[Xen-devel] Re: SKB paged fragment lifecycle on receive

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Mon, 2011-06-27 at 23:49 +0100, David Miller wrote:
> From: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
> Date: Mon, 27 Jun 2011 15:42:04 +0100
> 
> > However it seems like this might still have a problem if your SKBs are
> > ever cloned. What happens in this case, e.g if a user of AF_PACKET sends
> > a broadcast via a device associated with a bridge[1] (where it would be
> > flooded)?
> 
> You don't need a bridge to get a clone on transmit, the packet
> scheduler can do clones.  Just grep for skb_clone in the packet
> action handlers net/sched/act_*.c

Are you sure? I only see skb_cloned() and skb_clone_writeable() under
there )(3.0-rc4) and not any actual skb_clone()s.

The only actual clone I see under there is in net/sched/sch_netem.c.

However it sounds like it is expected that a clone can happen on pretty
any skb which makes the frag lifecycle issue seem like one which could
effect anything which sends a page to the network without relinquishing
complete control of it (common in any kind of zero-copy scenario).

Ian.


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