defer func() {
		s := recover()
		if s == nil {
			t.Fatal("did not panic")
		}
		if s.(string) != "callback panic" {
			t.Fatal("wrong panic:", s)
		}
		if lockedOSThread() {
			t.Fatal("locked OS thread on exit from TestCallbackPanic")
		}
	}()
	nestedCall(func() { panic("callback panic") })
	panic("nestedCall returned")
}

func testCallbackPanicLoop(t *testing.T) {
	// Make sure we don't blow out m->g0 stack.