--disable-gil --enable-experimental-jit=yes-off: test_jit_is_active fails

Bug report

Bug description:

Hello.

When we started to build the JIT in Fedora's Python, we didn't do it for the freethreading build, as I was told it's not yet ready. I circled back to the referenced issue https://github.com/python/cpython/issues/118844 and saw it is long closed. Hence, I tried to build the JIT with the freethreading build as well. It builds fine, but the tests fail:

Re-running test_sys in verbose mode (matching: test_jit_is_active)
test_jit_is_active (test.test_sys.TestSysJIT.test_jit_is_active) ... FAIL
======================================================================
FAIL: test_jit_is_active (test.test_sys.TestSysJIT.test_jit_is_active)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/builddir/build/BUILD/python3.15-3.15.0_a2-build/Python-3.15.0a2/Lib/test/test_sys.py", line 2275, in test_jit_is_active
    assert_python_ok("-c", script.format(enabled=available), PYTHON_JIT="1")
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/python3.15-3.15.0_a2-build/Python-3.15.0a2/Lib/test/support/script_helper.py", line 182, in assert_python_ok
    return _assert_python(True, *args, **env_vars)
  File "/builddir/build/BUILD/python3.15-3.15.0_a2-build/Python-3.15.0a2/Lib/test/support/script_helper.py", line 167, in _assert_python
    res.fail(cmd_line)
    ~~~~~~~~^^^^^^^^^^
  File "/builddir/build/BUILD/python3.15-3.15.0_a2-build/Python-3.15.0a2/Lib/test/support/script_helper.py", line 80, in fail
    raise AssertionError(f"Process return code is {exitcode}\n"
    ...<10 lines>...
                         f"---")
AssertionError: Process return code is 1
command line: ['/builddir/build/BUILD/python3.15-3.15.0_a2-build/Python-3.15.0a2/build/freethreading-debug/python', '-X', 'faulthandler', '-c', '\nimport _testcapi\nimport _testinternalcapi\nimport sys\n\ndef frame_0_interpreter() -> None:\n    assert sys._jit.is_active() is False\n\ndef frame_1_interpreter() -> None:\n    assert sys._jit.is_active() is False\n    frame_0_interpreter()\n    assert sys._jit.is_active() is False\n\ndef frame_2_jit(expected: bool) -> None:\n    # Inlined into the last loop of frame_3_jit:\n    assert sys._jit.is_active() is expected\n    # Insert C frame:\n    _testcapi.pyobject_vectorcall(frame_1_interpreter, None, None)\n    assert sys._jit.is_active() is expected\n\ndef frame_3_jit() -> None:\n    # JITs just before the last loop:\n    # 1 extra iteration for tracing.\n    for i in range(_testinternalcapi.TIER2_THRESHOLD + 2):\n        # Careful, doing this in the reverse order breaks tracing:\n        expected = True and i >= _testinternalcapi.TIER2_THRESHOLD + 1\n        assert sys._jit.is_active() is expected\n        frame_2_jit(expected)\n        assert sys._jit.is_active() is expected\n\ndef frame_4_interpreter() -> None:\n    assert sys._jit.is_active() is False\n    frame_3_jit()\n    assert sys._jit.is_active() is False\n\nassert sys._jit.is_active() is False\nframe_4_interpreter()\nassert sys._jit.is_active() is False\n']
stdout:
---
---
stderr:
---
Traceback (most recent call last):
  File "<string>", line 37, in <module>
    frame_4_interpreter()
    ~~~~~~~~~~~~~~~~~~~^^
  File "<string>", line 33, in frame_4_interpreter
    frame_3_jit()
    ~~~~~~~~~~~^^
  File "<string>", line 27, in frame_3_jit
    assert sys._jit.is_active() is expected
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError
---
----------------------------------------------------------------------
Ran 1 test in 0.672s
FAILED (failures=1)
test test_sys failed
1 test failed again:
    test_sys
== Tests result: FAILURE then FAILURE ==

This is a build --with-pydebug --disable-gil --enable-experimental-jit=yes-off. An optimized build without pydebug behaves the same way. I am also testing with Python 3.14.

A full log with testinfo: build.log

The same test failure happens both on x86_64 and aarch64 Fedora. This is 3.15.0a2.

CPython versions tested on:

3.15

Operating systems tested on:

Linux

Start with Lib/test/test_sys.py and TestSysJIT.test_jit_is_active, then reproduce the failure using --with-pydebug --disable-gil --enable-experimental-jit=yes-off. Compare the reported behavior on freethreading builds with the test's expected JIT state across the traced loop and interpreter calls. Done means the test passes for the affected build configurations on the reported architectures.