From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cong Wang <amwang@redhat.com>
Subject: Re: [Patch net-next v1 1/3] igmp: avoid taking RTNL for
 ip_mc_find_dev()
Date: Wed, 05 Jun 2013 13:23:19 +0800
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	 <1370405222.24311.231.camel@edumazet-glaptop>
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Cc: netdev@vger.kernel.org, "David S. Miller" <davem@davemloft.net>
To: Eric Dumazet <eric.dumazet@gmail.com>
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On Tue, 2013-06-04 at 21:07 -0700, Eric Dumazet wrote:
> On Wed, 2013-06-05 at 11:33 +0800, Cong Wang wrote:
> > +		rcu_read_lock();
> >  		imr->imr_ifindex = dev->ifindex;
> > -		idev = __in_dev_get_rtnl(dev);
> > +		idev = __in_dev_get_rcu(dev);
> > +		rcu_read_unlock();
> >  	}
> >  	return idev;
> >  }
> 
> 
> You must be kidding.
> 
> This is obviously wrong.
> 

Oops, rcu_read_lock should be taken for the whole life of 'idev'...