netdev - Re: [PATCH] appletalk: Set skb with destructor

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Date:	Mon, 07 Jul 2014 10:57:36 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrey Utkin <andrey.krieger.utkin@...il.com>
Cc:	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
	acme@...stprotocols.net, netdev@...r.kernel.org,
	davem@...emloft.net
Subject: Re: [PATCH] appletalk: Set skb with destructor

On Mon, 2014-07-07 at 11:03 +0300, Andrey Utkin wrote:
> 2014-07-07 0:42 GMT+03:00 Eric Dumazet <eric.dumazet@...il.com>:
> >>       /* Queue packet (standard) */
> >> +     sock_hold(sock);
> >> +     skb->destructor = atalk_skb_destructor;
> >>       skb->sk = sock;
> >
> > This part is not needed : sock_queue_rcv_skb() already does the right
> > thing : It calls skb_set_owner_r(skb, sk);
> >
> > You should therefore remove the "skb->sk = sock;" line
> 
> If it is so, i think this should be as another patch with its own reasoning.
> 

No it is not.

Its illegal to set skb->sk to a socket without taking proper reference.

But it is useless to do this before calling sock_queue_rcv_skb(), as I
explained to you.

This is adding two extra atomic operations for nothing: skb_orphan() is
called from sock_queue_rcv_skb(), so it is kind of stupid to set a
destructor that _will_ be immediately called.

We do not do defensive programming, we try to do logical things, and
only logical things.

Please re-spin your patch, by integrating my feedback.

Thanks !

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