Re: [PATCH v3 mptcp-next 2/7] mptcp: avoid unneeded subflow-level drops.

[Matthieu Baerts <matttbe@kernel.org>]

Hi Paolo,

On 07/11/2025 09:32, Paolo Abeni wrote:
> The rcv window is shared among all the subflows. Currently, MPTCP sync
> the TCP-level rcv window with the MPTCP one at tcp_transmit_skb() time.
> 
> The above means that incoming data may sporadically observe outdated
> TCP-level rcv window and being wrongly dropped by TCP.
> 
> Address the issue checking for the edge condition before queuing the data
> at TCP level, and eventually syncing the rcv window as needed.
> 
> Note that the issue is actually present from the very first MPTCP
> implementation, but backports older than the blamed commit below will range
> from impossible to useless.

Thank you for this patch!

It looks good to me:

Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

> Before:
> nstat >/dev/null ;sleep 1; nstat -z TcpExtBeyondWindow
> TcpExtBeyondWindow              14                 0.0
> 
> After:
> nstat >/dev/null ;sleep 1; nstat -z TcpExtBeyondWindow
> TcpExtBeyondWindow              0                  0.0
Should we eventually track this MIB counter in mptcp_connect.sh?

> Fixes: fa3fe2b15031 ("mptcp: track window announced to peer")

While there are still discussions on patch 6/7, to ease things, I
suggest already applying only this patch in our tree (fixes for -net),
the only material for 'net' from what I understood.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.