netdev - Re: [PATCH net-next 1/2] tcp: do not set a zero size receive buffer

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Message-ID: <4b9bf13b-1c5e-4262-8315-6b88fe3eb32c@kernel.org>
Date: Sat, 19 Jul 2025 00:15:15 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, Neal Cardwell <ncardwell@...gle.com>,
 Kuniyuki Iwashima <kuniyu@...gle.com>, "David S. Miller"
 <davem@...emloft.net>, David Ahern <dsahern@...nel.org>,
 Simon Horman <horms@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] tcp: do not set a zero size receive buffer

Hi Paolo,

On 18/07/2025 19:25, Paolo Abeni wrote:
> The nipa CI is reporting frequent failures in the mptcp_connect
> self-tests.
> 
> In the failing scenarios (TCP -> MPTCP) the involved sockets are
> actually plain TCP ones, as fallback for passive socket at 2whs
> time cause the MPTCP listener to actually create a TCP socket.
> 
> The transfer is stuck due to the receiver buffer being zero.
> With the stronger check in place, tcp_clamp_window() can be invoked
> while the TCP socket has sk_rmem_alloc == 0, and the receive buffer
> will be zeroed, too.
> 
> Pass to tcp_clamp_window() even the current skb truesize, so that
> such helper could compute and use the actual limit enforced by
> the stack.

Thank you for this fix!

Acked-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>

I guess we can drop "mptcp-connect-sh" from the ignored tests then :)

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