Hi, Srivatsa
On 06/28/2013 03:54 AM, Srivatsa S. Bhat wrote:
[snip]
> @@ -625,8 +632,9 @@ EXPORT_SYMBOL(on_each_cpu_mask);
> * The function might sleep if the GFP flags indicates a non
> * atomic allocation is allowed.
> *
> - * Preemption is disabled to protect against CPUs going offline but not online.
> - * CPUs going online during the call will not be seen or sent an IPI.
> + * We use get/put_online_cpus_atomic() to protect against CPUs going
> + * offline but not online. CPUs going online during the call will
> + * not be seen or sent an IPI.
I was a little confused about this comment, if the offline-cpu still
have chances to become online, then there is chances that we will pick
it from for_each_online_cpu(), isn't it? Did I miss some point?
Regards,
Michael Wang
> *
> * You must not call this function with disabled interrupts or
> * from a hardware interrupt handler or from a bottom half handler.
> @@ -641,26 +649,26 @@ void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
> might_sleep_if(gfp_flags & __GFP_WAIT);
>
> if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
> - preempt_disable();
> + get_online_cpus_atomic();
> for_each_online_cpu(cpu)
> if (cond_func(cpu, info))
> cpumask_set_cpu(cpu, cpus);
> on_each_cpu_mask(cpus, func, info, wait);
> - preempt_enable();
> + put_online_cpus_atomic();
> free_cpumask_var(cpus);
> } else {
> /*
> * No free cpumask, bother. No matter, we'll
> * just have to IPI them one by one.
> */
> - preempt_disable();
> + get_online_cpus_atomic();
> for_each_online_cpu(cpu)
> if (cond_func(cpu, info)) {
> ret = smp_call_function_single(cpu, func,
> info, wait);
> WARN_ON_ONCE(!ret);
> }
> - preempt_enable();
> + put_online_cpus_atomic();
> }
> }
> EXPORT_SYMBOL(on_each_cpu_cond);
>
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