netdev - Re: [PATCH] ipv6: slightly simplify keeping IPv6 addresses on link down

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Message-ID: <20101201130421.0ac08bcd@nehalam>
Date:	Wed, 1 Dec 2010 13:04:21 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Lorenzo Colitti <lorenzo@...gle.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH] ipv6: slightly simplify keeping IPv6 addresses on link
 down

On Wed, 1 Dec 2010 12:52:42 -0800
Lorenzo Colitti <lorenzo@...gle.com> wrote:

> On Wed, Dec 1, 2010 at 12:22 PM, Stephen Hemminger
> <shemminger@...tta.com> wrote:
> > > --- a/net/ipv6/addrconf.c
> > > +++ b/net/ipv6/addrconf.c
> > > @@ -2663,7 +2663,8 @@ static int addrconf_ifdown(struct net_device *dev, int how)
> > >  {
> > >       struct net *net = dev_net(dev);
> > >       struct inet6_dev *idev;
> > > -     struct inet6_ifaddr *ifa, *ifn;
> > > +     struct inet6_ifaddr *ifa;
> > > +     LIST_HEAD(keep_list);
> > >       int state;
> >
> > Your patch is backwards? The existing code is:
> 
> Oops, yes. Wrong order of arguments. Another one coming up.
> 
> > Also, the addrconf_ifdown can race with other updates to idev->addr_list
> > from addrconf timers etc.  Therefore even list_for_each_entry_safe is not safe.
> 
> No, wait... The loop is protected by idev->lock, and the code just
> before it that clears the temporary address list is essentially
> identical (except it looks over tempaddr_list instead). Wouldn't that
> blow up as well?

The old code walked the list until it was empty. New code could
get confused if list changed by other changes during the
period when idev->lock is dropped and notifier is called.



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