linux-kernel - Re: [PATCH] prevent ia64 from invoking irq handlers on offline CPUs

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Date:	Sun, 31 Aug 2008 11:06:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
Cc:	linux-kernel@...r.kernel.org, tony.luck@...el.com, jes@....com,
	manfred@...orfullife.com, akpm@...ux-foundation.org
Subject: Re: [PATCH] prevent ia64 from invoking irq handlers on offline CPUs

On Sun, Aug 31, 2008 at 07:53:32PM +0200, Vegard Nossum wrote:
> On Sun, Aug 31, 2008 at 7:51 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> >> > @@ -751,6 +749,7 @@ int __cpu_disable(void)
> >> >        remove_siblinginfo(cpu);
> >> >        cpu_clear(cpu, cpu_online_map);
> 
> Here ^^^
> 
> >> >        fixup_irqs();
> >> > +       cpu_clear(cpu, cpu_online_map);
> >> >        local_flush_tlb_all();
> >> >        cpu_clear(cpu, cpu_callin_map);
> >> >        return 0;
> >>
> >> Hm. Maybe my eyes are going bad. But isn't that now clearing the cpu
> >> both before and after calling fixup_irqs()?
> >
> > I don't believe so...  I removed the earlier one and added the later
> > one.  Or is there another one hidden somewhere that I missed?
> 
> See marker above. It's not removed, is it?

Right you are!!!  There were two to begin with, and I moved the first
one only.  The attached updated patch removes the extra one.

						Thanx, Paul

Make ia64 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.  Also remove the existing
redundant cpu_clear(cpu, cpu_online_map).

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---

diff --git a/arch/ia64/kernel/smpboot.c b/arch/ia64/kernel/smpboot.c
index bcea81e..d8f05e5 100644
--- a/arch/ia64/kernel/smpboot.c
+++ b/arch/ia64/kernel/smpboot.c
@@ -741,16 +741,14 @@ int __cpu_disable(void)
 			return -EBUSY;
 	}
 
-	cpu_clear(cpu, cpu_online_map);
-
 	if (migrate_platform_irqs(cpu)) {
 		cpu_set(cpu, cpu_online_map);
 		return (-EBUSY);
 	}
 
 	remove_siblinginfo(cpu);
-	cpu_clear(cpu, cpu_online_map);
 	fixup_irqs();
+	cpu_clear(cpu, cpu_online_map);
 	local_flush_tlb_all();
 	cpu_clear(cpu, cpu_callin_map);
 	return 0;
--
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