When cpu_up() fails, we can discern the most likely cause.
If cpu_present() is false, this means the cpu did not appear
in the MD. If -ENODEV is the error return value, then
the processor did not boot properly into the kernel.
Pass this information back in the dr-cpu response packet.
Signed-off-by: David S. Miller <davem@davemloft.net>
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