Messages in this thread | | | From | Johannes Weiner <> | Subject | Re: [BUG] While changing the cpufreq governor, kernel hits a bug in workqueue.c | Date | Tue, 01 Jul 2008 16:00:34 +0200 |
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Hi,
Nageswara R Sastry <rnsastry@linux.vnet.ibm.com> writes:
> 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 > =======================
Okay, the problem is in cpufreq_conservative.c. We cancel_delayed_work_sync() while holding the mutex, but the work itself tries to grab it and there it deadlocks; lockdep caught that right.
The hunk for _ondemand is correct, but the one for _conservative is obviously wrong, sorry :/
I will whip something up and get back to you. Thanks a lot for testing!
Hannes
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