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[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Fri, 02 Sep 2011 16:47:06 +0200
Cc: Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Marcelo Tosatti <mtosatti@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, KVM <kvm@xxxxxxxxxxxxxxx>, maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Andi Kleen <andi@xxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, the
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On Thu, 2011-09-01 at 17:55 -0700, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> 
> We need to make sure interrupts are disabled while we're relying on the
> contents of the per-cpu lock_waiting values, otherwise an interrupt
> handler could come in, try to take some other lock, block, and overwrite
> our values.

Would this make it illegal to take a spinlock from NMI context?

I know that its generally considered bad form, but there's at least one
spinlock that's only taken from NMI context and thus hasn't got any
deadlock potential.

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