linux-kernel - Re: [PATCH cgroup/for-4.8] cgroup: allow NULL return from ss->css

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Message-ID: <20160621181404.GB4501@cmpxchg.org>
Date:	Tue, 21 Jun 2016 14:14:04 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH cgroup/for-4.8] cgroup: allow NULL return from
 ss->css_alloc()

On Tue, Jun 21, 2016 at 01:06:24PM -0400, Tejun Heo wrote:
> cgroup core expected css_alloc to return an ERR_PTR value on failure
> and caused NULL deref if it returned NULL.  It's an easy mistake to
> make from an alloc function and there's no ambiguity in what's being
> indicated.  Update css_create() so that it interprets NULL return from
> css_alloc as -ENOMEM.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>

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?