netdev - Re: [PATCH v2 net-next 1/2] tcp: do not set a zero size receive buffer

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Message-ID: <CANn89i+pNkbsF-1jHZzCg7bebAABTAtMOWgyCyf5erOszb3dBA@mail.gmail.com>
Date: Mon, 21 Jul 2025 11:21:22 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Neal Cardwell <ncardwell@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>, 
	Matthieu Baerts <matttbe@...nel.org>
Subject: Re: [PATCH v2 net-next 1/2] tcp: do not set a zero size receive buffer

On Mon, Jul 21, 2025 at 10:21 AM Paolo Abeni <pabeni@...hat.com> 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.
>
> Check for the critical condition in tcp_prune_queue() and just
> drop the packet without shrinking the receiver buffer.
>
> Fixes: 1d2fbaad7cd8 ("tcp: stronger sk_rcvbuf checks")
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks a lot !