[rds-devel] [PATCH net-next] RDS-TCP: Reset tcp callbacks if re-using an outgoing socket in rds_tcp_accept_one()

[David Miller]

From: Sowmini Varadhan <sowmini.varadhan at oracle.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 at oracle.com>

Applied.