netdev - Re: [Patch net 2/2] ipmr,ip6mr: call list_del_rcu() when deleting mr table from list

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Date:	Wed, 25 Mar 2015 21:21:54 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: [Patch net 2/2] ipmr,ip6mr: call list_del_rcu() when deleting mr
 table from list

On Wed, Mar 25, 2015, at 21:07, Hannes Frederic Sowa wrote:
> On Wed, Mar 25, 2015, at 20:05, Cong Wang wrote:
> > Probably not a big deal, just for corretness.
> > 
> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> > ---
> >  net/ipv4/ipmr.c  | 2 +-
> >  net/ipv6/ip6mr.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
> > index d6fede8..68f67b8 100644
> > --- a/net/ipv4/ipmr.c
> > +++ b/net/ipv4/ipmr.c
> > @@ -280,7 +280,7 @@ static void __net_exit ipmr_rules_exit(struct net
> > *net)
> >  
> >  	rtnl_lock();
> >  	list_for_each_entry_safe(mrt, next, &net->ipv4.mr_tables, list) {
> > -               list_del(&mrt->list);
> > +               list_del_rcu(&mrt->list);
> >  		ipmr_free_table(mrt);
> >  	}
> >  	rtnl_unlock();
> 
> I really do wonder if we have the rcu locking correct in there:
> 
> Looking into getsockopt/setsockopt operations, we might have socket
> lock, but I cannot see where we lock rcu, so the ipmr_get_table call is
> safe. Do you also see the problem?

Also ipmr_free_table does need a kfree_rcu as we need to have those
tables rcu protected (we use them from softirq, so rtnl_lock is not
feasible here).

Bye,
Hannes
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