linux-kernel - Re: [PATCH printk v2 22/38] serial: kgdboc: document console

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Message-ID: <Y1D770/QciPCy3ds@kroah.com>
Date:   Thu, 20 Oct 2022 09:42:39 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org
Subject: Re: [PATCH printk v2 22/38] serial: kgdboc: document console_lock
 usage

On Wed, Oct 19, 2022 at 05:01:44PM +0206, John Ogness wrote:
> kgdboc_earlycon_init() uses the console_lock to ensure that no consoles
> are unregistered until the kgdboc_earlycon is setup. This is necessary
> because the trapping of the exit() callback assumes that the exit()
> callback is not called before the trap is setup.
> 
> Explicitly document this non-typical console_lock usage.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  drivers/tty/serial/kgdboc.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index e9d3f8c6e3dc..48000666789a 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -545,6 +545,14 @@ static int __init kgdboc_earlycon_init(char *opt)
>  	 * Look for a matching console, or if the name was left blank just
>  	 * pick the first one we find.
>  	 */
> +
> +	/*
> +	 * Hold the console_lock to guarantee that no consoles are
> +	 * unregistered until the kgdboc_earlycon setup is complete.
> +	 * Trapping the exit() callback relies on exit() not being
> +	 * called until the trap is setup. This also allows safe
> +	 * traversal of the console list.
> +	 */
>  	console_lock();
>  	for_each_console(con) {
>  		if (con->write && con->read &&
> -- 
> 2.30.2
>

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>