Re: [PATCH] PPPOE can kfree SKB twice (was Re: kernel panic problem. (smp, iptables?))

[kuznet@xxxxxxxxxxxxx]

Hello!

> However, could we not have dev_queue_xmit behave as such (not free
> frame on failure)?  

If you need to hold original skb, you may hold its refcnt.

However, this feature inevitably results in big troubles: dev_queue_xmit()
is allowed to change skb and you cannot assume anything about this.
So that resuing skb dev_queue_xmit() is fatal bug not depending on anything.


> The reason why I'm proposing this is that ppp_generic.c assumes that
> the skb is still available after a transmission failure via pppoe.  To
> support the semantics of dev_queue_xmit and ppp_generic we would have
> to always copy skb's inside pppoe_xmit.  Then, if dev_queue_xmit fails
> the original is deleted.

You need not copy it. I said "clone".

Nobody is allowed to touch _data_ part of skb, so that you need not
to copy data.

Alexey