[3.15] gh-153292: Fix data race in threading.RLock.__repr__ in FT builds (GH-153299) (#153314)

gh-153292: Fix data race in `threading.RLock.__repr__` in FT builds (GH-153299)
(cherry picked from commit 1051384)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Lib/test/test_free_threading/test_threading.py

@@ -0,0 +1,26 @@
+import unittest
+from test.support import threading_helper
+
+threading_helper.requires_working_threading(module=True)
+
+
+class TestRlock(unittest.TestCase):
+    def test_repr_race(self):
+        # gh-153292
+        import _thread
+        r = _thread.RLock()
+
+        def repr_thread():
+            for _ in range(2000):
+                repr(r)
+
+        def mutate_thread():
+            for _ in range(2000):
+                r.acquire()
+                r.release()
+
+        threading_helper.run_concurrently([repr_thread, mutate_thread])
+
+
+if __name__ == "__main__":
+    unittest.main()

Misc/NEWS.d/next/Library/2026-07-08-01-03-17.gh-issue-153292.oHDt3l.rst

@@ -0,0 +1 @@
+Fix data race in repr of :class:`threading.RLock` in free-threading build.

Modules/_threadmodule.c

@@ -1288,7 +1288,7 @@ static PyObject *
 rlock_repr(PyObject *op)
 {
     rlockobject *self = rlockobject_CAST(op);
-    PyThread_ident_t owner = self->lock.thread;
+    PyThread_ident_t owner = FT_ATOMIC_LOAD_ULLONG_RELAXED(self->lock.thread);
     int locked = rlock_locked_impl(self);
     size_t count;
     if (locked) {