RE: [Hotplug_sig] [patch 1/1] Hot plug CPU to support physical add of new processors (i386)

[Protasevich, Natalie]

> > +#ifdef CONFIG_HOTPLUG_CPU
> > +	if (cpu_online(cpu)) {
> > +#else
> >  	if (cpu_online(cpu) || !cpu_present(cpu)) {
> > +#endif
> >  		ret = -EINVAL;
> >  		goto out;
> >  	}
> 
> Why this change?  I think the cpu_present check is needed for 
> ppc64 since it has non-present cpus in sysfs.
> 

The new processor was never brought up, its bit is only set in
cpu_possible_map, but not in present map. 

        ... 
        if (boot_error) {
                /* Try to put things back the way they were before ...
*/
                unmap_cpu_to_logical_apicid(cpu);
                cpu_clear(cpu, cpu_callout_map); /* was set here
(do_boot_cpu()) */
                cpu_clear(cpu, cpu_initialized); /* was set by
cpu_init() */
                cpucount--;
        } else {
                x86_cpu_to_apicid[cpu] = apicid;
                cpu_set(cpu, cpu_present_map);  <=====================
        }
        ...
So if someone tries to boot a CPU up first time during runtime it always
fails this check.
Thanks,
--Natalie
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