linux-kernel - Re: [PATCH printk v2 02/38] printk: Convert console

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Message-ID: <Y1FAsgNc8Bh2si0U@alley>
Date:   Thu, 20 Oct 2022 14:36:02 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH printk v2 02/38] printk: Convert console_drivers list to
 hlist

On Wed 2022-10-19 17:01:24, John Ogness wrote:
> Replace the open coded single linked list with a hlist so a conversion
> to SRCU protected list walks can reuse the existing primitives.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Just one nit below.

> @@ -3229,32 +3244,30 @@ int unregister_console(struct console *console)
>  	if (res > 0)
>  		return 0;
>  
> -	res = -ENODEV;
>  	console_lock();
> -	if (console_drivers == console) {
> -		console_drivers=console->next;
> -		res = 0;
> -	} else {
> -		for_each_console(con) {
> -			if (con->next == console) {
> -				con->next = console->next;
> -				res = 0;
> -				break;
> -			}
> -		}
> +
> +	/* Disable it unconditionally */
> +	console->flags &= ~CON_ENABLED;
> +
> +	if (hlist_unhashed(&console->node)) {
> +		res = -ENODEV;
> +		goto out_unlock;

Nit: It might make sense to replace this with:

		console_unlock();
		return -ENODEV;

This is the only code path using the extra goto target.

It is just an idea. I do not resist on this change.

>  	}
>  
> -	if (res)
> -		goto out_disable_unlock;
> +	hlist_del_init(&console->node);
>  
>  	/*
> +	 * <HISTORICAL>
>  	 * If this isn't the last console and it has CON_CONSDEV set, we
>  	 * need to set it on the next preferred console.
> +	 * </HISTORICAL>
> +	 *
> +	 * The above makes no sense as there is no guarantee that the next
> +	 * console has any device attached. Oh well....
>  	 */
> -	if (console_drivers != NULL && console->flags & CON_CONSDEV)
> -		console_drivers->flags |= CON_CONSDEV;
> +	if (!hlist_empty(&console_list) && console->flags & CON_CONSDEV)
> +		console_first()->flags |= CON_CONSDEV;
>  
> -	console->flags &= ~CON_ENABLED;
>  	console_unlock();
>  	console_sysfs_notify();
>  
> @@ -3263,10 +3276,8 @@ int unregister_console(struct console *console)
>  
>  	return res;
>  
> -out_disable_unlock:
> -	console->flags &= ~CON_ENABLED;
> +out_unlock:
>  	console_unlock();
> -
>  	return res;
>  }
>  EXPORT_SYMBOL(unregister_console);

Best Regards,
Petr