Subject: Re: [PATCH] af_packet: Don't use skb after dev_queue_xmit()

From: Stephen Hemminger <[email-masked]>
Date: Tue, 19 Jan 2010 17:10:13 -0800

On Tue, 19 Jan 2010 20:01:10 -0500
Michael Breuer <[email-masked]> wrote:

> On 1/19/2010 5:45 PM, Jarek Poplawski wrote:
> > On Tue, Jan 19, 2010 at 03:06:01PM -0500, Michael Breuer wrote:
> >    
> >> On 1/19/2010 2:59 PM, Jarek Poplawski wrote:
> >>      
> >>> On Tue, Jan 19, 2010 at 10:47:27AM -0500, Michael Breuer wrote:
> >>> ...
> >>>        
> >>>> Still get the warning... but now 60 bytes.
> >>>> Jan 19 10:43:50 mail kernel: ------------[ cut here ]------------
> >>>> Jan 19 10:43:50 mail kernel: WARNING: at lib/dma-debug.c:902
> >>>>          
> >>> Thanks for trying this.
> >>> Jarek P.
> >>>        
> >> NP. Let me know what else I can do to help with this one. Note that
> >> it seems innocuous. I'll continue with the older set and no dmar for
> >> now and see if I get another crash.
> >>      
> > Maybe one more idea to try (not compiled).
> >
> > Jarek P.
> > ---
> >
> >   drivers/net/sky2.c |    6 ++++--
> >   1 files changed, 4 insertions(+), 2 deletions(-)
> >
> > 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);
> >   	}
> >    
> That not only compiled, but it cleared the error as well. Additionally, 
> I used to see a bit of a delay receiving the login prompt when first 
> connecting to the box by ssh. That delay is gone with this patch. I'd 
> guess that the warning wasn't quite as innocuous as I thought.
> Note: tested on 2.6.32.4.  I'll leave this up for a bit before 
> attempting to move back to head.

Seems like an underlying bug in the DMA api. Maybe it just can't
handle operations on partial mapping.

Other drivers with same problem:
  bnx2, cassini, pcnet32, r8169, rrunner, skge, sungem, tg3, 

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