netdev - Re: [PATCH 2.6.30-rc5] ehea: fix invalid pointer access

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Date:	Tue, 05 May 2009 13:19:54 +0100
From:	David Howells <dhowells@...hat.com>
To:	Hannes Hering <hannes.hering@...ux.vnet.ibm.com>
Cc:	dhowells@...hat.com, David Miller <davem@...emloft.net>,
	themann@...ibm.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, raisch@...ibm.com,
	ossrosch@...ux.vnet.ibm.com, linuxppc-dev@...abs.org,
	ossthema@...ibm.com, osstklei@...ibm.com
Subject: Re: [PATCH 2.6.30-rc5] ehea: fix invalid pointer access

Hannes Hering <hannes.hering@...ux.vnet.ibm.com> wrote:

> this is an ehea driver problem, which is occuring when the receive queue runs
> empty. The faulting code is more specifically the following line:
> 
> 	pref = (skb_array[x]->data);

In that case, you might want to move the prefetchw() calls in the following:

		pref = skb_array[x];
	-	prefetchw(pref);
	-	prefetchw(pref + EHEA_CACHE_LINE);
	+	if (pref) {
	+		prefetchw(pref);
	+		prefetchw(pref + EHEA_CACHE_LINE);

to before the if-statement.  That way the CPU can be attempting the prefetch
whilst it's chewing over the test and branch.  prefetching shouldn't fault on
a bad address.

David
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