linux-kernel - Re: [PATCH v2 2/2] hwmon: nzxt-smart2: add a check of devm_add_action in nzxt_smart2_hid

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Message-ID: <f5043281-9b3e-e454-16fe-ef4cde36dfdb@roeck-us.net>
Date:   Sun, 26 Feb 2023 20:21:42 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     void0red <void0red@...il.com>
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, mezin.alexander@...il.com
Subject: Re: [PATCH v2 2/2] hwmon: nzxt-smart2: add a check of devm_add_action
 in nzxt_smart2_hid_probe

On 2/26/23 19:09, void0red wrote:
> From: Kang Chen <void0red@...il.com>
> 
> devm_add_action may fails, check it and return early.
> 
> Signed-off-by: Kang Chen <void0red@...il.com>
> ---
> v2 -> v1: split the patch
> 
>   drivers/hwmon/nzxt-smart2.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/nzxt-smart2.c b/drivers/hwmon/nzxt-smart2.c
> index 2b93ba896..725974cb3 100644
> --- a/drivers/hwmon/nzxt-smart2.c
> +++ b/drivers/hwmon/nzxt-smart2.c
> @@ -737,8 +737,10 @@ static int nzxt_smart2_hid_probe(struct hid_device *hdev,
>   	init_waitqueue_head(&drvdata->wq);
>   
>   	mutex_init(&drvdata->mutex);
> -	devm_add_action(&hdev->dev, (void (*)(void *))mutex_destroy,
> +	ret = devm_add_action(&hdev->dev, (void (*)(void *))mutex_destroy,
>   			&drvdata->mutex);

Please watch for multi-line alignment. Also, turns out the original
code is wrong: Type casting a function pointer argument like this,
while it typically works in practice, is undefined in C. The function
pointer passed to devm_add_action() needs to point to a local
function with void * argument, and that function needs to call
mutex_destroy() with the same argument. Also, based on the context,
this needs to call devm_add_action_or_reset() to ensure that
the destroy function is called on error.

Thanks,
Guenter

> +	if (ret)
> +		return ret;
>   
>   	ret = hid_parse(hdev);
>   	if (ret)