netdev - Re: [PATCH] bridge: update mdb expiration timer upon reports.

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Message-Id: <20131011.005730.1355286910518558752.davem@davemloft.net>
Date:	Fri, 11 Oct 2013 00:57:30 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	vyasevic@...hat.com, netdev@...r.kernel.org,
	xiyou.wangcong@...il.com, stephen@...workplumber.org
Subject: Re: [PATCH] bridge: update mdb expiration timer upon reports.

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Fri, 11 Oct 2013 07:48:56 +0800

> On Thu, Oct 10, 2013 at 03:57:59PM -0400, Vlad Yasevich wrote:
>> commit 9f00b2e7cf241fa389733d41b615efdaa2cb0f5b
>> 	bridge: only expire the mdb entry when query is received
>> changed the mdb expiration timer to be armed only when QUERY is
>> received.  Howerver, this causes issues in an environment where
>> the multicast server socket comes and goes very fast while a client
>> is trying to send traffic to it.
>> 
>> The root cause is a race where a sequence of LEAVE followed by REPORT
>> messages can race against QUERY messages generated in response to LEAVE.
>> The QUERY ends up starting the expiration timer, and that timer can
>> potentially expire after the new REPORT message has been received signaling
>> the new join operation.  This leads to a significant drop in multicast
>> traffic and possible complete stall. 
>> 
>> The solution is to have REPORT messages update the expiration timer
>> on entries that already exist.
>> 
>> CC: Cong Wang <xiyou.wangcong@...il.com>
>> CC: Herbert Xu <herbert@...dor.apana.org.au>
>> CC: Stephen Hemminger <stephen@...workplumber.org>
>> Signed-off-by: Vlad Yasevich <vyasevic@...hat.com>
> 
> Good catch.  Thanks!
> 
> Acked-by: Herbert Xu <herbert@...dor.apana.org.au>

Applied, and queued up for -stable, thanks everyone.
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