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

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Message-Id: <20200415.162404.1740698602850159370.davem@davemloft.net>
Date:   Wed, 15 Apr 2020 16:24:04 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     tuong.t.lien@...tech.com.au
Cc:     jmaloy@...hat.com, maloy@...jonn.com, ying.xue@...driver.com,
        netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net
Subject: Re: [net] tipc: fix incorrect increasing of link window

From: Tuong Lien <tuong.t.lien@...tech.com.au>
Date: Wed, 15 Apr 2020 18:34:49 +0700

> 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.
> 
> Fixes: 16ad3f4022bb ("tipc: introduce variable window congestion control")
> Acked-by: Jon Maloy <jmaloy@...hat.com>
> Signed-off-by: Tuong Lien <tuong.t.lien@...tech.com.au>

Applied, thanks.