netdev - Re: [PATCH net] tcp: refactor tcp_retransmit

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Date:   Tue, 3 Dec 2019 11:08:21 -0500
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH net] tcp: refactor tcp_retransmit_timer()

On Tue, Dec 3, 2019 at 11:05 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> It appears linux-4.14 stable needs a backport of commit
> 88f8598d0a30 ("tcp: exit if nothing to retransmit on RTO timeout")
>
> Since tcp_rtx_queue_empty() is not in pre 4.15 kernels,
> let's refactor tcp_retransmit_timer() to only use tcp_rtx_queue_head()
>
> I will provide to stable teams the squashed patches.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

Thanks, Eric!

> ---
>  net/ipv4/tcp_timer.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index dd5a6317a8018a45ad609f832ced6df2937ad453..1097b438befe14ae3f375f3dbcc1f2d375a93879 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -434,6 +434,7 @@ void tcp_retransmit_timer(struct sock *sk)
>         struct net *net = sock_net(sk);
>         struct inet_connection_sock *icsk = inet_csk(sk);
>         struct request_sock *req;
> +       struct sk_buff *skb;
>
>         req = rcu_dereference_protected(tp->fastopen_rsk,
>                                         lockdep_sock_is_held(sk));
> @@ -446,7 +447,12 @@ void tcp_retransmit_timer(struct sock *sk)
>                  */
>                 return;
>         }
> -       if (!tp->packets_out || WARN_ON_ONCE(tcp_rtx_queue_empty(sk)))
> +
> +       if (!tp->packets_out)
> +               return;
> +
> +       skb = tcp_rtx_queue_head(sk);
> +       if (WARN_ON_ONCE(!skb))
>                 return;
>
>         tp->tlp_high_seq = 0;
> @@ -480,7 +486,7 @@ void tcp_retransmit_timer(struct sock *sk)
>                         goto out;
>                 }
>                 tcp_enter_loss(sk);
> -               tcp_retransmit_skb(sk, tcp_rtx_queue_head(sk), 1);
> +               tcp_retransmit_skb(sk, skb, 1);
>                 __sk_dst_reset(sk);
>                 goto out_reset_timer;
>         }
> --
> 2.24.0.393.g34dc348eaf-goog
>