linux-kernel - Re: [lkp-robot] [sched/fair] fbd5188493: WARNING:inconsistent_lock

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Date:   Thu, 5 Jul 2018 16:59:02 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Matt Fleming <matt@...eblueprint.co.uk>
Cc:     kernel test robot <xiaolong.ye@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Mike Galbraith <umgwanakikbuti@...il.com>, lkp@...org
Subject: Re: [lkp-robot] [sched/fair] fbd5188493:
 WARNING:inconsistent_lock_state

On 07/05/2018 03:24 PM, Matt Fleming wrote:
> On Thu, 05 Jul, at 11:52:21AM, Dietmar Eggemann wrote:
>>
>> Moving the code from _nohz_idle_balance to nohz_idle_balance let it disappear:
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 02be51c9dcc1..070924f07c68 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9596,16 +9596,6 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
>>           */
>>          smp_mb();
>>   
>> -       /*
>> -        * Ensure this_rq's clock and load are up-to-date before we
>> -        * rebalance since it's possible that they haven't been
>> -        * updated for multiple schedule periods, i.e. many seconds.
>> -        */
>> -       raw_spin_lock_irq(&this_rq->lock);
>> -       update_rq_clock(this_rq);
>> -       cpu_load_update_idle(this_rq);
>> -       raw_spin_unlock_irq(&this_rq->lock);
>> -
>>          for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
>>                  if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
>>                          continue;
>> @@ -9701,6 +9691,16 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>>          if (!(flags & NOHZ_KICK_MASK))
>>                  return false;
>>   
>> +       /*
>> +        * Ensure this_rq's clock and load are up-to-date before we
>> +        * rebalance since it's possible that they haven't been
>> +        * updated for multiple schedule periods, i.e. many seconds.
>> +        */
>> +       raw_spin_lock_irq(&this_rq->lock);
>> +       update_rq_clock(this_rq);
>> +       cpu_load_update_idle(this_rq);
>> +       raw_spin_unlock_irq(&this_rq->lock);
>> +
>>          _nohz_idle_balance(this_rq, flags, idle);
>>   
>>          return true;
>>
> 
> Hmm.. it still looks to me like we should be saving and restoring IRQs
> since this can be called from IRQ context, no?

You mean in nohz_idle_balance()? Yes.

I just wanted to hint that since you need this cpu_load_update_idle() in 
the nohz idle balance case and not in idle balance, you could just 
update it in nohz_idle_balance() rather than in _nohz_idle_balance() 
(which is also called in nohz_newidle_balance()) avoiding this 
inconsistent lock state warning.

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