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

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Message-ID: <Y1e10nnjR6zysUwh@alley>
Date:   Tue, 25 Oct 2022 12:09:22 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     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>,
        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 22/38] serial: kgdboc: document console_lock
 usage

On Wed 2022-10-19 17:01:44, 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.

Great catch!

Note: This behavior might be dangerous. printk_late_init() checks if
      the early console code is in the init section. It unregisters
      such consoles even when keep_bootcon parameter is used.

      Well, it is "not serious" and might be improved later.
      If the early console has this code in the early section
      then it is a bug and should be fixed. printk_late_init() does
      the best effort because this problem would block all consoles
      and would be hard to debug. It is the same with kgdb but
      it is still only a corner case and just the best effort.

> Explicitly document this non-typical console_lock usage.
> 
> Signed-off-by: John Ogness <john.ogness@...utronix.de>

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr