linux-kernel - Re: [PATCH 3/8] sched: Dont run cpu-online with balance

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Message-ID: <YAMFxk311hkpQYl3@hirez.programming.kicks-ass.net>
Date:   Sat, 16 Jan 2021 16:27:02 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     mingo@...nel.org, tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, jiangshanlai@...il.com,
        valentin.schneider@....com, cai@...hat.com,
        vincent.donnefort@....com, decui@...rosoft.com, paulmck@...nel.org,
        vincent.guittot@...aro.org, rostedt@...dmis.org, tj@...nel.org
Subject: Re: [PATCH 3/8] sched: Dont run cpu-online with balance_push()
 enabled

On Sat, Jan 16, 2021 at 12:30:36PM +0100, Peter Zijlstra wrote:
> @@ -7608,6 +7614,12 @@ int sched_cpu_dying(unsigned int cpu)
>  	}
>  	rq_unlock_irqrestore(rq, &rf);
>  
> +	/*
> +	 * Should really be after we clear cpu_online(), but we're in
> +	 * stop_machine(), so it all works.
> +	 */
> +	balance_push_set(cpu, false);

Looking at the RCU thing just now made me realize we run all the DYING
notifiers with cpu_online() already false, so the above comment is wrong
and ordering in fact perfect.