linux-kernel - Re: [PATCH v1 1/3] ACPI: video: Fix refcounting in apple_gmux_backlight

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Date:   Mon, 23 Jan 2023 18:46:44 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        acpica-devel@...ts.linuxfoundation.org
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>
Subject: Re: [PATCH v1 1/3] ACPI: video: Fix refcounting in
 apple_gmux_backlight_present()

Hi Andy,

On 1/23/23 18:10, Andy Shevchenko wrote:
> acpi_dev_get_first_match_dev() gets ACPI device with the bumped
> refcount. The caller must drop it when it's done.
> 
> Fix ACPI device refcounting in apple_gmux_backlight_present().
> 
> Fixes: 3cf3b7f012f3 ("ACPI: video: Fix Apple GMUX backlight detection")
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

Thank you for your work on this, much appreciated and I like
the new acpi_get_first_match_physical_node().

But I don't think this patch is a good idea. There is a
regression related to apple_gmux_backlight_present()
with a patch-set fixing it pending.

And that patch-set actually removes this function. Adding
a fix for this real, but not really important leak now,
will just make backporting the actual fix harder.

So I would prefer for this patch to not go in and to
go for (a to be submitted v2) of the patch-set fixing
the regression right away instead.

Regards,

Hans



> ---
>  drivers/acpi/video_detect.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
> index 65cec7bb6d96..0ccde0d4c527 100644
> --- a/drivers/acpi/video_detect.c
> +++ b/drivers/acpi/video_detect.c
> @@ -114,12 +114,14 @@ static bool apple_gmux_backlight_present(void)
>  {
>  	struct acpi_device *adev;
>  	struct device *dev;
> +	bool ret;
>  
>  	adev = acpi_dev_get_first_match_dev(GMUX_ACPI_HID, NULL, -1);
>  	if (!adev)
>  		return false;
>  
> -	dev = acpi_get_first_physical_node(adev);
> +	dev = get_device(acpi_get_first_physical_node(adev));
> +	acpi_dev_put(adev);
>  	if (!dev)
>  		return false;
>  
> @@ -127,7 +129,9 @@ static bool apple_gmux_backlight_present(void)
>  	 * drivers/platform/x86/apple-gmux.c only supports old style
>  	 * Apple GMUX with an IO-resource.
>  	 */
> -	return pnp_get_resource(to_pnp_dev(dev), IORESOURCE_IO, 0) != NULL;
> +	ret = pnp_get_resource(to_pnp_dev(dev), IORESOURCE_IO, 0) != NULL;
> +	put_device(dev);
> +	return ret;
>  }
>  
>  /* Force to use vendor driver when the ACPI device is known to be