On Sat, Oct 24, 2015 at 01:16:21AM +0900, byungchul.p...@lge.com wrote:
> +++ b/kernel/sched/core.c
> @@ -1264,6 +1264,8 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
>  
>  void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
>  {
> +     unsigned int prev_cpu = task_cpu(p);
> +
>  #ifdef CONFIG_SCHED_DEBUG
>       /*
>        * We should never call set_task_cpu() on a blocked task,
> @@ -1289,15 +1291,14 @@ void set_task_cpu(struct task_struct *p, unsigned int 
> new_cpu)
>  #endif
>  
>       trace_sched_migrate_task(p, new_cpu);
> +     __set_task_cpu(p, new_cpu);
>  
> -     if (task_cpu(p) != new_cpu) {
> +     if (prev_cpu != new_cpu) {
>               if (p->sched_class->migrate_task_rq)
> -                     p->sched_class->migrate_task_rq(p, new_cpu);
> +                     p->sched_class->migrate_task_rq(p, prev_cpu);
>               p->se.nr_migrations++;
>               perf_event_task_migrate(p);
>       }
> -
> -     __set_task_cpu(p, new_cpu);
>  }

I don't think this is safe, see the comment in __set_task_cpu(). We want
that to be last.

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