netdev - Re: deadlocks if use htb

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Message-ID: <20090114143922.GB6643@ff.dom.local>
Date:	Wed, 14 Jan 2009 14:39:22 +0000
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Denys Fedoryschenko <denys@...p.net.lb>,
	Chris Caputo <ccaputo@....net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Badalian Vyacheslav <slavon@...telecom.ru>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: deadlocks if use htb

On Wed, Jan 14, 2009 at 03:28:03PM +0100, Peter Zijlstra wrote:
> On Wed, 2009-01-14 at 14:13 +0000, Jarek Poplawski wrote:
> > On Wed, Jan 14, 2009 at 02:32:26PM +0100, Peter Zijlstra wrote:
> > > On Wed, 2009-01-14 at 13:26 +0000, Jarek Poplawski wrote:
> > > 
> > > > OK, I hope Denys can apply more, but what about others? Without any
> > > > patches the hole seems to be much bigger.
> > > 
> > > OK, I read most of this thread on netdev, but didn't find a clear clue
> > > on the specific hrtimer insertion race.
> > 
> > There is something at the beginning of this thread, plus earlier
> > threads mostly with Denys as sender, and "htb bug" in the subject.
> > 
> > > 
> > > Do you have any clear ideas or should I poke at the htb/hrtimer code a
> > > little?
> > > 
> > 
> > ....And htb code is htb_dequeue(): qdisc_watchdog_schedule().
> 
> Right, found all that...
> 
> Can't spot anything obviously wrong though.. hrtimer_start*() does
> remove_hrtimer() which checks STATE_ENQUEUED, STATE_PENDING and pulls it
> off the relevant list before it continues the enqueue.
> 
> However a loop in enqueue_hrtimer() would suggest a corrupted RB-tree,
> but I cannot find an RB-op that doesn't hold base-lock.
> 

Anyway I think some trace in rbtree seemed to show the parent is the
same with the node, if I didn't mess anything.

Jarek P.
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