netdev - Re: [PATCH net-next] RDS-TCP: Reset tcp callbacks if re-using an outgoing socket in rds_tcp_accept

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Message-Id: <20151013.042314.2113017864511427578.davem@davemloft.net>
Date:	Tue, 13 Oct 2015 04:23:14 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	sowmini.varadhan@...cle.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	rds-devel@....oracle.com, ajaykumar.hotchandani@...cle.com,
	igor.maximov@...cle.com, santosh.shilimkar@...cle.com
Subject: Re: [PATCH net-next] RDS-TCP: Reset tcp callbacks if re-using an
 outgoing socket in rds_tcp_accept_one()

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Sun, 11 Oct 2015 16:49:44 -0400

> 
> Consider the following "duelling syn" sequence between two peers A and B:
>         	A		B
>         	SYN1     -->
>         	    	<--	SYN2
>         	SYN2ACK  -->
> 
> Note that the SYN/ACK has already been sent out by TCP before
> rds_tcp_accept_one() gets invoked as part of callbacks.
> 
> If the inet_addr(A) is numerically less than inet_addr(B),
> the arbitration scheme in rds_tcp_accept_one() will prefer the
> TCP connection triggered by SYN1, and will send a CLOSE for the
> SYN2 (just after the SYN2ACK was sent).
> 
> Since B also follows the same arbitration scheme, it will send the SYN-ACK
> for SYN1 that will set up a healthy ESTABLISHED connection on both sides.
> B will also get a  CLOSE for SYN2, which should result in the cleanup
> of the TCP state machine for SYN2, but it should not trigger any
> stale RDS-TCP callbacks (such as ->writespace, ->state_change etc),
> that would disrupt the progress of the SYN2 based RDS-TCP  connection.
> 
> Thus the arbitration scheme in rds_tcp_accept_one() should restore
> rds_tcp callbacks for the winner before setting them up for the
> new accept socket, and also make sure that conn->c_outgoing
> is set to 0 so that we do not trigger any reconnect attempts on the
> passive side of the tcp socket in the future, in conformance with
> commit c82ac7e69efe ("net/rds: RDS-TCP: only initiate reconnect attempt
> on outgoing TCP socket.")
> 
> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>

Applied.
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