linux-kernel - replay log: Re: [PATCH printk v4 38/39] printk: relieve console

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Message-ID: <Y3Oxck0/LAHFLYip@alley>
Date:   Tue, 15 Nov 2022 16:34:10 +0100
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
Subject: replay log: Re: [PATCH printk v4 38/39] printk: relieve console_lock
 of list synchronization duties

On Mon 2022-11-14 17:35:31, John Ogness wrote:
> The console_list_lock provides synchronization for console list and
> console->flags updates. All call sites that were using the console_lock
> for this synchronization have either switched to use the
> console_list_lock or the SRCU list iterator.
> 
> Remove console_lock usage for console list updates and console->flags
> updates.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3334,6 +3330,11 @@ void register_console(struct console *newcon)
>  		 * boot console that is the furthest behind.
>  		 */
>  		if (bootcon_registered && !keep_bootcon) {
> +			/*
> +			 * Hold the console_lock to guarantee safe access to
> +			 * console->seq.
> +			 */
> +			console_lock();
>  			for_each_console(con) {
>  				if ((con->flags & CON_BOOT) &&
>  				    (con->flags & CON_ENABLED) &&
> @@ -3341,6 +3342,7 @@ void register_console(struct console *newcon)
>  					newcon->seq = con->seq;
>  				}
>  			}
> +			console_unlock();

Thinking more about it. This console_unlock() will actually cause
flushing the boot consoles. A solution would be to call
console_flush_all() here.

And we could/should solve this in a separate patch. This code was not locked
before. It is a corner case. It could be solved later.

>  		}
>  	}
>  

Best Regards,
Petr