Christoph,

Here is another trace:

[   43.224124] numa_remove_cpu cpu 1 node 0: mask now 0
[   43.273080] smpboot: CPU 1 is now offline
[   43.274096] BUG: unable to handle kernel paging request at ffffffff822e1650
[   43.275010] IP: [<ffffffff81a3c047>] slab_cpuup_callback+0x65/0x10e
[   43.275010] PGD 1f7d067 PUD 1f81063 PMD 1e22c063 PTE 22e1162
[   43.275010] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
[   43.275010] Modules linked in:
[   43.275010] CPU 0 
[   43.275010] Pid: 2975, comm: 01-cpu-hotplug Not tainted 3.7.0-rc1-00016-gb59d450 #1592 Bochs Bochs
[   43.275010] RIP: 0010:[<ffffffff81a3c047>]  [<ffffffff81a3c047>] slab_cpuup_callback+0x65/0x10e
[   43.275010] RSP: 0018:ffff880017029d28  EFLAGS: 00010016
[   43.275010] RAX: 0000000000001400 RBX: ffff88001f5d69e0 RCX: ffff88001715cf06
[   43.275010] RDX: 0000000000000006 RSI: ffffffff81a3c047 RDI: ffffffff810bcca1
[   43.275010] RBP: ffff880017029d48 R08: ffff880017029cc8 R09: 0000000000000000
[   43.275010] R10: ffff88001f20a000 R11: ffff88001f20a000 R12: ffffffff822e1650
[   43.275010] R13: 0000000000000206 R14: 0000000000000001 R15: ffffffff82087a70
[   43.275010] FS:  00007f62c0cb4700(0000) GS:ffff88001f200000(0000) knlGS:0000000000000000
[   43.275010] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[   43.275010] CR2: ffffffff822e1650 CR3: 0000000017058000 CR4: 00000000000006f0
[   43.275010] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   43.275010] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   43.275010] Process 01-cpu-hotplug (pid: 2975, threadinfo ffff880017028000, task ffff88001715c7c0)
[   43.275010] Stack:
[   43.275010]  0000000000000001 00000000fffffff4 ffffffff82087bd0 0000000000000000
[   43.275010]  ffff880017029d98 ffffffff81a5c1c8 0000000000000001 0000000000000007
[   43.275010]  ffff880017029db8 0000000000000001 0000000000000000 0000000000000000
[   43.275010] Call Trace:
[   43.275010]  [<ffffffff81a5c1c8>] notifier_call_chain+0x65/0x95
[   43.275010]  [<ffffffff81094d22>] __raw_notifier_call_chain+0xe/0x10
[   43.275010]  [<ffffffff8106f8b0>] __cpu_notify+0x20/0x37
[   43.275010]  [<ffffffff8106f8da>] cpu_notify+0x13/0x15
[   43.275010]  [<ffffffff8106fa02>] cpu_notify_nofail+0xe/0x16
[   43.275010]  [<ffffffff81a0007b>] _cpu_down+0x193/0x26d
[   43.275010]  [<ffffffff81a0017d>] cpu_down+0x28/0x3c
[   43.275010]  [<ffffffff81a02ade>] store_online+0x3e/0x8f
[   43.275010]  [<ffffffff8156a180>] dev_attr_store+0x18/0x24
[   43.275010]  [<ffffffff811be980>] sysfs_write_file+0xee/0x126
[   43.275010]  [<ffffffff81165a0d>] vfs_write+0xa6/0x152
[   43.275010]  [<ffffffff81165cd4>] sys_write+0x4c/0x80
[   43.275010]  [<ffffffff81a5fc59>] system_call_fastpath+0x16/0x1b
[   43.275010] Code: e8 1d 98 01 00 4c 8b 25 a8 d1 57 00 49 83 ec 68 e9 8e 00 00 00 9c 58 0f 1f 44 00 00 49 89 c5 fa 66 0f 1f 44 00 00 e8 4d 0c 68 ff <49> 8b 04 24 48 89 c3 4a 03 1c f5 00 3f 09 82 74 35 48 83 7b 10 
[   43.275010] RIP  [<ffffffff81a3c047>] slab_cpuup_callback+0x65/0x10e
[   43.275010]  RSP <ffff880017029d28>
[   43.275010] CR2: ffffffff822e1650

Thanks,
Fengguang