linux-kernel - Re: [PATCH] ip6_offload: check segs for NULL in ipv6_gso

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Message-ID: <1480606078.18162.297.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 01 Dec 2016 07:27:58 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Artem Savkov <asavkov@...hat.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, jstancek@...hat.com,
        steffen.klassert@...unet.com, alexander.h.duyck@...el.com,
        YOSHIFUJI Hideaki /
         吉藤英明 
        <yoshfuji@...ux-ipv6.org>
Subject: Re: [PATCH] ip6_offload: check segs for NULL in ipv6_gso_segment.

On Thu, 2016-12-01 at 16:07 +0100, Artem Savkov wrote:

> I am not, but this would have the same behavior as pre-07b26c9 code and
> IS_ERR_OR_NULL is used in ipv4's inet_gso_segment().

My concern might have been that IS_ERR_OR_NULL() considers the !ptr to
be unlikely.

But in this code path, we really can not tell.

segs == NULL can be quite likely in TUN case, because of DODGY bit

Commit 50c3a487d50756 replaced the perfectly fine :

if (!segs || IS_ERR(segs))

into dubious

if (IS_ERR_OR_NULL(segs))

segs = NULL is not an error, but use of IS_ERR_OR_NULL() might mislead
programmers trying to understand this code.