kernel version : Linux localhost 2.6.17-1.2356.fc6 #1 SMP Thu Jul 6 01:10:48 EDT
2006 i686 i686 i386 GNU/Linux

On an Intel Centrino Duo (Dell D620) the kernel reports the following possible
circular locking dependency detected...

Not sure if this should be reported in the Fedora kernel, the cpuspeed package
or upstream. I figure its coming from the kernel so here's as good as anywhere else.

=======================================================
[ INFO: possible circular locking dependency detected ]
-------------------------------------------------------
S06cpuspeed/1812 is trying to acquire lock:
 (dbs_mutex){--..}, at: [<c060d6bb>] mutex_lock+0x21/0x24

but task is already holding lock:
 (cpucontrol){--..}, at: [<c060d6bb>] mutex_lock+0x21/0x24

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (cpucontrol){--..}:
       [<c043c546>] lock_acquire+0x4b/0x6d
       [<c060d51e>] __mutex_lock_slowpath+0xbf/0x23b
       [<c060d6bb>] mutex_lock+0x21/0x24
       [<c0440009>] __lock_cpu_hotplug+0x36/0x56
       [<c0440042>] lock_cpu_hotplug+0xa/0xc
       [<c04337de>] __create_workqueue+0x52/0x168
       [<f8b3b32e>] cpufreq_governor_dbs+0x9e/0x2cb [cpufreq_ondemand]
       [<c05a724b>] __cpufreq_governor+0x57/0xd8
       [<c05a7409>] __cpufreq_set_policy+0x13d/0x1a9
       [<c05a760c>] store_scaling_governor+0x128/0x151
       [<c05a6c67>] store+0x37/0x48
       [<c04ab4cc>] sysfs_write_file+0xab/0xd1
       [<c047248b>] vfs_write+0xab/0x157
       [<c0472ace>] sys_write+0x3b/0x60
       [<c0403f2f>] syscall_call+0x7/0xb

-> #0 (dbs_mutex){--..}:
       [<c043c546>] lock_acquire+0x4b/0x6d
       [<c060d51e>] __mutex_lock_slowpath+0xbf/0x23b
       [<c060d6bb>] mutex_lock+0x21/0x24
       [<f8b3b503>] cpufreq_governor_dbs+0x273/0x2cb [cpufreq_ondemand]
       [<c05a724b>] __cpufreq_governor+0x57/0xd8
       [<c05a7463>] __cpufreq_set_policy+0x197/0x1a9
       [<c05a760c>] store_scaling_governor+0x128/0x151
       [<c05a6c67>] store+0x37/0x48
       [<c04ab4cc>] sysfs_write_file+0xab/0xd1
       [<c047248b>] vfs_write+0xab/0x157
       [<c0472ace>] sys_write+0x3b/0x60
       [<c0403f2f>] syscall_call+0x7/0xb

other info that might help us debug this:

2 locks held by S06cpuspeed/1812:
 #0:  (&policy->lock){--..}, at: [<c060d6bb>] mutex_lock+0x21/0x24
 #1:  (cpucontrol){--..}, at: [<c060d6bb>] mutex_lock+0x21/0x24

stack backtrace:
 [<c0405167>] show_trace_log_lvl+0x54/0xfd
 [<c040571e>] show_trace+0xd/0x10
 [<c040583d>] dump_stack+0x19/0x1b
 [<c043b63d>] print_circular_bug_tail+0x59/0x64
 [<c043be35>] __lock_acquire+0x7ed/0x98d
 [<c043c546>] lock_acquire+0x4b/0x6d
 [<c060d51e>] __mutex_lock_slowpath+0xbf/0x23b
 [<c060d6bb>] mutex_lock+0x21/0x24
 [<f8b3b503>] cpufreq_governor_dbs+0x273/0x2cb [cpufreq_ondemand]
 [<c05a724b>] __cpufreq_governor+0x57/0xd8
 [<c05a7463>] __cpufreq_set_policy+0x197/0x1a9
 [<c05a760c>] store_scaling_governor+0x128/0x151
 [<c05a6c67>] store+0x37/0x48
 [<c04ab4cc>] sysfs_write_file+0xab/0xd1
 [<c047248b>] vfs_write+0xab/0x157
 [<c0472ace>] sys_write+0x3b/0x60
 [<c0403f2f>] syscall_call+0x7/0xb