Re: [PATCH -next] backlight: backlight: Use DEFINE_MUTEX() for mutex lock

From: Daniel Thompson <daniel.thompson@linaro.org>
To: Zheng Yongjun <zhengyongjun3@huawei.com>
Cc: Lee Jones <lee.jones@linaro.org>,
	Jingoo Han <jingoohan1@gmail.com>,
	dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
	kernel-janitors@vger.kernel.org, Hulk Robot <hulkci@huawei.com>
Subject: Re: [PATCH -next] backlight: backlight: Use DEFINE_MUTEX() for mutex lock
Date: Tue, 6 Apr 2021 09:51:40 +0100	[thread overview]
Message-ID: <20210406085140.b7zffcrkdquxxsxs@holly.lan> (raw)
In-Reply-To: <20210405101440.14937-1-zhengyongjun3@huawei.com>

On Mon, Apr 05, 2021 at 06:14:40PM +0800, Zheng Yongjun wrote:
> mutex lock can be initialized automatically with DEFINE_MUTEX()
> rather than explicitly calling mutex_init().
> 
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>

This patch looks like a resend of this one (but with a different revision
number):
https://lkml.org/lkml/2020/12/24/229

A resend should always maintain the version number and be clearly marked
as a resend.  In this case, there is also a pending review comment that
you have ignored.  Given I also clarified when you asked (off-list) for
additional details I'm very surprised to see this patch circulated again
without modification.

I have repeated the feedback below.

> ---
>  drivers/video/backlight/backlight.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 537fe1b376ad..d7a09c422547 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -64,7 +64,7 @@
>   */
>  
>  static struct list_head backlight_dev_list;
> -static struct mutex backlight_dev_list_mutex;
> +static DEFINE_MUTEX(backlight_dev_list_mutex);
>  static struct blocking_notifier_head backlight_notifier;
>  
>  static const char *const backlight_types[] = {
> @@ -757,7 +757,6 @@ static int __init backlight_class_init(void)
>  	backlight_class->dev_groups = bl_device_groups;
>  	backlight_class->pm = &backlight_class_dev_pm_ops;
>  	INIT_LIST_HEAD(&backlight_dev_list);
> -	mutex_init(&backlight_dev_list_mutex);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&backlight_notifier);

On Mon, 4 Jan 2021 at 14:19, Daniel Thompson wrote:
: the purpose of backlight_dev_list_mutex is (as the name suggests) to
: protect backlight_dev_list. It makes no sense to initialize these
: variables from different places within the code. It just makes it
: harder to reason about the lifetimes of the variables.
:
: To be clear, switching over to static initializers is a good change,
: but please change all three in one patch.

Daniel.