>
> Current, synchronize_sched() ignores preempt-disable()
> sequences in the idle loop. It makes synchronize_sched()
> is not so pure, and it hurts tracing.
>
> Paul have a proposal before:
>
http://lkml.org/lkml/2009/4/5/140
>
http://lkml.org/lkml/2009/4/6/496
> But old fix needs to hack into all architectures' idle loops.
>
> This is another try, it uses the fact that idle loops
> are executing with preept_count()=1.
> But I didn't look deep into all idle loops.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 3ec8160..0761723 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -80,6 +80,10 @@ DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
> struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
> DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
>
> +#ifndef IDLE_CORE_LOOP_PREEMPT_COUNT
> +#define IDLE_CORE_LOOP_PREEMPT_COUNT (1)
> +#endif
> +
> /*
> * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
> * permit this function to be invoked without holding the root rcu_node
> @@ -1114,6 +1118,26 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
> raise_softirq(RCU_SOFTIRQ);
> }
>
> +static inline int rcu_idle_qs(int cpu)
> +{
> + if (!idle_cpu(cpu))
> + return 0;
> +
> + if (!rcu_scheduler_active)
> + return 0;
> +
> + if (in_softirq())
> + return 0;
> +
> + if (hardirq_count() > (1 << HARDIRQ_SHIFT))
> + return 0;
> +
> + if ((preempt_count() & PREEMPT_MASK) > IDLE_CORE_LOOP_PREEMPT_COUNT)
> + return 0;
