linux-kernel - Re: [PATCH printk v4 09/27] printk: nbcon: Implement processing in port->lock wrapper

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Message-ID: <87cyr6y8yr.fsf@jogness.linutronix.de>
Date: Wed, 03 Apr 2024 13:41:56 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, Steven Rostedt
 <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>,
 linux-kernel@...r.kernel.org, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, Russell
 King <linux@...linux.org.uk>, Tony Lindgren <tony@...mide.com>, Ilpo
 Järvinen <ilpo.jarvinen@...ux.intel.com>, Andy Shevchenko
 <andriy.shevchenko@...ux.intel.com>, Uwe Kleine-König
 <u.kleine-koenig@...gutronix.de>, Théo Lebrun
 <theo.lebrun@...tlin.com>,
 Linus Walleij <linus.walleij@...aro.org>, Lino Sanfilippo
 <l.sanfilippo@...bus.com>, Fabio Estevam <festevam@...x.de>, Arnd Bergmann
 <arnd@...db.de>, linux-serial@...r.kernel.org, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>
Subject: Re: [PATCH printk v4 09/27] printk: nbcon: Implement processing in
 port->lock wrapper

On 2024-04-03, John Ogness <john.ogness@...utronix.de> wrote:
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index d6a58a9e072a..2652b4d5c944 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -3146,7 +3146,7 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
>  	uport->state = state;
>  
>  	state->pm_state = UART_PM_STATE_UNDEFINED;
> -	uport->cons = drv->cons;
> +	uart_port_set_cons(uport, drv->cons);
>  	uport->minor = drv->tty_driver->minor_start + uport->line;
>  	uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name,
>  				drv->tty_driver->name_base + uport->line);

Sebastian Siewior pointed out that the port lock is initialized shortly
after this code. Since uart_port_set_cons() uses the port lock, the
spinlock initialization must come first. The changes for serial_core.c
should be:

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index d6a58a9e072a..0c13ea6a3afa 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3145,8 +3145,15 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	state->uart_port = uport;
 	uport->state = state;
 
+	/*
+	 * If this port is in use as a console then the spinlock is already
+	 * initialised.
+	 */
+	if (!uart_console_registered(uport))
+		uart_port_spin_lock_init(uport);
+
 	state->pm_state = UART_PM_STATE_UNDEFINED;
-	uport->cons = drv->cons;
+	uart_port_set_cons(uport, drv->cons);
 	uport->minor = drv->tty_driver->minor_start + uport->line;
 	uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name,
 				drv->tty_driver->name_base + uport->line);
@@ -3155,13 +3162,6 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 		goto out;
 	}
 
-	/*
-	 * If this port is in use as a console then the spinlock is already
-	 * initialised.
-	 */
-	if (!uart_console_registered(uport))
-		uart_port_spin_lock_init(uport);
-
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);