linux-kernel - Re: [PATCH] net: sctp: recover a tranport when an ack comes

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Date:	Thu, 14 Nov 2013 21:34:55 -0500
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Chang Xiangzhong <changxiangzhong@...il.com>, nhorman@...driver.com
CC:	davem@...emloft.net, linux-sctp@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	dreibh@...ula.no, ernstgr@...ula.no
Subject: Re: [PATCH] net: sctp: recover a tranport when an ack comes

On 11/14/2013 03:40 PM, Chang Xiangzhong wrote:
> Expected Behavior:
> When hearing an ack from a tranport/path, set its state to normal/on if it's
> in abnormal(__partial_failure__ or inactive) state.
>
> state machine of tranport->state
> Whenever a T3_RTX timer expires, then transport->error_count++.
> When (association->pf_retrans < transport->error_count < tranport->pathmaxrtx)
> 	transport->state = SCTP_PF //partial failure
>
> When a heartbeat-ack comes or conventional ack acknowledged its availability,
> 	transport->state = SCTP_ON
>
> Signed-off-by: Chang Xiangzhong <changxiangzhong@...il.com>
> Fixes: 5aa93bcf66f ("sctp: Implement quick failover draft from tsvwg")

I don't think this is right.  The spec states:
  8.  ACKs for retransmissions do not transition a PF destination back
        to Active state, since a sender cannot disambiguate whether the
        ack was for the original transmission or the retransmission(s).


Now, the proper way to this would would be modify 
sctp_assoc_control_transport() to transition the transport state to
ACTIVE if it was PF transport that was chosen to send data.

-vlad

> ---
>   net/sctp/outqueue.c |    1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
> index 94df758..2557fa5 100644
> --- a/net/sctp/outqueue.c
> +++ b/net/sctp/outqueue.c
> @@ -1517,6 +1517,7 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>   			 * active if it is not so marked.
>   			 */
>   			if ((transport->state == SCTP_INACTIVE ||
> +			     transport->state == SCTP_PF ||
>   			     transport->state == SCTP_UNCONFIRMED) &&
>   			    sctp_cmp_addr_exact(&transport->ipaddr, saddr)) {
>   				sctp_assoc_control_transport(
>

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