linux-kernel - Re: [PATCH] [ARM] Unconditional call to smp_cross

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Date:	Mon, 16 Jul 2012 12:22:22 +0100
From:	Will Deacon <will.deacon@....com>
To:	Shawn Guo <shawn.guo@...aro.org>
Cc:	Pantelis Antoniou <panto@...oniou-consulting.com>,
	"mporter@...com" <mporter@...com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"Russ.Dill@...com" <Russ.Dill@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] [ARM] Unconditional call to smp_cross_call on UP crashes
 (take #2)

On Fri, Jul 13, 2012 at 08:59:39AM +0100, Shawn Guo wrote:
> > diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> > index 8f46446..7babc3f 100644
> > --- a/arch/arm/kernel/smp.c
> > +++ b/arch/arm/kernel/smp.c
> > @@ -590,7 +590,8 @@ void smp_send_stop(void)
> >  
> >  	cpumask_copy(&mask, cpu_online_mask);
> >  	cpumask_clear_cpu(smp_processor_id(), &mask);
> > -	smp_cross_call(&mask, IPI_CPU_STOP);
> > +	if (!cpumask_empty(&mask))
> > +		smp_cross_call(&mask, IPI_CPU_STOP);

I wonder whether we shouldn't have a default smp_cross_call implementation
with BUG_ON(!cpumask_empty(&mask)). It's marginally nicer than an explicit NULL
deference and it would also fix your problem.

Will
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