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

[Peter Zijlstra]

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.