linux-kernel - Re: [PATCH 6/7] debug: kgd_io: Don't check for CON

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Message-ID: <aFAiq3IEic8DuATR@pathway.suse.cz>
Date: Mon, 16 Jun 2025 15:56:59 +0200
From: Petr Mladek <pmladek@...e.com>
To: Marcos Paulo de Souza <mpdesouza@...e.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Jason Wessel <jason.wessel@...driver.com>,
	Daniel Thompson <danielt@...nel.org>,
	Douglas Anderson <dianders@...omium.org>,
	Richard Weinberger <richard@....at>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	kgdb-bugreport@...ts.sourceforge.net, linux-um@...ts.infradead.org
Subject: Re: [PATCH 6/7] debug: kgd_io: Don't check for CON_ENABLED

On Fri 2025-06-06 23:53:48, Marcos Paulo de Souza wrote:
> All consoles found on for_each_console_srcu are registered, meaning that all of
> them are CON_ENABLED. The code tries to find an active console, so check if the
> console is not suspended instead.
> 
> Signed-off-by: Marcos Paulo de Souza <mpdesouza@...e.com>
> ---
>  kernel/debug/kdb/kdb_io.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 9b11b10b120cf07e451a7a4d92ce50f9a6c066b2..cdc1ee81d7332a9a00b967af719939f438f26cef 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -589,7 +589,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
>  	 */
>  	cookie = console_srcu_read_lock();
>  	for_each_console_srcu(c) {
> -		if (!(console_srcu_read_flags(c) & CON_ENABLED))
> +		if (console_srcu_read_flags(c) & CON_SUSPENDED)
>  			continue;

I think that this is similar to the 5th patch. We should check
here is_console_usable(con, console_srcu_read_flags(c), true)
because it checks more conditions:

     + the global console_suspended flag. The consoles drivers should
       not be used when it is set...

     + whether NBCON console driver has con->write_atomic

and we should also fix kdb_msg_write() to actually use
con->write_atomic() when it is a NBCON console driver.
There is hard-coded con->write() at the moment.

But it might get more complicated. It would be nice to do it correctly
and use con->write_atomit() only when nbcon_context_try_acquire()
succeeds. We probably should use a context with NBCON_PRIO_EMERGENCY.

And this should be fixed at the beginning of the patchset because
it actually fixes the support of the new NBCON console drivers.

Best Regards,
Petr

>  		if (c == dbg_io_ops->cons)
>  			continue;
> 
> -- 
> 2.49.0