A problem with percpu variable cpu_number

Hi :

At the beginning of start_kernel() -- init/main.c
boot_cpu_init() is called

and in boot_cpu_init() will call smp_processor_id()
it's a macro
and it will be expanded as (percpu_read(cpu_number)) and so on

but i noticed that it's before setup_per_cpu_areas() in start_kernel()
is that mean the percpu areas hadn't be initialized yet
but why smp_processor_id() could be called before setup_per_cpu_areas()


Thank you.

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jiangtao