If stopping is an action one can stop that action. If you are stopping something, I might tell you to stop stopping it. If you are stopping by, I might tell you to stop stopping by. If the circus has been stopping by every year on its route, but then it stopped stopping by as it usually did, then the circus would have stopped the stop. Then if it stopped the stop in a deliberate enough way as to warrant special attention, but later decided to resume the stop you could say that it stopped stopping the stop.