Re: [PATCH 11/21] fbcon: Extract fbcon_open/release helpers

[Sam Ravnborg <sam@ravnborg.org>]

Hi Daniel,

On Mon, Jan 31, 2022 at 10:05:42PM +0100, Daniel Vetter wrote:
> There's two minor behaviour changes in here:
> - in error paths we now consistently call fb_ops->fb_release
> - fb_release really can't fail (fbmem.c ignores it too) and there's no
>   reasonable cleanup we can do anyway.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Claudio Suarez <cssk@net-c.es>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Du Cheng <ducheng2@gmail.com>
> ---
>  drivers/video/fbdev/core/fbcon.c | 107 +++++++++++++++----------------
>  1 file changed, 53 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index fa30e1909164..eea2ee14b64c 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -680,19 +680,37 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)
>  
>  #endif /* CONFIG_MISC_TILEBLITTING */
>  
> +static int fbcon_open(struct fb_info *info)
> +{
> +	if (!try_module_get(info->fbops->owner))
> +		return -ENODEV;
> +
> +	if (info->fbops->fb_open &&
> +	    info->fbops->fb_open(info, 0)) {
> +		module_put(info->fbops->owner);
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static void fbcon_release(struct fb_info *info)
> +{
> +	if (info->fbops->fb_release)
> +		info->fbops->fb_release(info, 0);
> +
> +	module_put(info->fbops->owner);
> +}
>  
>  static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
>  				  int unit, int oldidx)
>  {
>  	struct fbcon_ops *ops = NULL;
> -	int err = 0;
> -
> -	if (!try_module_get(info->fbops->owner))
> -		err = -ENODEV;
> +	int err;
>  
> -	if (!err && info->fbops->fb_open &&
> -	    info->fbops->fb_open(info, 0))
> -		err = -ENODEV;
> +	err = fbcon_open(info);
> +	if (err)
> +		return err;
>  
>  	if (!err) {
>  		ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
> @@ -713,7 +731,7 @@ static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
>  
>  	if (err) {
>  		con2fb_map[unit] = oldidx;
> -		module_put(info->fbops->owner);
> +		fbcon_release(info);
>  	}
>  
>  	return err;
> @@ -724,45 +742,34 @@ static int con2fb_release_oldinfo(struct vc_data *vc, struct fb_info *oldinfo,
>  				  int oldidx, int found)
>  {
>  	struct fbcon_ops *ops = oldinfo->fbcon_par;
> -	int err = 0, ret;
> +	int ret;
>  
> -	if (oldinfo->fbops->fb_release &&
> -	    oldinfo->fbops->fb_release(oldinfo, 0)) {
> -		con2fb_map[unit] = oldidx;
The old code assigns con2fb_map[unit] before is calls
newinfo->fbops->fb_release).
I wonder if there can be any callback to fbcon where the value
of con2fb_map[unit] matters?


> -		if (!found && newinfo->fbops->fb_release)
> -			newinfo->fbops->fb_release(newinfo, 0);
> -		if (!found)
> -			module_put(newinfo->fbops->owner);
> -		err = -ENODEV;
> -	}
> +	fbcon_release(oldinfo);
>  
> -	if (!err) {
> -		fbcon_del_cursor_work(oldinfo);
> -		kfree(ops->cursor_state.mask);
> -		kfree(ops->cursor_data);
> -		kfree(ops->cursor_src);
> -		kfree(ops->fontbuffer);
> -		kfree(oldinfo->fbcon_par);
> -		oldinfo->fbcon_par = NULL;
> -		module_put(oldinfo->fbops->owner);
> -		/*
> -		  If oldinfo and newinfo are driving the same hardware,
> -		  the fb_release() method of oldinfo may attempt to
> -		  restore the hardware state.  This will leave the
> -		  newinfo in an undefined state. Thus, a call to
> -		  fb_set_par() may be needed for the newinfo.
> -		*/
> -		if (newinfo && newinfo->fbops->fb_set_par) {
> -			ret = newinfo->fbops->fb_set_par(newinfo);
> +	fbcon_del_cursor_work(oldinfo);


> +	kfree(ops->cursor_state.mask);
> +	kfree(ops->cursor_data);
> +	kfree(ops->cursor_src);
> +	kfree(ops->fontbuffer);
> +	kfree(oldinfo->fbcon_par);
> +	oldinfo->fbcon_par = NULL;
These all look like candidates to stuff into fbcon_release()
That would drop the nice symmetry but make it more consistent.

I think we miss freeing ops->cursor_data in fbcon_exit(),
but I did not follow all the code.

With my ramblings considered the patch is
Acked-by: Sam Ravnborg <sam@ravnborg.org>

	Sam

> +	/*
> +	  If oldinfo and newinfo are driving the same hardware,
> +	  the fb_release() method of oldinfo may attempt to
> +	  restore the hardware state.  This will leave the
> +	  newinfo in an undefined state. Thus, a call to
> +	  fb_set_par() may be needed for the newinfo.
> +	*/
> +	if (newinfo && newinfo->fbops->fb_set_par) {
> +		ret = newinfo->fbops->fb_set_par(newinfo);
>  
> -			if (ret)
> -				printk(KERN_ERR "con2fb_release_oldinfo: "
> -					"detected unhandled fb_set_par error, "
> -					"error code %d\n", ret);
> -		}
> +		if (ret)
> +			printk(KERN_ERR "con2fb_release_oldinfo: "
> +				"detected unhandled fb_set_par error, "
> +				"error code %d\n", ret);
>  	}
>  
> -	return err;
> +	return 0;
>  }
>  
>  static void con2fb_init_display(struct vc_data *vc, struct fb_info *info,
> @@ -917,7 +924,6 @@ static const char *fbcon_startup(void)
>  	struct fbcon_display *p = &fb_display[fg_console];
>  	struct vc_data *vc = vc_cons[fg_console].d;
>  	const struct font_desc *font = NULL;
> -	struct module *owner;
>  	struct fb_info *info = NULL;
>  	struct fbcon_ops *ops;
>  	int rows, cols;
> @@ -936,17 +942,12 @@ static const char *fbcon_startup(void)
>  	if (!info)
>  		return NULL;
>  	
> -	owner = info->fbops->owner;
> -	if (!try_module_get(owner))
> +	if (fbcon_open(info))
>  		return NULL;
> -	if (info->fbops->fb_open && info->fbops->fb_open(info, 0)) {
> -		module_put(owner);
> -		return NULL;
> -	}
>  
>  	ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
>  	if (!ops) {
> -		module_put(owner);
> +		fbcon_release(info);
>  		return NULL;
>  	}
>  
> @@ -3331,10 +3332,6 @@ static void fbcon_exit(void)
>  		}
>  
>  		if (mapped) {
> -			if (info->fbops->fb_release)
> -				info->fbops->fb_release(info, 0);
> -			module_put(info->fbops->owner);
> -
>  			if (info->fbcon_par) {
>  				struct fbcon_ops *ops = info->fbcon_par;
>  
> @@ -3344,6 +3341,8 @@ static void fbcon_exit(void)
>  				kfree(info->fbcon_par);
>  				info->fbcon_par = NULL;
>  			}
> +
> +			fbcon_release(info);
>  		}
>  	}
>  }
> -- 
> 2.33.0