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

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Message-ID: <87czagf8hf.fsf@jogness.linutronix.de>
Date:   Tue, 25 Oct 2022 13:34:12 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Doug Anderson <dianders@...omium.org>
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>,
        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 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 ?

You are correct that it is not a data race (because of the
console_list_lock being held.) Petr has suggested adding a separate
function for non-data-race callers. For v3 I will do this and use it
here, probably called console_is_enabled_locked().

Usually CON_ENABLED is the only flag that is interesting during normal
operation. The kgdboc case is an exception. I thought about if we should
have console_flags() and console_flags_locked() to be able to handle
general con->flags access. console_flags() would be marked with
data_race(), console_flags_locked() would use lockdep to ensure the
console_list_lock is held.

But I would also like to have the _is_enabled special variant because
how we check if a console is enabled will be different for the atomic
consoles. I would like to hide those details in the _is_enabled
implementation.

John Ogness