linux-kernel - Re: [PATCH printk v2 12/38] tty: serial: kgdboc: use console_is

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Message-ID: <Y2jGKnSw02QLecx+@alley>
Date:   Mon, 7 Nov 2022 09:47:38 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Doug Anderson <dianders@...omium.org>,
        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>,
        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 v2 12/38] tty: serial: kgdboc: use
 console_is_enabled()

On Fri 2022-11-04 17:29:15, John Ogness wrote:
> On 2022-10-24, Doug Anderson <dianders@...omium.org> wrote:
> > It actually only holds console_list_lock() even at the end of the
> > series. Still, it seems weird that we're declaring the `data_race` on
> > CON_ENABLED but not CON_BOOT ?
> 
> For my upcoming v3 I decided to drop this patch and will keep the
> existing direct reading of @flags. Instead of this patch, for v3 the
> comment will additionally mention why @flags is allowed to be directly
> read:
> 
> /*
>  * Hold the console_lock to guarantee that no consoles are
              ^^^^^^^^^^^^
>  * unregistered until the kgdboc_earlycon setup is complete.

My understanding is that this is synchronized by console_list_lock.
Or do I miss something?

>  * Trapping the exit() callback relies on exit() not being
>  * called until the trap is setup. This also allows safe
>  * traversal of the console list and race-free reading of @flags.
>  */

Best Regards,
Petr