Hi Daniel,

When doing CPU hotplug tests, I got the following bug

[   25.979429] KVM setup async PF for cpu 1
[   25.980593] kvm-stealtime: cpu 1, msr 1f40d140
[   25.982728] BUG: unable to handle kernel NULL pointer dereference at           (null)
[   25.982741] IP: [<ffffffff81678fad>] cpuidle_disable_device+0xc/0x5c
[   25.982744] PGD 1adb6067 PUD 18d97067 PMD 0 
[   25.982747] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
[   25.982749] Modules linked in:
[   25.982753] CPU 0 
[   25.982753] Pid: 2273, comm: 01-cpu-hotplug Not tainted 3.6.0-00324-g8937cc5 #1290 Bochs Bochs
[   25.982756] RIP: 0010:[<ffffffff81678fad>]  [<ffffffff81678fad>] cpuidle_disable_device+0xc/0x5c
[   25.982760] RSP: 0018:ffff880018c75cd8  EFLAGS: 00010246
[   25.982761] RAX: ffff880018c75fd8 RBX: ffff88001b49c000 RCX: ffff880018c3aaf0
[   25.982762] RDX: 0000000000000006 RSI: ffff880018c3aaf0 RDI: 0000000000000000
[   25.982764] RBP: ffff880018c75ce8 R08: ffff880018c75c88 R09: 000000000000000a
[   25.982765] R10: ffff88001f20a000 R11: ffff880018c3aaf0 R12: 0000000000000000
[   25.982766] R13: 0000000000000000 R14: 0000000000000000 R15: ffffffff81ce2a70
[   25.982767] FS:  00007f286a3fc700(0000) GS:ffff88001f200000(0000) knlGS:0000000000000000
[   25.982769] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[   25.982770] CR2: 0000000000000000 CR3: 0000000018c7c000 CR4: 00000000000006f0
[   25.982774] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   25.982778] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   25.982779] Process 01-cpu-hotplug (pid: 2273, threadinfo ffff880018c74000, task ffff880018c3a350)
[   25.982780] Stack:
[   25.982782]  ffff88001b49c000 0000000000000000 ffff880018c75d18 ffffffff8137732f
[   25.982785]  ffff88001b49c000 ffff88001b49c000 0000000000000002 ffffffff81c81c01
[   25.982787]  ffff880018c75d48 ffffffff81374dd7 0000000000000001 0000000000000001
[   25.982788] Call Trace:
[   25.982799]  [<ffffffff8137732f>] acpi_processor_hotplug+0x55/0x97
[   25.982801]  [<ffffffff81374dd7>] acpi_cpu_soft_notify+0x92/0xcd
[   25.982804]  [<ffffffff817e1c2b>] notifier_call_chain+0x65/0x95
[   25.982812]  [<ffffffff8105c9ae>] __raw_notifier_call_chain+0xe/0x10
[   25.982816]  [<ffffffff810384ec>] __cpu_notify+0x20/0x37
[   25.982819]  [<ffffffff81038516>] cpu_notify+0x13/0x15
[   25.982834]  [<ffffffff817c57fb>] _cpu_up+0x16c/0x1ae
[   25.982837]  [<ffffffff817c58ac>] cpu_up+0x6f/0x81
[   25.982839]  [<ffffffff8178cffd>] store_online+0x5f/0x8f
[   25.982847]  [<ffffffff813cb558>] dev_attr_store+0x18/0x24
[   25.982857]  [<ffffffff81176ab0>] sysfs_write_file+0xee/0x126
[   25.982865]  [<ffffffff81119129>] vfs_write+0xa6/0x132
[   25.982868]  [<ffffffff811193b0>] sys_write+0x4c/0x80
[   25.982871]  [<ffffffff817e581e>] tracesys+0xd0/0xd5
[   25.982898] Code: d8 48 01 d6 48 81 fe ff ff ff 7f 48 0f 4e ce 41 89 4c 24 08 48 83 c4 28 5b 41 5c 41 5d 5d c3 0f 1f 44 00 00 55 48 89 e5 41 54 53 <f6> 07 02 48 89 fb 74 43 e8 e2 05 00 00 48 85 c0 74 39 48 83 3d 
[   25.982900] RIP  [<ffffffff81678fad>] cpuidle_disable_device+0xc/0x5c
[   25.982901]  RSP <ffff880018c75cd8>
[   25.982902] CR2: 0000000000000000

which is bisected to:

3d339dcbb56d8d70c1b959aff87d74adc3a84eea is the first bad commit
commit 3d339dcbb56d8d70c1b959aff87d74adc3a84eea
Author: Daniel Lezcano <daniel.lezcano@linaro.org>
Date:   Mon Sep 17 23:01:56 2012 +0200

    cpuidle / ACPI : move cpuidle_device field out of the acpi_processor_power structure

Thanks,
Fengguang