linux-kernel - Re: [PATCH printk v2 24/38] xen: fbfront: use srcu console list iterator

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Message-ID: <Y1fnHH2J4bIS59ER@alley>
Date:   Tue, 25 Oct 2022 15:39:40 +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, Helge Deller <deller@....de>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, Tom Rix <trix@...hat.com>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH printk v2 24/38] xen: fbfront: use srcu console list
 iterator

On Wed 2022-10-19 17:01:46, John Ogness wrote:
> Since the console_lock is not being used for anything other than
> safe console list traversal, use srcu console list iteration instead.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

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

> ---
>  drivers/video/fbdev/xen-fbfront.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/video/fbdev/xen-fbfront.c b/drivers/video/fbdev/xen-fbfront.c
> index 4d2694d904aa..2552c853c6c2 100644
> --- a/drivers/video/fbdev/xen-fbfront.c
> +++ b/drivers/video/fbdev/xen-fbfront.c
> @@ -500,16 +500,18 @@ static int xenfb_probe(struct xenbus_device *dev,
>  static void xenfb_make_preferred_console(void)

Just for record. This function is a dirty hack how to associate "ttyX"
console with /dev/console.

A clean solution would be to just reshuffle console_drivers list. I
have a patch for this in my bottom drawer. It is part of a bigger
clean up that it not ready for upstreaming yet.

Best Regards,
Petr

>  {
>  	struct console *c;
> +	int cookie;
>  
>  	if (console_set_on_cmdline)
>  		return;
>  
> -	console_lock();
> -	for_each_console(c) {
> +	cookie = console_srcu_read_lock();
> +	for_each_console_srcu(c) {
>  		if (!strcmp(c->name, "tty") && c->index == 0)
>  			break;
>  	}
> -	console_unlock();
> +	console_srcu_read_unlock(cookie);
> +
>  	if (c) {
>  		unregister_console(c);
>  		c->flags |= CON_CONSDEV;
> -- 
> 2.30.2