linux-kernel - RE: [RFC][PATCH] irq_work: Don't ignore possible cmpxchg failure

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Date:	Tue, 16 Nov 2010 10:57:02 -0600
From:	"Aguirre, Sergio" <saaguirre@...com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Huang Ying <ying.huang@...el.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, Kyle McMartin <kyle@...artin.ca>
Subject: RE: [RFC][PATCH] irq_work: Don't ignore possible cmpxchg failure

Hi Peter,

> -----Original Message-----
> From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl]
> Sent: Tuesday, November 16, 2010 10:45 AM
> To: Aguirre, Sergio
> Cc: LKML; Huang Ying; Martin Schwidefsky; Ingo Molnar; Kyle McMartin
> Subject: Re: [RFC][PATCH] irq_work: Don't ignore possible cmpxchg failure
> 
> On Tue, 2010-11-16 at 10:32 -0600, Sergio Aguirre wrote:
> > Although is very unlikely, it's better to make sure we're not
> > letting this happen.
> >
> > This solves this compilation warning:
> >
> > kernel/irq_work.c: In function 'irq_work_run':
> > kernel/irq_work.c:148: warning: value computed is not used
> >
> 
> > @@ -145,7 +145,10 @@ void irq_work_run(void)
> >  		 * Clear the BUSY bit and return to the free state if
> >  		 * no-one else claimed it meanwhile.
> >  		 */
> > -		cmpxchg(&entry->next, next_flags(NULL, IRQ_WORK_BUSY), NULL);
> > +		xchgres = cmpxchg(&entry->next,
> > +				  next_flags(NULL, IRQ_WORK_BUSY),
> > +				  NULL);
> > +		BUG_ON(unlikely(xchgres != next_flags(NULL, IRQ_WORK_BUSY)));
> 
> simply adding (void) in front would be much easier.

But isn't that still leaving the remote possibility of a hidden cmpxchg
Failure open?

Regards,
Sergio
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