netdev - Re: [PATCH net-next v2 4/6] tcp: rstreason: introduce SK_RST_REASON_TCP

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Message-ID: <CANn89iJGco0f2RLBm4bW3QpRHwscwZhc287RX+mWA0Q_=hfTYA@mail.gmail.com>
Date: Thu, 1 Aug 2024 08:56:12 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, 
	dsahern@...nel.org, kuniyu@...zon.com, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v2 4/6] tcp: rstreason: introduce
 SK_RST_REASON_TCP_STATE for active reset

On Wed, Jul 31, 2024 at 2:10 PM Jason Xing <kerneljasonxing@...il.com> wrote:
>
> From: Jason Xing <kernelxing@...cent.com>
>
> Introducing a new type TCP_STATE to handle some reset conditions
> appearing in RFC 793 due to its socket state. Actually, we can look
> into RFC 9293 which has no discrepancy about this part.
>
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
> V2
> Link: https://lore.kernel.org/all/20240730200633.93761-1-kuniyu@amazon.com/
> 1. use RFC 9293 instead of RFC 793 which is too old (Kuniyuki)
> ---
>  include/net/rstreason.h | 6 ++++++
>  net/ipv4/tcp.c          | 4 ++--
>  net/ipv4/tcp_timer.c    | 2 +-
>  3 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/include/net/rstreason.h b/include/net/rstreason.h
> index eef658da8952..bbf20d0bbde7 100644
> --- a/include/net/rstreason.h
> +++ b/include/net/rstreason.h
> @@ -20,6 +20,7 @@
>         FN(TCP_ABORT_ON_CLOSE)          \
>         FN(TCP_ABORT_ON_LINGER)         \
>         FN(TCP_ABORT_ON_MEMORY)         \
> +       FN(TCP_STATE)                   \
>         FN(MPTCP_RST_EUNSPEC)           \
>         FN(MPTCP_RST_EMPTCP)            \
>         FN(MPTCP_RST_ERESOURCE)         \
> @@ -102,6 +103,11 @@ enum sk_rst_reason {
>          * corresponding to LINUX_MIB_TCPABORTONMEMORY
>          */
>         SK_RST_REASON_TCP_ABORT_ON_MEMORY,
> +       /**
> +        * @SK_RST_REASON_TCP_STATE: abort on tcp state
> +        * Please see RFC 9293 for all possible reset conditions
> +        */
> +       SK_RST_REASON_TCP_STATE,
>
>         /* Copy from include/uapi/linux/mptcp.h.
>          * These reset fields will not be changed since they adhere to
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index fd928c447ce8..64a49cb714e1 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3031,7 +3031,7 @@ int tcp_disconnect(struct sock *sk, int flags)
>                 /* The last check adjusts for discrepancy of Linux wrt. RFC
>                  * states
>                  */
> -               tcp_send_active_reset(sk, gfp_any(), SK_RST_REASON_NOT_SPECIFIED);
> +               tcp_send_active_reset(sk, gfp_any(), SK_RST_REASON_TCP_STATE);

I disagree with this. tcp_disconnect() is initiated by the user.

You are conflating two possible conditions :

1) tcp_need_reset(old_state)
2) (tp->snd_nxt != tp->write_seq && (1 << old_state) & (TCPF_CLOSING |
TCPF_LAST_ACK)))

>                 WRITE_ONCE(sk->sk_err, ECONNRESET);
>         } else if (old_state == TCP_SYN_SENT)
>                 WRITE_ONCE(sk->sk_err, ECONNRESET);
> @@ -4649,7 +4649,7 @@ int tcp_abort(struct sock *sk, int err)
>         if (!sock_flag(sk, SOCK_DEAD)) {
>                 if (tcp_need_reset(sk->sk_state))
>                         tcp_send_active_reset(sk, GFP_ATOMIC,
> -                                             SK_RST_REASON_NOT_SPECIFIED);
> +                                             SK_RST_REASON_TCP_STATE);
>                 tcp_done_with_error(sk, err);
>         }
>
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index 0fba4a4fb988..3910f6d8614e 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -779,7 +779,7 @@ static void tcp_keepalive_timer (struct timer_list *t)
>                                 goto out;
>                         }
>                 }
> -               tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_NOT_SPECIFIED);
> +               tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_TCP_STATE);
>                 goto death;
>         }
>
> --
> 2.37.3
>