netdev - RE: [PATCH] net: Fix skb_under_panic oops in neigh_resolve

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Date:	Fri, 5 Oct 2012 12:33:03 -0400
From:	Ramesh Nagappa <ramesh.nagappa@...csson.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"ramesh.nagappa@...il.com" <ramesh.nagappa@...il.com>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"ebiederm@...ssion.com" <ebiederm@...ssion.com>,
	"xemul@...allels.com" <xemul@...allels.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] net: Fix skb_under_panic oops in neigh_resolve_output

Hi Eric,

Yes, that is a good optimization. neigh_resolve_output() also has the
__skb_pull() outside the loop, is that required ? The changes would be
like ...

neigh_resolve_output()
...
-        __skb_pull(skb, skb_network_offset(skb));


        if (!neigh_event_send(neigh, skb)) {
                int err;
                struct net_device *dev = neigh->dev;
                unsigned int seq;

                if (dev->header_ops->cache && !neigh->hh.hh_len)
                        neigh_hh_init(neigh, dst);

                do {                        
+			      __skb_pull(skb, skb_network_offset(skb));
                        seq = read_seqbegin(&neigh->ha_lock);
                        err = dev_hard_header(skb, dev, ntohs(skb->protocol),
                                              neigh->ha, NULL, skb->len);
                } while (read_seqretry(&neigh->ha_lock, seq));

Thanks,
Ramesh
 

> -----Original Message-----
> From: Eric Dumazet [mailto:eric.dumazet@...il.com] 
> >  	do {
> >  		seq = read_seqbegin(&neigh->ha_lock);
> > +		__skb_pull(skb, skb_network_offset(skb));
> 
> This __skb_pull() could be done before the read_seqbegin() to 
> keep the protected section short.
> 
> >  		err = dev_hard_header(skb, dev, ntohs(skb->protocol),
> >  				      neigh->ha, NULL, skb->len);
> >  	} while (read_seqretry(&neigh->ha_lock, seq));
> 
> Thanks
> 
> 
> --
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