netdev - Re: Regression with commit 971f10eca186 ("tcp: better TCP_SKB

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Message-ID: <54984CBB.6090605@6wind.com>
Date:	Mon, 22 Dec 2014 17:54:19 +0100
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev <netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: Regression with commit 971f10eca186 ("tcp: better TCP_SKB_CB
 layout to reduce cache line misses")

Le 22/12/2014 17:15, Eric Dumazet a écrit :
> On Mon, 2014-12-22 at 16:17 +0100, Nicolas Dichtel wrote:
>> One of our engineer (Huaibin Wang <huaibin.wang@...nd.com>) has reported and
>> analysed this bug:
>>
>> This commit introduces a regression with IPv6 + IPsec transport + TCP.
>>
>> In TCP (net/ipv6/tcp_ipv6.c), xfrm6_policy_check() is called and thus, after
>> some intermediate functions, _decode_session6() is also called.
>>
>> This function uses IP6CB() (u8 nexthdr = nh[IP6CB(skb)->nhoff]), which is wrong
>> becauses it has been moved to the end of TCP_SKB_CB().
>>
>> Not sure what is the best way to fix this, any suggestion?
>
> Thanks for the report
>
> Presumably tcp_v6_rcv() needs to be reordered so that
> xfrm6_policy_check() calls are done before the CB swap.
>
> swap should probably be done right before bh_lock_sock_nested()
>
> I am currently traveling and I am not sure if I can get Internet access
> to post a patch soon.
Ok, thank you for the tip. I will try to cook a patch.
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