Commit edadedf1 authored Apr 15, 2020 by Tuong Lien Committed by David S. Miller Apr 15, 2020

tipc: fix incorrect increasing of link window



In commit 16ad3f40 ("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.

Fixes: 16ad3f40 ("tipc: introduce variable window congestion control")
Acked-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Tuong Lien <tuong.t.lien@dektech.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5309960e

net/tipc/link.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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 */

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