linux-kernel - Re: Hang: 2.6.32.4 sky2/DMAR (was [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902 check

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Date:	Wed, 27 Jan 2010 20:23:12 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Michael Breuer <mbreuer@...jas.com>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	flyboy@...il.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Michael Chan <mchan@...adcom.com>,
	Don Fry <pcnet32@...izon.net>,
	Francois Romieu <romieu@...zoreil.com>,
	Matt Carlson <mcarlson@...adcom.com>
Subject: Re: Hang: 2.6.32.4 sky2/DMAR (was [PATCH] sky2: Fix WARNING: at
 lib/dma-debug.c:902 check_sync)

On Wed, Jan 27, 2010 at 01:45:27PM -0500, Michael Breuer wrote:
> On 1/27/2010 1:08 PM, Michael Breuer wrote:
> >On 01/27/2010 12:56 PM, Stephen Hemminger wrote:
> >>--- a/drivers/net/sky2.c    2010-01-27 09:46:10.940005248 -0800
> >>+++ b/drivers/net/sky2.c    2010-01-27 09:53:47.141267850 -0800
> >>@@ -2257,13 +2257,16 @@ static struct sk_buff *receive_copy(stru
> >>
> >>      skb = netdev_alloc_skb_ip_align(sky2->netdev, length);
> >>      if (likely(skb)) {
> >>+        unsigned dma_align = dma_get_cache_alignment();
> >>+        unsigned dma_size = ALIGN(length+1, dma_align);
> >>+
> >>          pci_dma_sync_single_for_cpu(sky2->hw->pdev, re->data_addr,
> >>-                        length, PCI_DMA_FROMDEVICE);
> >>+                        dma_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);
> >>+                           dma_size, PCI_DMA_FROMDEVICE);
> >>          re->skb->ip_summed = CHECKSUM_NONE;
> >>          skb_put(skb, length);
> >>      }
> >This doesn't apply - I'm missing some intermediate patch.
> >
> >I've got (both in 2.6.32.4 and 2.6.33-rc5: pci_unmap_len(re,
> >data_size) vs., "length." I assume that I can just replace the
> >pci_unmap_len with dma_size... but perhaps the intermediate change
> >may have affected this as well?
> >
> Never mind - that was from one of the earlier patches I had been
> trying out. will try the above patch after reestablishing that the
> system still crashes without copybreak=1.
> 

Stephen, I'm not sure this patch can show much after the patch with
"legal" dma_size == re->data_addr didn't help. It looks like David
was right: dma_sync can't affect dmar, because it doesn't use it at
all.

Then I'd rather suggest to test if using copybreak more often, e.g.
with copybreak=1000 or even more can trigger these errors faster.

Jarek P.
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