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disable_nonboot_cpus calls _cpu_down. But _cpu_down requires that the
caller already created the stop_machine workqueue (like cpu_down does).
Otherwise a call to stop_machine will lead to accesses to random memory
regions.

When introducing this new interface (9ea09af3
"stop_machine: introduce stop_machine_create/destroy") I missed the second
call site of _cpu_down.
So add the missing stop_machine_create/destroy calls to disable_nonboot_cpus
as well.

Fixes suspend-to-ram/disk and also this bug:

[  286.547348] BUG: unable to handle kernel paging request at 6b6b6b6b
[  286.548940] IP: [<c0150ca4>] __stop_machine+0x88/0xe3
[  286.550598] Oops: 0002 [#1] SMP
[  286.560580] Pid: 3273, comm: halt Not tainted (2.6.28-06127-g238c6d54
[  286.560580] EIP: is at __stop_machine+0x88/0xe3
[  286.560580] Process halt (pid: 3273, ti=f1a28000 task=f4530f30
[  286.560580] Call Trace:
[  286.560580]  [<c03d04e4>] ? _cpu_down+0x10f/0x234
[  ...