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SubjectRe: [BUG] While changing the cpufreq governor, kernel hits a bug in workqueue.c
Hi,

Johannes Weiner wrote:

> From: Johannes Weiner <hannes@saeurebad.de>
> Subject: cpufreq: cancel self-rearming work synchroneuously
>
> The ondemand and conservative governor workers are self-rearming.
> Cancel them synchroneously to avoid nasty races.
>
> Reported-by: Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>
> Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
> ---
>
> diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
> index 5d3a04b..78bac06 100644
> --- a/drivers/cpufreq/cpufreq_conservative.c
> +++ b/drivers/cpufreq/cpufreq_conservative.c
> @@ -467,7 +467,7 @@ static inline void dbs_timer_init(void)
>
> static inline void dbs_timer_exit(void)
> {
> - cancel_delayed_work(&dbs_work);
> + cancel_delayed_work_sync(&dbs_work);
> return;
> }
>
> diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
> index d2af20d..1eb8c58 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -490,7 +490,7 @@ static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
> static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
> {
> dbs_info->enable = 0;
> - cancel_delayed_work(&dbs_info->work);
> + cancel_delayed_work_sync(&dbs_info->work);
> }
>
> static int cpufreq_governor_dbs(struct cpufreq_policy *policy,

Applied the above patch only and compiled the kernel and seeing an
Circular lock related issue at the time of booting. First I am checking
this and will let you the results by applying both the patches.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.25.7.cpufreq_patch #2
-------------------------------------------------------
S06cpuspeed/3493 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: [<c041e7cb>] cpufreq_governor_dbs+0x25e/0x2ed

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
[<c041e5e1>] cpufreq_governor_dbs+0x74/0x2ed
[<c013d1b4>] lock_acquire+0x5f/0x79
[<c041e5e1>] cpufreq_governor_dbs+0x74/0x2ed
[<c04cdaa7>] mutex_lock_nested+0xce/0x222
[<c041e5e1>] cpufreq_governor_dbs+0x74/0x2ed
[<c041e5e1>] cpufreq_governor_dbs+0x74/0x2ed
[<c041e5e1>] cpufreq_governor_dbs+0x74/0x2ed
[<c041c87a>] __cpufreq_governor+0x73/0xa6
[<c041c9e8>] __cpufreq_set_policy+0x13b/0x19e
[<c041d6b5>] cpufreq_add_dev+0x3b4/0x4aa
[<c041d296>] handle_update+0x0/0x21
[<c02ee310>] sysdev_driver_register+0x48/0x9a
[<c041c75b>] 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
[<c041d194>] lock_policy_rwsem_write+0x30/0x56
[<c010a83b>] save_stack_trace+0x1a/0x35
[<c013d1b4>] lock_acquire+0x5f/0x79
[<c041d194>] lock_policy_rwsem_write+0x30/0x56
[<c04cdfd9>] down_write+0x2b/0x44
[<c041d194>] lock_policy_rwsem_write+0x30/0x56
[<c041d194>] lock_policy_rwsem_write+0x30/0x56
[<c041e35e>] do_dbs_timer+0x40/0x24f
[<c012ee7f>] run_workqueue+0x81/0x187
[<c012eeba>] run_workqueue+0xbc/0x187
[<c012ee7f>] run_workqueue+0x81/0x187
[<c041e31e>] 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
[<c041e7cb>] cpufreq_governor_dbs+0x25e/0x2ed
[<c041e7dd>] cpufreq_governor_dbs+0x270/0x2ed
[<c041c87a>] __cpufreq_governor+0x73/0xa6
[<c041c9d6>] __cpufreq_set_policy+0x129/0x19e
[<c041ce0b>] store_scaling_governor+0x112/0x135
[<c041d296>] handle_update+0x0/0x21
[<c0410065>] atkbd_set_leds+0x9/0xcf
[<c041ccf9>] store_scaling_governor+0x0/0x135
[<c041d7e7>] store+0x3c/0x54
[<c01a09a0>] sysfs_write_file+0xa9/0xdd
[<c01a08f7>] sysfs_write_file+0x0/0xdd
[<c016e412>] vfs_write+0x83/0xf6
[<c016e958>] 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/3493:
#0: (&buffer->mutex){--..}, at: [<c01a091b>] sysfs_write_file+0x24/0xdd
#1: (&per_cpu(cpu_policy_rwsem, cpu)){----}, at: [<c041d194>]
lock_policy_rwsem_write+0x30/0x56
#2: (dbs_mutex){--..}, at: [<c041e7cb>] cpufreq_governor_dbs+0x25e/0x2ed

stack backtrace:
Pid: 3493, comm: S06cpuspeed Not tainted 2.6.25.7.cpufreq_patch #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
[<c041e7cb>] cpufreq_governor_dbs+0x25e/0x2ed
[<c041e7dd>] cpufreq_governor_dbs+0x270/0x2ed
[<c041c87a>] __cpufreq_governor+0x73/0xa6
[<c041c9d6>] __cpufreq_set_policy+0x129/0x19e
[<c041ce0b>] store_scaling_governor+0x112/0x135
[<c041d296>] handle_update+0x0/0x21
[<c0410065>] atkbd_set_leds+0x9/0xcf
[<c041ccf9>] store_scaling_governor+0x0/0x135
[<c041d7e7>] store+0x3c/0x54
[<c01a09a0>] sysfs_write_file+0xa9/0xdd
[<c01a08f7>] sysfs_write_file+0x0/0xdd
[<c016e412>] vfs_write+0x83/0xf6
[<c016e958>] sys_write+0x3c/0x63
[<c0104816>] sysenter_past_esp+0x5f/0xa5
=======================


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