The 'intel_idle_probe' probes the CPU and sets the CPU notifier.
But if later on during the module initialization we fail (say
in cpuidle_register_driver), we stop loading, but we neglect
to unregister the CPU notifier.  This means that during CPU
hotplug events the system will fail:

calling  intel_idle_init+0x0/0x326 @ 1
intel_idle: MWAIT substates: 0x1120
intel_idle: v0.4 model 0x2A
intel_idle: lapic_timer_reliable_states 0xffffffff
intel_idle: intel_idle yielding to none
initcall intel_idle_init+0x0/0x326 returned -19 after 14 usecs

... some time later, offlining and onlining a CPU:

cpu 3 spinlock event irq 62
BUG: unable to ] __cpuidle_register_device+0x1c/0x120
PGD 99b8b067 PUD 99b95067 PMD 0
Oops: 0000 [#1] SMP
Modules linked in: xen_evtchn nouveau mxm_wmi wmi radeon ttm i915 fbcon tileblit font atl1c bitblit softcursor drm_kms_helper video xen_blkfront xen_netfront fb_sys_fops sysimgblt sysfillrect syscopyarea xenfs xen_privcmd mperf
CPU 0
Pid: 2302, comm: udevd Not tainted 3.8.0-rc3upstream-00249-g09ad159 #1 MSI MS-7680/H61M-P23 (MS-7680)
RIP: e030:[<ffffffff814d956c>]  [<ffffffff814d956c>] __cpuidle_register_device+0x1c/0x120
RSP: e02b:ffff88009dacfcb8  EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff880105380000 RCX: 000000000000001c
RDX: 0000000000000000 RSI: 0000000000000055 RDI: ffff880105380000
RBP: ffff88009dacfce8 R08: ffffffff81a4f048 R09: 0000000000000008
R10: 0000000000000008 R11: 0000000000000000 R12: ffff880105380000
R13: 00000000ffffffdd R14: 0000000000000000 R15: ffffffff81a523d0
FS:  00007f37bd83b7a0(0000) GS:ffff880105200000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 00000000a09ea000 CR4: 0000000000042660
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process udevd (pid: 2302, threadinfo ffff88009dace000, task ffff88009afb47f0)
Stack:
 ffffffff8107f2d0 ffffffff810c2fb7 ffff88009dacfce8 00000000ffffffea
 ffff880105380000 00000000ffffffdd ffff88009dacfd08 ffffffff814d9882
 0000000000000003 ffff880105380000 ffff88009dacfd28 ffffffff81340afd
Call Trace:
 [<ffffffff8107f2d0>] ? collect_cpu_info_local+0x30/0x30
 [<ffffffff810c2fb7>] ? __might_sleep+0xe7/0x100
 [<ffffffff814d9882>] cpuidle_register_device+0x32/0x70
 [<ffffffff81340afd>] intel_idle_cpu_init+0xad/0x110
 [<ffffffff81340bc8>] cpu_hotplug_notify+0x68/0x80
 [<ffffffff8166023d>] notifier_call_chain+0x4d/0x70
 [<ffffffff810bc369>] __raw_notifier_call_chain+0x9/0x10
 [<ffffffff81094a4b>] __cpu_notify+0x1b/0x30
 [<ffffffff81652cf7>] _cpu_up+0x103/0x14b
 [<ffffffff81652e18>] cpu_up+0xd9/0xec
 [<ffffffff8164a254>] store_online+0x94/0xd0
 [<ffffffff814122fb>] dev_attr_store+0x1b/0x20
 [<ffffffff81216404>] sysfs_write_file+0xf4/0x170
 [<ffffffff811a1024>] vfs_write+0xb4/0x130
 [<ffffffff811a17ea>] sys_write+0x5a/0xa0
 [<ffffffff816643a9>] system_call_fastpath+0x16/0x1b
Code: 03 18 00 c9 c3 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 48 83 ec 30 48 89 5d e8 4c 89 65 f0 48 89 fb 4c 89 6d f8 e8 84 08 00 00 <48> 8b 78 08 49 89 c4 e8 f8 7f c1 ff 89 c2 b8 ea ff ff ff 84 d2
RIP  [<ffffffff814d956c>] __cpuidle_register_device+0x1c/0x120
 RSP <ffff88009dacfcb8>

This patch fixes that by moving the CPU notifier registration
as the last item to be done by the module.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: 3.6+ <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>