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

From: Sergey Senozhatsky
Date: Sun Jul 14 2013 - 07:48:58 EST

On (07/11/13 10:43), Michael Wang wrote:
> [..]
> Nice to know you have some idea on solving the issue ;-)
>
> I'm not sure whether I catch the idea, but seems like you are trying
> to re-organize the timing of add/remove device.
>
> I'm sure that we have more than one way to solve the issues, but what
> we need is the cure of root...
>
> As Srivatsa discovered, the root issue may be:
> gov_cancel_work() failed to stop all the work after it's return.
>
> And Viresh also confirmed that this is not by-designed.
>
> Which means gov_queue_work() invoked by od_dbs_timer() is supposed to
> never happen after CPUFREQ_GOV_STOP notify, the whole policy should
> stop working at that time.
>
> But it failed to, and the work concurrent with cpu dying caused the
> first problem.
>
> Thus I think we should focus on this and suggested below fix, I'd like
> to know your opinions :)
>

Hello,

I just realized that lockdep was disabling itself at startup (after recent AMD
radeon patch set) due to radeon kms error:

[ 4.790019] [drm] Loading CEDAR Microcode
[ 4.790943] r600_cp: Failed to load firmware "radeon/CEDAR_smc.bin"
[ 4.791152] [drm:evergreen_startup] *ERROR* Failed to load firmware!
[ 4.791330] radeon 0000:01:00.0: disabling GPU acceleration
[ 4.792633] INFO: trying to register non-static key.
[ 4.792792] the code is fine but needs lockdep annotation.
[ 4.792953] turning off the locking correctness validator.


Now, as I fixed radeon kms, I can see:

[ 806.660530] ------------[ cut here ]------------
[ 806.660539] WARNING: CPU: 0 PID: 2389 at arch/x86/kernel/smp.c:124
native_smp_send_reschedule+0x57/0x60()

[ 806.660572] Workqueue: events od_dbs_timer
[ 806.660575] 0000000000000009 ffff8801531cfbd8 ffffffff816044ee
0000000000000000
[ 806.660577] ffff8801531cfc10 ffffffff8104995d 0000000000000003
ffff8801531f8000
[ 806.660579] 000000010001ee39 0000000000000003 0000000000000003
ffff8801531cfc20
[ 806.660580] Call Trace:
[ 806.660587] [<ffffffff816044ee>] dump_stack+0x4e/0x82
[ 806.660591] [<ffffffff8104995d>] warn_slowpath_common+0x7d/0xa0
[ 806.660593] [<ffffffff81049a3a>] warn_slowpath_null+0x1a/0x20
[ 806.660595] [<ffffffff8102ca07>] native_smp_send_reschedule+0x57/0x60
[ 806.660599] [<ffffffff81085211>] wake_up_nohz_cpu+0x61/0xb0
[ 806.660603] [<ffffffff8105cb6d>] add_timer_on+0x8d/0x1e0
[ 806.660607] [<ffffffff8106cc66>] __queue_delayed_work+0x166/0x1a0
[ 806.660609] [<ffffffff8106d6a9>] ? try_to_grab_pending+0xd9/0x1a0
[ 806.660611] [<ffffffff8106d7bf>] mod_delayed_work_on+0x4f/0x90
[ 806.660613] [<ffffffff8150f436>] gov_queue_work+0x56/0xd0
[ 806.660615] [<ffffffff8150e740>] od_dbs_timer+0xc0/0x160
[ 806.660617] [<ffffffff8106dbcd>] process_one_work+0x1cd/0x6a0
[ 806.660619] [<ffffffff8106db63>] ? process_one_work+0x163/0x6a0
[ 806.660622] [<ffffffff8106e8d1>] worker_thread+0x121/0x3a0
[ 806.660627] [<ffffffff810b668d>] ? trace_hardirqs_on+0xd/0x10
[ 806.660629] [<ffffffff8106e7b0>] ? manage_workers.isra.24+0x2a0/0x2a0
[ 806.660633] [<ffffffff810760cb>] kthread+0xdb/0xe0
[ 806.660635] [<ffffffff81075ff0>] ? insert_kthread_work+0x70/0x70
[ 806.660639] [<ffffffff8160de6c>] ret_from_fork+0x7c/0xb0
[ 806.660640] [<ffffffff81075ff0>] ? insert_kthread_work+0x70/0x70
[ 806.660642] ---[ end trace 01ae278488a0ad6d ]---


The same problem why get/put_online_cpus() has been added to __gov_queue_work()

commit 2f7021a815f20f3481c10884fe9735ce2a56db35
Author: Michael Wang

cpufreq: protect 'policy->cpus' from offlining during
__gov_queue_work()

-ss

> Regards,
> Michael Wang
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index dc9b72e..a64b544 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -178,13 +178,14 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
> {
> int i;
>
> + if (dbs_data->queue_stop)
> + return;
> +
> 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();
> }
> }
> EXPORT_SYMBOL_GPL(gov_queue_work);
> @@ -193,12 +194,27 @@ static inline void gov_cancel_work(struct dbs_data *dbs_data,
> struct cpufreq_policy *policy)
> {
> struct cpu_dbs_common_info *cdbs;
> - int i;
> + int i, round = 2;
>
> + dbs_data->queue_stop = 1;
> +redo:
> + round--;
> for_each_cpu(i, policy->cpus) {
> cdbs = dbs_data->cdata->get_cpu_cdbs(i);
> cancel_delayed_work_sync(&cdbs->work);
> }
> +
> + /*
> + * Since there is no lock to prvent re-queue the
> + * cancelled work, some early cancelled work might
> + * have been queued again by later cancelled work.
> + *
> + * Flush the work again with dbs_data->queue_stop
> + * enabled, this time there will be no survivors.
> + */
> + if (round)
> + goto redo;
> + dbs_data->queue_stop = 0;
> }
>
> /* Will return if we need to evaluate cpu load again or not */
> diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
> index e16a961..9116135 100644
> --- a/drivers/cpufreq/cpufreq_governor.h
> +++ b/drivers/cpufreq/cpufreq_governor.h
> @@ -213,6 +213,7 @@ struct dbs_data {
> unsigned int min_sampling_rate;
> int usage_count;
> void *tuners;
> + int queue_stop;
>
> /* dbs_mutex protects dbs_enable in governor start/stop */
> struct mutex mutex;
>
> >
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
> >
> > ---
> >
> > 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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