Index: Python/ceval.c
===================================================================
--- Python/ceval.c      (revision 64788)
+++ Python/ceval.c      (working copy)
@@ -274,6 +274,9 @@
 void
 PyEval_ReInitThreads(void)
 {
+       PyObject *threading, *lock;
+       PyThreadState *tstate;
+
        if (!interpreter_lock)
                return;
        /*XXX Can't use PyThread_free_lock here because it does too
@@ -283,6 +286,32 @@
        interpreter_lock = PyThread_allocate_lock();
        PyThread_acquire_lock(interpreter_lock, 1);
        main_thread = PyThread_get_thread_ident();
+
+       /* Reset threading._active_limbo_lock, in case we forked just
+        * when a thread was starting of stopping
+        */
+
+       tstate = PyThreadState_GET();
+       threading = PyMapping_GetItemString(tstate->interp->modules,
+                                           "threading");
+       if (threading == NULL) {
+           /* threading not imported */
+           PyErr_Clear();
+           return;
+       }
+       lock = PyObject_GetAttrString(threading, "_active_limbo_lock");
+       if (lock == NULL)
+           PyErr_WriteUnraisable(threading);
+       else {
+           PyObject *res = PyObject_CallMethod(lock, "release", NULL);
+           if (res == NULL)
+               /* Ignore the "release unlocked lock" error */
+               PyErr_Clear();
+           else
+               Py_DECREF(res);
+           Py_DECREF(lock);
+       }
+       Py_DECREF(threading);
 }
 #endif