gh-129732: Fix race in on shared->array in qsbr code under free-threa…

[hawkinsp]

…ding.

The read of shared->array should happen under the lock to avoid a race.

Fixes #129732

• Issue: Race between grow_thread_array and _Py_qsbr_reserve under free threading #129732

[colesbury]

This LGTM, just needs a NEWS blurb

[hawkinsp]

This LGTM, just needs a NEWS blurb

Done. I'm not sure how these normally look, let me know if you need something different.

[colesbury]

Thanks!

[miss-islington-app]

Thanks @hawkinsp for the PR, and @colesbury for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hawkinsp and @colesbury, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker b4ff8b22b3066b814c3758f87eaddfa923e657ed 3.13

[bedevere-app]

GH-129747 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 RHEL8 LTO 3.13 has failed when building commit f7cc862.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1393/builds/515) and take a look at the build logs.
4. Check if the failure is related to this commit (f7cc862) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1393/builds/515

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/threading.py", line 1041, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/threading.py", line 992, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/test/test_interpreters/test_stress.py", line 47, in run
    interp = interpreters.create()
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/test/support/interpreters/__init__.py", line 76, in create
    id = _interpreters.create(reqrefs=True)
interpreters.InterpreterError: interpreter creation failed
k


Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/threading.py", line 1041, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/threading.py", line 992, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/test/test_interpreters/test_stress.py", line 30, in task
    interp = interpreters.create()
  File "/home/buildbot/buildarea/3.13.cstratak-RHEL8-aarch64.lto/build/Lib/test/support/interpreters/__init__.py", line 76, in create
    id = _interpreters.create(reqrefs=True)
interpreters.InterpreterError: interpreter creation failed
k

[colesbury]

The buildbot failure looks unrelated. The modified file is only used in the free threading build and the failed buildbot is for the default (GIL-enabled) build.

EDIT: See #128381