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Message-ID: <a4bb64e8-126c-6a50-bd39-77926aa6010e@linux.intel.com>
Date: Tue, 20 Aug 2024 14:12:15 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
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>,
LKML <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>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Arnd Bergmann <arnd@...db.de>,
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>,
Konrad Dybcio <konrad.dybcio@...aro.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
linux-serial <linux-serial@...r.kernel.org>
Subject: Re: [PATCH printk v8 11/35] serial: core: Introduce wrapper to set
@uart_port->cons
On Tue, 20 Aug 2024, John Ogness wrote:
> Introduce uart_port_set_cons() as a wrapper to set @cons of a
> uart_port. The wrapper sets @cons under the port lock in order
> to prevent @cons from disappearing while another context is
> holding the port lock. This is necessary for a follow-up
> commit relating to the port lock wrappers, which rely on @cons
> not changing between lock and unlock.
>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> Tested-by: Théo Lebrun <theo.lebrun@...tlin.com> # EyeQ5, AMBA-PL011
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
--
i.
> ---
> drivers/tty/serial/8250/8250_core.c | 6 +++---
> drivers/tty/serial/amba-pl011.c | 2 +-
> drivers/tty/serial/serial_core.c | 16 ++++++++--------
> include/linux/serial_core.h | 17 +++++++++++++++++
> 4 files changed, 29 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 29e4b83e0376..5f9f06911795 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -423,11 +423,11 @@ static int univ8250_console_setup(struct console *co, char *options)
>
> port = &serial8250_ports[co->index].port;
> /* link port to console */
> - port->cons = co;
> + uart_port_set_cons(port, co);
>
> retval = serial8250_console_setup(port, options, false);
> if (retval != 0)
> - port->cons = NULL;
> + uart_port_set_cons(port, NULL);
> return retval;
> }
>
> @@ -485,7 +485,7 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
> continue;
>
> co->index = i;
> - port->cons = co;
> + uart_port_set_cons(port, co);
> return serial8250_console_setup(port, options, true);
> }
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 8b1644f5411e..7d0134ecd82f 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -2480,7 +2480,7 @@ static int pl011_console_match(struct console *co, char *name, int idx,
> continue;
>
> co->index = i;
> - port->cons = co;
> + uart_port_set_cons(port, co);
> return pl011_console_setup(co, options);
> }
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 9a18d0b95a41..61c7e1268957 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -3168,8 +3168,15 @@ 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);
> @@ -3178,13 +3185,6 @@ 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);
>
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 8872cd21e70a..2cf03ff2056a 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -608,6 +608,23 @@ static inline void __uart_port_unlock_irqrestore(struct uart_port *up, unsigned
> spin_unlock_irqrestore(&up->lock, flags);
> }
>
> +/**
> + * uart_port_set_cons - Safely set the @cons field for a uart
> + * @up: The uart port to set
> + * @con: The new console to set to
> + *
> + * This function must be used to set @up->cons. It uses the port lock to
> + * synchronize with the port lock wrappers in order to ensure that the console
> + * cannot change or disappear while another context is holding the port lock.
> + */
> +static inline void uart_port_set_cons(struct uart_port *up, struct console *con)
> +{
> + unsigned long flags;
> +
> + __uart_port_lock_irqsave(up, &flags);
> + up->cons = con;
> + __uart_port_unlock_irqrestore(up, flags);
> +}
> /**
> * uart_port_lock - Lock the UART port
> * @up: Pointer to UART port structure
>
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