linux-kernel - Re: deadlocks if use htb

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Message-Id: <1231943283.14825.14.camel@laptop>
Date:	Wed, 14 Jan 2009 15:28:03 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jarek Poplawski <jarkao2@...il.com>
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, 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.

Hohumm..

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