Re: [PATCH v6 3/5] sched: Enforce user requested affinity

[Peter Zijlstra]

On Wed, Aug 31, 2022 at 11:18:22AM +0200, Peter Zijlstra wrote:
> On Thu, Aug 25, 2022 at 09:01:17PM -0400, Waiman Long wrote:
> 
> > @@ -9352,6 +9381,11 @@ int sched_cpu_activate(unsigned int cpu)
> >  		sched_update_numa(cpu, true);
> >  		sched_domains_numa_masks_set(cpu);
> >  		cpuset_cpu_active();
> > +		/*
> > +		 * Preallocated scratch cpumask
> > +		 */
> > +		if (!rq->scratch_mask)
> > +			rq->scratch_mask = kmalloc(cpumask_size(), GFP_KERNEL);
> >  	}
> 
> this is too late; I think you'll have to add a sched_cpu_prepare() and
> simply fail the cpu-up when the allocation fails.

Alternatively, waste some more memory and add yet another per-cpu
cpumask.