linux-kernel - Re: [PATCH printk v2 04/26] printk: Consider nbcon boot consoles on seq init

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Date: Tue, 20 Feb 2024 11:26:41 +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: Re: [PATCH printk v2 04/26] printk: Consider nbcon boot consoles on
 seq init

On Sun 2024-02-18 20:03:04, John Ogness wrote:
> If a non-boot console is registering and boot consoles exist, the
> consoles are flushed before being unregistered. This allows the
> non-boot console to continue where the boot console left off.
> 
> If for whatever reason flushing fails, the lowest seq found from
> any of the enabled boot consoles is used. Until now con->seq was
> checked. However, if it is an nbcon boot console, the function
> nbcon_seq_read() must be used to read seq because con->seq is
> always 0.

This says that con->seq is always 0.

> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3391,11 +3391,20 @@ static void console_init_seq(struct console *newcon, bool bootcon_registered)
>  
>  				newcon->seq = prb_next_seq(prb);
>  				for_each_console(con) {
> -					if ((con->flags & CON_BOOT) &&
> -					    (con->flags & CON_ENABLED) &&
> -					    con->seq < newcon->seq) {
> -						newcon->seq = con->seq;
> +					u64 seq;
> +
> +					if (!((con->flags & CON_BOOT) &&
> +					      (con->flags & CON_ENABLED))) {
> +						continue;
>  					}
> +
> +					if (con->flags & CON_NBCON)
> +						seq = nbcon_seq_read(con);
> +					else
> +						seq = con->seq;
> +
> +					if (seq < newcon->seq)
> +						newcon->seq = seq;

But this sets con->seq to some value even for nbcon consoles.

It would make more sense to use nbcon_seq_force() for nbcon
consoles here and remove the copying from nbcon_init().

Otherwise, it looks good.

Best Regards,
Petr