netdev - Re: [PATCH] net: mv643xx_eth: reclaim TX skbs only when released by the HW

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Message-ID: <20141105150521.GA25354@magnum.frso.rivierawaves.com>
Date:	Wed, 5 Nov 2014 16:05:21 +0100
From:	Karl Beldan <karl.beldan@...il.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	David Miller <davem@...emloft.net>,
	Ian Campbell <ijc@...lion.org.uk>,
	Karl Beldan <karl.beldan@...ierawaves.com>,
	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH] net: mv643xx_eth: reclaim TX skbs only when released by
 the HW

On Wed, Nov 05, 2014 at 11:46:16AM -0300, Ezequiel Garcia wrote:
> Hi Karl,
> 
> On 11/05/2014 11:32 AM, Karl Beldan wrote:> From: Karl Beldan <karl.beldan@...ierawaves.com>
> > 
> > ATM, txq_reclaim will dequeue and free an skb for each tx desc released
> > by the hw that has TX_LAST_DESC set. However, in case of TSO, each
> > hw desc embedding the last part of a segment has TX_LAST_DESC set,
> > losing the one-to-one 'last skb frag'/'TX_LAST_DESC set' correspondance,
> > which causes data corruption.
> > 
> > Fix this by checking TX_ENABLE_INTERRUPT instead of TX_LAST_DESC, and
> > warn when trying to dequeue from an empty txq (which can be symptomatic
> > of releasing skbs prematurely).
> > 
> > Fixes: 3ae8f4e0b98 ('net: mv643xx_eth: Implement software TSO')
> 
> Although your change makes sense, this isn't fixing the issue for me,
> neither did the previous one.
> 
This change fixes a serious issue.
On my side I can now trigger misc NFS and md5sums errors very easily,
which I haven't detected so far with it applied.
Are you running little endian ? Do you have the tso alignment fix
a63ba13e (I don't expect it to be required but I don't know what SoC you
are using) ? I suppose you are running with all 3 fixes applied.
 
Karl

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