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

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 == 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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