From 1407cda1bb8eb3a2af42efd982aec38677c76566 Mon Sep 17 00:00:00 2001
From: edward_xu <xuxiangad@gmail.com>
Date: Mon, 25 May 2026 23:41:49 +0800
Subject: [PATCH 1/2] fix `gc_generation.count` race

---
 Lib/test/test_free_threading/test_gc.py | 29 +++++++++++++++++++++++++
 Modules/gcmodule.c                      |  6 ++---
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/Lib/test/test_free_threading/test_gc.py b/Lib/test/test_free_threading/test_gc.py
index 8b45b6e2150c288..54cb8ccee395e3e 100644
--- a/Lib/test/test_free_threading/test_gc.py
+++ b/Lib/test/test_free_threading/test_gc.py
@@ -94,6 +94,35 @@ def evil():
         thread.start()
         thread.join()
 
+    def test_get_count(self):
+        class CyclicReference:
+            def __init__(self):
+                self.ref = self
+
+        NUM_ALLOCATORS = 7
+        NUM_READERS = 1
+        NUM_THREADS = NUM_ALLOCATORS + NUM_READERS
+        NUM_ITERS = 200_000
+
+        barrier = threading.Barrier(NUM_THREADS)
+
+        def allocator():
+            barrier.wait()
+            for _ in range(NUM_ITERS):
+                CyclicReference()
+
+
+        def reader():
+            barrier.wait()
+            for _ in range(NUM_ITERS):
+                gc.get_count()
+
+        threads = [Thread(target=allocator) for _ in range(NUM_ALLOCATORS)]
+        threads.extend(Thread(target=reader) for _ in range(NUM_READERS))
+
+        with threading_helper.start_threads(threads):
+            pass
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 12f93ac0fdea14b..e13acc859cab5a8 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -230,9 +230,9 @@ gc_get_count_impl(PyObject *module)
                          gcstate->generations[2].count);
 #else
     return Py_BuildValue("(iii)",
-                         gcstate->young.count,
-                         gcstate->old[0].count,
-                         gcstate->old[1].count);
+                         _Py_atomic_load_int_relaxed(&gcstate->young.count),
+                         _Py_atomic_load_int_relaxed(&gcstate->old[0].count),
+                         _Py_atomic_load_int_relaxed(&gcstate->old[1].count));
 #endif
 }
 

From 99086336c5304a1daea4e988438c813f650bf1fb Mon Sep 17 00:00:00 2001
From: edward_xu <xuxiangad@gmail.com>
Date: Tue, 26 May 2026 00:06:37 +0800
Subject: [PATCH 2/2] add blurb

---
 .../2026-05-26-00-06-30.gh-issue-150411.u-d-_5.rst              | 2 ++
 1 file changed, 2 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-05-26-00-06-30.gh-issue-150411.u-d-_5.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-05-26-00-06-30.gh-issue-150411.u-d-_5.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-26-00-06-30.gh-issue-150411.u-d-_5.rst
new file mode 100644
index 000000000000000..5b19a4fff5ddc73
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-05-26-00-06-30.gh-issue-150411.u-d-_5.rst
@@ -0,0 +1,2 @@
+Fix a data race in the free-threaded build when :func:`gc.get_count` reads
+the young generation allocation count while another thread updates it.