linux-kernel - Using nested locking for spin_lock

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Message-ID: <2108147.Aqyix6xDmB@bentobox>
Date:	Wed, 28 Mar 2012 18:36:39 +0200
From:	Sven Eckelmann <sven@...fation.org>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Cc:	simon.wunderlich@...03.tu-chemnitz.de,
	Marek Lindner <lindner_marek@...oo.de>
Subject: Using nested locking for spin_lock_bh

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. 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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