From what I've seen, even China is getting sick of North Korean antics and have started applying political pressure behind the scenes for them to chill out. Unfortunately, it seems as though NK is ignoring it and going rogue, which is a really bad idea as it's really only the influence that China wields that keeps them from getting steamrolled by any of several other countries or groups.
If anybody here would like to understand the situation in North Korea better, I highly recommend reading Victor Cha's book _The Impossible State: North Korea, Past and Future_. Cha worked for the George W. Bush administration and he's an expert on North Korea. Not to digress, but it would really be helpful is President Obama would make somebody in his staff who pays attention to North Korea read this too. Secretary of State Kerry keeps demanding that China do more. If he'd just read the book or have a staffer summarize it for him, he'd understand why they won't.
Here's the deal. North Korea started the Korean War on their own and Mao and Stalin weren't really happy about it. Stalin refused to get involved although he was willing to for Soviet pilots to serve as the de facto North Korean Air Force during the war. China committed troops only when it looked like MacArthur might actually get up to the border with China and possibly invade China. China paid a real price in blood to save North Korea. Mao's own son was killed in the fighting. So while the old line of North Korea and China being "closer than lips and teeth" is no longer really true, China does feel involved because a lot of her soldiers died in that war and they don't want it to be for nothing.
What Kerry, Obama and others in the US need to understand is what Cha points out in his book. Namely, that China really doesn't like North Korea causing problems but it views all possible outcomes of a post-North Korea version of Korea as really bad for China. China feels stuck in that it knows that North Korea's regime can't last forever, but if it puts too much pressure on them, they may collapse soon and remember, they view all post-DPRNK outcomes as very very bad for China. China fears that a unified Korea will have US soldiers stationed in what is now North Korea, so that means right on its borders. China also fears that once North Korea falls, the border will be overrun with North Koreans (there is an area of China near the border that is majority ethnic Korean, so refugees would likely go there) and China will have a humanitarian disaster on its hands that it will have to spend time and resources to deal with. Additionally, in exchange for their financial support, North Korea is basically selling its rare earths to China at below market prices, so China is financially very vested in maintaining this. A unified Korea is not likely to let China continue to destroy the North Korean countryside to get rare earths at a discount. China doesn't see any possible outcome of a post-North Korea world where things aren't a lot worse for China, so they are caught in rarely using the influence they have. However, outsiders, especially the Obama administration, seem to greatly overestimate what influence China actually has. The reality is that China has more influence than they are willing to use, but not as much as everybody else thinks. The Kim regime will do what it can to survive and if that means going against China, no problem there. China is simply never going to stop providing money and assistance as long as the regime exists, so expecting China to do anything but maintain the status quo is not very likely to happen.