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Message-ID: <20240129110108.GK401354@kernel.org>
Date: Mon, 29 Jan 2024 11:01:08 +0000
From: Simon Horman <horms@...nel.org>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: edumazet@...gle.com, davem@...emloft.net, dsahern@...nel.org,
kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3] net: tcp: accept old ack during closing
On Fri, Jan 26, 2024 at 12:05:19PM +0800, Menglong Dong wrote:
> For now, the packet with an old ack is not accepted if we are in
> FIN_WAIT1 state, which can cause retransmission. Taking the following
> case as an example:
>
> Client Server
> | |
> FIN_WAIT1(Send FIN, seq=10) FIN_WAIT1(Send FIN, seq=20, ack=10)
> | |
> | Send ACK(seq=21, ack=11)
> Recv ACK(seq=21, ack=11)
> |
> Recv FIN(seq=20, ack=10)
>
> In the case above, simultaneous close is happening, and the FIN and ACK
> packet that send from the server is out of order. Then, the FIN will be
> dropped by the client, as it has an old ack. Then, the server has to
> retransmit the FIN, which can cause delay if the server has set the
> SO_LINGER on the socket.
>
> Old ack is accepted in the ESTABLISHED and TIME_WAIT state, and I think
> it should be better to keep the same logic.
>
> In this commit, we accept old ack in FIN_WAIT1/FIN_WAIT2/CLOSING/LAST_ACK
> states. Maybe we should limit it to FIN_WAIT1 for now?
>
> Signed-off-by: Menglong Dong <menglong8.dong@...il.com>
> ---
> v3:
> - fix unsigned/signed compare error
Thanks for the update.
I wish this could be done without a cast.
But I do see that what you have done is
consistent with at least one other use of tcp_ack().
So from that point of view:
Reviewed-by: Simon Horman <horms@...nel.org>
...
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