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

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Date:	Fri, 02 Sep 2011 12:30:29 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Peter Zijlstra <peterz@...radead.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 09/02/2011 07:48 AM, Peter Zijlstra wrote:
> 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.

Yeah, that's the "two line comment style" next to "big block comment"
style - but you're right they look pretty bad juxtaposed like that.

    J

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