IS_ERR_OR_NULL - please STOP telling people to use this on a whim

On Wed, Oct 17, 2012 at 11:28:48PM +0300, Phil Carmody wrote:

So, what to do? It can and has been used sensibly, so I don't think removing
it is the best option.

Well, the first thing that needs to be done is a full review of every user
and fixes applied.

The second thing is that we need eyes on code _and_ review comments, and
educate those who are telling people to use IS_ERR_OR_NULL() whenever they
see an IS_ERR() to think about the code a little more - that's kind of the
purpose of my email.

Unfortunately, it's going to take time to achieve a change, and if I end
up being the only one who's spotting these errors, I'm going to get
incredibly pissed off at doing so (because it will feel like I'm being
ignored when there's a constant stream of it.)

Another thing would be to work out whether we can get checkpatch to
detect usage of IS_ERR_OR_NULL(p) followed by PTR_ERR(p) without any
explicit NULL checks against p in the same block.  That's probably
going to be interesting to code up in perl.