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Subject: Re: [PATCH] devfreq: Use lockdep asserts instead of manual checks
 for locked mutex
To:     Krzysztof Kozlowski <krzk@kernel.org>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <b758daaa-aa7a-30a6-5947-395ff30da66a@samsung.com>
Date:   Tue, 12 May 2020 17:06:21 +0900
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References: <CGME20200512064211epcas1p1f8e6cac8f2927bd703e133282313dd43@epcas1p1.samsung.com>
        <20200512064158.7957-1-krzk@kernel.org>
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Hi Krzysztof,

On 5/12/20 3:41 PM, Krzysztof Kozlowski wrote:
> Instead of warning when mutex_is_locked(), just use the lockdep
> framework.  The code is smaller and checks could be disabled for
> production environments (it is useful only during development).
> 
> Put asserts at beginning of function, even before validating arguments.
> 
> The behavior of update_devfreq() is now changed because lockdep assert
> will only print a warning, not return with EINVAL.
> 
> Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
> ---
>  drivers/devfreq/devfreq.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index ef3d2bc3d1ac..52b9c3e141f3 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -60,12 +60,12 @@ static struct devfreq *find_device_devfreq(struct device *dev)
>  {
>  	struct devfreq *tmp_devfreq;
>  
> +	lockdep_assert_held(&devfreq_list_lock);
> +
>  	if (IS_ERR_OR_NULL(dev)) {
>  		pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
>  		return ERR_PTR(-EINVAL);
>  	}
> -	WARN(!mutex_is_locked(&devfreq_list_lock),
> -	     "devfreq_list_lock must be locked.");
>  
>  	list_for_each_entry(tmp_devfreq, &devfreq_list, node) {
>  		if (tmp_devfreq->dev.parent == dev)
> @@ -258,12 +258,12 @@ static struct devfreq_governor *find_devfreq_governor(const char *name)
>  {
>  	struct devfreq_governor *tmp_governor;
>  
> +	lockdep_assert_held(&devfreq_list_lock);
> +
>  	if (IS_ERR_OR_NULL(name)) {
>  		pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
>  		return ERR_PTR(-EINVAL);
>  	}
> -	WARN(!mutex_is_locked(&devfreq_list_lock),
> -	     "devfreq_list_lock must be locked.");
>  
>  	list_for_each_entry(tmp_governor, &devfreq_governor_list, node) {
>  		if (!strncmp(tmp_governor->name, name, DEVFREQ_NAME_LEN))
> @@ -289,12 +289,12 @@ static struct devfreq_governor *try_then_request_governor(const char *name)
>  	struct devfreq_governor *governor;
>  	int err = 0;
>  
> +	lockdep_assert_held(&devfreq_list_lock);
> +
>  	if (IS_ERR_OR_NULL(name)) {
>  		pr_err("DEVFREQ: %s: Invalid parameters\n", __func__);
>  		return ERR_PTR(-EINVAL);
>  	}
> -	WARN(!mutex_is_locked(&devfreq_list_lock),
> -	     "devfreq_list_lock must be locked.");
>  
>  	governor = find_devfreq_governor(name);
>  	if (IS_ERR(governor)) {
> @@ -392,10 +392,7 @@ int update_devfreq(struct devfreq *devfreq)
>  	int err = 0;
>  	u32 flags = 0;
>  
> -	if (!mutex_is_locked(&devfreq->lock)) {
> -		WARN(true, "devfreq->lock must be locked by the caller.\n");
> -		return -EINVAL;
> -	}
> +	lockdep_assert_held(&devfreq->lock);
>  
>  	if (!devfreq->governor)
>  		return -EINVAL;
> 

It is reasonable. It looks good.
Applied it. Thank


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics