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From: "Jan Beulich" <JBeulich@suse.com>
To: "Ian Campbell" <ian.campbell@citrix.com>
Cc: "Wei Liu" <wei.liu2@citrix.com>, <davem@davemloft.net>,
	"Dion Kant" <g.w.kant@hunenet.nl>, <xen-devel@lists.xen.org>,
	<netdev@vger.kernel.org>, <stable@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen-netfront: pull on receive skb may need to happen earlier
Date: Wed, 10 Jul 2013 14:58:42 +0100	[thread overview]
Message-ID: <51DD84B202000078000E3EF8@nat28.tlf.novell.com> (raw)
In-Reply-To: <1373460644.5453.109.camel@hastur.hellion.org.uk>

>>> On 10.07.13 at 14:50, Ian Campbell <ian.campbell@citrix.com> wrote:
> On Wed, 2013-07-10 at 11:46 +0100, Jan Beulich wrote:
>> >>> On 10.07.13 at 12:04, Wei Liu <wei.liu2@citrix.com> wrote:
>> > Jan, looking at the commit log, the overrun issue in
>> > xennet_get_responses was not introduced by __pskb_pull_tail. The call to
>> > xennet_fill_frags has always been in the same place.
>> 
>> I'm convinced it was: Prior to that commit, if the first response slot
>> contained up to RX_COPY_THRESHOLD bytes, it got entirely
>> consumed into the linear portion of the SKB, leaving the number of
>> fragments available for filling at MAX_SKB_FRAGS. Said commit
>> dropped the early copying, leaving the fragment count at 1
>> unconditionally, and now accumulates all of the response slots into
>> fragments, only pulling after all of them got filled in. It neglected to
>> realize - due to the count now always being 1 at the beginning - that
>> this can lead to MAX_SKB_FRAGS + 1 frags getting filled, corrupting
>> memory.
> 
> That argument makes sense to me.
> 
> Is it possible to hit a scenario where we need to pull more than
> RX_COPY_THRESHOLD in order to fit all of the data in MAX_SKB_FRAGS ?

I'm not aware of any, but I'm no expert here in any way.

> Does this relate somehow to the patch Annie has sent out recently too?

I don't think so.

Jan

  parent reply	other threads:[~2013-07-10 13:58 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <8511913.uMAmUdIO30@eistomin.edss.local>
     [not found] ` <20130517085923.GC14401@zion.uk.xensource.com>
     [not found]   ` <51D57C1F.8070909@hunenet.nl>
     [not found]     ` <20130704150137.GW7483@zion.uk.xensource.com>
2013-07-05  9:32       ` [PATCH] xen-netfront: pull on receive skb may need to happen earlier Jan Beulich
2013-07-05 14:53         ` Wei Liu
2013-07-07  1:10           ` David Miller
2013-07-08  9:59           ` Jan Beulich
2013-07-08 12:16             ` Dion Kant
2013-07-08 12:41               ` Jan Beulich
2013-07-08 14:20             ` [Xen-devel] " Jan Beulich
2013-07-08 15:22               ` Eric Dumazet
2013-07-09  7:47                 ` Jan Beulich
2013-07-08 15:48               ` Wei Liu
2013-07-09  6:52                 ` Jan Beulich
2013-07-09 16:51                   ` Wei Liu
2013-07-10  6:58                     ` Jan Beulich
2013-07-10 10:04                       ` Wei Liu
2013-07-10 10:46                         ` Jan Beulich
2013-07-10 12:50                           ` Ian Campbell
2013-07-10 12:53                             ` Wei Liu
2013-07-10 13:58                             ` Jan Beulich [this message]
2013-07-10 13:19                       ` Eric Dumazet
2013-07-12  8:32               ` Wei Liu
2013-07-12  8:56                 ` Jan Beulich
2013-07-13 11:26                   ` Dion Kant

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