HEAD_LOCK() the thread state list.

Author: ZeroIntensity

Python/ceval.c

@@ -266,12 +266,14 @@ Py_SetRecursionLimit(int new_limit)
 {
     PyInterpreterState *interp = _PyInterpreterState_GET();
     _PyEval_StopTheWorld(interp);
+    HEAD_LOCK(interp->runtime);
     interp->ceval.recursion_limit = new_limit;
     for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
         int depth = p->py_recursion_limit - p->py_recursion_remaining;
         p->py_recursion_limit = new_limit;
         p->py_recursion_remaining = new_limit - depth;
     }
+    HEAD_UNLOCK(interp->runtime);
     _PyEval_StartTheWorld(interp);
 }