cpu/hotplug: Reset task stack state in _cpu_up()

Commit dce1ca0525bf ("sched/scs: Reset task stack state in bringup_cpu()")
ensured that the shadow call stack and KASAN poisoning were removed from
a CPU's stack each time that CPU is brought up, not just once.

This is not incorrect. However, with parallel bringup the idle thread setup
will happen at a different step. As a consequence the cleanup in
bringup_cpu() would be too late.

Move the SCS/KASAN cleanup to the generic _cpu_up() function instead,
which already ensures that the new CPU's stack is available, purely to
allow for early failure. This occurs when the CPU to be brought up is
in the CPUHP_OFFLINE state, which should correctly do the cleanup any
time the CPU has been taken down to the point where such is needed.

Signed-off-by: David Woodhouse <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Mark Rutland <[email protected]>
Tested-by: Mark Rutland <[email protected]>
Tested-by: Michael Kelley <[email protected]>
Tested-by: Oleksandr Natalenko <[email protected]>
Tested-by: Helge Deller <[email protected]> # parisc
Tested-by: Guilherme G. Piccoli <[email protected]> # Steam Deck
Link: https://lore.kernel.org/r/[email protected]

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