From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH 3/4 v2 net-next] net: make GRO aware of skb->head_frag
Date: Tue, 01 May 2012 08:39:38 +0200
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Cc: Alexander Duyck <alexander.h.duyck@intel.com>,
	David Miller <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
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	Ben Hutchings <bhutchings@solarflare.com>,
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To: Alexander Duyck <alexander.duyck@gmail.com>
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On Mon, 2012-04-30 at 22:33 -0700, Alexander Duyck wrote:

> The question I had was more specific to GRO.  As long as we have
> skb->users == 1 and the skb isn't cloned we should be fine.   It just
> hadn't occurred to me before that napi_gro_receive had the extra
> requirement that the skb couldn't be cloned.
> 

OK

By the way, even if skb was cloned, we would be allowed to steal
skb->head.

When we clone an oskb we :

1) allocate a struct nskb sk_buff (or use the shadow in case of TCP)
2) increment dataref
3) link skb->head

After cloning()  nskb->users == 1, and oskb->users is unchanged

I believe you are referring to skb_get(oskb), that ones increment
oskb->users and skb_shared(oskb) then returns true.