netdev - Re: [PATCH net-next] tcp: accept RST for rcv_nxt

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Message-ID: <1484679754.13165.70.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 17 Jan 2017 11:02:34 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jason Baron <jbaron@...mai.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] tcp: accept RST for rcv_nxt - 1 after
 receiving a FIN

On Tue, 2017-01-17 at 13:37 -0500, Jason Baron wrote:
> From: Jason Baron <jbaron@...mai.com>
> 
> Using a Mac OSX box as a client connecting to a Linux server, we have found
> that when certain applications (such as 'ab'), are abruptly terminated
> (via ^C), a FIN is sent followed by a RST packet on tcp connections. The
> FIN is accepted by the Linux stack but the RST is sent with the same
> sequence number as the FIN, and Linux responds with a challenge ACK per
> RFC 5961. The OSX client then sometimes (they are rate-limited) does not
> reply with any RST as would be expected on a closed socket.
> 
> This results in sockets accumulating on the Linux server left mostly in
> the CLOSE_WAIT state, although LAST_ACK and CLOSING are also possible.
> This sequence of events can tie up a lot of resources on the Linux server
> since there may be a lot of data in write buffers at the time of the RST.
> Accepting a RST equal to rcv_nxt - 1, after we have already successfully
> processed a FIN, has made a significant difference for us in practice, by
> freeing up unneeded resources in a more expedient fashion.

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

Thanks Jason !