Re: [LOCKDEP] cpufreq: possible circular locking dependency detected

[Michael Wang <wangyun@linux.vnet.ibm.com>]

Hi, Sergey

On 06/26/2013 05:15 AM, Sergey Senozhatsky wrote:
[snip]
> 
> [   60.277848] Chain exists of:
>   (&(&j_cdbs->work)->work) --> &j_cdbs->timer_mutex --> cpu_hotplug.lock
> 
> [   60.277864]  Possible unsafe locking scenario:
> 
> [   60.277869]        CPU0                    CPU1
> [   60.277873]        ----                    ----
> [   60.277877]   lock(cpu_hotplug.lock);
> [   60.277885]                                lock(&j_cdbs->timer_mutex);
> [   60.277892]                                lock(cpu_hotplug.lock);
> [   60.277900]   lock((&(&j_cdbs->work)->work));
> [   60.277907] 
>  *** DEADLOCK ***

It may caused by that 'j_cdbs->work.work' and 'j_cdbs->timer_mutex'
has the same lock class, although they are different lock...

This may help fix the issue:

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 5af40ad..aa05eaa 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -229,6 +229,8 @@ static void set_sampling_rate(struct dbs_data *dbs_data,
        }
 }
 
+static struct lock_class_key j_cdbs_key;
+
 int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                struct common_dbs_data *cdata, unsigned int event)
 {
@@ -366,6 +368,8 @@ int (struct cpufreq_policy *policy,
                                        kcpustat_cpu(j).cpustat[CPUTIME_NICE];
 
                        mutex_init(&j_cdbs->timer_mutex);
+                       lockdep_set_class(&j_cdbs->timer_mutex, &j_cdbs_key);
+
                        INIT_DEFERRABLE_WORK(&j_cdbs->work,
                                             dbs_data->cdata->gov_dbs_timer);
                }

Would you like to take a try?

Regards,
Michael Wang

> 
> [   60.277915] 6 locks held by bash/2225:
> [   60.277919]  #0:  (sb_writers#6){.+.+.+}, at: [<ffffffff81168173>] vfs_write+0x1c3/0x1f0
> [   60.277937]  #1:  (&buffer->mutex){+.+.+.}, at: [<ffffffff811d9e3c>] sysfs_write_file+0x3c/0x150
> [   60.277954]  #2:  (s_active#61){.+.+.+}, at: [<ffffffff811d9ec3>] sysfs_write_file+0xc3/0x150
> [   60.277972]  #3:  (x86_cpu_hotplug_driver_mutex){+.+...}, at: [<ffffffff81024cf7>] cpu_hotplug_driver_lock+0x17/0x20
> [   60.277990]  #4:  (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff815a0d32>] cpu_down+0x22/0x50
> [   60.278007]  #5:  (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff81042d8b>] cpu_hotplug_begin+0x2b/0x60
> [   60.278023] 
> stack backtrace:
> [   60.278031] CPU: 3 PID: 2225 Comm: bash Not tainted 3.10.0-rc7-dbg-01385-g241fd04-dirty #1744
> [   60.278037] Hardware name: Acer             Aspire 5741G    /Aspire 5741G    , BIOS V1.20 02/08/2011
> [   60.278042]  ffffffff8204e110 ffff88014df6b9f8 ffffffff815b3d90 ffff88014df6ba38
> [   60.278055]  ffffffff815b0a8d ffff880150ed3f60 ffff880150ed4770 3871c4002c8980b2
> [   60.278068]  ffff880150ed4748 ffff880150ed4770 ffff880150ed3f60 ffff88014df6bb00
> [   60.278081] Call Trace:
> [   60.278091]  [<ffffffff815b3d90>] dump_stack+0x19/0x1b
> [   60.278101]  [<ffffffff815b0a8d>] print_circular_bug+0x2b6/0x2c5
> [   60.278111]  [<ffffffff810ab826>] __lock_acquire+0x1766/0x1d30
> [   60.278123]  [<ffffffff81067e08>] ? __kernel_text_address+0x58/0x80
> [   60.278134]  [<ffffffff810ac6d4>] lock_acquire+0xa4/0x200
> [   60.278142]  [<ffffffff810621b5>] ? flush_work+0x5/0x280
> [   60.278151]  [<ffffffff810621ed>] flush_work+0x3d/0x280
> [   60.278159]  [<ffffffff810621b5>] ? flush_work+0x5/0x280
> [   60.278169]  [<ffffffff810a9b14>] ? mark_held_locks+0x94/0x140
> [   60.278178]  [<ffffffff81062d77>] ? __cancel_work_timer+0x77/0x120
> [   60.278188]  [<ffffffff810a9cbd>] ? trace_hardirqs_on_caller+0xfd/0x1c0
> [   60.278196]  [<ffffffff81062d8a>] __cancel_work_timer+0x8a/0x120
> [   60.278206]  [<ffffffff81062e53>] cancel_delayed_work_sync+0x13/0x20
> [   60.278214]  [<ffffffff814b89d9>] cpufreq_governor_dbs+0x529/0x6f0
> [   60.278225]  [<ffffffff814b76a7>] cs_cpufreq_governor_dbs+0x17/0x20
> [   60.278234]  [<ffffffff814b5df8>] __cpufreq_governor+0x48/0x100
> [   60.278244]  [<ffffffff814b6b80>] __cpufreq_remove_dev.isra.14+0x80/0x3c0
> [   60.278255]  [<ffffffff815adc0d>] cpufreq_cpu_callback+0x38/0x4c
> [   60.278265]  [<ffffffff81071a4d>] notifier_call_chain+0x5d/0x110
> [   60.278275]  [<ffffffff81071b0e>] __raw_notifier_call_chain+0xe/0x10
> [   60.278284]  [<ffffffff815a0a68>] _cpu_down+0x88/0x330
> [   60.278292]  [<ffffffff81024cf7>] ? cpu_hotplug_driver_lock+0x17/0x20
> [   60.278302]  [<ffffffff815a0d46>] cpu_down+0x36/0x50
> [   60.278311]  [<ffffffff815a2748>] store_online+0x98/0xd0
> [   60.278320]  [<ffffffff81452a28>] dev_attr_store+0x18/0x30
> [   60.278329]  [<ffffffff811d9edb>] sysfs_write_file+0xdb/0x150
> [   60.278337]  [<ffffffff8116806d>] vfs_write+0xbd/0x1f0
> [   60.278347]  [<ffffffff81185950>] ? fget_light+0x320/0x4b0
> [   60.278355]  [<ffffffff811686fc>] SyS_write+0x4c/0xa0
> [   60.278364]  [<ffffffff815bbbbe>] tracesys+0xd0/0xd5
> [   60.280582] smpboot: CPU 1 is now offline
> 
> 
> 	-ss
> 
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