Re: [PATCH 22/30] fbdev/smscufx: Detect registered fb_info from refcount

Javier Martinez Canillas
2023-06-07T22:22:50Z

Thomas Zimmermann <tzimmermann@suse.de> writes:

> Detect registered instances of fb_info by reading the reference
> counter from struct fb_info.read. Avoids looking at the dev field
> and prepares fbdev for making struct fb_info.dev optional.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Steve Glendinning <steve.glendinning@shawell.net>
> ---
> drivers/video/fbdev/smscufx.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/smscufx.c b/drivers/video/fbdev/smscufx.c
> index 17cec62cc65d..adb2b1fe8383 100644
> --- a/drivers/video/fbdev/smscufx.c
> +++ b/drivers/video/fbdev/smscufx.c
> @@ -1496,7 +1496,7 @@ static int ufx_setup_modes(struct ufx_data *dev, struct fb_info *info,
> u8 *edid;
> int i, result = 0, tries = 3;
>
> - if (info->dev) /* only use mutex if info has been registered */
> + if (refcount_read(&info->count)) /* only use mutex if info has been registered */

The struct fb_info .count refcount is protected by the registration_lock
mutex in register_framebuffer(). I think this operation isn't thread safe ?

But that was also the case for info->dev check, so I guess is OK and this
change is for an old fbdev driver anyways.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

--
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat