linux-kernel - Re: [PATCH net v2 2/2] tcp: limit wake-up for crossed SYN cases to SYN-ACK

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Message-ID: <CANn89iKOa8YKYjz4jVN0R+3qCpcALTAJ_8W+pd+022jAMT+Zjw@mail.gmail.com>
Date: Tue, 23 Jul 2024 16:32:29 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>, Jerry Chu <hkchu@...gle.com>, netdev@...r.kernel.org, 
	mptcp@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2 2/2] tcp: limit wake-up for crossed SYN cases to SYN-ACK

On Thu, Jul 18, 2024 at 12:34 PM Matthieu Baerts (NGI0)
<matttbe@...nel.org> wrote:
>
> sk->sk_socket will be assigned in case of marginal crossed SYN, but also
> in other cases, e.g.
>
>  - With TCP Fast Open, if the connection got accept()'ed before
>    receiving the 3rd ACK ;
>
>  - With MPTCP, when accepting additional subflows to an existing MPTCP
>    connection.
>
> In these cases, the switch to TCP_ESTABLISHED is done when receiving the
> 3rd ACK, without the SYN flag then.
>
> To properly restrict the wake-up to crossed SYN cases, it is then
> required to also limit the check to packets containing the SYN-ACK
> flags.
>
> While at it, also update the attached comment: sk->sk_sleep has been
> removed in 2010, and replaced by sk->sk_wq in commit 43815482370c ("net:
> sock_def_readable() and friends RCU conversion").
>
> Fixes: 168a8f58059a ("tcp: TCP Fast Open Server - main code path")
> Suggested-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
> ---
> Notes:
>  - The above 'Fixes' tag should correspond to the commit introducing the
>    possibility to have sk->sk_socket being set there in other cases than
>    the crossed SYN one. But I might have missed other cases. Maybe
>    1da177e4c3f4 ("Linux-2.6.12-rc2") might be safer? On the other hand,
>    I don't think this wake-up was causing any visible issue, apart from
>    not being needed.

This seems a net-next candidate to me ?