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

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Message-ID: <ab8b02fb-c387-47e3-a732-9fad9d5ef48b@kernel.org>
Date: Tue, 23 Jul 2024 16:40:08 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
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

Hi Eric,

Thank you for the review!

On 23/07/2024 16:32, Eric Dumazet wrote:
> 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 ?

Fine by me!

I modified this line mainly because Kuniyuki mentioned that it was the
same check as the new one, modified in patch 1/2. I didn't find any
visible issue with the wakeup, so I guess it can go to net-next.

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