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Subject: Re: [RFC][PATCH] irq_work -v2
From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>, Ingo Molnar <mingo@elte.hu>,
       "H.PeterA" <"nvin hpa"@zytor.com>, linux-kernel@vger.kernel.org,
       tglx <tglx@linutronix.de>, davem <davem@davemloft.net>,
       paulus <paulus@samba.org>
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Date: Fri, 25 Jun 2010 21:47:03 +0200
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On Fri, 2010-06-25 at 21:30 +0200, Andi Kleen wrote:
> > +             entry->next = next_flags(NULL, IRQ_WORK_BUSY);
> > +             entry->func(entry);
> 
> Needs compiler memory barrier here I think.
> 
> > +             /*
> > +              * 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);
> > +     } 

Both the (indirect) function call and the cmpxchg imply a compiler
barrier.