netdev - Re: tcp: Do not apply TSO segment limit to non-TSO packets

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Message-Id: <20150102.161355.1471650729858130736.davem@davemloft.net>
Date:	Fri, 02 Jan 2015 16:13:55 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	thomas.jarosch@...ra2net.com, netdev@...r.kernel.org,
	edumazet@...gle.com, steffen.klassert@...unet.com,
	bhutchings@...arflare.com
Subject: Re: tcp: Do not apply TSO segment limit to non-TSO packets

From: Herbert Xu <herbert@...dor.apana.org.au>
Date: Thu, 1 Jan 2015 00:39:23 +1100

> Thomas Jarosch reported IPsec TCP stalls when a PMTU event occurs.
> 
> In fact the problem was completely unrelated to IPsec.  The bug is
> also reproducible if you just disable TSO/GSO.
> 
> The problem is that when the MSS goes down, existing queued packet
> on the TX queue that have not been transmitted yet all look like
> TSO packets and get treated as such.
> 
> This then triggers a bug where tcp_mss_split_point tells us to
> generate a zero-sized packet on the TX queue.  Once that happens
> we're screwed because the zero-sized packet can never be removed
> by ACKs.
> 
> Fixes: 1485348d242 ("tcp: Apply device TSO segment limit earlier")
> Reported-by: Thomas Jarosch <thomas.jarosch@...ra2net.com>
> Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>

Applied and queued up for -stable, thanks Herbert.
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