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

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Date:   Wed, 31 Aug 2022 11:18:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH v6 3/5] sched: Enforce user requested affinity

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.