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Date: Thu, 21 Jan 2010 21:41:33 +0100
From: Jarek Poplawski <jarkao2@gmail.com>
To: Michael Breuer <mbreuer@majjas.com>
Cc: David Miller <davem@davemloft.net>,
       Stephen Hemminger <shemminger@linux-foundation.org>,
       akpm@linux-foundation.org, flyboy@gmail.com,
       linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
       Michael Chan <mchan@broadcom.com>, Don Fry <pcnet32@verizon.net>,
       Francois Romieu <romieu@fr.zoreil.com>,
       Matt Carlson <mcarlson@broadcom.com>
Subject: Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check_sync
Message-ID: <20100121204133.GB3085@del.dom.local>
References: <20100120094103.GA6225@ff.dom.local>
 <4B58B217.8030001@majjas.com>
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On Thu, Jan 21, 2010 at 02:59:19PM -0500, Michael Breuer wrote:
> On 1/20/2010 4:41 AM, Jarek Poplawski wrote:
> >[ previously: Re: [PATCH] af_packet: Don't use skb after dev_queue_xmit() ]
> >diff --git a/drivers/net/sky2.c b/drivers/net/sky2.c
> >index 7650f73..cdebdd3 100644
> >--- a/drivers/net/sky2.c
> >+++ b/drivers/net/sky2.c
> >@@ -2252,12 +2252,14 @@ static struct sk_buff *receive_copy(struct sky2_port *sky2,
> >  	skb = netdev_alloc_skb_ip_align(sky2->netdev, length);
> >  	if (likely(skb)) {
> >  		pci_dma_sync_single_for_cpu(sky2->hw->pdev, re->data_addr,
> >-					    length, PCI_DMA_FROMDEVICE);
> >+					    pci_unmap_len(re, data_size),
> >+					    PCI_DMA_FROMDEVICE);
> >  		skb_copy_from_linear_data(re->skb, skb->data, length);
> >  		skb->ip_summed = re->skb->ip_summed;
> >  		skb->csum = re->skb->csum;
> >  		pci_dma_sync_single_for_device(sky2->hw->pdev, re->data_addr,
> >-					       length, PCI_DMA_FROMDEVICE);
> >+					       pci_unmap_len(re, data_size),
> >+					       PCI_DMA_FROMDEVICE);
> >  		re->skb->ip_summed = CHECKSUM_NONE;
> >  		skb_put(skb, length);
> >  	}
> Just a testing update: I went back to CONFIG_DMAR=Y yesterday and
> have not (yet) encountered the sky2 crash I'd been having prior to
> this fix. I've been pumping traffic through, and based on pre-patch
> experience, it would likely have crashed by now.
> 
> Will keep the system up for the next couple of days w/o reboot to
> confirm that the sky2 lockup I'd been seeing has stopped happening
> with this patch.
> 
> Test notes:
> 
> 1) Warning previously apparent on start (dma_debug check_sync) with
> CONFIG_DMAR=n is gone.
> 2) W/o the above patch, I was getting sky2 DMAR errors and
> subsequent TX hangs requiring reboot to clear. The hangs happened
> after at least 12 hours of uptime, and under RX load at the time of
> the hang.
> 3) With the above patch (and no other changes) I have not been able
> to recreate the crash - the system is stable.

Btw, could you remind us if during last dmar bugs jumbo frames might
have been used or maybe mtu was changed, and the current test setting?

> 
> I have been following the discussion about the DMA api would suggest
> that the length issue when DMAR is enabled is less innocuous than
> previously believed.

Actually, the last conclusions are - it's more innocuous than ever
believed, and I completely agree with this (at least until the next
week ;-).

Thanks,
Jarek P.
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