From: Pablo Galindo Salgado <Pablogsal@gmail.com>
Date: Mon, 15 Sep 2025 10:39:41 +0000 (+0100)
Subject: gh-137992: Stop the world when calling PyRefTracer_SetTracer (#137994)
X-Git-Tag: v3.15.0a1~371
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=c5180d74e199e5bdb8f1c149dc3e956071ebf365;p=thirdparty%2FPython%2Fcpython.git

gh-137992: Stop the world when calling PyRefTracer_SetTracer (#137994)
---

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-08-20-14-17-47.gh-issue-137992.fcL3SK.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-20-14-17-47.gh-issue-137992.fcL3SK.rst
new file mode 100644
index 000000000000..068f04120daa
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-20-14-17-47.gh-issue-137992.fcL3SK.rst
@@ -0,0 +1,2 @@
+Ensure that  :c:func:`PyRefTracer_SetTracer` sync with all existing threads when called
+to avoid races in the free threaded build. Patch by Pablo Galindo
diff --git a/Objects/object.c b/Objects/object.c
index 2c07c2e9841b..c9bcc0c7b09e 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -3287,6 +3287,8 @@ _Py_SetRefcnt(PyObject *ob, Py_ssize_t refcnt)
 
 int PyRefTracer_SetTracer(PyRefTracer tracer, void *data) {
     _Py_AssertHoldsTstate();
+
+    _PyEval_StopTheWorldAll(&_PyRuntime);
     if (_PyRuntime.ref_tracer.tracer_func != NULL) {
         _PyReftracerTrack(NULL, PyRefTracer_TRACKER_REMOVED);
         if (PyErr_Occurred()) {
@@ -3295,6 +3297,7 @@ int PyRefTracer_SetTracer(PyRefTracer tracer, void *data) {
     }
     _PyRuntime.ref_tracer.tracer_func = tracer;
     _PyRuntime.ref_tracer.tracer_data = data;
+    _PyEval_StartTheWorldAll(&_PyRuntime);
     return 0;
 }