Re: [PATCH cgroup/for-4.8] cgroup: allow NULL return from ss->css_alloc()

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Jun 21, 2016 at 02:14:04PM -0400, Johannes Weiner wrote:
> Would it be better to remove the error code instead and have everybody
> return NULL? AFAICS, everybody is returning either the object or the
> -ENOMEM error code right now.
> 
> What error condition is there for an allocation function?

I already changed cgroup core to interpret NULL return as -ENOMEM.
Maybe we can drop ERR_PTR handling altogether in the future but I'm
not sure.  e.g. memcg's id allocation and -ENOSPC check could be in
css_alloc.  The thing is css_online is only necessary if there are
requirements around css id or iteration, so css_alloc can easily be
the only alloc / init point and thus should be able to indicate
different failure conditions.

Thanks.

-- 
tejun