linux-kernel - Re: [PATCH 10/13] xen/pvticket: allow interrupts to be enabled while blocking

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Date:	Fri, 02 Sep 2011 16:48:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM <kvm@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>,
	Xen Devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 10/13] xen/pvticket: allow interrupts to be enabled
 while blocking

On Thu, 2011-09-01 at 17:55 -0700, Jeremy Fitzhardinge wrote:
> +       /* Make sure an interrupt handler can't upset things in a
> +          partially setup state. */
>         local_irq_save(flags);
>  
> +       /*
> +        * We don't really care if we're overwriting some other
> +        * (lock,want) pair, as that would mean that we're currently
> +        * in an interrupt context, and the outer context had
> +        * interrupts enabled.  That has already kicked the VCPU out
> +        * of xen_poll_irq(), so it will just return spuriously and
> +        * retry with newly setup (lock,want).
> +        *
> +        * The ordering protocol on this is that the "lock" pointer
> +        * may only be set non-NULL if the "want" ticket is correct.
> +        * If we're updating "want", we must first clear "lock".
> +        */
> +       w->lock = NULL; 

I mean, I don't much care about Xen code, but that's two different
comment styles.
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