netdev - Re: + gen_estimator-fix-locking-and-timer-related-bugs.patch added to -mm tree

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Date:	Sat, 7 Jul 2007 17:10:54 +0200 (CEST)
From:	Patrick McHardy <kaber@...sh.net>
To:	Ranko Zivojnovic <ranko@...dernet.net>
cc:	Jarek Poplawski <jarkao2@...pl>, akpm@...ux-foundation.org,
	netdev@...r.kernel.org
Subject: Re: + gen_estimator-fix-locking-and-timer-related-bugs.patch added
 to -mm tree

On Sat, 7 Jul 2007, Ranko Zivojnovic wrote:

>> On Fri, 2007-07-06 at 16:21 +0200, Patrick McHardy wrote:
>>> There is at least one ABBA deadlock, est_timer does:
>>>
>>> read_lock(&est_lock)
>>> spin_lock(e->stats_lock) (which is dev->queue_lock)
>>>
>>> and qdisc_destroy calls htb_destroy under dev->queue_lock, which
>>> calls htb_destroy_class, then gen_kill_estimator and this
>>> write_locks est_lock.
>>>
>>> I can't see the problem above though, the qdisc_run path only takes
>>> dev->queue_lock. Please enable lockdep and post the output if any.
>>
>
> I've got both code paths this time. It shows exactly the ABBA deadlock
> you describe above. The details are below.


Thanks. I'm still wondering whats causing the other lockup
you're seeing.

> Maybe the appropriate way to fix this would to call gen_kill_estimator,
> with the appropriate lock order, before the call to qdisc_destroy, so
> when dev->queue_lock is taken for qdisc_destroy - the structure is
> already off the list.


Probably easier to just kill est_lock and use rcu lists.
I'm currently travelling, I'll look into it tomorrow.
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