netdev - Re: [v2 PATCH] net: Stop decapitating clones that have a head

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Date:	Thu, 03 May 2012 01:39:00 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	alexander.h.duyck@...el.com, netdev@...r.kernel.org,
	edumazet@...gle.com, jeffrey.t.kirsher@...el.com
Subject: Re: [v2 PATCH] net: Stop decapitating clones that have a head_frag

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 03 May 2012 06:33:58 +0200

> On Wed, 2012-05-02 at 21:18 -0700, Alexander Duyck wrote:
>> This change is meant ot prevent stealing the skb->head to use as a page in
>> the event that the skb->head was cloned.  This allows the other clones to
>> track each other via shinfo->dataref.
>> 
>> Without this we break down to two methods for tracking the reference count,
>> one being dataref, the other being the page count.  As a result it becomes
>> difficult to track how many references there are to skb->head.
>> 
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
...
> Acked-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks.

These tests of the form:

	head_frag || cloned

and

	head_frag && cloned

will probably crop up in other places.  Therefore we should probably
add a "skb_head_is_locked()" helper function to skbuff.h

Well, there are already two instances, which is candidate enough. :-)
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