linux-kernel - Re: [PATCH RFC 1/2] net: macb: Check DMA mappings for error

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Date:	Wed, 26 Feb 2014 10:36:42 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Ben Hutchings <ben@...adent.org.uk>
CC:	Nicolas Ferre <nicolas.ferre@...el.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH RFC 1/2] net: macb: Check DMA mappings for error

On Sun, 2014-02-23 at 12:13AM +0000, Ben Hutchings wrote:
> On Fri, 2014-02-21 at 11:30 -0800, Soren Brinkmann wrote:
> [...]
> > --- a/drivers/net/ethernet/cadence/macb.c
> > +++ b/drivers/net/ethernet/cadence/macb.c
> > @@ -632,11 +632,16 @@ static void gem_rx_refill(struct macb *bp)
> >  					   "Unable to allocate sk_buff\n");
> >  				break;
> >  			}
> > -			bp->rx_skbuff[entry] = skb;
> >  
> >  			/* now fill corresponding descriptor entry */
> >  			paddr = dma_map_single(&bp->pdev->dev, skb->data,
> >  					       bp->rx_buffer_size, DMA_FROM_DEVICE);
> > +			if (dma_mapping_error(&bp->pdev->dev, paddr)) {
> > +				dev_kfree_skb(skb);
> > +				break;
> > +			}
> > +
> > +			bp->rx_skbuff[entry] = skb;
> 
> This bit looks good.
> 
> >  			if (entry == RX_RING_SIZE - 1)
> >  				paddr |= MACB_BIT(RX_WRAP);
> > @@ -1040,6 +1045,10 @@ static int macb_start_xmit(struct sk_buff *skb, struct net_device *dev)
> >  	netdev_vdbg(bp->dev, "Allocated ring entry %u\n", entry);
> >  	mapping = dma_map_single(&bp->pdev->dev, skb->data,
> >  				 len, DMA_TO_DEVICE);
> > +	if (dma_mapping_error(&bp->pdev->dev, mapping)) {
> > +		dev_kfree_skb(skb);
> 
> You need to unlock bp->lock before returning.  Also, I think this should
> be kfree_skb(), as that can be observed through dropwatch whereas
> dev_kfree_skb() is completely silent.

I interpret Ben's comments as: This series is not utterly wrong and
wanted. I'll send a v2 with the changes Ben suggested.
Thanks for reviewing.

	Sören


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