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Date:   Thu, 14 Feb 2019 11:07:41 -0800
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Lukasz Luba <l.luba@partner.samsung.com>
Cc:     MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Chanwoo Choi <cw00.choi@samsung.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-tegra@vger.kernel.org
Subject: Re: [PATCH 4/4] PM / devfreq: Handle monitor start/stop in the
 devfreq core
Message-ID: <20190214190741.GC117604@google.com>
References: <20190214013042.254790-1-mka@chromium.org>
 <CGME20190214013154epcas1p31326fdc127b3a75d566426e4f785121b@epcas1p3.samsung.com>
 <20190214013042.254790-5-mka@chromium.org>
 <1771fe9e-c107-f133-7b39-f4d7dbb004c5@partner.samsung.com>
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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?

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) {