Re: [PATCH] fbdev/xen-fbfront: Assign fb_info->device

[Thomas Zimmermann]

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@xxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=LkXWeiSiTKsDY-cOe8QksWhFvcCneOKfrKd0ZajA@xxxxxxxxxxxxxx/
> > Tested-by: Arthur Borsboom <arthurborsboom@xxxxxxxxx>
> > CC: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Jason Andryuk <jason.andryuk@xxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>
> > ---
> > 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)