Re: [PATCH for-next 3/6] xen/sched: Fix build when NR_CPUS == 1

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2021-02-26 at 09:31 +0100, Jan Beulich wrote:
> On 26.02.2021 04:08, Connor Davis wrote:
> > On Thu, Feb 25, 2021 at 04:50:02PM +0100, Jan Beulich wrote:
> > > On 25.02.2021 16:24, Connor Davis wrote:
> > > > index 9745a77eee..f5ec65bf9b 100644
> > > > --- a/xen/common/sched/core.c
> > > > +++ b/xen/common/sched/core.c
> > > > @@ -2763,7 +2763,7 @@ static int cpu_schedule_up(unsigned int
> > > > cpu)
> > > >      cpumask_set_cpu(cpu, &sched_res_mask);
> > > >  
> > > >      /* Boot CPU is dealt with later in scheduler_init(). */
> > > > -    if ( cpu == 0 )
> > > > +    if ( cpu == 0 || NR_CPUS == 1 )
> > > >          return 0;
> > > >  
> > > >      if ( idle_vcpu[cpu] == NULL )
> 
> @@ -2769,6 +2769,12 @@ static int cpu_schedule_up(unsigned int
>      if ( cpu == 0 )
>          return 0;
>  
> +    /*
> +     * Guard in particular also against the compiler suspecting out-
> of-bounds
> +     * array accesses below when NR_CPUS=1.
> +     */
> +    BUG_ON(cpu >= NR_CPUS);
> +
>
I would be fine with this.

Actually, I do prefer it too, over the "is index 0 or is the array
length 1" check, which I also find confusing.

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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