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); > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev