From: Stefan Bader <stefan.bader@canonical•com>
To: Zoltan Kiss <zoltan.kiss@linaro•org>,
Eric Dumazet <eric.dumazet@gmail•com>
Cc: netdev@vger•kernel.org, "David S. Miller" <davem@davemloft•net>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle•com>,
Boris Ostrovsky <boris.ostrovsky@oracle•com>,
David Vrabel <david.vrabel@citrix•com>,
Jay Vosburgh <jay.vosburgh@canonical•com>,
linux-kernel@vger•kernel.org, xen-devel@lists•xenproject.org
Subject: Re: [Xen-devel] BUG in xennet_make_frags with paged skb data
Date: Fri, 07 Nov 2014 13:28:33 +0100 [thread overview]
Message-ID: <545CBAF1.4020207@canonical.com> (raw)
In-Reply-To: <545CB92E.9050106@linaro.org>
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On 07.11.2014 13:21, Zoltan Kiss wrote:
>
>
> On 07/11/14 12:15, Stefan Bader wrote:
>> On 07.11.2014 12:22, Eric Dumazet wrote:
>>> On Fri, 2014-11-07 at 09:25 +0000, Zoltan Kiss wrote:
>>>
>>> Please do not top post.
>>>
>>>> Hi,
>>>>
>>>> AFAIK in this scenario your skb frag is wrong. The page pointer should
>>>> point to the original compound page (not a member of it), and offset
>>>> should be set accordingly.
>>>> For example, if your compound page is 16K (4 page), then the page
>>>> pointer should point to the first page, and if the data starts at the
>>>> 3rd page, then offset should be >8K
>>>
>>> This is not accurate.
>>>
>>> This BUG_ON() is wrong.
>>>
>>> It should instead be :
>>>
>>> BUG_ON(len + offset > PAGE_SIZE<<compound_order(compound_head(page)));
>>
>> would that not have to be
>>
>> BUG_ON((page-compound_head(page)*PAGE_SIZE)+offset+len >
>> PAGE_SIZE<<compound_order(compound_head(page)));
>
> There should be a parentheses around "page-compound_head(page)".
*sigh* before submitting anything I'll have to make sure I run it past the
compiler at least. I never manager to type the beast without some error.
But you got the drift...
>>
>> since offset is adjusted to start from the tail page in that case.
>>>
>>> splice() code can generate such cases.
>>>
>>>
>>
>>
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next prev parent reply other threads:[~2014-11-07 12:28 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-06 21:49 BUG in xennet_make_frags with paged skb data Seth Forshee
2014-11-07 9:25 ` [Xen-devel] " Zoltan Kiss
2014-11-07 11:22 ` Eric Dumazet
2014-11-07 12:15 ` Stefan Bader
2014-11-07 12:21 ` Zoltan Kiss
2014-11-07 12:28 ` Stefan Bader [this message]
2014-11-07 10:44 ` David Vrabel
2014-11-07 11:08 ` Stefan Bader
2014-11-07 14:51 ` [Xen-devel] " Zoltan Kiss
2014-11-10 14:35 ` Seth Forshee
2014-11-10 14:41 ` David Vrabel
2014-11-10 16:39 ` [Xen-devel] " Zoltan Kiss
2014-11-10 16:42 ` David Vrabel
2014-11-10 17:02 ` Eric Dumazet
2014-11-10 17:20 ` Frediano Ziglio
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