Re: [PATCH 17/19] xen: don't free percpu areas during suspend

[Juergen Gross <jgross@xxxxxxxx>]

On 07.10.22 12:32, Mykyta Poturai wrote:
> From: Juergen Gross <jgross@xxxxxxxx>
>
> Instead of freeing percpu areas during suspend and allocating them
> again when resuming keep them. Only free an area in case a cpu didn't
> come up again when resuming.
>
> It should be noted that there is a potential change in behaviour as
> the percpu areas are no longer zeroed out during suspend/resume. While
> I have checked the called cpu notifier hooks to cope with that there
> might be some well hidden dependency on the previous behaviour. OTOH
> a component not registering itself for cpu down/up and expecting to
> see a zeroed percpu variable after suspend/resume is kind of broken
> already. And the opposite case, where a component is not registered
> to be called for cpu down/up and is not expecting a percpu variable
> suddenly to be zero due to suspend/resume is much more probable,
> especially as the suspend/resume functionality seems not to be tested
> that often.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
I can't remember having written this patch. The one I remember was for
x86.

> Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>
I doubt that, reasoning see above.


Juergen

> ---
>   xen/arch/arm/percpu.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/xen/arch/arm/percpu.c b/xen/arch/arm/percpu.c
> index 25442c48fe..0642705544 100644
> --- a/xen/arch/arm/percpu.c
> +++ b/xen/arch/arm/percpu.c
> @@ -58,10 +58,13 @@ static int cpu_percpu_callback(
>       switch ( action )
>       {
>       case CPU_UP_PREPARE:
> +      if ( system_state != SYS_STATE_resume )
>           rc = init_percpu_area(cpu);
>           break;
>       case CPU_UP_CANCELED:
>       case CPU_DEAD:
> +    case CPU_RESUME_FAILED:
> +      if ( system_state != SYS_STATE_suspend )
>           free_percpu_area(cpu);
>           break;
>       default:

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