netdev - Re: [PATCH net 1/1] tipc: fix problem with parallel link synchronization mechanism

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Message-Id: <20150429.150923.1291697432920867232.davem@davemloft.net>
Date:	Wed, 29 Apr 2015 15:09:23 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	jon.maloy@...csson.com
Cc:	netdev@...r.kernel.org, paul.gortmaker@...driver.com,
	erik.hugne@...csson.com, ying.xue@...driver.com, maloy@...jonn.com,
	tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH net 1/1] tipc: fix problem with parallel link
 synchronization mechanism

From: Jon Maloy <jon.maloy@...csson.com>
Date: Tue, 28 Apr 2015 16:59:04 -0400

> Currently, we try to accumulate arrived packets in the links's
> 'deferred' queue during the parallel link syncronization phase.
> 
> This entails two problems:
> 
> - With an unlucky combination of arriving packets the algorithm
>   may go into a lockstep with the out-of-sequence handling function,
>   where the synch mechanism is adding a packet to the deferred queue,
>   while the out-of-sequence handling is retrieving it again, thus
>   ending up in a loop inside the node_lock scope.
> 
> - Even if this is avoided, the link will very often send out
>   unnecessary protocol messages, in the worst case leading to
>   redundant retransmissions.
> 
> We fix this by just dropping arriving packets on the upcoming link
> during the synchronization phase, thus relying on the retransmission
> protocol to resolve the situation once the two links have arrived to
> a synchronized state.
> 
> Reviewed-by: Erik Hugne <erik.hugne@...csson.com>
> Reviewed-by: Ying Xue <ying.xue@...driver.com>
> Signed-off-by: Jon Maloy <jon.maloy@...csson.com>

Applied, thanks Jon.
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