On Wed, Jan 28, 2015 at 01:24:11AM +0100, Frederic Weisbecker wrote:
> +++ b/kernel/sched/core.c
> @@ -2760,7 +2760,6 @@ static void __sched __schedule(void)
>       struct rq *rq;
>       int cpu;
>  
> -     preempt_disable();

Implies barrier();

>       cpu = smp_processor_id();
>       rq = cpu_rq(cpu);
>       rcu_note_context_switch();
> @@ -2822,8 +2821,6 @@ static void __sched __schedule(void)
>               raw_spin_unlock_irq(&rq->lock);
>  
>       post_schedule(rq);

implies barrier();

> -
> -     sched_preempt_enable_no_resched();
>  }
>  
>  static inline void sched_submit_work(struct task_struct *tsk)

> @@ -2883,9 +2882,9 @@ void __sched schedule_preempt_disabled(void)
>  static void preempt_schedule_common(void)
>  {
>       do {
> -             preempt_count_add(PREEMPT_ACTIVE);
> +             preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);

Does _NOT_ imply barrier();

>               __schedule();
> -             preempt_count_sub(PREEMPT_ACTIVE);

idem.

> +             preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
>  
>               /*
>                * Check again in case we missed a preemption opportunity
--
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