Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping.

[Tang Chen]

On 09/27/2015 01:56 AM, Tejun Heo wrote:
> On Sat, Sep 26, 2015 at 05:52:09PM +0800, Tang Chen wrote:
> > > > +static int allocate_logical_cpuid(int apicid)
> > > > +{
> > > > +	int i;
> > > > +
> > > > +	/*
> > > > +	 * cpuid <-> apicid mapping is persistent, so when a cpu is up,
> > > > +	 * check if the kernel has allocated a cpuid for it.
> > > > +	 */
> > > > +	for (i = 0; i < max_logical_cpuid; i++) {
> > > > +		if (cpuid_to_apicid[i] == apicid)
> > > > +			return i;
> > > > +	}
> > > > +
> > > > +	/* Allocate a new cpuid. */
> > > > +	if (max_logical_cpuid >= nr_cpu_ids) {
> > > > +		WARN_ONCE(1, "Only %d processors supported."
> > > > +			     "Processor %d/0x%x and the rest are ignored.\n",
> > > > +			     nr_cpu_ids - 1, max_logical_cpuid, apicid);
> > > > +		return -1;
> > > > +	}
> > > So, the original code didn't have this failure mode, why is this
> > > different for the new code?
> > It is not different. Since max_logical_cpuid is new, this is ensure it won't
> > go beyond NR_CPUS.
> If the above condition can happen, the original code should have had a
> similar check as above, right?  Sure, max_logical_cpuid is a new thing
> but that doesn't seem to change whether the above condition can happen
> or not, no?

Right, indeed. It is in

generic_processor_info()
|--> if (num_processors >= nr_cpu_ids)

Will remove my new added check.

Thanks.

> Thanks.

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