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

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Message-ID: <80acd903-3cde-4232-8a78-ce20a3e746fa@kernel.org>
Date: Mon, 3 Jun 2024 15:57:06 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Jason Xing <kerneljasonxing@...il.com>
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

Hi Jason,

On 03/06/2024 15:26, Jason Xing wrote:
> 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"
> ?
Yes, thank you, it looks good to me. But while at it, you can also add
the reason:

  case TCP_CLOSE_WAIT:
          /* Unlike TCP, MPTCP sk would not have the TCP_SYN_RECV state:
           * MPTCP "accepted" sockets will be created later on. So no
           * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
           */

WDYT?

Cheers,
Matt
-- 
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