Hi Ingo, this is happening in a brand new laptop, a Lenovo t61 with a
7700 processor and the Santa Rosa chipset. 

Lukewarm IQ detected in hotplug locking
BUG: at kernel/cpu.c:44 lock_cpu_hotplug()
 [<c0405f88>] dump_trace+0x64/0x105
 [<c0406041>] show_trace_log_lvl+0x18/0x2c
 [<c040664e>] show_trace+0xf/0x11
 [<c04066cf>] dump_stack+0x12/0x14
 [<c0447519>] lock_cpu_hotplug+0x51/0x74
 [<c0426251>] sched_setaffinity+0x13/0xe5
 [<c045bee7>] __synchronize_sched+0x35/0x5a
 [<c04244f1>] arch_reinit_sched_domains+0x13/0x29
 [<c0424543>] sched_power_savings_store+0x3c/0x49
 [<c0554680>] sysdev_class_store+0x1e/0x22
 [<c04b32f7>] sysfs_write_file+0xa3/0xc6
 [<c047beb3>] vfs_write+0xa8/0x154
 [<c047c4ce>] sys_write+0x41/0x67
 [<c0404f7c>] syscall_call+0x7/0xb
 [<b7fb3410>] 0xb7fb3410
 =======================
Lukewarm IQ detected in hotplug locking
BUG: at kernel/cpu.c:44 lock_cpu_hotplug()
 [<c0405f88>] dump_trace+0x64/0x105
 [<c0406041>] show_trace_log_lvl+0x18/0x2c
 [<c040664e>] show_trace+0xf/0x11
 [<c04066cf>] dump_stack+0x12/0x14
 [<c0447519>] lock_cpu_hotplug+0x51/0x74
 [<c0426251>] sched_setaffinity+0x13/0xe5
 [<c045bf09>] __synchronize_sched+0x57/0x5a
 [<c04244f1>] arch_reinit_sched_domains+0x13/0x29
 [<c0424543>] sched_power_savings_store+0x3c/0x49
 [<c0554680>] sysdev_class_store+0x1e/0x22
 [<c04b32f7>] sysfs_write_file+0xa3/0xc6
 [<c047beb3>] vfs_write+0xa8/0x154
 [<c047c4ce>] sys_write+0x41/0x67
 [<c0404f7c>] syscall_call+0x7/0xb
 [<b7fb3410>] 0xb7fb3410
 =======================

I'm attaching the full output of dmesg FYI, let me know if you need
something else to make sense of this. 

[BTW, I tried to unsuccessfully boot rt18 today in one of my CCRMA
machines but the boot hung when trying to start the acpi daemon - this
was on FC6, I'll try to find out more tomorrow. We are seeing some hungs
with rt17 that I have not tried to diagnose yet]

-- Fernando