linux-hardening - Re: [PATCH 15/19] drivers: tty: serial: mux.c: Migrate to register_console

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Message-ID: <aWoMHbbn-BmmbZMg@pathway.suse.cz>
Date: Fri, 16 Jan 2026 10:59:57 +0100
From: Petr Mladek <pmladek@...e.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	Daniel Thompson <danielt@...nel.org>,
	Douglas Anderson <dianders@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jiri Slaby <jirislaby@...nel.org>, Breno Leitao <leitao@...ian.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
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	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
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	Shan-Chun Hung <schung@...oton.com>,
	Laurentiu Tudor <laurentiu.tudor@....com>,
	linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org,
	netdev@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
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Subject: Re: [PATCH 15/19] drivers: tty: serial: mux.c: Migrate to
 register_console_force helper

On Sat 2025-12-27 09:16:22, Marcos Paulo de Souza wrote:
> The register_console_force function was introduced to register consoles
> even on the presence of default consoles, replacing the CON_ENABLE flag
> that was forcing the same behavior.
> 
> --- a/drivers/tty/serial/mux.c
> +++ b/drivers/tty/serial/mux.c
> @@ -390,7 +390,7 @@ static struct console mux_console = {
>  	.write =	mux_console_write,
>  	.device =	uart_console_device,
>  	.setup =	mux_console_setup,
> -	.flags =	CON_ENABLED | CON_PRINTBUFFER,
> +	.flags =	CON_PRINTBUFFER,
>  	.index =	0,
>  	.data =		&mux_driver,
>  };
> @@ -547,7 +547,7 @@ static int __init mux_init(void)
>  		mod_timer(&mux_timer, jiffies + MUX_POLL_DELAY);
>  
>  #ifdef CONFIG_SERIAL_MUX_CONSOLE
> -	        register_console(&mux_console);
> +		register_console_force(&mux_console);

The situation here is the same as in 16th patch for
ma35d1serial_console().

Also "mux_console" is assigned to

static int __init mux_probe(struct parisc_device *dev)
{
[...]
		mux_driver.cons = MUX_CONSOLE;

		status = uart_register_driver(&mux_driver);
[...]
		status = uart_add_one_port(&mux_driver, port);
[...]
}

So, that it can get registered also by:

  + mux_probe()
    + uart_add_one_port()
      + serial_ctrl_register_port()
	+ serial_core_register_port()
	  + serial_core_add_one_port()
	    + uart_configure_port()
	      + register_console()

And we would need to pass the "force" information via CON_FORCE flag.

Best Regards,
Petr