netdev - Re: [net-next 1/1] tipc: don't send gap blocks in ACK messages

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Message-Id: <20191217.141718.1870382028958768011.davem@davemloft.net>
Date:   Tue, 17 Dec 2019 14:17:18 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     jon.maloy@...csson.com
Cc:     netdev@...r.kernel.org, tung.q.nguyen@...tech.com.au,
        hoang.h.le@...tech.com.au, lxin@...hat.com, shuali@...hat.com,
        ying.xue@...driver.com, edumazet@...gle.com,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [net-next 1/1] tipc: don't send gap blocks in ACK messages

From: Jon Maloy <jon.maloy@...csson.com>
Date: Mon, 16 Dec 2019 19:21:02 +0100

> In the commit referred to below we eliminated sending of the 'gap'
> indicator in regular ACK messages, reserving this to explicit NACK
> ditto.
> 
> Unfortunately we missed to also eliminate building of the 'gap block'
> area in ACK messages. This area is meant to report gaps in the
> received packet sequence following the initial gap, so that lost
> packets can be retransmitted earlier and received out-of-sequence
> packets can be released earlier. However, the interpretation of those
> blocks is dependent on a complete and correct sequence of gaps and
> acks. Hence, when the initial gap indicator is missing a single gap
> block will be interpreted as an acknowledgment of all preceding
> packets. This may lead to packets being released prematurely from the
> sender's transmit queue, with easily predicatble consequences.
> 
> We now fix this by not building any gap block area if there is no
> initial gap to report.
> 
> Fixes: commit 02288248b051 ("tipc: eliminate gap indicator from ACK messages")
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied, thanks Jon.