Re: Q: smp.c && barriers (Was: [PATCH 1/4] generic-smp: removesingle ipi fallback for smp_call_function_many())

[Oleg Nesterov]

On 02/17, Paul E. McKenney wrote:
>
> On Tue, Feb 17, 2009 at 08:28:10PM +0100, Oleg Nesterov wrote:
> >
> > So the question is: is there any arch which surely needs this barrier?
> >
> > IOW,
> > 	int COND;
> >
> > 	void smp_xxx_interrupt(regs)
> > 	{
> > 		BUG_ON(!COND);
> > 	}
> >
> > 	COND = 1;
> > 	mb();
> > 	smp_send_xxx(cpu);
> >
> > can we really hit the BUG_ON() above on some arch?
>
> If all of the above is executed by the same task, tripping the BUG_ON()
> means either a compiler or CPU bug.

I think you misunderstood...

smp_send_xxx() sends the ipi to another CPU, and smp_xxx_interrupt() is
the handler.

Oleg.

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