Creating a subinterpreter when Python is run with -X tracemalloc leads to segfault

Crash report

What happened?

Minimal reproducer:

import _interpreters

_interpreters.create()

python -X tracemalloc subtest.py

This also fails if one submits a task to concurrent.futures.InterpreterPoolExecutor.

Example output when run with -X tracemalloc:

Python/tracemalloc.c:705: _Py_NegativeRefcount: Assertion failed: object has negative ref count
<object at 0x200041899d0 is freed>
Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: finalizing (tstate=0x0000559f74721680)

Stack (most recent call first):
  <no Python frame>
Aborted (core dumped)

That points here:
https://github.com/python/cpython/blob/f478331f98930d94f7efc741f3bed4b693d5cec1/Python/tracemalloc.c#L701-L706

I presume the issue is that the filename is not populated for the subinterpreter?

I'm on Ubuntu 24.04 on an x86_64 machine if that makes a difference. My latest configure command line is:

./configure --config-cache --with-pydebug --disable-gil CC=clang-20

Note that this also reproduces with the GIL enabled, (but it just outputs an unhelpful "segmentation fault").

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.15.0a0 experimental free-threading build (heads/main:f478331f989, May 23 2025, 16:17:11) [Clang 20.1.5 (++20250430014901+ebfae55af454-1exp120250430014920.111)]

Linked PRs

• gh-134667

Review linked PR gh-134667 first, then inspect Python/tracemalloc.c around lines 701-706 and reproduce with the _interpreters.create() script under -X tracemalloc. Done means creating a subinterpreter, including through InterpreterPoolExecutor, no longer triggers the assertion or segmentation fault.