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

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Message-ID: <20080322134656.173de045@laptopd505.fenrus.org>
Date:	Sat, 22 Mar 2008 13:46:56 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: How to avoid spurious lockdep warnings?

On Thu, 20 Mar 2008 16:02:11 -0700
Jeremy Fitzhardinge <jeremy@...p.org> 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?


what's the ordering guarantee between these locks ?


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