initialize cold executor vm_data fields

[BHUVANSH855]

Issue

Fixes gh-154014.

Summary

make_cold_executor() allocates cold executors directly via
allocate_executor() and bypasses _Py_ExecutorInit(). As a result,
vm_data.valid and vm_data.pending_deletion remain uninitialized.

During interpreter shutdown, interpreter_clear() asserts that
cold->vm_data.valid is true, causing assertion failures when CPython is
built with --enable-experimental-jit --with-assertions.

This change initializes the required vm_data fields for cold executors,
restoring the expected invariant during shutdown.

Testing

Reproduced the original crash reported in the issue using:

./configure --enable-experimental-jit --with-assertions
make -j$(nproc)

Before this change, _bootstrap_python aborted with:

Assertion `cold->vm_data.valid' failed.

After this change:

• make -j$(nproc) completes successfully.
• The full CPython regression test suite passes.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[Fidget-Spinner]

Looks good, just needs style cleanups.

[Fidget-Spinner]

Please add a news entry as well, and a test reproducer in Lib/test/test_capi/test_opt.py.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[BHUVANSH855]

Thanks for the review @Fidget-Spinner

I've addressed the requested changes:

• removed the stray formatting changes,
• added a NEWS entry,
• added a regression test in Lib/test/test_capi/test_opt.py.

The CI is now running on the updated branch. I'd appreciate another look when you have a chance. Thanks!

[cocolato]

we can release unregistered cold executors directly

[cocolato]

Thanks! let's wait for Ken Jin's review :)

[Fidget-Spinner]

@cocolato do you know if this fixes the reproducer on your system? If you're able to, can you please check? Really appreciate being able to outsource some of the work to you, thanks a lot!

[cocolato]

@cocolato do you know if this fixes the reproducer on your system? If you're able to, can you please check? Really appreciate being able to outsource some of the work to you, thanks a lot!

I have verified that the cold executor assertion in the issue has been fixed. I also reproduced a scenario where _PyJIT_Compile() fails; the original Py_DECREF(cold) would incorrectly call unlink_executor(), but this issue has been resolved by using _PyExecutor_Free(cold) instead.

[miss-islington-app]

Thanks @BHUVANSH855 for the PR, and @Fidget-Spinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-154457 is a backport of this pull request to the 3.15 branch.

[Fidget-Spinner]

Note: The SC has paused all JIT development with the exception of bugfixes. As this is a bugfix, I'm merging it.