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

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Message-ID: <1414862766.31792.7.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Sat, 01 Nov 2014 10:26:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Lior Amsalem <alior@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>
Subject: Re: [PATCH 0/1] mv643xx_eth: Disable TSO by default

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.



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