linux-kernel - Re: [PATCH v2 net-next] inet: do not set backlog if listen fails

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Date:   Mon, 8 Oct 2018 18:46:58 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] inet: do not set backlog if listen fails

On Mon, Oct 8, 2018 at 1:39 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 10/07/2018 06:36 AM, Yafang Shao wrote:
> > We don't need to set the backlog if listen fails.
> > The sk_max_ack_backlog will be set in the caller inet_listen() and
> > dccp_listen_start() if inet_csk_listen_start() return without error.
> > So just remove this line to avoid this unnecessary operation.
> >
> > Regarding sk_ack_backlog, we have to set it before a TCP/DCCP socket is
> > ready to accept new flows to avoid race, because dccp and tcp have lockless
> > listeners
> >
>
> Really could you not add irrelevant stuff in the changelog ?
>

Sure, I will remove it.

> This patch simply removes one redundant setting, you do not have to explain
> about dccp/tcp being lockless and that sk_ack_backlog is not touched by this patch.
>
> Also the title is misleading, since we will still set the backlog even if the listen
> fails.
>
> If you really want sk_max_ack_backlog being not changed if listen() fails,
> then I am afraid you will need to submit a different patch.

After this patch, sk_max_ack_backlog will only be set after the sk is
successfully added to listening hash table,
and then 0 is returned, that means listen()  is successful.

Take inet_listen() for example,

if (old_state != TCP_LISTEN) {
    err = inet_csk_listen_start(sk, backlog);
    if (err)
        goto out;
}

// it can only be set if err is 0.
sk->sk_max_ack_backlog = backlog;
err = 0;

out:
    return err;


Pls. correct me if I missed something.

Thanks
Yafang