Re: [PATCH] irq: Exclude percpu IRQs from being fixed up

[Fengzhe Zhang <fengzhe.zhang@intel.com>]

On 2011/2/17 15:52, Jan Beulich wrote:
>>>> On 17.02.11 at 01:15, Fengzhe Zhang<fengzhe.zhang@intel.com>  wrote:
>> On 2011/2/16 22:53, Jan Beulich wrote:
>>>>>> On 16.02.11 at 15:26, "Zhang, Fengzhe"<fengzhe.zhang@intel.com>   wrote:
>>>> irq: Exclude percpu IRQs from being fixed up
>>>>
>>>> Xen spin unlock uses spurious ipi "lock_kicker_irq" to wake up blocked vCPUs
>>>> waiting on that lock. This irq should always be disabled. However, when Dom0
>>>> is shuting down, function fixup_irqs is called which unmasks all irqs.
>>>> Function unmask_irq effectively re-enables lock_kicker_irq and its irq
>> handler
>>>> is invoked which reports bug and crashes Dom0.
>>>>
>>>> This patch sets IRQ_PER_CPU flag in irq desc and excludes percpu IRQs from
>>>> being fixed up when taking CPUs down.
>>>>
>>>> Signed-off-by: Fengzhe Zhang<fengzhe.zhang@intel.com>
>>>>
>>>> diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
>>>> index 977d8b4..f0f9450 100644
>>>> --- a/arch/x86/kernel/irq_64.c
>>>> +++ b/arch/x86/kernel/irq_64.c
>>>> @@ -80,6 +80,9 @@ void fixup_irqs(void)
>>>>    		if (irq == 2)
>>>>    			continue;
>>>>
>>>> +		if (desc->status&   IRQ_PER_CPU)
>>>> +			continue;
>>>> +
>>>>    		/* interrupt's are disabled at this point */
>>>>    		spin_lock(&desc->lock);
>>>>
>>>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>>>> index f34e231..26bc55a 100644
>>>> --- a/kernel/irq/manage.c
>>>> +++ b/kernel/irq/manage.c
>>>> @@ -727,10 +727,9 @@ __setup_irq(unsigned int irq, struct irq_desc *desc,
>>>> struct irqaction *new)
>>>>    				goto out_thread;
>>>>    		} else
>>>>    			compat_irq_chip_set_default_handler(desc);
>>>> -#if defined(CONFIG_IRQ_PER_CPU)
>>>
>>> Why? XEN should select IRQ_PER_CPU instead in its Kconfig.
>>>
>>> Jan
>>>
>> IRQ_PER_CPU switch is not found in current Kconfig. I'm not sure if this
>
> kernel/irq/Kconfig (introduced as a generic option in 2.6.38-rc2). In
> prior kernel you'd have to add a respective Kconfig item in
> drivers/xen/Kconfig.
>
>> feature is going to be brought back in the short term. I remove the
>> ifdef to set IRQ_PER_CPU flag in desc by default but still leave the IRQ
>> handling logic unchanged. This is a temporary solution to fix system
>> crash on poweroff. And this is the fix with minimum impact among the
>> several solutions we tried.
>
> But it's more a hack than a fix. And making per-CPU IRQs properly

Yes, that's true. Switching on IRQ_PER_CPU can make this patch neat. But 
that isn't my call.

-Fengzhe

> treated as such isn't a bad idea in any case, I would say.
>
> Jan
>