netdev - Re: [PATCH net v2] sctp: donot reset the overall_error_count in SHUTDOWN

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Date:	Wed, 26 Aug 2015 11:19:20 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Xin Long <lucien.xin@...il.com>,
	network dev <netdev@...r.kernel.org>
CC:	mleitner@...hat.com, tgraf@...radead.org, davem@...emloft.net
Subject: Re: [PATCH net v2] sctp: donot reset the overall_error_count in SHUTDOWN_RECEIVE
 state

On 08/23/2015 07:30 AM, Xin Long wrote:
> commit f8d960524 fix the 0 peer.rwnd issue in SHUTDOWN_PENDING state through
> not reseting the overall_error_count when receive a heartbeat, but the same
> issue also exists in SHUTDOWN_RECEIVE state.
> 
> so we change the condition to state < SCTP_STATE_SHUTDOWN_PENDING to reset the
> overall_error_count when receive a heartbeat, which can avoid the issue happen
> in SCTP_STATE_SHUTDOWN_RECEIVE.
> 
> as to SCTP_STATE_SHUTDOWN_ACK_SENT and SCTP_STATE_SHUTDOWN_SENT state, with
> this patch, it will not be affected by the heartbeat, cause these two states
> have been taken charge of by t2 timer.
> 
> Fixes: f8d960524 ("sctp: Enforce retransmission limit during shutdown")
> Signed-off-by: Xin Long <lucien.xin@...il.com>

The code is OK, but the change log could use some help.

How is this for the explanation:

Commit f8d960524 ("sctp: Enforce retransmission limit during shutdown") fixed a
problem with excessive retransmissions in the SHUTDOWN_PENDING by not resetting
the association overall_error_count.  This allowed the association to better
enforce assoc.max_retrans limit.

However, the same issue still exists when the association is in SHUTDOWN_RECEIVED
state.  In this state, HB-ACKs will continue to reset the overall_error_count
for the association would extend the lifetime of association unnecessarily.

This patch solves this by resetting the overall_error_count whenever the current
state is small then SCTP_STATE_SHUTDOWN_PENDING.  As a small side-effect, we
end up also handling SCTP_STATE_SHUTDOWN_ACK_SENT and SCTP_STATE_SHUTDOWN_SENT
states, but they are not really impacted because we disable Heartbeats in those
states.

Thanks
-vlad

> ---
>  net/sctp/sm_sideeffect.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index fef2acd..85e6f03 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -702,7 +702,7 @@ static void sctp_cmd_transport_on(sctp_cmd_seq_t *cmds,
>  	 * outstanding data and rely on the retransmission limit be reached
>  	 * to shutdown the association.
>  	 */
> -	if (t->asoc->state != SCTP_STATE_SHUTDOWN_PENDING)
> +	if (t->asoc->state < SCTP_STATE_SHUTDOWN_PENDING)
>  		t->asoc->overall_error_count = 0;
>  
>  	/* Clear the hb_sent flag to signal that we had a good
> 

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