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Subject[PATCH] CPEI gets warning at kernel/irq/migration.c:27/move_masked_irq()
Hi,

While running my MCA test (hardware error injection) on 2.6.19,
I got some warning like following:

> BUG: warning at kernel/irq/migration.c:27/move_masked_irq()
>
> Call Trace:
> [<a000000100013d20>] show_stack+0x40/0xa0
> sp=e00000006b2578d0 bsp=e00000006b2510b0
> [<a000000100013db0>] dump_stack+0x30/0x60
> sp=e00000006b257aa0 bsp=e00000006b251098
> [<a0000001000de430>] move_masked_irq+0xb0/0x240
> sp=e00000006b257aa0 bsp=e00000006b251070
> [<a0000001000de6a0>] move_native_irq+0xe0/0x180
> sp=e00000006b257aa0 bsp=e00000006b251040
> [<a00000010004ff50>] iosapic_end_level_irq+0x30/0xe0
> sp=e00000006b257aa0 bsp=e00000006b251020
> [<a0000001000d94d0>] __do_IRQ+0x170/0x400
> sp=e00000006b257aa0 bsp=e00000006b250fd8
> [<a0000001000116f0>] ia64_handle_irq+0x1b0/0x260
> sp=e00000006b257aa0 bsp=e00000006b250fa8
> [<a00000010000c3a0>] ia64_leave_kernel+0x0/0x280
> sp=e00000006b257aa0 bsp=e00000006b250fa8
> [<a000000100690cf0>] _spin_unlock_irqrestore+0x30/0x60
> sp=e00000006b257c70 bsp=e00000006b250f90

It comes from:

[kernel/irq/migration.c]
26 if (CHECK_IRQ_PER_CPU(desc->status)) {
27 WARN_ON(1);
28 return;
29 }

By putting some printk in kernel, I found that irqbalance is trying to
move CPEI which is handled as PER_CPU irq. That's why.

CPEI(Corrected Platform Error Interrupt) is ia64 specific irq, is
allowed to pin to particular processor which selected by the platform, and
even it is PER_CPU but it has set_affinity handler (=iosapic_set_affinity)
as same as other IO-SAPIC-level interrupts. (I don't know why, but
I guess that there would be typical situation where the handler for
migration is needed, such as hotplug - the processor going to be
offline/hot-removed.)

To shut up this warning, there are 2 way at least:
a) fix CPEI stuff
b) prohibit setting affinity to PER_CPU irq

I'm not sure what stuff of CPEI need to be fixed, but I think that
returning error to attempting move PER_CPU irq is useful for all
applications since it will never work.

Following small patch takes b) style.
It works, the warning disappeared and irqbalance still runs well.

Thanks,
H.Seto

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

---
kernel/irq/proc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6.19/kernel/irq/proc.c
===================================================================
--- linux-2.6.19.orig/kernel/irq/proc.c
+++ linux-2.6.19/kernel/irq/proc.c
@@ -54,7 +54,8 @@ static int irq_affinity_write_proc(struc
unsigned int irq = (int)(long)data, full_count = count, err;
cpumask_t new_value, tmp;

- if (!irq_desc[irq].chip->set_affinity || no_irq_affinity)
+ if (!irq_desc[irq].chip->set_affinity || no_irq_affinity ||
+ CHECK_IRQ_PER_CPU(irq_desc[irq].status))
return -EIO;

err = cpumask_parse_user(buffer, count, new_value);

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