Re: [PATCH 4/8] PM / devfreq: Don't take lock in devfreq_add_device

From: Matthias Kaehlcke <mka@chromium.org>
To: Leonard Crestez <leonard.crestez@nxp.com>
Cc: "MyungJoo Ham" <myungjoo.ham@samsung.com>,
	"Kyungmin Park" <kyungmin.park@samsung.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Artur Świgoń" <a.swigon@partner.samsung.com>,
	"Saravana Kannan" <saravanak@google.com>,
	"Krzysztof Kozlowski" <krzk@kernel.org>,
	"Alexandre Bailon" <abailon@baylibre.com>,
	"Georgi Djakov" <georgi.djakov@linaro.org>,
	"Abel Vesa" <abel.vesa@nxp.com>, "Jacky Bai" <ping.bai@nxp.com>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/8] PM / devfreq: Don't take lock in devfreq_add_device
Date: Wed, 18 Sep 2019 17:20:13 -0700	[thread overview]
Message-ID: <20190919002013.GR133864@google.com> (raw)
In-Reply-To: <2fe8d1000bed5de70b08ed77fc8360d159ae4434.1568764439.git.leonard.crestez@nxp.com>

On Wed, Sep 18, 2019 at 03:18:23AM +0300, Leonard Crestez wrote:
> A device usually doesn't need to lock itself during initialization
> because it is not yet reachable from other threads.
> 
> This simplifies the code and helps avoid recursive lock warnings.
> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> ---
>  drivers/devfreq/devfreq.c | 10 ----------
>  1 file changed, 10 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 57a217fc92de..860cbbab476c 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -634,11 +634,10 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  		err = -ENOMEM;
>  		goto err_out;
>  	}
>  
>  	mutex_init(&devfreq->lock);
> -	mutex_lock(&devfreq->lock);
>  	devfreq->dev.parent = dev;
>  	devfreq->dev.class = devfreq_class;
>  	devfreq->dev.release = devfreq_dev_release;
>  	INIT_LIST_HEAD(&devfreq->node);
>  	devfreq->profile = profile;
> @@ -647,28 +646,24 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	devfreq->last_status.current_frequency = profile->initial_freq;
>  	devfreq->data = data;
>  	devfreq->nb.notifier_call = devfreq_notifier_call;
>  
>  	if (!devfreq->profile->max_state && !devfreq->profile->freq_table) {
> -		mutex_unlock(&devfreq->lock);
>  		err = set_freq_table(devfreq);
>  		if (err < 0)
>  			goto err_dev;
> -		mutex_lock(&devfreq->lock);
>  	}
>  
>  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
>  	if (!devfreq->scaling_min_freq) {
> -		mutex_unlock(&devfreq->lock);
>  		err = -EINVAL;
>  		goto err_dev;
>  	}
>  	devfreq->min_freq = devfreq->scaling_min_freq;
>  
>  	devfreq->scaling_max_freq = find_available_max_freq(devfreq);
>  	if (!devfreq->scaling_max_freq) {
> -		mutex_unlock(&devfreq->lock);
>  		err = -EINVAL;
>  		goto err_dev;
>  	}
>  	devfreq->max_freq = devfreq->scaling_max_freq;
>  
> @@ -679,20 +674,18 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  			array3_size(sizeof(unsigned int),
>  				    devfreq->profile->max_state,
>  				    devfreq->profile->max_state),
>  			GFP_KERNEL);
>  	if (!devfreq->trans_table) {
> -		mutex_unlock(&devfreq->lock);
>  		err = -ENOMEM;
>  		goto err_dev;
>  	}
>  
>  	devfreq->time_in_state = kcalloc(devfreq->profile->max_state,
>  					 sizeof(unsigned long),
>  					 GFP_KERNEL);
>  	if (!devfreq->time_in_state) {
> -		mutex_unlock(&devfreq->lock);
>  		err = -ENOMEM;
>  		goto err_dev;
>  	}
>  
>  	devfreq->last_stat_updated = jiffies;
> @@ -701,17 +694,14 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  
>  	dev_set_name(&devfreq->dev, "devfreq%d",
>  				atomic_inc_return(&devfreq_no));
>  	err = device_register(&devfreq->dev);
>  	if (err) {
> -		mutex_unlock(&devfreq->lock);
>  		put_device(&devfreq->dev);
>  		goto err_out;
>  	}
>  
> -	mutex_unlock(&devfreq->lock);
> -
>  	mutex_lock(&devfreq_list_lock);
>  
>  	governor = try_then_request_governor(devfreq->governor_name);
>  	if (IS_ERR(governor)) {
>  		dev_err(dev, "%s: Unable to find governor for the device\n",

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>