linux-kernel - Re: [PATCH] qlge: fix size of external list for TX address descriptors

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Date:	Wed, 23 Nov 2011 19:10:18 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	cascardo@...ux.vnet.ibm.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-driver@...gic.com, ron.mercer@...gic.com,
	jitendra.kalsaria@...gic.com, anirban.chakraborty@...gic.com
Subject: Re: [PATCH] qlge: fix size of external list for TX address
 descriptors

From: Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>
Date: Wed, 23 Nov 2011 21:10:42 -0200

> When transmiting a fragmented skb, qlge fills a descriptor with the
> fragment addresses, after DMA-mapping them. If there are more than eight
> fragments, it will use the eighth descriptor as a pointer to an external
> list. After mapping this external list, called OAL to a structure
> containing more descriptors, it fills it with the extra fragments.
> 
> However, considering that systems with pages larger than 8KiB would have
> less than 8 fragments, which was true before commit a715dea3c8e, it
> defined a macro for the OAL size as 0 in those cases.
> 
> Now, if a skb with more than 8 fragments (counting skb->data as one
> fragment), this would start overwriting the list of addresses already
> mapped and would make the driver fail to properly unmap the right
> addresses on architectures with pages larger than 8KiB.
> 
> Besides that, the list of mappings was one size too small, since it must
> have a mapping for the maxinum number of skb fragments plus one for
> skb->data and another for the OAL. So, even on architectures with page
> sizes 4KiB and 8KiB, a skb with the maximum number of fragments would
> make the driver overwrite its counter for the number of mappings, which,
> again, would make it fail to unmap the mapped DMA addresses.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>

Applied, thanks for the detailed commit message.
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