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

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Date:   Mon, 24 Oct 2022 17:49:34 -0700
From:   Doug Anderson <dianders@...omium.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>,
        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()

Hi,

On Mon, Oct 24, 2022 at 3:46 PM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Wed, Oct 19, 2022 at 7:56 AM John Ogness <john.ogness@...utronix.de> wrote:
> >
> > Replace (console->flags & CON_ENABLED) usage with console_is_enabled().
> >
> > Signed-off-by: John Ogness <john.ogness@...utronix.de>
> > ---
> >  drivers/tty/serial/kgdboc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> > index e76f0186c335..b17aa7e49894 100644
> > --- a/drivers/tty/serial/kgdboc.c
> > +++ b/drivers/tty/serial/kgdboc.c
> > @@ -533,7 +533,7 @@ static int __init kgdboc_earlycon_init(char *opt)
> >         console_lock();
> >         for_each_console(con) {
> >                 if (con->write && con->read &&
> > -                   (con->flags & (CON_BOOT | CON_ENABLED)) &&
> > +                   (console_is_enabled(con) || (con->flags & CON_BOOT)) &&
>
> <shrug>. I guess this is OK, but it feels a little pointless. If we're
> still directly looking at the CON_BOOT bit in con->flags it seems
> weird to be accessing CON_ENABLED through a special wrapper that's
> marked as a `data_race`. In our case it's _not_ a data race, right,
> since this function continues to hold the console_lock() even at the
> end of the series? I personally would drop this patch but if you
> really want it I won't object.

I realized that my statement isn't quite true. 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 ?