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SubjectRe: [PATCH 1/1] arm64: Prevent offline CPU handling IRQs.
On Wed, Jul 13, 2022 at 09:28:43PM +0800, alvinzhan1234@gmail.com wrote:
> From: Alvin Zhan <alvinzhan1234@gmail.com>
>
> Migrate all of the IRQs on this CPU after setting it offline may still cause
> the IRQs to be dispatched to this CPU.

I was under the impression that __cpu_disable() was called with interrupts
masked, since it's called via stop_machine_cpuslocked(), and hence interrupts
cannot be taken here (ignoring pseudo-NMIs for the moment).

Have you ever seen that actually happen?

Mark.

> To prevent offline CPU handling IRQs, we should migrate the IRQs away from
> this CPU before it is powered off.
>
> Signed-off-by: Alvin Zhan <alvinzhan1234@gmail.com>
> ---
> arch/arm64/kernel/smp.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index 62ed361a4..c4c3c5ed5 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -302,6 +302,11 @@ int __cpu_disable(void)
> remove_cpu_topology(cpu);
> numa_remove_cpu(cpu);
>
> + /*
> + * Migrate IRQs away from this CPU first.
> + */
> + irq_migrate_all_off_this_cpu();
> +
> /*
> * Take this CPU offline. Once we clear this, we can't return,
> * and we must not schedule until we're ready to give up the cpu.
> @@ -309,11 +314,6 @@ int __cpu_disable(void)
> set_cpu_online(cpu, false);
> ipi_teardown(cpu);
>
> - /*
> - * OK - migrate IRQs away from this CPU
> - */
> - irq_migrate_all_off_this_cpu();
> -
> return 0;
> }
>
> --
> 2.34.1
>

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