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

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Date:	Fri, 11 Oct 2013 07:48:56 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Vlad Yasevich <vyasevic@...hat.com>
Cc:	netdev@...r.kernel.org, Cong Wang <xiyou.wangcong@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH] bridge: update mdb expiration timer upon reports.

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>
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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