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Message-ID: <20130710231305.GA4046@swordfish>
Date: Thu, 11 Jul 2013 02:13:05 +0300
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...en8.de>,
"Rafael J. Wysocki" <rjw@...k.pl>,
Viresh Kumar <viresh.kumar@...aro.org>,
"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org,
linux-pm@...r.kernel.org
Subject: Re: [LOCKDEP] cpufreq: possible circular locking dependency detected
On (07/01/13 12:42), Michael Wang wrote:
> 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?
>
Hello,
sorry for long reply. unfortunately it seems it doesn't.
Please kindly review the following patch.
Remove cpu device only upon succesful cpu down on CPU_POST_DEAD event,
so we can kill off CPU_DOWN_FAILED case and eliminate potential extra
remove/add path:
hotplug lock
CPU_DOWN_PREPARE: __cpufreq_remove_dev
CPU_DOWN_FAILED: cpufreq_add_dev
hotplug unlock
Since cpu still present on CPU_DEAD event, cpu stats table should be
kept longer and removed later on CPU_POST_DEAD as well.
Because CPU_POST_DEAD action performed with hotplug lock released, CPU_DOWN
might block existing gov_queue_work() user (blocked on get_online_cpus())
and unblock it with one of policy->cpus offlined, thus cpu_is_offline()
check is performed in __gov_queue_work().
Besides, existing gov_queue_work() hotplug guard extended to protect all
__gov_queue_work() calls: for both all_cpus and !all_cpus cases.
CPUFREQ_GOV_START performs direct __gov_queue_work() call because hotplug
lock already held there, opposing to previous gov_queue_work() and nested
get/put_online_cpus().
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
drivers/cpufreq/cpufreq.c | 5 +----
drivers/cpufreq/cpufreq_governor.c | 17 +++++++++++------
drivers/cpufreq/cpufreq_stats.c | 2 +-
3 files changed, 13 insertions(+), 11 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6a015ad..f8aacf1 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1943,13 +1943,10 @@ static int __cpuinit cpufreq_cpu_callback(struct notifier_block *nfb,
case CPU_ONLINE:
cpufreq_add_dev(dev, NULL);
break;
- case CPU_DOWN_PREPARE:
+ case CPU_POST_DEAD:
case CPU_UP_CANCELED_FROZEN:
__cpufreq_remove_dev(dev, NULL);
break;
- case CPU_DOWN_FAILED:
- cpufreq_add_dev(dev, NULL);
- break;
}
}
return NOTIFY_OK;
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 4645876..681d5d6 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -125,7 +125,11 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
unsigned int delay)
{
struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
-
+ /* cpu offline might block existing gov_queue_work() user,
+ * unblocking it after CPU_DEAD and before CPU_POST_DEAD.
+ * thus potentially we can hit offlined CPU */
+ if (unlikely(cpu_is_offline(cpu)))
+ return;
mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay);
}
@@ -133,15 +137,14 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
unsigned int delay, bool all_cpus)
{
int i;
-
+ get_online_cpus();
if (!all_cpus) {
__gov_queue_work(smp_processor_id(), dbs_data, delay);
} else {
- get_online_cpus();
for_each_cpu(i, policy->cpus)
__gov_queue_work(i, dbs_data, delay);
- put_online_cpus();
}
+ put_online_cpus();
}
EXPORT_SYMBOL_GPL(gov_queue_work);
@@ -354,8 +357,10 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
/* Initiate timer time stamp */
cpu_cdbs->time_stamp = ktime_get();
- gov_queue_work(dbs_data, policy,
- delay_for_sampling_rate(sampling_rate), true);
+ /* hotplug lock already held */
+ for_each_cpu(j, policy->cpus)
+ __gov_queue_work(j, dbs_data,
+ delay_for_sampling_rate(sampling_rate));
break;
case CPUFREQ_GOV_STOP:
diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index cd9e817..833816e 100644
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -355,7 +355,7 @@ static int __cpuinit cpufreq_stat_cpu_callback(struct notifier_block *nfb,
case CPU_DOWN_PREPARE:
cpufreq_stats_free_sysfs(cpu);
break;
- case CPU_DEAD:
+ case CPU_POST_DEAD:
cpufreq_stats_free_table(cpu);
break;
case CPU_UP_CANCELED_FROZEN:
--
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