linux-kernel - Re: [PATCH] tcp: fix TCP socks unreleased in BBR mode

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Date:   Wed, 3 Jun 2020 08:02:13 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Jason Xing <kerneljasonxing@...il.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, liweishi@...ishou.com,
        Shujin Li <lishujin@...ishou.com>
Subject: Re: [PATCH] tcp: fix TCP socks unreleased in BBR mode

On Wed, Jun 3, 2020 at 1:44 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Jun 2, 2020 at 10:05 PM Jason Xing <kerneljasonxing@...il.com> wrote:
> >
> > Hi Eric,
> >
> > I'm still trying to understand what you're saying before. Would this
> > be better as following:
> > 1) discard the tcp_internal_pacing() function.
> > 2) remove where the tcp_internal_pacing() is called in the
> > __tcp_transmit_skb() function.
> >
> > If we do so, we could avoid 'too late to give up pacing'. Meanwhile,
> > should we introduce the tcp_wstamp_ns socket field as commit
> > (864e5c090749) does?
> >
>
> Please do not top-post on netdev mailing list.
>
>
> I basically suggested double-checking which point in TCP could end up
> calling tcp_internal_pacing()
> while the timer was already armed.
>
> I guess this is mtu probing.

Perhaps this could also happen from some of the retransmission code
paths that don't use tcp_xmit_retransmit_queue()? Perhaps
tcp_retransmit_timer() (RTO) and  tcp_send_loss_probe() TLP? It seems
they could indirectly cause a call to __tcp_transmit_skb() and thus
tcp_internal_pacing() without first checking if the pacing timer was
already armed?

neal