netdev - Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

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Date: Mon, 6 Nov 2023 09:18:54 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Mat Martineau <martineau@...nel.org>, Matthieu Baerts <matttbe@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org, 
	mptcp@...ts.linux.dev
Subject: Re: [PATCH net-next 9/9] mptcp: refactor sndbuf auto-tuning

On Mon, Nov 6, 2023 at 8:22 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> Hi,
>
> On Thu, 2023-11-02 at 18:19 +0100, Eric Dumazet wrote:
> > On Mon, Oct 23, 2023 at 10:45 PM Mat Martineau <martineau@...nel.org> wrote:
> > >
> > > From: Paolo Abeni <pabeni@...hat.com>
> > >
> > > The MPTCP protocol account for the data enqueued on all the subflows
> > > to the main socket send buffer, while the send buffer auto-tuning
> > > algorithm set the main socket send buffer size as the max size among
> > > the subflows.
> > >
> > > That causes bad performances when at least one subflow is sndbuf
> > > limited, e.g. due to very high latency, as the MPTCP scheduler can't
> > > even fill such buffer.
> > >
> > > Change the send-buffer auto-tuning algorithm to compute the main socket
> > > send buffer size as the sum of all the subflows buffer size.
> > >
> > > Reviewed-by: Mat Martineau <martineau@...nel.org>
> > > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > > Signed-off-by: Mat Martineau <martineau@...nel.org
> >
> > ...
> >
> > > diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> > > index df208666fd19..2b43577f952e 100644
> > > --- a/net/mptcp/subflow.c
> > > +++ b/net/mptcp/subflow.c
> > > @@ -421,6 +421,7 @@ static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct soc
> > >
> > >  void __mptcp_set_connected(struct sock *sk)
> > >  {
> > > +       __mptcp_propagate_sndbuf(sk, mptcp_sk(sk)->first);
> >
> > ->first can be NULL here, according to syzbot.
>
> I'm sorry for the latency on my side, I had a different kind of crash
> to handle here.
>
> Do you have a syzkaller report available? Or the call trace landing
> here?

Sure, let me release the report.