From 53e6d76aa30eb760fb8ff788815f22a0e6c101cd Mon Sep 17 00:00:00 2001 From: "T. Wouters" Date: Tue, 6 May 2025 13:23:10 +0200 Subject: [PATCH] gh-132917: Fix data race detected by tsan (#133508) Fix data race detected by tsan (https://github.com/python/cpython/actions/runs/14857021107/job/41712717208?pr=133502): young.count can be modified by other threads even while the gcstate is locked. This is the simplest fix to (potentially) unblock beta 1, although this particular code path seems like it could just be an atomic swap followed by an atomic add, without having the lock at all. --- Python/gc_free_threading.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c index f1ba5de51704..757e9cb3227e 100644 --- a/Python/gc_free_threading.c +++ b/Python/gc_free_threading.c @@ -2074,10 +2074,9 @@ gc_should_collect_mem_usage(GCState *gcstate) // clear the young object count so we don't check memory usage again // on the next call to gc_should_collect(). PyMutex_Lock(&gcstate->mutex); + int young_count = _Py_atomic_exchange_int(&gcstate->young.count, 0); _Py_atomic_store_ssize_relaxed(&gcstate->deferred_count, - gcstate->deferred_count + - gcstate->young.count); - _Py_atomic_store_int(&gcstate->young.count, 0); + gcstate->deferred_count + young_count); PyMutex_Unlock(&gcstate->mutex); return false; } -- 2.47.3