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Date:   Tue, 30 Jul 2019 09:22:40 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@kernel.org, juri.lelli@redhat.com,
        linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com,
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Subject: Re: [RFC][PATCH 02/13] stop_machine: Fix stop_cpus_in_progress
 ordering
Message-ID: <20190730092240.42383953@gandalf.local.home>
In-Reply-To: <20190726161357.455421817@infradead.org>
References: <20190726145409.947503076@infradead.org>
        <20190726161357.455421817@infradead.org>
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On Fri, 26 Jul 2019 16:54:11 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> Make sure the entire for loop has stop_cpus_in_progress set.


>  kernel/stop_machine.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -383,6 +383,7 @@ static bool queue_stop_cpus_work(const s
>  	 */
>  	preempt_disable();
>  	stop_cpus_in_progress = true;
> +	barrier();

Like smp_mb() shouldn't barrier() have a comment to what is being
ordered and why?

-- Steve

>  	for_each_cpu(cpu, cpumask) {
>  		work = &per_cpu(cpu_stopper.stop_work, cpu);
>  		work->fn = fn;
> @@ -391,6 +392,7 @@ static bool queue_stop_cpus_work(const s
>  		if (cpu_stop_queue_work(cpu, work))
>  			queued = true;
>  	}
> +	barrier();
>  	stop_cpus_in_progress = false;
>  	preempt_enable();
>  
>