From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while
 blocking
Date: Fri, 02 Sep 2011 16:47:06 +0200
Message-ID: <1314974826.1861.1.camel@twins>
References: <cover.1314922370.git.jeremy.fitzhardinge@citrix.com>
	 <38bb37e15f6e5056d5238adac945bc1837a996ec.1314922370.git.jeremy.fitzhardinge@citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8BIT
Return-path: <kvm-owner@vger.kernel.org>
In-Reply-To: <38bb37e15f6e5056d5238adac945bc1837a996ec.1314922370.git.jeremy.fitzhardinge@citrix.com>
Sender: kvm-owner@vger.kernel.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>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Nick Piggin <npiggin@kernel.dk>, Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>, Andi Kleen <andi@firstfloor.org>, Xen Devel <xen-devel@lists.xensource.com>, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
List-Id: xen-devel@lists.xenproject.org

On Thu, 2011-09-01 at 17:55 -0700, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> 
> 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.