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From:   Eric Dumazet <edumazet@google.com>
Date:   Mon, 9 Nov 2020 14:36:33 +0100
Message-ID: <CANn89iJNYyON8khtQYzZi2LdV1ZSopGfnXB1ev9bZ2cDUdekHw@mail.gmail.com>
Subject: Re: [PATCH] net: tcp: ratelimit warnings in tcp_recvmsg
To:     menglong8.dong@gmail.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>
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On Mon, Nov 9, 2020 at 2:07 PM <menglong8.dong@gmail.com> wrote:
>
> From: Menglong Dong <dong.menglong@zte.com.cn>
>
> 'before(*seq, TCP_SKB_CB(skb)->seq) == true' means that one or more
> skbs are lost somehow. Once this happen, it seems that it will
> never recover automatically. As a result, a warning will be printed
> and a '-EAGAIN' will be returned in non-block mode.
>
> As a general suituation, users call 'poll' on a socket and then receive
> skbs with 'recv' in non-block mode. This mode will make every
> arriving skb of the socket trigger a warning. Plenty of skbs will cause
> high rate of kernel log.
>
> Besides, WARN is for indicating kernel bugs only and should not be
> user-triggable. Replace it with 'net_warn_ratelimited' here.
>
> Signed-off-by: Menglong Dong <dong.menglong@zte.com.cn>

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.