netdev - Re: [PATCH bpf-next v2 3/4] bpf, sockmap: Fix more uncharged while msg has more

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Message-ID: <43486167-1d02-c053-96f4-55a2683f3da8@huawei.com>
Date:   Fri, 4 Mar 2022 15:08:35 +0800
From:   wangyufen <wangyufen@...wei.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     <john.fastabend@...il.com>, <daniel@...earbox.net>,
        <jakub@...udflare.com>, <lmb@...udflare.com>,
        <davem@...emloft.net>, <edumazet@...gle.com>,
        <yoshfuji@...ux-ipv6.org>, <dsahern@...nel.org>, <kuba@...nel.org>,
        <ast@...nel.org>, <andrii@...nel.org>, <kafai@...com>,
        <songliubraving@...com>, <yhs@...com>, <kpsingh@...nel.org>,
        <netdev@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 3/4] bpf, sockmap: Fix more uncharged while
 msg has more_data


在 2022/3/3 14:14, Cong Wang 写道:
> On Wed, Mar 02, 2022 at 10:27:54AM +0800, Wang Yufen wrote:
>> In tcp_bpf_send_verdict(), if msg has more data after
>> tcp_bpf_sendmsg_redir():
>>
>> tcp_bpf_send_verdict()
>>   tosend = msg->sg.size  //msg->sg.size = 22220
>>   case __SK_REDIRECT:
>>    sk_msg_return()  //uncharged msg->sg.size(22220) sk->sk_forward_alloc
>>    tcp_bpf_sendmsg_redir() //after tcp_bpf_sendmsg_redir, msg->sg.size=11000
>>   goto more_data;
>>   tosend = msg->sg.size  //msg->sg.size = 11000
>>   case __SK_REDIRECT:
>>    sk_msg_return()  //uncharged msg->sg.size(11000) to sk->sk_forward_alloc
>>
>> The msg->sg.size(11000) has been uncharged twice, to fix we can charge the
>> remaining msg->sg.size before goto more data.
> It looks like bpf_exec_tx_verdict() has the same issue.
>
> .

In bpf_exec_tx_verdict(), case __SK_REDIRECT,  msg_redir is used and 
msg->sg.size is deducted in advance.

Therefore, this issue (more uncharged) does not exist.

However, I think that if msg_redir processing cannot be completed , that 
is msg_redir has more data,

and there is no subsequent processing,  maybe that is another problem.


Thanks.