Re: [PATCH] xen/sched: fix get_cpu_idle_time() for smt=0 suspend/resume

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.08.2021 12:21, Juergen Gross wrote:
> With smt=0 during a suspend/resume cycle of the machine the threads
> which have been parked before will briefly come up again. This can
> result in problems e.g. with cpufreq driver being active as this will
> call into get_cpu_idle_time() for a cpu without initialized scheduler
> data.
> 
> Fix that by letting get_cpu_idle_time() deal with this case.
> 
> Fixes: 132cbe8f35632fb2 ("sched: fix get_cpu_idle_time() with core 
> scheduling")
> Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Tested-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

> --- a/xen/common/sched/core.c
> +++ b/xen/common/sched/core.c
> @@ -337,7 +337,7 @@ uint64_t get_cpu_idle_time(unsigned int cpu)
>      struct vcpu_runstate_info state = { 0 };
>      const struct vcpu *v = idle_vcpu[cpu];
>  
> -    if ( cpu_online(cpu) && v )
> +    if ( cpu_online(cpu) && v && get_sched_res(cpu) )
>          vcpu_runstate_get(v, &state);

My earlier question was aiming at getting rid of the (now) middle part
of the condition; I thought this may be okay to do as a secondary change
here. But perhaps you intentionally left it there, so I'm unsure whether
to suggest to make the adjustment while committing (awaiting a
maintainer ack first anyway).

Jan