Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] net: tcp: ratelimit warnings in tcp_recvmsg
To:     Menglong Dong <menglong8.dong@gmail.com>,
        Eric Dumazet <edumazet@google.com>
Cc:     David Miller <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Menglong Dong <dong.menglong@zte.com.cn>
References: <5fa93ef0.1c69fb81.bff98.2afc@mx.google.com>
 <CANn89iJNYyON8khtQYzZi2LdV1ZSopGfnXB1ev9bZ2cDUdekHw@mail.gmail.com>
 <CADxym3bP=BRbVAnDCzmrrAyh3i=QO3gAWnUwpU==TskFY-GHYg@mail.gmail.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <0ccc35a7-3d19-e37d-52d1-7e900091cc1b@gmail.com>
Date:   Mon, 9 Nov 2020 16:39:24 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.3.1
MIME-Version: 1.0
In-Reply-To: <CADxym3bP=BRbVAnDCzmrrAyh3i=QO3gAWnUwpU==TskFY-GHYg@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 11/9/20 3:48 PM, Menglong Dong wrote:
> On Mon, Nov 9, 2020 at 9:36 PM Eric Dumazet <edumazet@google.com> wrote:
>>
>> I do not think this patch is useful. That is simply code churn.
>>
>> Can you trigger the WARN() in the latest upstream version ?
>> If yes this is a serious bug that needs urgent attention.
>>
>> Make sure you have backported all needed fixes into your kernel, if
>> you get this warning on a non pristine kernel.
> 
> Theoretically, this WARN() shouldn't be triggered in any branches.
> Somehow, it just happened in kernel v3.10. This really confused me. I
> wasn't able to keep tracing it, as it is a product environment.
> 
> I notice that the codes for tcp skb receiving didn't change much
> between v3.10 and the latest upstream version, and guess the latest
> version can be triggered too.
> 
> If something is fixed and this WARN() won't be triggered, just ignore me.
> 

Yes, I confirm this WARN() should not trigger.

The bug is not in tcp recvmsg(), that is why you do not see obvious
fix for this issue in 3.10