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Re: [Xen-devel] [PATCH] VMX: avoid taking locks with irqs disabled

To: "Tian, Kevin" <kevin.tian@xxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] VMX: avoid taking locks with irqs disabled
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 21 Oct 2008 13:37:27 +0100
Cc: "Wei, Gang" <gang.wei@xxxxxxxxx>
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On 21/10/08 13:29, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:

>> Actually this new partitioning of locks into two equivalence classes is
>> begging for some run-time checking in debug builds. I'll sort
>> out a patch
>> for that.
> 
> Did you flush out the patch into xen bits? I guess there may
> be other instances breaking that guideline. Just curious whether
> Linux side already recognized similar constraints. It's possibly
> not. Then another angle is, instead of pushing constraint on
> spinlock usage, could we instead change timer rendezvous
> style? Use softirq instead of call function should release the
> constraints like stop_machine. :-)

I'm flushing out fixes for this class of race before I check in the debug
code. I don't think it's an unreasonable new constraint, it just hasn't been
enforced before and so various Xen code breaks. I should get the patches
flushed out later today.

 -- Keir



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