netdev - Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl

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Date:	Thu, 21 Aug 2008 10:18:30 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	denys@...p.net.lb
Subject: Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().

On Thu, Aug 21, 2008 at 10:11:45AM +0000, Jarek Poplawski wrote:
> On Thu, Aug 21, 2008 at 03:05:23AM -0700, David Miller wrote:
> > From: Jarek Poplawski <jarkao2@...il.com>
> > Date: Thu, 21 Aug 2008 10:01:55 +0000
> > 
> > > If we do this with child qdisc from qdisc_graft() it's without
> > > deactivation. The rest of the tree can be dequeued in the meantime
> > > and call qdisc_tree_decrease_qlen() (like hfsc, tbf, netem), which
> > > uses qdisc_lookup() to access this list. We list_del() under rtnl
> > > lock only, they lookup under sch_tree_lock(). Is it a bit unsafe
> > > or I miss something?
> > 
> > They hold RTNL as well.
> > 
> > Remember, sch_tree_lock() uses qdisc_root_lock() which as I've
> > told you at least twice now asserts that RTNL is held :-)
> 
> Actually, I've called it wrong, they hold qdisc root lock, but they
> certainly can't have rtnl_lock() at the moment!

I mean here: hfsc_dequeue(), netem_dequeue() and tbf_dequeue().

Jarek P.
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