Bug report

Bug description:

In the free-threaded build, new_threadstate() reserves a QSBR thread-state slot and a TLBC index before it can fail for other reasons, but the failure paths only free the _PyThreadStateImpl.

Found while reviewing GH-148953. I think explaining the monotonic memory growth in the corresponding issue is unlikely, since this leak only happens in the failure case. Still good to fix though.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155363: Fix QSBR slot leak on thread state creation failure #155365
• [3.15] gh-155363: Fix QSBR slot leak on thread state creation failure (gh-155365) #155579