linux-kernel - Re: [PATCH][netdev-next] gre: remove duplicated assignment of iph

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Date:   Wed, 23 Aug 2017 11:46:11 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     colin.king@...onical.com
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][netdev-next] gre: remove duplicated assignment of iph

From: Colin King <colin.king@...onical.com>
Date: Wed, 23 Aug 2017 12:13:05 +0100

> From: Colin Ian King <colin.king@...onical.com>
> 
> iph is being assigned the same value twice; remove the redundant
> second assignment.
> 
> Fixes warning:
> net/ipv4/ip_gre.c:265:2: warning: Value stored to 'iph' is never read
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

It is always necessary to reload any SKB header pointer after calls
to functions which potentially change the data buffer of the SKB.

pskb_may_pull() is one such call.

Therefore your patch is adding a bug.

If you want to remove the dup, you must remove the first not
the second one.