linux-kernel - Re: [PATCH printk v3 36/40] tty: serial: kgdboc: use console_list

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Message-ID: <20221109090631.wbtar2ho45x5yanl@ash.lan>
Date:   Wed, 9 Nov 2022 09:06:31 +0000
From:   Daniel Thompson <daniel.thompson@...aro.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>,
        Douglas Anderson <dianders@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        kgdb-bugreport@...ts.sourceforge.net, linux-serial@...r.kernel.org
Subject: Re: [PATCH printk v3 36/40] tty: serial: kgdboc: use
 console_list_lock for list traversal

On Mon, Nov 07, 2022 at 03:22:34PM +0106, John Ogness wrote:
> configure_kgdboc() uses the console_lock for console list iteration. Use
> the console_list_lock instead because list synchronization responsibility
> will be removed from the console_lock in a later change.
>
> The SRCU iterator could have been used here, but a later change will
> relocate the locking of the console_list_lock to also provide
> synchronization against register_console().
>
> Note, the console_lock is still needed to serialize the device()
> callback with other console operations.
>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  drivers/tty/serial/kgdboc.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 5be381003e58..82b4b4d67823 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -451,6 +463,7 @@ static void kgdboc_earlycon_pre_exp_handler(void)
>  {
>  	struct console *con;
>  	static bool already_warned;
> +	int cookie;
>
>  	if (already_warned)
>  		return;
> @@ -463,9 +476,14 @@ static void kgdboc_earlycon_pre_exp_handler(void)
>  	 * serial drivers might be OK with this, print a warning once per
>  	 * boot if we detect this case.
>  	 */
> -	for_each_console(con)
> +	cookie = console_srcu_read_lock();
> +	for_each_console_srcu(con) {
>  		if (con == kgdboc_earlycon_io_ops.cons)
> -			return;
> +			break;
> +	}
> +	console_srcu_read_unlock(cookie);
> +	if (con)
> +		return;

This change isn't mentioned in the patch description.


Daniel.