netdev - Re: [net PATCH] atl1c: Fix misuse of netdev_alloc

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Date:	Sat, 27 Jul 2013 01:02:51 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	<netdev@...r.kernel.org>, Jay Cliburn <jcliburn@...il.com>,
	"David S. Miller" <davem@...emloft.net>, <stable@...r.kernel.org>
Subject: Re: [net PATCH] atl1c: Fix misuse of netdev_alloc_skb in refilling
 rx ring

On Fri, 2013-07-26 at 12:47 -0400, Neil Horman wrote:
> atl1c uses netdev_alloc_skb to refill its rx dma ring, but that call makes no
> guarantees about the suitability of the memory for use in DMA.  As a result
> we've gotten reports of atl1c drivers occasionally hanging and needing to be
> reset:
> https://bugzilla.kernel.org/show_bug.cgi?id=54021
> 
> Fix this by modifying the call to use the internal version __netdev_alloc_skb,
> where you can set the gfp_mask explicitly to include GFP_DMA.

This is a really bad idea.  GFP_DMA means allocation from the ISA DMA
region (< 16 MB).  pci_map_single() takes care of allocating a bounce
buffer if necessary.

Ben.

> Tested by two reporters in the above bug, who have the hardware to validate it.
> Both report immediate cessation of the problem with this patch
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Jay Cliburn <jcliburn@...il.com>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: stable@...r.kernel.org
> Tested-by: Luis Henrix <luis.henrix@...il.com>
> Tested-by: Vincent Alquier <vincent.alquier@...il.com>
> ---
>  drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> index 786a874..d5e38d1 100644
> --- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> +++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
> @@ -1660,7 +1660,7 @@ static int atl1c_alloc_rx_buffer(struct atl1c_adapter *adapter)
>  	while (next_info->flags & ATL1C_BUFFER_FREE) {
>  		rfd_desc = ATL1C_RFD_DESC(rfd_ring, rfd_next_to_use);
>  
> -		skb = netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len);
> +		skb = __netdev_alloc_skb(adapter->netdev, adapter->rx_buffer_len, GFP_ATOMIC|GFP_DMA);
>  		if (unlikely(!skb)) {
>  			if (netif_msg_rx_err(adapter))
>  				dev_warn(&pdev->dev, "alloc rx buffer failed\n");

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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