netdev - Re: Multicast routing stops functioning after 4G multicast packets recived.

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Message-ID: <20140110075005.GD17866@order.stressinduktion.org>
Date:	Fri, 10 Jan 2014 08:50:05 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Bob Falken <NetFestivalHaveFun@....com>,
	Julian Anastasov <ja@....bg>, netdev@...r.kernel.org,
	kaber@...sh.net, tgraf@...g.ch
Subject: Re: Multicast routing stops functioning after 4G multicast packets recived.

On Fri, Jan 10, 2014 at 08:43:25AM +0100, Hannes Frederic Sowa wrote:
> On Thu, Jan 09, 2014 at 11:32:59PM -0800, Eric Dumazet wrote:
> > On Fri, 2014-01-10 at 08:10 +0100, Hannes Frederic Sowa wrote:
> > > On Thu, Jan 09, 2014 at 11:01:46PM -0800, Eric Dumazet wrote:
> > > > Its not clear to me why you expand ipmr_fib_lookup()
> > > > 
> > > > Is there something wrong with existing code ?
> > > 
> > > There are three users of ipmr_fib_lookup, two of them are in rcu_read_lock
> > > section, one is not.
> > > 
> > > ipmr_fib_lookup does not pass down arg.rule reference, so I don't have a
> > > chance to call fib_rule_put(arg.rule) on it. Thus I left ipmr_fib_lookup,
> > > just adding FIB_LOOKUP_NOREF and expanding ipmr_fib_lookup into the
> > > other function so I still have access to arg.rule to decrement the
> > > reference counter.
> > > 
> > > Do you agree?
> > 
> > Hmm, I see the problem now.
> > 
> > What about adding a parameter to ipmr_fib_lookup(),
> > to keep its spirit ?
> > 
> > ipmr_fib_lookup(net, &fl4, &mrt);
> > ->
> > ipmr_fib_lookup(net, &fl4, &mrt, &rule);
> > 
> > Since ipmr_rt_fib_lookup() has the same rule leak, no ?
> 
> No, ipmr_rt_fib_lookup is fine. This function gets called only from
> rcu read locked section and we don't take table reference because of
> FIB_LOOKUP_NOREF, so we don't need to put reference counter on arg.table.

arg.rule not table, actually.

> We could add the additional argument, just ignoring it in ipmr_rt_fib_lookup.
> 
> > 
> > Its a bit late here, so maybe following is just stupid :
> > Cant we do the fib_rule_put() inside ipmr_fib_lookup() ?
> 
> We could add bool noref to ipmr_fib_lookup indicating we want to drop
> reference to rule just after lookup.
> 
> I'll check if freeing a rule has additional side-effects on dependencies
> in reg_vif_xmit. That would be a nice solution actually, thanks!

Hmm, rule holds a reference to the net namespace in use. I don't know
if we want to add this special case. I guess net-namespace reference
cannot be removed while processing ndo_start_xmit callback but I don't
like this special case somehow. But I guess it is possible.

Your opinion on that?

Thanks,

  Hannes
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