Re: [RFC PATCH v1 0/4] arm/arm64: fix a migrating irq bug when hotplug cpu

From: Yang Yingliang
Date: Sun Sep 06 2015 - 22:55:23 EST

On 2015/9/6 16:07, Jiang Liu wrote:
On 2015/9/6 12:23, Yang Yingliang wrote:
Hi All,

There is a bug:

When cpu is disabled, all irqs will be migratged to another cpu.
In some cases, a new affinity is different, it needed to be coppied
to irq's affinity. But if the type of irq is LPI, it's affinity will
not be coppied because of irq_set_affinity's return value.

As Marc and Will suggested, I refactor the arm/arm64 migrating interrupts
code and fix the migrating irq bug while cpu is offline.

I'm trying let the core code do the migrating interrupts matter. kernel/irq/migration.c
depends on CONFIG_GENERIC_PENDING_IRQ, so I make it selected by CONFIG_SMP and
CONFIG_HOTPLUG_CPU and rename it to CONFIG_GENERIC_IRQ_MIGRATION for more general.
When CONFIG_GENERIC_IRQ_MIGRATION is enabled, an interrupt whose state_use_accessors
is not set with IRQD_MOVE_PCNTXT won't be migrated immediately in irq_set_affinity_locked().
So introduce irq_settings_set_move_pcntxt() helper to set the state in gic_irq_domain_map().

With the above preparation, move the migrating interrupts code into kernel/irq/migration.c
and fix the bug by using irq_do_set_affinity().
Hi Yingliang,
As we are going to move migrate_irqs() to generic kernel
code, and powerpc, metag, xtensa, sh, ia64 mn10300 also defines
migrate_irqs() too. It would be great if we could consolidate
all these.
And as we are going to refine these code, there's another
issue need attention. On x86, we need to allocate a CPU vector
if an irq is directed to a CPU. So there's possibility that
we run out of CPU vectors after CPU hot-removal. So we have a
mechanism to detect whether we will run out of CPU vector
after removing a CPU, and reject CPU hot-removal if that will
So the key point is, if we a need to allocate some sort
of resource on the target CPUs for an irq, we need two steps
when removing a CPU
1) check whether resources are available after removing the CPU,
and reject CPU removal request if we ran out of resource
2) fix irqs after hot-removing the CPU.

On arm, as I know, it doesn't need extra resource for an irq.
I am not sure other platform need this way besides x86.

I think we could consolidate all migrate_irqs() later. I am not
sure if it's good to do so big changing and modify other arch code in
a patchset that supposed to fix a bug of arm.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at