linux-kernel - Re: [PATCH] fbdev: Use helper to get fb

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Message-ID: <YnFi2nrK0I7893S2@ravnborg.org>
Date:   Tue, 3 May 2022 19:14:02 +0200
From:   Sam Ravnborg <sam@...nborg.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Junxiao Chang <junxiao.chang@...el.com>,
        dri-devel@...ts.freedesktop.org, Maxime Ripard <maxime@...no.tech>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH] fbdev: Use helper to get fb_info in all file operations

Hi Javier,

On Tue, May 03, 2022 at 06:46:16PM +0200, Javier Martinez Canillas wrote:
> A reference to the framebuffer device struct fb_info is stored in the file
> private data, but this reference could no longer be valid and must not be
> accessed directly. Instead, the file_fb_info() accessor function must be
> used since it does sanity checking to make sure that the fb_info is valid.
> 
> This can happen for example if the registered framebuffer device is for a
> driver that just uses a framebuffer provided by the system firmware. In
> that case, the fbdev core would unregister the framebuffer device when a
> real video driver is probed and ask to remove conflicting framebuffers.
> 
> Most fbdev file operations already use the helper to get the fb_info but
> get_fb_unmapped_area() and fb_deferred_io_fsync() don't. Fix those two.
> 
> Since fb_deferred_io_fsync() is not in fbmem.o, the helper has to be
> exported. Rename it and add a fb_ prefix to denote that is public now.
> 
> Reported-by: Junxiao Chang <junxiao.chang@...el.com>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
>  drivers/video/fbdev/core/fb_defio.c |  5 ++++-
>  drivers/video/fbdev/core/fbmem.c    | 24 +++++++++++++++---------
>  include/linux/fb.h                  |  1 +
>  3 files changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
> index 842c66b3e33d..ac1c88b3fbb5 100644
> --- a/drivers/video/fbdev/core/fb_defio.c
> +++ b/drivers/video/fbdev/core/fb_defio.c
> @@ -68,12 +68,15 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
>  
>  int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasync)
>  {
> -	struct fb_info *info = file->private_data;
> +	struct fb_info *info = fb_file_fb_info(file->private_data);
This looks wrong. I assume you wanted to write:
> +	struct fb_info *info = fb_file_fb_info(file);


	Sam