[3.14] gh-136870: fix data race in PyThreadState_Clear on sys_tracing_threads (GH-136951) (#136953)

miss-islington · kumaraditya303 · web-flow · commit 718fc5b1393d · 2025-07-21T21:01:14.000Z
gh-136870: fix data race in `PyThreadState_Clear` on `sys_tracing_threads` (GH-136951) In free-threading, multiple threads can be cleared concurrently as such the modifications on `sys_tracing_threads` should be done while holding the profile lock, otherwise it can race with other threads setting up profiling. (cherry picked from commit f183996) Co-authored-by: Kumar Aditya <kumaraditya@python.org>
diff --git a/Python/pystate.c b/Python/pystate.c
@@ -1793,6 +1793,10 @@ PyThreadState_Clear(PyThreadState *tstate)
           "PyThreadState_Clear: warning: thread still has a generator\n");
     }
 
+#ifdef Py_GIL_DISABLED
+    PyMutex_Lock(&_PyRuntime.ceval.sys_trace_profile_mutex);
+#endif
+
     if (tstate->c_profilefunc != NULL) {
         tstate->interp->sys_profiling_threads--;
         tstate->c_profilefunc = NULL;
@@ -1801,6 +1805,11 @@ PyThreadState_Clear(PyThreadState *tstate)
         tstate->interp->sys_tracing_threads--;
         tstate->c_tracefunc = NULL;
     }
+
+#ifdef Py_GIL_DISABLED
+    PyMutex_Unlock(&_PyRuntime.ceval.sys_trace_profile_mutex);
+#endif
+
     Py_CLEAR(tstate->c_profileobj);
     Py_CLEAR(tstate->c_traceobj);
 
