netdev - Re: [PATCH net v4 2/2] mptcp: count CLOSE-WAIT sockets for MPTCP_MIB

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Message-ID: <CAL+tcoAa+8pEcW5C3jjU4cieHBm8PUWMKUR=hP8sqQbh1gmVug@mail.gmail.com>
Date: Mon, 3 Jun 2024 21:26:12 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, 
	davem@...emloft.net, dsahern@...nel.org, martineau@...nel.org, 
	geliang@...nel.org, netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net v4 2/2] mptcp: count CLOSE-WAIT sockets for MPTCP_MIB_CURRESTAB

Hello Matthieu,

On Mon, Jun 3, 2024 at 8:47 PM Matthieu Baerts <matttbe@...nel.org> wrote:
>
> Hi Jason,
>
> On 31/05/2024 11:17, Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Like previous patch does in TCP, we need to adhere to RFC 1213:
> >
> >   "tcpCurrEstab OBJECT-TYPE
> >    ...
> >    The number of TCP connections for which the current state
> >    is either ESTABLISHED or CLOSE- WAIT."
> >
> > So let's consider CLOSE-WAIT sockets.
> >
> > The logic of counting
> > When we increment the counter?
> > a) Only if we change the state to ESTABLISHED.
> >
> > When we decrement the counter?
> > a) if the socket leaves ESTABLISHED and will never go into CLOSE-WAIT,
> > say, on the client side, changing from ESTABLISHED to FIN-WAIT-1.
> > b) if the socket leaves CLOSE-WAIT, say, on the server side, changing
> > from CLOSE-WAIT to LAST-ACK.
>
> Thank you for this modification, and for having updated the Fixes tag.
>
> > Fixes: d9cd27b8cd19 ("mptcp: add CurrEstab MIB counter support")
> > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > ---
> >  net/mptcp/protocol.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> > index 7d44196ec5b6..6d59c1c4baba 100644
> > --- a/net/mptcp/protocol.c
> > +++ b/net/mptcp/protocol.c
> > @@ -2916,9 +2916,10 @@ void mptcp_set_state(struct sock *sk, int state)
> >               if (oldstate != TCP_ESTABLISHED)
> >                       MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
> >               break;
> > -
> > +     case TCP_CLOSE_WAIT:
> > +             break;
>
> The modification is correct: currently, and compared to TCP, the MPTCP
> "accepted" socket will not go through the TCP_SYN_RECV state because it
> will be created later on.
>
> Still, I wonder if it would not be clearer to explicitly mention this
> here, and (or) in the commit message, to be able to understand why the
> logic is different here, compared to TCP. I don't think the SYN_RECV
> state will be used in the future with MPTCP sockets, but just in case,
> it might help to mention TCP_SYN_RECV state here. Could add a small
> comment here above please?

Sure, but what comments do you suggest?
For example, the comment above the case statement is:
"Unlike TCP, MPTCP would not have TCP_SYN_RECV state, so we can skip
it directly"
?

Thanks,
Jason

>
> >       default:
> > -             if (oldstate == TCP_ESTABLISHED)
> > +             if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
> >                       MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);
> >       }
> >
>
> Cheers,
> Matt
> --
> Sponsored by the NGI0 Core fund.
>