netdev - Re: [PATCH net-next] tcp: fix RFS vs lockless listeners

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Date:	Thu, 8 Oct 2015 14:11:52 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix RFS vs lockless listeners

On Thu, Oct 8, 2015 at 11:16 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> Before recent TCP listener patches, we were updating listener
> sk->sk_rxhash before the cloning of master socket.
>
> children sk_rxhash was therefore correct after the normal 3WHS.
>
> But with lockless listener, we no longer dirty/change listener sk_rxhash
> as it would be racy.
>
> We need to correctly update the child sk_rxhash, otherwise first data
> packet wont hit correct cpu if RFS is used.
>
> Fixes: 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Willem de Bruijn <willemb@...gle.com>
> Cc: Tom Herbert <tom@...bertland.com>
> ---
>  net/ipv4/syncookies.c    |    1 +
>  net/ipv4/tcp_minisocks.c |    1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
> index 8113c30ccf96..2dbb11331f6c 100644
> --- a/net/ipv4/syncookies.c
> +++ b/net/ipv4/syncookies.c
> @@ -225,6 +225,7 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
>         child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
>         if (child) {
>                 atomic_set(&req->rsk_refcnt, 1);
> +               sock_rps_save_rxhash(child, skb);
>                 inet_csk_reqsk_queue_add(sk, req, child);
>         } else {
>                 reqsk_free(req);
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index 9adf1e2c3170..1079e6ad77fe 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -768,6 +768,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
>         if (!child)
>                 goto listen_overflow;
>
> +       sock_rps_save_rxhash(child, skb);
>         tcp_synack_rtt_meas(child, req);
>         inet_csk_reqsk_queue_drop(sk, req);
>         inet_csk_reqsk_queue_add(sk, req, child);
>
>
Acked-by: Tom Herbert <tom@...bertland.com>
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