linux-kernel - Re: [PATCH net-next 0/9] net: add skb drop reasons to TCP packet receive

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Message-ID: <CANn89i+gBxse3zf2gSvm5AU3D_2MSztGArKQxF4B2rTpWNUSwA@mail.gmail.com>
Date:   Wed, 16 Feb 2022 09:04:50 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Menglong Dong <menglong8.dong@...il.com>
Cc:     David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Menglong Dong <imagedong@...cent.com>,
        Talal Ahmad <talalahmad@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Alexander Lobakin <alobakin@...me>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Antoine Tenart <atenart@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Paolo Abeni <pabeni@...hat.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Arnd Bergmann <arnd@...db.de>,
        Yajun Deng <yajun.deng@...ux.dev>,
        Roopa Prabhu <roopa@...dia.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Cong Wang <cong.wang@...edance.com>,
        Luiz Augusto von Dentz <luiz.von.dentz@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        flyingpeng@...cent.com
Subject: Re: [PATCH net-next 0/9] net: add skb drop reasons to TCP packet receive

On Tue, Feb 15, 2022 at 7:54 PM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> In this series patches, reasons for skb drops are added to TCP layer, and
> both TCPv4 and TCPv6 are considered.
>
> in this series patches, the process of packet ingress in TCP layer is
> considered, as skb drops hardly happens in the egress path.
>
> However, it's a little complex for TCP state processing, as I find that
> it's hard to report skb drop reasons to where it is freed. For example,
> when skb is dropped in tcp_rcv_state_process(), the reason can be caused
> by the call of tcp_v4_conn_request(), and it's hard to return a drop
> reason from tcp_v4_conn_request(). So I just skip such case for this
> moment.
>

I think you should add at least in this cover letter, or better in a
document that can be amended,
how this can be used on a typical TCP session.
For someone who is having issues with TCP flows, what would they need to do.
Think of something that we (kernel dev) could copy paste to future
email replies.
It might be mostly clear for some of us reviewing patches at this
moment, but in one year we will all forget about the details.


>
> Menglong Dong (9):
>   net: tcp: introduce tcp_drop_reason()
>   net: tcp: add skb drop reasons to tcp_v4_rcv()
>   net: tcp: use kfree_skb_reason() for tcp_v6_rcv()
>   net: tcp: add skb drop reasons to tcp_v{4,6}_inbound_md5_hash()
>   net: tcp: add skb drop reasons to tcp_add_backlog()
>   net: tcp: use kfree_skb_reason() for tcp_v{4,6}_do_rcv()
>   net: tcp: use tcp_drop_reason() for tcp_rcv_established()
>   net: tcp: use tcp_drop_reason() for tcp_data_queue()
>   net: tcp: use tcp_drop_reason() for tcp_data_queue_ofo()
>
>  include/linux/skbuff.h     | 28 +++++++++++++++++++++++++
>  include/net/tcp.h          |  3 ++-
>  include/trace/events/skb.h | 10 +++++++++
>  net/ipv4/tcp_input.c       | 42 +++++++++++++++++++++++++++++---------
>  net/ipv4/tcp_ipv4.c        | 36 ++++++++++++++++++++++++--------
>  net/ipv6/tcp_ipv6.c        | 42 +++++++++++++++++++++++++++++---------
>  6 files changed, 131 insertions(+), 30 deletions(-)
>
> --
> 2.34.1
>