Re: [tipc-discussion] [net] tipc: fix incorrect increasing of link window

[Jon M. <jm...@re...>]

Hmm, I was sure I already did.
But anyway:

Acked-by: Jon Maloy <jm...@re...>


On 4/14/20 3:54 AM, Tuong Tong Lien wrote:
> Hi Jon, all,
>
> I understand that you have agreed on the solution to the issue in previous discussions, but please make a formal "ack-by" so I will send it to net.
> Thanks a lot!
>
> BR/Tuong
>
> -----Original Message-----
> From: Tuong Lien <tuo...@de...>
> Sent: Friday, March 27, 2020 7:31 PM
> To: jm...@re...; ma...@do...; yin...@wi...; tip...@li...
> Cc: tip...@de...
> Subject: [net] tipc: fix incorrect increasing of link window
>
> In commit 16ad3f4022bb ("tipc: introduce variable window congestion
> control"), we allow link window to change with the congestion avoidance
> algorithm. However, there is a bug that during the slow-start if packet
> retransmission occurs, the link will enter the fast-recovery phase, set
> its window to the 'ssthresh' which is never less than 300, so the link
> window suddenly increases to that limit instead of decreasing.
>
> Consequently, two issues have been observed:
>
> - For broadcast-link: it can leave a gap between the link queues that a
> new packet will be inserted and sent before the previous ones, i.e. not
> in-order.
>
> - For unicast: the algorithm does not work as expected, the link window
> jumps to the slow-start threshold whereas packet retransmission occurs.
>
> This commit fixes the issues by avoiding such the link window increase,
> but still decreasing if the 'ssthresh' is lowered.
>
> Signed-off-by: Tuong Lien <tuo...@de...>
> ---
>   net/tipc/link.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/tipc/link.c b/net/tipc/link.c
> index 467c53a1fb5c..d4675e922a8f 100644
> --- a/net/tipc/link.c
> +++ b/net/tipc/link.c
> @@ -1065,7 +1065,7 @@ static void tipc_link_update_cwin(struct tipc_link *l, int released,
>   	/* Enter fast recovery */
>   	if (unlikely(retransmitted)) {
>   		l->ssthresh = max_t(u16, l->window / 2, 300);
> -		l->window = l->ssthresh;
> +		l->window = min_t(u16, l->ssthresh, l->window);
>   		return;
>   	}
>   	/* Enter slow start */