netdev - Re: [PATCH net-next 6/6] tcp: set TCP_DEFER

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Date: Fri, 4 Aug 2023 14:14:01 -0400
From: Soheil Hassas Yeganeh <soheil@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 6/6] tcp: set TCP_DEFER_ACCEPT locklessly

On Fri, Aug 4, 2023 at 10:46 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> rskq_defer_accept field can be read/written without
> the need of holding the socket lock.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>

Very nice series! Thank you!  I doulbechecked every field and they are
all READ_ONCE/WRITE_ONCE paired.

> ---
>  net/ipv4/tcp.c           | 13 ++++++-------
>  net/ipv4/tcp_input.c     |  2 +-
>  net/ipv4/tcp_minisocks.c |  2 +-
>  3 files changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 5c71b4fe11d1c34456976d60eb8742641111dd62..4fbc7ff8c53c05cbef3d108527239c7ec8c1363e 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -3479,6 +3479,12 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
>                 else
>                         WRITE_ONCE(tp->linger2, val * HZ);
>                 return 0;
> +       case TCP_DEFER_ACCEPT:
> +               /* Translate value in seconds to number of retransmits */
> +               WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
> +                          secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
> +                                          TCP_RTO_MAX / HZ));
> +               return 0;
>         }
>
>         sockopt_lock_sock(sk);
> @@ -3584,13 +3590,6 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname,
>                         tp->save_syn = val;
>                 break;
>
> -       case TCP_DEFER_ACCEPT:
> -               /* Translate value in seconds to number of retransmits */
> -               WRITE_ONCE(icsk->icsk_accept_queue.rskq_defer_accept,
> -                          secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
> -                                          TCP_RTO_MAX / HZ));
> -               break;
> -
>         case TCP_WINDOW_CLAMP:
>                 err = tcp_set_window_clamp(sk, val);
>                 break;
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index f445f5a7c0ebf5f7ab2b2402357f3749d954c0e8..972c3b16369589293eb15febe52e72d5c596b032 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -6325,7 +6325,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
>                 if (fastopen_fail)
>                         return -1;
>                 if (sk->sk_write_pending ||
> -                   icsk->icsk_accept_queue.rskq_defer_accept ||
> +                   READ_ONCE(icsk->icsk_accept_queue.rskq_defer_accept) ||
>                     inet_csk_in_pingpong_mode(sk)) {
>                         /* Save one ACK. Data will be ready after
>                          * several ticks, if write_pending is set.
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index c8f2aa0033871ed3f8b6b045c2cbca6e88bf2b61..32a70e3530db3247986ab5cb08c8a46babf86ad6 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -794,7 +794,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
>                 return sk;
>
>         /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
> -       if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
> +       if (req->num_timeout < READ_ONCE(inet_csk(sk)->icsk_accept_queue.rskq_defer_accept) &&
>             TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
>                 inet_rsk(req)->acked = 1;
>                 __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);
> --
> 2.41.0.640.ga95def55d0-goog
>