linux-kernel - Re: How to avoid spurious lockdep warnings?

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Message-Id: <1206056698.6437.70.camel@lappy>
Date:	Fri, 21 Mar 2008 00:44:58 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: How to avoid spurious lockdep warnings?

On Thu, 2008-03-20 at 16:02 -0700, Jeremy Fitzhardinge wrote:
> In a Xen system, when a new pagetable is about to be put in use it is 
> "pinned", meaning that each page in the pagetable is registered with the 
> hypervisor.  This is done in arch/x86/xen/mmu.c:pin_page().
> 
> In order to make this efficient, the hypercalls for pinning are batched, 
> so that multiple pages are submitted at once in a single multicall.  
> While a page is batched pending the hypercall, its corresponding 
> pte_lock is held.
> 
> This means that the code can end up holding multiple pte locks at once, 
> though it is guaranteed to never try to hold the same lock at once.  
> However, because these locks are in the same lock class, I get a 
> spurious warning from lockdep.  Is there some way I can get rid of this 
> warning?

How many locks at once?

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