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

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Date:	Wed, 5 Nov 2014 19:31:45 +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 04:05:21PM +0100, Karl Beldan wrote:
> 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.
>  
Also, I haven't checked SMP issues and I only have one core, if you are
using SMP it might be worth looking into that, maybe try running on one
core only (I only have an MV78200).
 
Karl
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