linux-kernel - Re: [PATCH] fbdev/xen-fbfront: Assign fb

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Message-ID: <ad9e19af-fabd-4ce0-a9ac-741149f9aab3@suse.de>
Date: Tue, 10 Sep 2024 09:29:30 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Roger Pau Monné <roger.pau@...rix.com>,
 Jason Andryuk <jandryuk@...il.com>
Cc: Helge Deller <deller@....de>, Arnd Bergmann <arnd@...db.de>,
 Sam Ravnborg <sam@...nborg.org>, xen-devel@...ts.xenproject.org,
 Jason Andryuk <jason.andryuk@....com>,
 Arthur Borsboom <arthurborsboom@...il.com>, stable@...r.kernel.org,
 linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fbdev/xen-fbfront: Assign fb_info->device

Hi

Am 10.09.24 um 09:22 schrieb Roger Pau Monné:
> On Mon, Sep 09, 2024 at 10:09:16PM -0400, Jason Andryuk wrote:
>> From: Jason Andryuk <jason.andryuk@....com>
>>
>> Probing xen-fbfront faults in video_is_primary_device().  The passed-in
>> struct device is NULL since xen-fbfront doesn't assign it and the
>> memory is kzalloc()-ed.  Assign fb_info->device to avoid this.
>>
>> This was exposed by the conversion of fb_is_primary_device() to
>> video_is_primary_device() which dropped a NULL check for struct device.
>>
>> Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
>> Reported-by: Arthur Borsboom <arthurborsboom@...il.com>
>> Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=LkXWeiSiTKsDY-cOe8QksWhFvcCneOKfrKd0ZajA@mail.gmail.com/
>> Tested-by: Arthur Borsboom <arthurborsboom@...il.com>
>> CC: stable@...r.kernel.org
>> Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> Reviewed-by: Roger Pau Monné <roger.pau@...rix.com>
>
>> ---
>> The other option would be to re-instate the NULL check in
>> video_is_primary_device()
> I do think this is needed, or at least an explanation.  The commit
> message in f178e96de7f0 doesn't mention anything about
> video_is_primary_device() not allowing being passed a NULL device
> (like it was possible with fb_is_primary_device()).
>
> Otherwise callers of video_is_primary_device() would need to be
> adjusted to check for device != NULL.

The helper expects a non-NULL pointer. We might want to document this.

Best regards
Thomas

>
> Thanks, Roger.
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)