Most recent kernel where this bug did not occur: no other kernels tested
Distribution: Fedora Core 4
Hardware Environment: AMD Sempron 3400+, GigaByte K8NS Pro, 2x512MB DDR memory
modules, custom BIOS version F14b (not publicly available)
Software Environment:
Problem Description: When cpufreq_ondemand "ondemand" mode is turned on,
computer sometimes lose its keyboard input, kernel oops'es, it's hardly possible
to reboot 'cause smth stange is happening to the kernel.

Here's an oopse I receive when the problem is triggered:

Unable to handle kernel paging request at virtual address 044002e8
 printing eip:
c02b02f9
*pde = 00000000
Oops: 0000 [#1]
PREEMPT
Modules linked in: snd_rtctimer ppp_synctty ppp_async crc_ccitt ppp_generic slhc
 cpufreq_powersave cpufreq_ondemand powernow_k8 eeprom it87 hwmon_vid i2c_isa vm
net parport_pc parport vmmon ip_conntrack_ftp ipt_state ip_conntrack nfnetlink i
pt_REJECT ipt_owner ipt_limit ipt_multiport iptable_filter ipt_ULOG ip_tables bi
nfmt_misc ntfs thermal processor fan button ohci1394 ieee1394 ohci_hcd ehci_hcd
nvidia amd64_agp agpgart i2c_nforce2 emu10k1_gp gameport snd_intel8x0 snd_emu10k
1_synth snd_emux_synth snd_seq_virmidi snd_seq_midi_emul snd_emu10k1 snd_rawmidi
 snd_ac97_codec snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_os
s snd_mixer_oss snd_pcm snd_timer snd_ac97_bus snd_page_alloc snd_util_mem snd_h
wdep snd skge crc32 sk98lin floppy sata_nv libata scsi_mod
CPU:    0
EIP:    0060:[<c02b02f9>]    Tainted: P      VLI
EFLAGS: 00010246   (2.6.14.4-k8)
EIP is at cpufreq_notify_transition+0x1a9/0x200
eax: 000f4240   ebx: c1963ed8   ecx: 0003b007   edx: 00000000
esi: c037ac60   edi: 00000000   ebp: 00000000   esp: c1963ea8
ds: 007b   es: 007b   ss: 0068
Process events/0 (pid: 4, threadinfo=c1962000 task=c1907a50)
Stack: 00000012 00000000 c1963ed8 c036408c 00000001 00000000 00000002 00000000
       f8cca2e8 c1963ed8 00000001 00000012 00000000 001e8480 000f4240 00000000
       f76cb940 00000006 f79806c0 0000000c f8cca45e f76cb940 00000001 00000000
Call Trace:
 [<f8cca2e8>] transition_frequency+0xc8/0x120 [powernow_k8]
 [<f8cca45e>] powernowk8_target+0x11e/0x1a0 [powernow_k8]
 [<f8c93475>] dbs_check_cpu+0x155/0x1e0 [cpufreq_ondemand]
 [<f8c9351b>] do_dbs_timer+0x1b/0x60 [cpufreq_ondemand]
 [<c012adad>] worker_thread+0x1dd/0x2d0
 [<f8c93500>] do_dbs_timer+0x0/0x60 [cpufreq_ondemand]
 [<c01159d0>] default_wake_function+0x0/0x20
 [<c012abd0>] worker_thread+0x0/0x2d0
 [<c012f446>] kthread+0xb6/0xc0
 [<c012f390>] kthread+0x0/0xc0
 [<c0101069>] kernel_thread_helper+0x5/0xc
Code: 85 c9 fe ff ff 8b 43 08 89 42 1c e9 be fe ff ff 89 f6 89 d0 31 d2 f7 f1 89
 d5 89 c3 e9 25 ff ff ff 89 f8 31 ff 8b 0d ec 02 40 c0 <f7> 25 e8 02 40 c0 85 d2
 89 c5 89 54 24 0c 74 0c 89 d0 31 d2 f7

Alt  + ScrollLock partial output (the PC was almost stuck - I couldn't save this
output in the file) right after kernel oopse:
Pid 0, Comm:                   Swapper
EIP: 0060 :[<f8b61b09>]        CPU: 0
EIP is at acpi_processor_idle + 0xf1/0x275 [processor]
...
[<c0100da4>] cpu_idle + 0x34/0x50
[<c03ac89a>] start_kernel + 0x17a/0x1a0
[<c03ac3c0>] unknown_bootoption + 0x0/0x1f0

Steps to reproduce: Turn on the PC with given hardware setup.

modprobe powernow-k8
modprobe cpufreq_ondemand
echo "ondemand" > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

After several hours the keyboard in X server stops functioning, kernel gives an
oopse then it takes as long as five minutes (usual shutdown time is around 40
seconds) to shut the PC down using a poweroff PC case button.