netdev - Re: [NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt

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Message-ID: <20080109144339.GF13714@linux.vnet.ibm.com>
Date:	Wed, 9 Jan 2008 06:43:39 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, herbert@...dor.apana.org.au,
	dipankar@...ibm.com, netdev@...r.kernel.org, josh@...edesktop.org
Subject: Re: [NET] ROUTE: fix rcu_dereference() uses in /proc/net/rt_cache

On Wed, Jan 09, 2008 at 06:31:26AM -0800, David Miller wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Date: Wed, 9 Jan 2008 06:22:58 -0800
> 
> > On Wed, Jan 09, 2008 at 11:37:27AM +0100, Eric Dumazet wrote:
> > > On Wed, 9 Jan 2008 20:46:37 +1100
> > > Herbert Xu <herbert@...dor.apana.org.au> wrote:
> > > 
> > > diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> > > index d337706..28484f3 100644
> > > --- a/net/ipv4/route.c
> > > +++ b/net/ipv4/route.c
> > > @@ -283,12 +283,12 @@ static struct rtable *rt_cache_get_first(struct seq_file *seq)
> > >  			break;
> > >  		rcu_read_unlock_bh();
> > >  	}
> > > -	return r;
> > > +	return rcu_dereference(r);
> > >  }
> > 
> > Would it be possible to tag rt_cache_get_first() with an __acquires(RCU)
> > to help out sparse?
> 
> Sparse can't handle conditional locking very well, as is done here.
> There is a seperate thread where Eric reworks how all of this
> locking is done in order to pacify sparse and be able to add the
> __acquires() etc. tags and some of us found it too ugly to
> swallow :-)

Ah!  ;-)

							Thanx, Paul
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