I think Russia doesn't fear China in that way.
They share the politics of communism in some way and Russia can always start a big nuclear war with China, so there isn't too much worry of invasion.
I agree.
I think that China and the USSR always had this same kind of relationship. The Chinese realized, I think, a long while back that the Russians were as fearless and unafraid of losing THOUSANDS of soldies as they were. In essence, they knew that the Russians were as crazy as they were.