Re: [patch 00/61] ANNOUNCE: lock validator -V1

[Michal Piotrowski]

Hi,

On 30/05/06, Arjan van de Ven <arjan@xxxxxxxxxxxxx> wrote:
> > I'm feeling a bit overwhelmed by the voluminous output of this checker.
> > Especially as (directly at least) cpufreq doesn't touch vma's, or mmap's.
>
> the reporter doesn't have CONFIG_KALLSYMS_ALL enabled which gives
> sometimes misleading backtraces (should lockdep just enable KALLSYMS_ALL
> to get more useful bugreports?)

Here is bug with CONFIG_KALLSYMS_ALL enabled.

=====================================================
[ BUG: possible circular locking deadlock detected! ]
-----------------------------------------------------
modprobe/1950 is trying to acquire lock:
(&sighand->siglock){.+..}, at: [<c102b632>] do_notify_parent+0x12b/0x1b9

but task is already holding lock:
(tasklist_lock){..-<B1>}, at: [<c1023473>] do_exit+0x608/0xa43

which lock already depends on the new lock,
which could lead to circular deadlocks!

the existing dependency chain (in reverse order) is:

-> #1 (cpucontrol){--..}:
      [<c10394be>] lockdep_acquire+0x69/0x82
      [<c11ed729>] __mutex_lock_slowpath+0xd0/0x347
      [<c11ed9bc>] mutex_lock+0x1c/0x1f
      [<c103dda5>] __lock_cpu_hotplug+0x36/0x56
      [<c103ddde>] lock_cpu_hotplug+0xa/0xc
      [<c1199dd6>] __cpufreq_driver_target+0x15/0x50
      [<c119a192>] cpufreq_governor_performance+0x1a/0x20
      [<c1198ada>] __cpufreq_governor+0xa0/0x1a9
      [<c1198cb2>] __cpufreq_set_policy+0xcf/0x100
      [<c1199196>] cpufreq_set_policy+0x2d/0x6f
      [<c1199c7e>] cpufreq_add_dev+0x34f/0x492
      [<c114b898>] sysdev_driver_register+0x58/0x9b
      [<c119a006>] cpufreq_register_driver+0x80/0xf4
      [<fd91402a>] ipt_local_out_hook+0x2a/0x65 [iptable_filter]
      [<c10410e1>] sys_init_module+0xa6/0x230
      [<c11ef97b>] sysenter_past_esp+0x54/0x8d

-> #0 (&sighand->siglock){.+..}:
      [<c10394be>] lockdep_acquire+0x69/0x82
      [<c11ed729>] __mutex_lock_slowpath+0xd0/0x347
      [<c11ed9bc>] mutex_lock+0x1c/0x1f
      [<c11990bb>] cpufreq_update_policy+0x34/0xd8
      [<fd9a350b>] cpufreq_stat_cpu_callback+0x1b/0x7c [cpufreq_stats]
      [<fd9a607d>] cpufreq_stats_init+0x7d/0x9b [cpufreq_stats]
      [<c10410e1>] sys_init_module+0xa6/0x230
      [<c11ef97b>] sysenter_past_esp+0x54/0x8d

other info that might help us debug this:

1 locks held by modprobe/1950:
#0:  (cpucontrol){--..}, at: [<c11ed9bc>] mutex_lock+0x1c/0x1f

stack backtrace:
[<c1003ed6>] show_trace+0xd/0xf
[<c10043e9>] dump_stack+0x17/0x19
[<c103863e>] print_circular_bug_tail+0x59/0x64
[<c1038e91>] __lockdep_acquire+0x848/0xa39
[<c10394be>] lockdep_acquire+0x69/0x82
[<c11ed729>] __mutex_lock_slowpath+0xd0/0x347
[<c11ed9bc>] mutex_lock+0x1c/0x1f
[<c11990bb>] cpufreq_update_policy+0x34/0xd8
[<fd9a350b>] cpufreq_stat_cpu_callback+0x1b/0x7c [cpufreq_stats]
[<fd9a607d>] cpufreq_stats_init+0x7d/0x9b [cpufreq_stats]
[<c10410e1>] sys_init_module+0xa6/0x230
[<c11ef97b>] sysenter_past_esp+0x54/0x8d


> the problem is this, there are 2 scenarios in this bug:
>
> One
> ---
> store_scaling_governor takes policy->lock and then calls __cpufreq_set_policy
> __cpufreq_set_policy calls __cpufreq_governor
> __cpufreq_governor  calls __cpufreq_driver_target via cpufreq_governor_performance
> __cpufreq_driver_target calls lock_cpu_hotplug() (which takes the hotplug lock)
>
>
> Two
> ---
> cpufreq_stats_init lock_cpu_hotplug() and then calls cpufreq_stat_cpu_callback
> cpufreq_stat_cpu_callback calls cpufreq_update_policy
> cpufreq_update_policy takes the policy->lock
>
>
> so this looks like a real honest AB-BA deadlock to me...

Regards,
Michal

--
Michal K. K. Piotrowski
LTG - Linux Testers Group
(http://www.stardust.webpages.pl/ltg/wiki/)
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