[PATCH printk v5 09/30] serial: core: Introduce wrapper to set @uart_port->cons

John Ogness
2024-05-02T21:38:49Z

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@linutronix.de>
---
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 b62ad9006780..41d74ee3d95a 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -627,11 +627,11 @@ 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;
}

@@ -689,7 +689,7 @@ 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 cf2c890a560f..347aacf8400f 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2496,7 +2496,7 @@ 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 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);

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index bb3324d49453..038693774f21 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -606,6 +606,23 @@ 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
--
2.39.2