The Paradox of North Korea and China

On the one hand China is really done with North Korea messing up it's International business with all it's tantrums. But, on the other hand it has also been sort of North Korea's big brother for at least 70 years now or longer. So, when push comes to shove in regard to China's businesses or it's military it is difficult to know exactly where China is going with all this both now and in the future. Is China actually pulling the strings here to accomplish something we don't yet understand militarily? Or is China just pissed off at it's little brother throwing yet another tantrum? This to me strategically might be the most important thing for the U.S. as well as the rest of the free world to consider here.