linux-kernel - Re: [PATCH] net: sctp: set chunk->tsn_gap

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Message-ID: <528F69B7.7020902@gmail.com>
Date:	Fri, 22 Nov 2013 09:27:03 -0500
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Chang Xiangzhong <changxiangzhong@...il.com>,
	nhorman@...driver.com, davem@...emloft.net
CC:	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sctp: set chunk->tsn_gap_acked at the end of cycle

On 11/22/2013 02:49 AM, Chang Xiangzhong wrote:
> tsn_gap_acked is an important state flag in chunk, which indicates if the
> chunk has been acked in gap reports before.

Actually, this bit indicates simply that the chunk has been acked.  It
doesn't state whether it's been acked in a gap report or via cumulative tsn.

> SFR-CACC algorithm depends on this
> variable. So set this at the end of each iteration, otherwise the SFR-CACC
> algorithm would never be toggled.
> 
> Signed-off-by: Chang Xiangzhong <changxiangzhong@...il.com>
> ---
>  net/sctp/outqueue.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/outqueue.c b/net/sctp/outqueue.c
> index 1b494fa..bff828c 100644
> --- a/net/sctp/outqueue.c
> +++ b/net/sctp/outqueue.c
> @@ -1396,7 +1396,6 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>  			 * while DATA was outstanding).
>  			 */
>  			if (!tchunk->tsn_gap_acked) {
> -				tchunk->tsn_gap_acked = 1;
>  				if (TSN_lt(*highest_new_tsn_in_sack, tsn))
>  					*highest_new_tsn_in_sack = tsn;
>  				bytes_acked += sctp_data_size(tchunk);
> @@ -1460,6 +1459,8 @@ static void sctp_check_transmitted(struct sctp_outq *q,
>  				 */
>  				list_add_tail(lchunk, &tlist);
>  			}
> +
> +			tchunk->tsn_gap_acked = 1;

The current code will set the state if it hasn't been set yet.  Why is
this needed?

Now there is an issue with tracking highest_new_tsn_in_sack.  The spec
is a little vague on this, but the highest_new_tsn_in_sack only supposed
to track tsns that have not been resent.  If a tsn has been reneged, and
then sent again, it is not considered 'new' thus should not count
toward highest_new_tsn_in_sack.  We currently do not track this right.

-vlad

-vlad

>  		} else {
>  			if (tchunk->tsn_gap_acked) {
>  				pr_debug("%s: receiver reneged on data TSN:0x%x\n",
> 

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