netdev - Re: [PATCH net-next] net/tcp_fastopen: remove tcp_fastopen_ctx

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Date:   Mon, 19 Jul 2021 08:46:58 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] net/tcp_fastopen: remove tcp_fastopen_ctx_lock

On Mon, Jul 19, 2021 at 3:11 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> Remove the (per netns) spinlock in favor of xchg() atomic operations.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Wei Wang <weiwan@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> ---

Acked-by: Wei Wang <weiwan@...gle.com>

>  include/net/netns/ipv4.h |  1 -
>  net/ipv4/tcp_fastopen.c  | 17 +++--------------
>  net/ipv4/tcp_ipv4.c      |  1 -
>  3 files changed, 3 insertions(+), 16 deletions(-)
>
> diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
> index b8620519eace8191c76c41f37bd51ac0d3788bc2..2f65701a43c953bd3a9a9e3d491882cb7bb11859 100644
> --- a/include/net/netns/ipv4.h
> +++ b/include/net/netns/ipv4.h
> @@ -174,7 +174,6 @@ struct netns_ipv4 {
>         int sysctl_tcp_fastopen;
>         const struct tcp_congestion_ops __rcu  *tcp_congestion_control;
>         struct tcp_fastopen_context __rcu *tcp_fastopen_ctx;
> -       spinlock_t tcp_fastopen_ctx_lock;
>         unsigned int sysctl_tcp_fastopen_blackhole_timeout;
>         atomic_t tfo_active_disable_times;
>         unsigned long tfo_active_disable_stamp;
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 47c32604d38fca960d2cd56f3588bfd2e390b789..1a9fbd5448a719bb5407a8d1e8fbfbe54f56f258 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -55,12 +55,7 @@ void tcp_fastopen_ctx_destroy(struct net *net)
>  {
>         struct tcp_fastopen_context *ctxt;
>
> -       spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
> -
> -       ctxt = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
> -                               lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
> -       rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, NULL);
> -       spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
> +       ctxt = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, NULL);
>
>         if (ctxt)
>                 call_rcu(&ctxt->rcu, tcp_fastopen_ctx_free);
> @@ -89,18 +84,12 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
>                 ctx->num = 1;
>         }
>
> -       spin_lock(&net->ipv4.tcp_fastopen_ctx_lock);
>         if (sk) {
>                 q = &inet_csk(sk)->icsk_accept_queue.fastopenq;
> -               octx = rcu_dereference_protected(q->ctx,
> -                       lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
> -               rcu_assign_pointer(q->ctx, ctx);
> +               octx = xchg((__force struct tcp_fastopen_context **)&q->ctx, ctx);
>         } else {
> -               octx = rcu_dereference_protected(net->ipv4.tcp_fastopen_ctx,
> -                       lockdep_is_held(&net->ipv4.tcp_fastopen_ctx_lock));
> -               rcu_assign_pointer(net->ipv4.tcp_fastopen_ctx, ctx);
> +               octx = xchg((__force struct tcp_fastopen_context **)&net->ipv4.tcp_fastopen_ctx, ctx);
>         }
> -       spin_unlock(&net->ipv4.tcp_fastopen_ctx_lock);
>
>         if (octx)
>                 call_rcu(&octx->rcu, tcp_fastopen_ctx_free);
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index b9dc2d6197be8b8b03a4d052ad1c87987c7a62aa..e9321dd39cdbcb664843d4ada09a21685b93abb7 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -2964,7 +2964,6 @@ static int __net_init tcp_sk_init(struct net *net)
>         net->ipv4.sysctl_tcp_comp_sack_slack_ns = 100 * NSEC_PER_USEC;
>         net->ipv4.sysctl_tcp_comp_sack_nr = 44;
>         net->ipv4.sysctl_tcp_fastopen = TFO_CLIENT_ENABLE;
> -       spin_lock_init(&net->ipv4.tcp_fastopen_ctx_lock);
>         net->ipv4.sysctl_tcp_fastopen_blackhole_timeout = 60 * 60;
>         atomic_set(&net->ipv4.tfo_active_disable_times, 0);
>
> --
> 2.32.0.402.g57bb445576-goog
>