On Fri, 26 Jul 2019 16:54:11 +0200
Peter Zijlstra <pet...@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();
>  
> 

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