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Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while
 blocking
From: Peter Zijlstra <peterz@infradead.org>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, the arch/x86 maintainers <x86@kernel.org>,
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        Andi Kleen <andi@firstfloor.org>,
        Xen Devel <xen-devel@lists.xensource.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Date: Fri, 02 Sep 2011 22:47:48 +0200
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On Fri, 2011-09-02 at 12:29 -0700, Jeremy Fitzhardinge wrote:
> 
> > 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.
> 
> Which one? 

arch/x86/kernel/traps.c:nmi_reason_lock

It serializes NMI access to the NMI reason port across CPUs.