linux-kernel - Re: [PATCH 2/7] devfreq: protect devfreq stats data with spinlock

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Date:   Wed, 13 Nov 2019 18:47:12 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Kamil Konieczny <k.konieczny@...sung.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Kamil Konieczny <k.konieczny@...tner.samsung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Subject: Re: [PATCH 2/7] devfreq: protect devfreq stats data with spinlock

Hi,

On 11/13/19 6:13 PM, Kamil Konieczny wrote:
> Protect access to devfreq transitions stats with spinlock.

You have to add the more detailed reason why spinlock is necessary.
And are there any issue without spinlock? 

In my case, I used the devfreq sysfs entries on Tizen Platfrom
for a long time, there are no any issue without spinlock.

Regards,
Chanwoo Choi

> 
> Signed-off-by: Kamil Konieczny <k.konieczny@...sung.com>
> ---
>  drivers/devfreq/devfreq.c | 18 +++++++++++++++---
>  include/linux/devfreq.h   |  3 +++
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 1602cca20fc4..ac04b5baef70 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -163,10 +163,16 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
>  	cur_time = get_jiffies_64();
>  
>  	/* Immediately exit if previous_freq is not initialized yet. */
> -	if (!devfreq->previous_freq)
> -		goto out;
> +	if (!devfreq->previous_freq) {
> +		spin_lock(&devfreq->stats_lock);
> +		devfreq->last_stat_updated = cur_time;
> +		spin_unlock(&devfreq->stats_lock);
> +		return 0;
> +	}
>  
>  	prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
> +
> +	spin_lock(&devfreq->stats_lock);
>  	if (prev_lev < 0) {
>  		ret = prev_lev;
>  		goto out;
> @@ -174,7 +180,6 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
>  
>  	devfreq->time_in_state[prev_lev] +=
>  			 cur_time - devfreq->last_stat_updated;
> -
>  	lev = devfreq_get_freq_level(devfreq, freq);
>  	if (lev < 0) {
>  		ret = lev;
> @@ -189,6 +194,7 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
>  
>  out:
>  	devfreq->last_stat_updated = cur_time;
> +	spin_unlock(&devfreq->stats_lock);
>  	return ret;
>  }
>  EXPORT_SYMBOL(devfreq_update_status);
> @@ -478,7 +484,9 @@ void devfreq_monitor_resume(struct devfreq *devfreq)
>  		queue_delayed_work(devfreq_wq, &devfreq->work,
>  			msecs_to_jiffies(devfreq->profile->polling_ms));
>  
> +	spin_lock(&devfreq->stats_lock);
>  	devfreq->last_stat_updated = get_jiffies_64();
> +	spin_unlock(&devfreq->stats_lock);
>  	devfreq->stop_polling = false;
>  
>  	if (devfreq->profile->get_cur_freq &&
> @@ -707,6 +715,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	}
>  
>  	devfreq->last_stat_updated = get_jiffies_64();
> +	spin_lock_init(&devfreq->stats_lock);
>  
>  	srcu_init_notifier_head(&devfreq->transition_notifier_list);
>  
> @@ -1405,6 +1414,8 @@ static ssize_t trans_stat_show(struct device *dev,
>  
>  	len = sprintf(buf, "     From  :   To\n");
>  	len += sprintf(buf + len, "           :");
> +
> +	spin_lock(&devfreq->stats_lock);
>  	for (i = 0; i < max_state; i++)
>  		len += sprintf(buf + len, "%10lu",
>  				devfreq->profile->freq_table[i]);
> @@ -1429,6 +1440,7 @@ static ssize_t trans_stat_show(struct device *dev,
>  
>  	len += sprintf(buf + len, "Total transition : %u\n",
>  					devfreq->total_trans);
> +	spin_unlock(&devfreq->stats_lock);
>  	return len;
>  }
>  static DEVICE_ATTR_RO(trans_stat);
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index b81a86e47fb9..a344e0be99f3 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -135,6 +135,8 @@ struct devfreq_dev_profile {
>   * @trans_table:	Statistics of devfreq transitions
>   * @time_in_state:	Statistics of devfreq states
>   * @last_stat_updated:	The last time stat updated
> + * @stats_lock:		Lock protecting trans_table, time_in_state, last_time
> + *			and total_trans used for statistics
>   * @transition_notifier_list: list head of DEVFREQ_TRANSITION_NOTIFIER notifier
>   *
>   * This structure stores the devfreq information for a give device.
> @@ -176,6 +178,7 @@ struct devfreq {
>  	unsigned int *trans_table;
>  	u64 *time_in_state;
>  	unsigned long long last_stat_updated;
> +	spinlock_t stats_lock;
>  
>  	struct srcu_notifier_head transition_notifier_list;
>  };
>