From: Shamil <ashm.tech@proton.me>
Date: Sat, 18 Oct 2025 11:01:53 +0000 (+0300)
Subject: gh-140257: fix data race on eval_breaker during finalization (#140265)
X-Git-Tag: v3.15.0a2~400
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c8729c9909e150989050ce2a435d018955bea41d;p=thirdparty%2FPython%2Fcpython.git

gh-140257: fix data race on eval_breaker during finalization (#140265)
---

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-10-17-20-23-19.gh-issue-140257.8Txmem.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-17-20-23-19.gh-issue-140257.8Txmem.rst
new file mode 100644
index 000000000000..50f7e0e48ae3
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-17-20-23-19.gh-issue-140257.8Txmem.rst
@@ -0,0 +1,2 @@
+Fix data race between interpreter_clear() and take_gil() on eval_breaker
+during finalization with daemon threads.
diff --git a/Python/pystate.c b/Python/pystate.c
index dbed609f29aa..c402d89a1614 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -763,10 +763,11 @@ interpreter_clear(PyInterpreterState *interp, PyThreadState *tstate)
 
     Py_CLEAR(interp->audit_hooks);
 
-    // At this time, all the threads should be cleared so we don't need atomic
-    // operations for instrumentation_version or eval_breaker.
+    // gh-140257: Threads have already been cleared, but daemon threads may
+    // still access eval_breaker atomically via take_gil() right before they
+    // hang. Use an atomic store to prevent data races during finalization.
     interp->ceval.instrumentation_version = 0;
-    tstate->eval_breaker = 0;
+    _Py_atomic_store_uintptr(&tstate->eval_breaker, 0);
 
     for (int i = 0; i < _PY_MONITORING_UNGROUPED_EVENTS; i++) {
         interp->monitors.tools[i] = 0;