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

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Message-ID: <19f34abd0808311046g47907414wf3ef939d0a7bbfdb@mail.gmail.com>
Date:	Sun, 31 Aug 2008 19:46:33 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	paulmck@...ux.vnet.ibm.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 7:28 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> 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.
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>
>  smpboot.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/arch/ia64/kernel/smpboot.c b/arch/ia64/kernel/smpboot.c
> index bcea81e..7a90f42 100644
> --- a/arch/ia64/kernel/smpboot.c
> +++ b/arch/ia64/kernel/smpboot.c
> @@ -741,8 +741,6 @@ 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);
> @@ -751,6 +749,7 @@ int __cpu_disable(void)
>        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;

Hm. Maybe my eyes are going bad. But isn't that now clearing the cpu
both before and after calling fixup_irqs()?


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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