Re: [PATCH 04/33] vt: More locking checks

[Daniel Vetter]

On Fri, May 24, 2019 at 10:53:25AM +0200, Daniel Vetter wrote:
> I honestly have no idea what the subtle differences between
> con_is_visible, con_is_fg (internal to vt.c) and con_is_bound are. But
> it looks like both vc->vc_display_fg and con_driver_map are protected
> by the console_lock, so probably better if we hold that when checking
> this.
> 
> To do that I had to deinline the con_is_visible function.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> Cc: Martin Hostettler <textshell@xxxxxxxxxxx>
> Cc: Adam Borowski <kilobyte@xxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>

Hi Greg,

Do you want to merge this through your console tree or ack for merging
through drm/fbdev? It's part of a bigger series, and I'd like to have more
testing with this in our trees, but also ok to merge stand-alone if you
prefer that. It's just locking checks and some docs.

Same for the preceeding patch in this series here.

Thanks, Daniel


> ---
>  drivers/tty/vt/vt.c            | 16 ++++++++++++++++
>  include/linux/console_struct.h |  5 +----
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index bc9813b14c58..a8988a085138 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3815,6 +3815,8 @@ int con_is_bound(const struct consw *csw)
>  {
>  	int i, bound = 0;
>  
> +	WARN_CONSOLE_UNLOCKED();
> +
>  	for (i = 0; i < MAX_NR_CONSOLES; i++) {
>  		if (con_driver_map[i] == csw) {
>  			bound = 1;
> @@ -3826,6 +3828,20 @@ int con_is_bound(const struct consw *csw)
>  }
>  EXPORT_SYMBOL(con_is_bound);
>  
> +/**
> + * con_is_visible - checks whether the current console is visible
> + * @vc: virtual console
> + *
> + * RETURNS: zero if not visible, nonzero if visible
> + */
> +bool con_is_visible(const struct vc_data *vc)
> +{
> +	WARN_CONSOLE_UNLOCKED();
> +
> +	return *vc->vc_display_fg == vc;
> +}
> +EXPORT_SYMBOL(con_is_visible);
> +
>  /**
>   * con_debug_enter - prepare the console for the kernel debugger
>   * @sw: console driver
> diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
> index ed798e114663..24d4c16e3ae0 100644
> --- a/include/linux/console_struct.h
> +++ b/include/linux/console_struct.h
> @@ -168,9 +168,6 @@ extern void vc_SAK(struct work_struct *work);
>  
>  #define CUR_DEFAULT CUR_UNDERLINE
>  
> -static inline bool con_is_visible(const struct vc_data *vc)
> -{
> -	return *vc->vc_display_fg == vc;
> -}
> +bool con_is_visible(const struct vc_data *vc);
>  
>  #endif /* _LINUX_CONSOLE_STRUCT_H */
> -- 
> 2.20.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch