netdev - Re: [PATCH 0/1] mv643xx_eth: Disable TSO by default

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Message-Id: <20141101.134215.1777123022766405287.davem@davemloft.net>
Date:	Sat, 01 Nov 2014 13:42:15 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ezequiel.garcia@...e-electrons.com, netdev@...r.kernel.org,
	thomas.petazzoni@...e-electrons.com,
	gregory.clement@...e-electrons.com, tawfik@...vell.com,
	alior@...vell.com, nadavh@...vell.com
Subject: Re: [PATCH 0/1] mv643xx_eth: Disable TSO by default

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 01 Nov 2014 10:26:06 -0700

> On Sat, 2014-11-01 at 12:30 -0300, Ezequiel Garcia wrote:
>> Several users ([1], [2]) have been reporting data corruption with TSO on
>> Kirkwood platforms (i.e. using the mv643xx_eth driver).
>> 
>> Until we manage to find what's causing this, this simple patch will make
>> the TSO path disabled by default. This patch should be queued for stable,
>> fixing the TSO feature introduced in v3.16.
>> 
>> The corruption itself is very easy to reproduce: checking md5sum on a mounted
>> NFS directory gives a different result each time. Same tests using the mvneta
>> driver (Armada 370/38x/XP SoC) pass with no issues.
>> 
>> Frankly, I'm a bit puzzled about this, and so any ideas or debugging hints
>> are well received.
> 
> lack of barriers maybe ?
> 
> It seems you might need to populate all TX descriptors but delay the
> first, like doing the populate in descending order.
> 
> If you take a look at txq_submit_skb(), you'll see the final
> desc->cmd_sts = cmd_sts (line 959) is done _after_ frags were cooked by
> txq_submit_frag_skb()
> 
> You should kick the nick only when all TX descriptors are ready and
> committed to memory.

Yes, please look into whether doing something like this fixes the
problem.
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