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Date: Tue, 08 Jul 2008 11:22:49 +0530
From: Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>
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To: Johannes Weiner <hannes@saeurebad.de>
CC: linux-kernel@vger.kernel.org, balbir@linux.vnet.ibm.com,
       ego@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com,
       davej@codemonkey.org.uk
Subject: Re: [BUG] While changing the cpufreq governor, kernel hits a bug
 in workqueue.c
References: <485F8028.1070302@linux.vnet.ibm.com> <87y74w41fp.fsf@skyscraper.fehenstaub.lan> <4860BB8E.2070505@linux.vnet.ibm.com> <87tzfh2t5l.fsf@skyscraper.fehenstaub.lan> <48638906.4090308@linux.vnet.ibm.com> <87y74l4scd.fsf@skyscraper.fehenstaub.lan> <87fxqp7nye.fsf@skyscraper.fehenstaub.lan> <4871E657.3040403@linux.vnet.ibm.com> <87d4lqq7ec.fsf@saeurebad.de>
In-Reply-To: <87d4lqq7ec.fsf@saeurebad.de>
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Hi Johannes,

Johannes Weiner wrote:

>> * I am seeing the circular locking dependency with the above patch
>> too.
> 
> Uhm.  Failure or no failure?  A possible dead-lock report _is_ a
> failure.  So, do you get one or not?  And if so, could you send me the
> dmesg parts?
> 
> Thanks a lot,
> 
> 	Hannes

I could see a circular locking dependency and sysfs hang with the new 
patch named "cpufreq: cancel self-rearming work synchroneously" also. 
Please find the dmesg output. Please let me know if you need more 
information. Thank a lot for your coordination.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.25.9.cpufreq #2
-------------------------------------------------------
S06cpuspeed/3427 is trying to acquire lock:
  (&(&dbs_info->work)->work){--..}, at: [<c012f46c>] 
__cancel_work_timer+0x80/0x177

but task is already holding lock:
  (dbs_mutex){--..}, at: [<c041e7db>] cpufreq_governor_dbs+0x26a/0x2f7

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (dbs_mutex){--..}:
        [<c013aa76>] add_lock_to_list+0x61/0x83
        [<c013cfa3>] __lock_acquire+0x953/0xb05
        [<c041e5e3>] cpufreq_governor_dbs+0x72/0x2f7
        [<c013d1b4>] lock_acquire+0x5f/0x79
        [<c041e5e3>] cpufreq_governor_dbs+0x72/0x2f7
        [<c04cdaa7>] mutex_lock_nested+0xce/0x222
        [<c041e5e3>] cpufreq_governor_dbs+0x72/0x2f7
        [<c041e5e3>] cpufreq_governor_dbs+0x72/0x2f7
        [<c041e5e3>] cpufreq_governor_dbs+0x72/0x2f7
        [<c041c87e>] __cpufreq_governor+0x73/0xa6
        [<c041c9ec>] __cpufreq_set_policy+0x13b/0x19e
        [<c041d6b9>] cpufreq_add_dev+0x3b4/0x4aa
        [<c041d29a>] handle_update+0x0/0x21
        [<c02ee310>] sysdev_driver_register+0x48/0x9a
        [<c041c75f>] cpufreq_register_driver+0x9b/0x147
        [<c06b742c>] kernel_init+0x130/0x26f
        [<c06b72fc>] kernel_init+0x0/0x26f
        [<c06b72fc>] kernel_init+0x0/0x26f
        [<c0105527>] kernel_thread_helper+0x7/0x10
        [<ffffffff>] 0xffffffff

-> #1 (&per_cpu(cpu_policy_rwsem, cpu)){----}:
        [<c013cfa3>] __lock_acquire+0x953/0xb05
        [<c041d198>] lock_policy_rwsem_write+0x30/0x56
        [<c010a83b>] save_stack_trace+0x1a/0x35
        [<c013d1b4>] lock_acquire+0x5f/0x79
        [<c041d198>] lock_policy_rwsem_write+0x30/0x56
        [<c04cdfd9>] down_write+0x2b/0x44
        [<c041d198>] lock_policy_rwsem_write+0x30/0x56
        [<c041d198>] lock_policy_rwsem_write+0x30/0x56
        [<c041e362>] do_dbs_timer+0x40/0x24f
        [<c012ee7f>] run_workqueue+0x81/0x187
        [<c012eeba>] run_workqueue+0xbc/0x187
        [<c012ee7f>] run_workqueue+0x81/0x187
        [<c041e322>] do_dbs_timer+0x0/0x24f
        [<c012f6fa>] worker_thread+0x0/0xbd
        [<c012f7ad>] worker_thread+0xb3/0xbd
        [<c0131acc>] autoremove_wake_function+0x0/0x2d
        [<c0131a1b>] kthread+0x38/0x5d
        [<c01319e3>] kthread+0x0/0x5d
        [<c0105527>] kernel_thread_helper+0x7/0x10
        [<ffffffff>] 0xffffffff

-> #0 (&(&dbs_info->work)->work){--..}:
        [<c013b6a2>] print_circular_bug_tail+0x2a/0x61
        [<c013cec8>] __lock_acquire+0x878/0xb05
        [<c013d1b4>] lock_acquire+0x5f/0x79
        [<c012f46c>] __cancel_work_timer+0x80/0x177
        [<c012f497>] __cancel_work_timer+0xab/0x177
        [<c012f46c>] __cancel_work_timer+0x80/0x177
        [<c013c0ee>] mark_held_locks+0x39/0x53
        [<c04cdbe8>] mutex_lock_nested+0x20f/0x222
        [<c013c277>] trace_hardirqs_on+0xe7/0x10e
        [<c04cdbf3>] mutex_lock_nested+0x21a/0x222
        [<c041e7db>] cpufreq_governor_dbs+0x26a/0x2f7
        [<c041e7ed>] cpufreq_governor_dbs+0x27c/0x2f7
        [<c041c87e>] __cpufreq_governor+0x73/0xa6
        [<c041c9da>] __cpufreq_set_policy+0x129/0x19e
        [<c041ce0f>] store_scaling_governor+0x112/0x135
        [<c041d29a>] handle_update+0x0/0x21
        [<c0410065>] atkbd_set_leds+0x5/0xcf
        [<c041ccfd>] store_scaling_governor+0x0/0x135
        [<c041d7eb>] store+0x3c/0x54
        [<c01a09e8>] sysfs_write_file+0xa9/0xdd
        [<c01a093f>] sysfs_write_file+0x0/0xdd
        [<c016e45a>] vfs_write+0x83/0xf6
        [<c016e9a0>] sys_write+0x3c/0x63
        [<c0104816>] sysenter_past_esp+0x5f/0xa5
        [<ffffffff>] 0xffffffff

other info that might help us debug this:

3 locks held by S06cpuspeed/3427:
  #0:  (&buffer->mutex){--..}, at: [<c01a0963>] sysfs_write_file+0x24/0xdd
  #1:  (&per_cpu(cpu_policy_rwsem, cpu)){----}, at: [<c041d198>] 
lock_policy_rwsem_write+0x30/0x56
  #2:  (dbs_mutex){--..}, at: [<c041e7db>] cpufreq_governor_dbs+0x26a/0x2f7

stack backtrace:
Pid: 3427, comm: S06cpuspeed Not tainted 2.6.25.9.cpufreq #2
  [<c013b6cf>] print_circular_bug_tail+0x57/0x61
  [<c013cec8>] __lock_acquire+0x878/0xb05
  [<c013d1b4>] lock_acquire+0x5f/0x79
  [<c012f46c>] __cancel_work_timer+0x80/0x177
  [<c012f497>] __cancel_work_timer+0xab/0x177
  [<c012f46c>] __cancel_work_timer+0x80/0x177
  [<c013c0ee>] mark_held_locks+0x39/0x53
  [<c04cdbe8>] mutex_lock_nested+0x20f/0x222
  [<c013c277>] trace_hardirqs_on+0xe7/0x10e
  [<c04cdbf3>] mutex_lock_nested+0x21a/0x222
  [<c041e7db>] cpufreq_governor_dbs+0x26a/0x2f7
  [<c041e7ed>] cpufreq_governor_dbs+0x27c/0x2f7
  [<c041c87e>] __cpufreq_governor+0x73/0xa6
  [<c041c9da>] __cpufreq_set_policy+0x129/0x19e
  [<c041ce0f>] store_scaling_governor+0x112/0x135
  [<c041d29a>] handle_update+0x0/0x21
  [<c0410065>] atkbd_set_leds+0x5/0xcf
  [<c041ccfd>] store_scaling_governor+0x0/0x135
  [<c041d7eb>] store+0x3c/0x54
  [<c01a09e8>] sysfs_write_file+0xa9/0xdd
  [<c01a093f>] sysfs_write_file+0x0/0xdd
  [<c016e45a>] vfs_write+0x83/0xf6
  [<c016e9a0>] sys_write+0x3c/0x63
  [<c0104816>] sysenter_past_esp+0x5f/0xa5
  =======================

Thanks!!
Regards
R.Nageswara Sastry
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