serial: core: Introduce wrapper to set @uart_port->cons

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>
Tested-by: Théo Lebrun <theo.lebrun@bootlin.com> # EyeQ5, AMBA-PL011
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240820063001.36405-12-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>

diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 29e4b83e03765156495ff15a96bda8085a366b39..5f9f06911795cc185907965effc2a0fc6e99017c 100644 (file)
--- 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 8b1644f5411ecf501663852a57145c225714a596..7d0134ecd82fa54765a46eb9fabe7caba18c0bf3 100644 (file)
--- 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 5bea3af46abcef688d72f1bcb19074a53003f0ec..1e3e28e364dfeb9b360f4fd1396dc2ff03b01f64 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3176,8 +3176,15 @@ 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);
@@ -3186,13 +3193,6 @@ 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 8872cd21e70a7d3ba2863651f1729bcadbe33a6c..2cf03ff2056acba80e774072da2eaa9bfcc5a8e7 100644 (file)
--- 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