Messages in this thread | | | Date | Wed, 10 Jul 2013 10:40:48 +0800 | From | Michael Wang <> | Subject | Re: [v3.10 regression] deadlock on cpu hotplug |
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On 07/09/2013 07:51 PM, Bartlomiej Zolnierkiewicz wrote: [snip] > > It doesn't help and unfortunately it just can't help as it only > addresses lockdep functionality while the issue is not a lockdep > problem but a genuine locking problem. CPU hot-unplug invokes > _cpu_down() which calls cpu_hotplug_begin() which in turn takes > &cpu_hotplug.lock. The lock is then hold during __cpu_notify() > call. Notifier chain goes up to cpufreq_governor_dbs() which for > CPUFREQ_GOV_STOP event does gov_cancel_work(). This function > flushes pending work and waits for it to finish. The all above > happens in one kernel thread. At the same time the other kernel > thread is doing the work we are waiting to complete and it also > happens to do gov_queue_work() which calls get_online_cpus(). > Then the code tries to take &cpu_hotplug.lock which is already > held by the first thread and deadlocks.
Hmm...I think I get your point, some thread hold the lock and flush some work which also try to hold the same lock, correct?
Ok, that's a problem, let's figure out a good way to solve it :)
Regards, Michael Wang
> > Best regards, > -- > Bartlomiej Zolnierkiewicz > Samsung R&D Institute Poland > Samsung Electronics > >> 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); >> } >> >> Regards, >> Michael Wang >
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