netdev - Re: [PATCH] ipv4/mptcp: fix divide error

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Message-ID: <f9b97b7f-cb48-f0bf-2dfb-a13bf1296b19@linux.intel.com>
Date:   Wed, 25 Aug 2021 10:56:14 -0700 (PDT)
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     Jiang Biao <benbjiang@...il.com>
cc:     Matthieu Baerts <matthieu.baerts@...sares.net>,
        davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        mptcp@...ts.linux.dev, linux-kernel <linux-kernel@...r.kernel.org>,
        Jiang Biao <benbjiang@...cent.com>,
        Jiang Biao <tcs_robot@...cent.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH] ipv4/mptcp: fix divide error


On Tue, 24 Aug 2021, Jiang Biao wrote:

> Hi,
>
> On Tue, 24 Aug 2021 at 15:36, Matthieu Baerts
> <matthieu.baerts@...sares.net> wrote:
>>
>> Hi Jiang,
>>
>> On 24/08/2021 09:19, Jiang Biao wrote:
>>
>> (...)
>>
>>> There is a fix divide error reported,
>>> divide error: 0000 [#1] PREEMPT SMP KASAN
>>> RIP: 0010:tcp_tso_autosize build/../net/ipv4/tcp_output.c:1975 [inline]
>>> RIP: 0010:tcp_tso_segs+0x14f/0x250 build/../net/ipv4/tcp_output.c:1992
>>
>> Thank you for this patch and validating MPTCP on your side!
>>
>> This issue is actively tracked on our Github project [1] and a patch is
>> already in our tree [2] but still under validation.
>>> It's introduced by non-initialized info->mss_now in __mptcp_push_pending.
>>> Fix it by adding protection in mptcp_push_release.
>>
>> Indeed, you are right, info->mss_now can be set to 0 in some cases but
>> that's not normal.
>>
>> Instead of adding a protection here, we preferred fixing the root cause,
>> see [2]. Do not hesitate to have a look at the other patch and comment
>> there if you don't agree with this version.
>> Except if [2] is difficult to backport, I think we don't need your extra
>> protection. WDYT?
>>
> Agreed, fixing the root cause is much better.
> Thanks for the reply.
>

Hi Jiang -

Could you try cherry-picking this commit to see if it eliminates the error 
in your system?

https://github.com/multipath-tcp/mptcp_net-next/commit/9ef5aea5a794f4a369e26ed816e9c80cdc5a5f86


Thanks!

--
Mat Martineau
Intel