Date: Wed, 26 Nov 2014 21:53:50 -0600
From: Seth Forshee <seth.forshee@canonical.com>
To: David Miller <davem@davemloft.net>
Cc: konrad.wilk@oracle.com, boris.ostrovsky@oracle.com,
        david.vrabel@citrix.com, zoltan.kiss@linaro.org,
        eric.dumazet@gmail.com, stefan.bader@canonical.com,
        xen-devel@lists.xenproject.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] xen-netfront: Remove BUGs on paged skb data which
 crosses a page boundary
Message-ID: <20141127035350.GA10833@ubuntu-mba51>
References: <1416968904-70874-1-git-send-email-seth.forshee@canonical.com>
 <20141126.122812.223757363894961994.davem@davemloft.net>
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On Wed, Nov 26, 2014 at 12:28:12PM -0500, David Miller wrote:
> From: Seth Forshee <seth.forshee@canonical.com>
> Date: Tue, 25 Nov 2014 20:28:24 -0600
> 
> > These BUGs can be erroneously triggered by frags which refer to
> > tail pages within a compound page. The data in these pages may
> > overrun the hardware page while still being contained within the
> > compound page, but since compound_order() evaluates to 0 for tail
> > pages the assertion fails. The code already iterates through
> > subsequent pages correctly in this scenario, so the BUGs are
> > unnecessary and can be removed.
> > 
> > Fixes: f36c374782e4 ("xen/netfront: handle compound page fragments on transmit")
> > Cc: <stable@vger.kernel.org> # 3.7+
> > Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> 
> Can I get some Xen developer reviews?

Fwiw this issue was discussed previously and this was the recommended
fix.

 http://article.gmane.org/gmane.linux.kernel/1825381

Since then I got some feedback from a tester that he didn't see any
problems with the BUGs removed (actually replaced with a WARN so I know
that he actually saw the condition which triggered the BUG).

Thanks,
Seth
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