linux-kernel - Re: [PATCH] prevent powerpc from invoking irq handlers on offline CPUs

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Message-ID: <20080901020640.GM7015@linux.vnet.ibm.com>
Date:	Sun, 31 Aug 2008 19:06:40 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org,
	jwboyer@...ux.vnet.ibm.com, tnt@...tNt.com,
	grant.likely@...retlab.ca, linuxppc-dev@...abs.org,
	manfred@...orfullife.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] prevent powerpc from invoking irq handlers on offline
	CPUs

On Mon, Sep 01, 2008 at 10:34:44AM +1000, Benjamin Herrenschmidt wrote:
> On Sun, 2008-08-31 at 10:31 -0700, Paul E. McKenney wrote:
> > Make powerpc refrain from clearing a given to-be-offlined CPU's bit in the
> > cpu_online_mask until it has processed pending irqs.  This change
> > prevents other CPUs from being blindsided by an apparently offline CPU
> > nevertheless changing globally visible state.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> 
> Sounds reasonable... the only possible worry here is if somebody tries
> an IPI ... The IPI code will and the target CPU mask with the online
> map, so it may try to send to the to-be-offlined CPU and timeout, no ?

OK.  Do we need separate IPI and online masks?

							Thanx, Paul

> Cheers,
> Ben.
> 
> >  smp.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index 5337ca7..1fedd7d 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -250,11 +250,11 @@ int generic_cpu_disable(void)
> >  	if (cpu == boot_cpuid)
> >  		return -EBUSY;
> >  
> > -	cpu_clear(cpu, cpu_online_map);
> >  #ifdef CONFIG_PPC64
> >  	vdso_data->processorCount--;
> >  	fixup_irqs(cpu_online_map);
> >  #endif
> > +	cpu_clear(cpu, cpu_online_map);
> >  	return 0;
> >  }
> >  
> 
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