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

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Message-ID: <A24693684029E5489D1D202277BE89447382A591@dlee02.ent.ti.com>
Date:	Tue, 16 Nov 2010 11:11:42 -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



> -----Original Message-----
> From: Peter Zijlstra [mailto:a.p.zijlstra@...llo.nl]
> Sent: Tuesday, November 16, 2010 11:09 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 10:57 -0600, Aguirre, Sergio wrote:
> 
> > > > @@ -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?
> 
> No, we don't care if it fails, read the comment. All we want to know is
> that if it still matched, we flipped the bit.

I understand. Will add just a (void) typecast, and resend then.

Regards,
Sergio
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