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

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] irq: Exclude percpu IRQs from being fixed up
From: Fengzhe Zhang <fengzhe.zhang@xxxxxxxxx>
Date: Thu, 17 Feb 2011 16:25:27 +0800
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Dong, Eddie" <eddie.dong@xxxxxxxxx>, "Li, Xin" <xin.li@xxxxxxxxx>
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On 2011/2/17 15:52, Jan Beulich wrote:
On 17.02.11 at 01:15, Fengzhe Zhang<fengzhe.zhang@xxxxxxxxx>  wrote:
On 2011/2/16 22:53, Jan Beulich wrote:
On 16.02.11 at 15:26, "Zhang, Fengzhe"<fengzhe.zhang@xxxxxxxxx>   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@xxxxxxxxx>

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



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