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

[Jiang Liu]

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
happen.
	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 affinity after removing the CPU.
Thanks!
Gerry

> 
> Cc: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
> Cc: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> 
> Yang Yingliang (4):
>   genirq: Introduce irq_settings_set_move_pcntxt() helper
>   irqchip: GICv3: set non-percpu irqs status with _IRQ_MOVE_PCNTXT
>   genirq: rename config GENERIC_PENDING_IRQ to GENERIC_IRQ_MIGRATION
>   arm/arm64: fix a migrating irq bug when hotplug cpu
> 
>  arch/arc/Kconfig               |  2 +-
>  arch/arm/Kconfig               |  1 +
>  arch/arm/include/asm/irq.h     |  1 -
>  arch/arm/kernel/irq.c          | 62 ------------------------------------------
>  arch/arm64/Kconfig             |  1 +
>  arch/arm64/include/asm/irq.h   |  1 -
>  arch/arm64/kernel/irq.c        | 62 ------------------------------------------
>  arch/hexagon/Kconfig           |  2 +-
>  arch/ia64/Kconfig              |  2 +-
>  arch/tile/Kconfig              |  2 +-
>  arch/x86/Kconfig               |  2 +-
>  arch/x86/kernel/apic/io_apic.c |  2 +-
>  drivers/irqchip/irq-gic-v3.c   |  2 ++
>  include/linux/irq.h            |  5 +++-
>  include/linux/irqdesc.h        |  2 +-
>  kernel/irq/Kconfig             |  4 +--
>  kernel/irq/Makefile            |  2 +-
>  kernel/irq/irqdesc.c           | 18 ++++++++++--
>  kernel/irq/manage.c            |  2 +-
>  kernel/irq/migration.c         | 62 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/irq/proc.c              |  2 +-
>  kernel/irq/settings.h          |  5 ++++
>  22 files changed, 102 insertions(+), 142 deletions(-)
> 
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