Re: the creation of boot_cpu_init() is wrong and accessing uninitialised data

[James Bottomley <James.Bottomley@SteelEye.com>]

On Sun, 2006-07-02 at 08:52 -0600, Eric W. Biederman wrote:
> What is the point of using a non-zero logical cpu id?
> I don't care about the apic id or the equivalent.

Logical CPUs were just an artifact to get dense CPU maps, which is now
no longer necessary.  There are architectures which have never used
logical CPUs.  For them, the boot CPU is whatever the BIOS says it is.

> There are cases like machine_shutdown where we care about who
> the boot cpu is so we can reboot on that cpu.

That's not at all safe:  one of the standard times for CPUs to be
deconfigured is on boot.  It's really not a good idea to rely on finding
the same CPU back again to boot on.

> As far as I know 
> the kernel has not abstraction to describe the boot cpu
> except for giving it logical cpu id 0.  Has an abstraction
> been added that I'm not aware of?

The kernel has never had an abstraction requiring logical CPUs, let
alone one requiring that the boot CPU be numbered zero.

James