Re: [PATCH v6 3/6] hw/loongarch/virt: Fix error handling in cpu unplug

[Markus Armbruster <armbru@redhat.com>]

Bibo Mao <maobibo@loongson.cn> writes:

> In function virt_cpu_unplug(), it will send cpu unplug message to
> interrupt controller extioi and ipi irqchip. If there is problem in
> this function, system should continue to run and keep state the same
> before cpu is removed.
>
> If error happends in cpu unplug stage, send cpu plug message to extioi
> and ipi irqchip to restore to previous stage, and then return immediately.
>
> Fixes: 2cd6857f6f5b (hw/loongarch/virt: Implement cpu unplug interface)
> Signed-off-by: Bibo Mao <maobibo@loongson.cn>
> ---
>  hw/loongarch/virt.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/hw/loongarch/virt.c b/hw/loongarch/virt.c
> index 8563967c8b..503362a69e 100644
> --- a/hw/loongarch/virt.c
> +++ b/hw/loongarch/virt.c
> @@ -958,6 +958,8 @@ static void virt_cpu_unplug(HotplugHandler *hotplug_dev,
>      hotplug_handler_unplug(HOTPLUG_HANDLER(lvms->extioi), dev, &err);
>      if (err) {
>          error_propagate(errp, err);
> +        hotplug_handler_plug(HOTPLUG_HANDLER(lvms->ipi), dev,
> +                             &error_abort);
>          return;
>      }
>  
> @@ -965,6 +967,10 @@ static void virt_cpu_unplug(HotplugHandler *hotplug_dev,
>      hotplug_handler_unplug(HOTPLUG_HANDLER(lvms->acpi_ged), dev, &err);
>      if (err) {
>          error_propagate(errp, err);
> +        hotplug_handler_plug(HOTPLUG_HANDLER(lvms->ipi), dev,
> +                             &error_abort);
> +        hotplug_handler_plug(HOTPLUG_HANDLER(lvms->extioi), dev,
> +                             &error_abort);
>          return;
>      }

virt_cpu_unplug() calls hotplug_handler_unplug() three times to notify
ipi, extioi, and acpi_get.  If any notification fails, virt_cpu_unplug()
calls hotplug_handler_plug() to "un-notify" the preceeding ones, if any.
This must not fail.

virt_cpu_plug() does it the other way round (see previous patch).

So, hotplug_handler_plug() must not fail in virt_cpu_unplug(), yet we
check for it to fail in virt_cpu_plug().

Can it really fail in virt_cpu_plug()?

If yes, why can't it fail in virt_cpu_unplug()?

Same questions for hotplug_handler_unplug().