linux-kernel - Re: [PATCH 4/4] PM / devfreq: Handle monitor start/stop in the devfreq core

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Date:   Fri, 15 Feb 2019 14:07:38 +0100
From:   Lukasz Luba <l.luba@...tner.samsung.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH 4/4] PM / devfreq: Handle monitor start/stop in the
 devfreq core

Hi Matthias,

On 2/14/19 8:07 PM, Matthias Kaehlcke wrote:
> Hi Lukasz,
> 
> On Thu, Feb 14, 2019 at 07:01:36PM +0100, Lukasz Luba wrote:
>> Hi Matthias,
>>
>> I have compiled and run your changes on Odroid xu3 and v5.0-rc6.
>> There are kernel warnings because of mutex not held in function
>> devfreq_monitor_[start|stop]() in use cases:
>>    1) a few times during registration of new devices devfreq_add_device()
>>    2) poking the device from sysfs
> 
> Thanks testing!
> 
> I messed up carrying over changes from my v4.19 device kernel
> to the tree used for upstreaming :(
> 
> Do you still see warnings with the below patch?
No, the warnings are no longer present in the log. The patch solves it.

Regards,
Lukasz
> 
> Thanks
> 
> Matthias
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index a42c37543c190..866fe711b43ca 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -440,7 +440,6 @@ static void devfreq_monitor_stop(struct devfreq *devfreq)
> 
>          mutex_lock(&devfreq->lock);
>          devfreq->monitor_state = DEVFREQ_MONITOR_STOPPED;
> -       mutex_unlock(&devfreq->lock);
>   }
> 
>   /**
> @@ -596,7 +595,9 @@ static int governor_start(struct devfreq *devfreq)
>                  return err;
>          }
> 
> +       mutex_lock(&devfreq->lock);
>          devfreq_monitor_start(devfreq);
> +       mutex_unlock(&devfreq->lock);
> 
>          return 0;
>   }
> @@ -614,7 +615,9 @@ static int governor_stop(struct devfreq *devfreq)
>                   "mutex must *not* be held by the caller\n"))
>                  return -EINVAL;
> 
> +       mutex_lock(&devfreq->lock);
>          devfreq_monitor_stop(devfreq);
> +       mutex_unlock(&devfreq->lock);
> 
>          err = devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_STOP, NULL);
>          if (err) {
> 
>