linux-kernel - Re: [PATCH printk v2 23/38] tty: tty_io: document console

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Date:   Thu, 20 Oct 2022 09:43:18 +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, Jiri Slaby <jirislaby@...nel.org>
Subject: Re: [PATCH printk v2 23/38] tty: tty_io: document console_lock usage

On Wed, Oct 19, 2022 at 05:01:45PM +0206, John Ogness wrote:
> show_cons_active() uses the console_lock to gather information
> on registered consoles. Since the console_lock is being used for
> multiple reasons, explicitly document these reasons. This will
> be useful when the console_lock is split into fine-grained
> locking.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
>  drivers/tty/tty_io.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
> index 2050e63963bb..333579bfa335 100644
> --- a/drivers/tty/tty_io.c
> +++ b/drivers/tty/tty_io.c
> @@ -3526,6 +3526,14 @@ static ssize_t show_cons_active(struct device *dev,
>  	struct console *c;
>  	ssize_t count = 0;
>  
> +	/*
> +	 * Hold the console_lock to guarantee that no consoles are
> +	 * unregistered until all console processing is complete.
> +	 * This also allows safe traversal of the console list.
> +	 *
> +	 * Stop console printing because the device() callback may
> +	 * assume the console is not within its write() callback.
> +	 */
>  	console_lock();
>  	for_each_console(c) {
>  		if (!c->device)
> -- 
> 2.30.2
> 

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