From: mpage <mpage@meta.com>
Date: Mon, 15 Apr 2024 16:17:33 +0000 (-0700)
Subject: gh-117657: Quiet TSAN warning about a data race between `start_the_world()` and ... 
X-Git-Tag: v3.13.0b1~419
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=6e0b327690c7dd2e4e9091f81f8ad43ad5eb1631;p=thirdparty%2FPython%2Fcpython.git

gh-117657: Quiet TSAN warning about a data race between `start_the_world()` and `tstate_try_attach()` (#117828)

TSAN erroneously reports a data race between the `_Py_atomic_compare_exchange_int`
on `tstate->state` in `tstate_try_attach()` and the non-atomic load of
`tstate->state` in `start_the_world`. The `_Py_atomic_compare_exchange_int` fails,
but TSAN erroneously treats it as a store.
---

diff --git a/Python/pystate.c b/Python/pystate.c
index acec905484c2..50454020b8fc 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2248,7 +2248,8 @@ start_the_world(struct _stoptheworld_state *stw)
     PyThreadState *t;
     _Py_FOR_EACH_THREAD(stw, i, t) {
         if (t != stw->requester) {
-            assert(t->state == _Py_THREAD_SUSPENDED);
+            assert(_Py_atomic_load_int_relaxed(&t->state) ==
+                   _Py_THREAD_SUSPENDED);
             _Py_atomic_store_int(&t->state, _Py_THREAD_DETACHED);
             _PyParkingLot_UnparkAll(&t->state);
         }