linux-kernel - Re: [PATCH 1/2] acpi: don't free non-existant backlight in acpi video module

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Date:	Mon, 13 Jul 2009 16:41:43 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	keithp@...thp.com
Cc:	rui.zhang@...el.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, keithp@...thp.com
Subject: Re: [PATCH 1/2] acpi: don't free non-existant backlight in acpi
 video module


> acpi: don't free non-existant backlight in acpi video module

"existent" :)

On Sat, 11 Jul 2009 23:47:31 -0700
keithp@...thp.com wrote:

> From: Keith Packard <keithp@...thp.com>
> 
> acpi_video_put_one_device was attempting to remove sysfs entries and
> unregister a backlight device without first checking that said backlight
> device structure had been created.
> 
> Signed-off-by: Keith Packard <keithp@...thp.com>
> ---
>  drivers/acpi/video.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c
> index 8851315..60ea984 100644
> --- a/drivers/acpi/video.c
> +++ b/drivers/acpi/video.c
> @@ -2004,8 +2004,11 @@ static int acpi_video_bus_put_one_device(struct acpi_video_device *device)
>  	status = acpi_remove_notify_handler(device->dev->handle,
>  					    ACPI_DEVICE_NOTIFY,
>  					    acpi_video_device_notify);
> -	sysfs_remove_link(&device->backlight->dev.kobj, "device");
> -	backlight_device_unregister(device->backlight);
> +	if (device->backlight) {
> +		sysfs_remove_link(&device->backlight->dev.kobj, "device");
> +		backlight_device_unregister(device->backlight);
> +		device->backlight = NULL;
> +	}
>  	if (device->cdev) {
>  		sysfs_remove_link(&device->dev->dev.kobj,
>  				  "thermal_cooling");

um, OK.

Under which circumstances was this observed?

For symmetry we could instead test acpi_video_backlight_support() here.

The patch assumes that someone initially zeroed device->backlight.  Is
that true and reliable?  If so, is the 

	memset(&device->cap, 0, sizeof(device->cap));

in acpi_video_device_find_cap() needed?


Where's [patch 2/2], btw?
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