Re: [patch net-next-2.6] bonding: remove skb_share_check in handle_frame

["Nicolas de Pesloüan" <nicolas.2p.debian@gmail.com>]

Le 01/03/2011 16:12, Changli Gao a écrit :
> On Tue, Mar 1, 2011 at 5:29 PM, Jiri Pirko<jpirko@redhat.com>  wrote:
>> Unapplicable, sorry (wrong branch :(). Here's corrected patch:
>>
>> Subject: [PATCH net-next-2.6 v2] bonding: remove skb_share_check in handle_frame
>>
>> No need to do share check here.
>>
>
> I don't think so. Although you avoid netif_rx(), you can't avoid
> ptype_all handlers. In fact, all the RX handlers should has this
> check(), if they may modify the skb.

Can you please develop your explanation?

In current __netif_receive_skb() (after the recent patch from Jiri), we deliver the skb to ptype_all 
handlers inside a loop, while possibly changing skb->dev inside this loop.

Then, at the end of __netif_receive_skb(), we loop on ptype_base, without changing anything in skb.

Should we consider ptype_*->func() to be called in a pure sequential way? Should we consider that 
when a ptype_*->func() returns, nothing from this handler will use the skb in anyway later, in a 
parallel way?

Or should we, instead, consider that special precautions must be taken, because protocol handlers 
may run in parallel for the same skb? Which kind of precautions?

Thanks.

	Nicolas.