linux-kernel - Re: Using nested locking for spin_lock

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Date:	Thu, 29 Mar 2012 11:11:37 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Sven Eckelmann <sven@...fation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	simon.wunderlich@...03.tu-chemnitz.de,
	Marek Lindner <lindner_marek@...oo.de>
Subject: Re: Using nested locking for spin_lock_bh

On Wed, Mar 28, 2012 at 06:36:39PM +0200, Sven Eckelmann wrote:
> Hi,
> 
> I started to run some experimental batman-adv code inside some virtual 
> machines with different debugging functions enabled. One of them was lockdep. 
> There we noticed a false positive for a lock class that is actually used in 
> two different data structures.

Hmm, I think you can initialize the lock class in the two differnent data
structures with differnt lock_class_key.

Thanks,
Yong

> Therefore, lockdep noticed that there could be 
> a deadlock for this class in a function that locks the two different data 
> structures.
> 
> To resolve this problem, I wanted to define two different subclasses and 
> replace the spin_lock_bh with its nested version. The only problem now is the 
> absence of spin_lock_bh_nested. I could only find spin_lock_bh and 
> spin_lock_irqsave_nested.
> 
> Is there another way how this should be done or is there a general problem why 
> there is no nested support for this incarnation of spin_lock?
> 
> Kind regards,
> 	Sven



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