From: Zoltan Kiss <zoltan.kiss@linaro•org>
To: Stefan Bader <stefan.bader@canonical•com>,
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 12:21:02 +0000 [thread overview]
Message-ID: <545CB92E.9050106@linaro.org> (raw)
In-Reply-To: <545CB7FF.8080003@canonical.com>
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)".
>
> since offset is adjusted to start from the tail page in that case.
>>
>> splice() code can generate such cases.
>>
>>
>
>
next prev parent reply other threads:[~2014-11-07 12:21 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 [this message]
2014-11-07 12:28 ` Stefan Bader
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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