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References: <20221107141638.3790965-1-john.ogness@linutronix.de> <20221107141638.3790965-24-john.ogness@linutronix.de>
In-Reply-To: <20221107141638.3790965-24-john.ogness@linutronix.de>
From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 8 Nov 2022 09:46:20 +0100
Message-ID: <CAMuHMdXuBh1PznFggpwSanBtHu9=ngJkVCRzdZVnjxWs2+cbxw@mail.gmail.com>
Subject: Re: [PATCH printk v3 23/40] serial_core: replace uart_console_enabled()
 with uart_console_registered()
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Tony Lindgren <tony@atomide.com>,
        Lukas Wunner <lukas@wunner.de>, linux-serial@vger.kernel.org
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Precedence: bulk

Hi John,

On Mon, Nov 7, 2022 at 3:16 PM John Ogness <john.ogness@linutronix.de> wrote:
> All users of uart_console_enabled() really want to know if a console
> is registered. It is not reliable to check for CON_ENABLED in order
> to identify if a console is registered. Use console_is_registered()
> instead.
>
> A _locked() variant is provided because uart_set_options() is always
> called with the console_list_lock held and must check if a console
> is registered in order to synchronize with kgdboc.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>

> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -743,9 +743,20 @@ static const bool earlycon_acpi_spcr_enable EARLYCON_USED_OR_UNUSED;
>  static inline int setup_earlycon(char *buf) { return 0; }
>  #endif
>
> -static inline bool uart_console_enabled(struct uart_port *port)
> +/* Variant of uart_console_registered() when the console_list_lock is held. */
> +static inline bool uart_console_registered_locked(struct uart_port *port)
>  {
> -       return uart_console(port) && (port->cons->flags & CON_ENABLED);
> +       return uart_console(port) && console_is_registered_locked(port->cons);
> +}
> +
> +static inline bool uart_console_registered(struct uart_port *port)
> +{
> +       bool ret;
> +
> +       console_list_lock();
> +       ret = uart_console_registered_locked(port);
> +       console_list_unlock();
> +       return ret;

Perhaps

    return uart_console(port) && console_is_registered();

to avoid locking the list when the first condition is not true?

>  }


Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds