netdev - Re: [PATCH net-next V3] net: dynamic ingress

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Message-ID: <20101004142415.GA2049@del.dom.local>
Date:	Mon, 4 Oct 2010 16:24:15 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	hadi@...erus.ca, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next V3] net: dynamic ingress_queue allocation

On Mon, Oct 04, 2010 at 02:52:00PM +0200, Eric Dumazet wrote:
> Le lundi 04 octobre 2010 ?? 14:06 +0200, Jarek Poplawski a écrit :
> 
> > Right, but then at least in qdisc_lookup():
> > 
> > if (dev_ingress_queue(dev))
> > 	q = qdisc_match_from_root(dev_ingress_queue(dev), handle);
> > 
> > you should use a variable instead of the second dereference (rtnl isn't
> > mandatory here).
> 
> I am lost.
> 
> If rntl is not mandatory, what is the lock that protects us ?
> 
> qdisc_lookup() _is_ called under the protection of a lock.
> Or as soon as we return from it, result could change under us.
> 
> Please name it, and I'll use it :
> 
> rcu_dereference_protected(dev->ingress_queue, lockdep_is_held(THISLOCK))
> 

You are right! There is no other lock. (I forgot I removed
qdisc_list_lock already ;-)

Sorry,
Jarek P.
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