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

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Date:   Thu, 5 Jul 2018 14:24:58 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
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 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?

The patch was a forward-port from one of our SLE kernels, and I messed
up the IRQ flag balancing for the v4.18-rc3 code :-(