Most recent kernel where this bug did not occur:       
Distribution:Gentoo      
Hardware Environment: Tyan k8w running dual opteron 248     
Software Environment:      
    
Gnu C                  3.4.4    
Gnu make               3.80    
binutils               2.16.1    
util-linux             2.12r    
mount                  2.12r    
module-init-tools      3.2.1    
e2fsprogs              1.38    
jfsutils               1.1.7    
reiserfsprogs          3.6.19    
reiser4progs           line    
xfsprogs               2.6.25    
nfs-utils              1.0.7    
Linux C Library        2.3.5    
Dynamic linker (ldd)   2.3.5    
Procps                 3.2.5    
Net-tools              1.60    
Kbd                    1.12    
Sh-utils               5.3.0    
udev                   078    
Modules Loaded         nvidia ipGnu C                  3.4.4    
Gnu make               3.80    
binutils               2.16.1    
util-linux             2.12r    
mount                  2.12r    
module-init-tools      3.2.1    
e2fsprogs              1.38    
jfsutils               1.1.7    
reiserfsprogs          3.6.19    
reiser4progs           line    
xfsprogs               2.6.25    
nfs-utils              1.0.7    
Linux C Library        2.3.5    
Dynamic linker (ldd)   2.3.5    
Procps                 3.2.5    
Net-tools              1.60    
Kbd                    1.12    
Sh-utils               5.3.0    
udev                   078    
Modules Loaded         nvidia ipt_TOS ipt_REJECT ipt_LOG ipt_state ipt_pkttype ipt_recent    
ipt_iprange ipt_multiport iptable_mangle iptable_nat ip_nat ip_conntrack iptable_filter    
ip_tables i2c_amd756 i2c_amd8111 usblp w83627hf hwmon_vid i2c_isa i2c_core    
snd_emu10k1 snd_rawmidi snd_seq_device snd_ac97_codec snd_pcm snd_timer    
snd_ac97_bus snd_page_alloc snd_util_mem snd_hwdep snd wacomt_TOS ipt_REJECT    
ipt_LOG ipt_state ipt_pkttype ipt_recent ipt_iprange ipt_multiport iptable_mangle    
iptable_nat ip_nat ip_conntrack iptable_filter ip_tables i2c_amd756 i2c_amd8111 usblp    
w83627hf hwmon_vid i2c_isa i2c_core snd_emu10k1 snd_rawmidi snd_seq_device    
snd_ac97_codec snd_pcm snd_timer snd_ac97_bus snd_page_alloc snd_util_mem snd_hwdep    
snd wacom    
    
Problem Description:      
   
Kernel oops when scaling cpu frequency.  I have run this bu the powernow-k8 maintainer   
and it looks like libata is involved.     
   
 
 
Last login: Sun Dec 11 13:17:01 2005 on ttyS0  
newman ~  # cat  
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies  
2200000 2000000 1800000 1000000  
  
newman ~ # echo 2000000 >  
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed  
  
newman ~ # cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq  
2000000  
  
echo 1000000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed  
  
newmannable to handle kernel NULL pointer dereference at  
0000000000000008 RIP:  
<ffffffff803115d5>{scsi_next_command+5}  
PGD 0  
Oops: 0000 [1] PREEMPT SMP  
/system/cpu/cpu0/cpufreq/scaling_available_frequencies  
CPU 1newmannable to handle kernel NULL pointer dereference at  
0000000000000008 RIP:  
<ffffffff803115d5>{scsi_next_command+5}  
PGD 0  
Oops: 0000 [1] PREEMPT SMP  
/system/cpu/cpu0/cpufreq/scaling_available_frequencies  
CPU 1  
01;34m ~ #  
  
When I recompile without Prempt, I get  
  
Last login: Sun Dec 11 13:44:31 2005 on ttyS0  
newmannable to handle kernel NULL pointer dereference at  
0000000000000000 RIP:  
[<0000000000000000>]  
PGD 1b23c067 <3>ata1: command 0x35 timeout, stat 0x50 host_stat 0x64  
  
The above was taken from 2.6.14, but I have also tried 2.6.15 and gotten similar results  
   
      
Steps to reproduce:      
 echo 1000000 
> /sys/devices/system/cpu/cpu0/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed