From c69bfa8a095ff89d420e1baf35b6fc56d5006b0b Mon Sep 17 00:00:00 2001
From: Neil Schemenauer <nas@arctrix.com>
Date: Tue, 11 Mar 2025 19:40:49 -0700
Subject: [PATCH] Move `assert()` inside lock to avoid data race.

We need to hold the lock to safely read the
`tstate->interp->sys_tracing_threads` value.
---
 Python/legacy_tracing.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Python/legacy_tracing.c b/Python/legacy_tracing.c
index 82465c66ab5231..32dadfb712e458 100644
--- a/Python/legacy_tracing.c
+++ b/Python/legacy_tracing.c
@@ -582,10 +582,10 @@ _PyEval_SetTrace(PyThreadState *tstate, Py_tracefunc func, PyObject *arg)
     if (_PySys_Audit(current_tstate, "sys.settrace", NULL) < 0) {
         return -1;
     }
-    assert(tstate->interp->sys_tracing_threads >= 0);
     // needs to be decref'd outside of the lock
     PyObject *old_traceobj;
     LOCK_SETUP();
+    assert(tstate->interp->sys_tracing_threads >= 0);
     Py_ssize_t tracing_threads = setup_tracing(tstate, func, arg, &old_traceobj);
     UNLOCK_SETUP();
     Py_XDECREF(old_traceobj);