[PATCH] m68k: nfcon: don't call console_is_registered in nfcon_device

[PATCH] m68k: nfcon: don't call console_is_registered in nfcon_device

[Andreas Schwab]

Since 7c2af0f634f1 ("tty: tty_io: use console_list_lock for list
synchronization") show_cons_active calls the device method under the
console_list_lock, but console_is_registered tries to acquire
console_list_lock as well, causing a deadlock.  It should not be necessary
to check console_is_registered here since the function should not be
called in the fist place when the console is not registered.

Fixes: 7c2af0f634f1 ("tty: tty_io: use console_list_lock for list synchronization")
Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
---
 arch/m68k/emu/nfcon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/m68k/emu/nfcon.c b/arch/m68k/emu/nfcon.c
index d41260672e24..f4657d9f4f15 100644
--- a/arch/m68k/emu/nfcon.c
+++ b/arch/m68k/emu/nfcon.c
@@ -49,7 +49,7 @@ static void nfcon_write(struct console *con, const char *str,
 static struct tty_driver *nfcon_device(struct console *con, int *index)
 {
 	*index = 0;
-	return console_is_registered(con) ? nfcon_tty_driver : NULL;
+	return nfcon_tty_driver;
 }
 
 static struct console nf_console = {
-- 
2.55.0


-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: [PATCH] m68k: nfcon: don't call console_is_registered in nfcon_device

[Geert Uytterhoeven]

Hi Andreas,

CC john, petr, serial

Thanks for your patch!

On Sat, 15 Aug 2026 at 09:33, Andreas Schwab <schwab@linux-m68k.org> wrote:
> Since 7c2af0f634f1 ("tty: tty_io: use console_list_lock for list
> synchronization") show_cons_active calls the device method under the
> console_list_lock, but console_is_registered tries to acquire
> console_list_lock as well, causing a deadlock.  It should not be necessary
> to check console_is_registered here since the function should not be
> called in the fist place when the console is not registered.

Nice catch!

> Fixes: 7c2af0f634f1 ("tty: tty_io: use console_list_lock for list synchronization")
> Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>

Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
i.e. will queue in the m68k tree for v7.3.

> --- a/arch/m68k/emu/nfcon.c
> +++ b/arch/m68k/emu/nfcon.c
> @@ -49,7 +49,7 @@ static void nfcon_write(struct console *con, const char *str,
>  static struct tty_driver *nfcon_device(struct console *con, int *index)
>  {
>         *index = 0;
> -       return console_is_registered(con) ? nfcon_tty_driver : NULL;

Interestingly, that call to console_is_registered() was added in
commit de61a1a3a0830710 ("tty: nfcon: use console_is_registered()"),
i.e. in the same series that added the extra locking...

> +       return nfcon_tty_driver;
>  }
>
>  static struct console nf_console = {

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