Data race reading `_thread.RLock` recursion count in `repr()` under free-threading

Bug report

Bug description:

This is a follow-up to #153292 (data race in repr() of _thread.RLock), which was fixed by making rlock_repr read the lock's owner with an atomic load. The fix covered the owner (self->lock.thread) field, but rlock_repr still reads self->lock.level with a plain (non-atomic) load to compute the recursion count:

https://github.com/python/cpython/blob/22a6c51c94a4fde986b8964f1d36d5ec3ac20dcc/Modules/_threadmodule.c#L1287-L1305

self->lock.level is written by acquire / release / _acquire_restore, e.g.:

https://github.com/python/cpython/blob/22a6c51c94a4fde986b8964f1d36d5ec3ac20dcc/Modules/_threadmodule.c#L1198-L1210

So on a free-threaded build, repr(rlock) concurrent with acquire() or release() is still a data race, now on the level field rather than the owner field the earlier fix addressed.

Reproducer:

import _thread
from threading import Thread, Barrier

shared_rlock = _thread.RLock()
state = (5, _thread.get_ident())

def chain1_thread():
    for _ in range(20000):
        try:
            shared_rlock._acquire_restore(state)
        except Exception:
            pass

def chain2_thread():
    for _ in range(20000):
        try:
            repr(shared_rlock)
        except Exception:
            pass

N_C1 = 2
N_C2 = 4
barrier = Barrier(N_C1 + N_C2)

def _c1():
    barrier.wait()
    chain1_thread()

def _c2():
    barrier.wait()
    chain2_thread()

threads  = [Thread(target=_c1) for _ in range(N_C1)]
threads += [Thread(target=_c2) for _ in range(N_C2)]
for t in threads: t.start()
for t in threads: t.join()

TSAN Report :

==================
WARNING: ThreadSanitizer: data race (pid=655652)
  Read of size 8 at 0x7fffb6610540 by thread T6:
    #0 rlock_repr /cpython/./Modules/_threadmodule.c:1295:28 
    #1 PyObject_Repr /cpython/Objects/object.c:784:11 
    #2 builtin_repr /cpython/Python/bltinmodule.c:2677:12 
    #3 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:2712:35  

  Previous write of size 8 at 0x7fffb6610540 by thread T1:
    #0 _thread_RLock__acquire_restore_impl /cpython/./Modules/_threadmodule.c:1210:22 
    #1 _thread_RLock__acquire_restore /cpython/./Modules/clinic/_threadmodule.c.h:537:20 
    #2 method_vectorcall_O /cpython/Objects/descrobject.c:476:24 
    #3 _PyObject_VectorcallTstate /cpython/./Include/internal/pycore_call.h:144:11 
    #4 PyObject_Vectorcall /cpython/Objects/call.c:327:12 
    #5 _Py_VectorCallInstrumentation_StackRefSteal /cpython/Python/ceval.c:768:11 
    #6 _PyEval_EvalFrameDefault /cpython/Python/generated_cases.c.h:1906:35

SUMMARY: ThreadSanitizer: data race /cpython/./Modules/_threadmodule.c:1295:28 in rlock_repr
==================

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155381

Bắt đầu trong Modules/_threadmodule.c tại rlock_repr và các phần triển khai acquire, release và _acquire_restore được mô tả trong báo cáo. Chạy reproducer được cung cấp trên một bản build free-threaded với ThreadSanitizer, sau đó kiểm tra các bài kiểm thử liên quan và xác minh rằng repr() chạy đồng thời và các cập nhật lock không còn báo cáo race.