Re: [PATCH] rcu: Is it safe to enter an RCU read-side criticalsection?

[Eric Dumazet]

On Fri, 2013-09-06 at 08:18 -0700, Paul E. McKenney wrote:

> int rcu_is_cpu_idle(void)
> {
> 	int ret;
> 
> 	preempt_disable();
> 	ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0;
> 	preempt_enable();
> 	return ret;
> }

Paul I find this very confusing.

If caller doesn't have preemption disabled, what could be the meaning of
this rcu_is_cpu_idle() call ?

Its result is meaningless if suddenly thread is preempted, so what is
the point ?

Sorry if this is obvious to you.


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