[PATCH] serial: Clear UPF_DEAD before calling tty_port_register_device_attr_serdev()

[PATCH] serial: Clear UPF_DEAD before calling tty_port_register_device_attr_serdev()

[Hans de Goede]

If a serdev_device_driver is already loaded for a serdev_tty_port when it
gets registered by tty_port_register_device_attr_serdev() then that
driver's probe() method will be called immediately.

The serdev_device_driver's probe() method should then be able to call
serdev_device_open() successfully, but because UPF_DEAD is still dead
serdev_device_open() will fail with -ENXIO in this scenario:

  serdev_device_open()
  ctrl->ops->open()	/* this callback being ttyport_open() */
  tty->ops->open()	/* this callback being uart_open() */
  tty_port_open()
  port->ops->activate()	/* this callback being uart_port_activate() */
  Find bit UPF_DEAD is set in uport->flags and fail with errno -ENXIO.

Fix this be clearing UPF_DEAD before tty_port_register_device_attr_serdev()
note this only moves up the UPD_DEAD clearing a small bit, before:

  tty_port_register_device_attr_serdev();
  mutex_unlock(&tty_port.mutex);
  uart_port.flags &= ~UPF_DEAD;
  mutex_unlock(&port_mutex);

after:

  uart_port.flags &= ~UPF_DEAD;
  tty_port_register_device_attr_serdev();
  mutex_unlock(&tty_port.mutex);
  mutex_unlock(&port_mutex);

Reported-by: Weifeng Liu <weifeng.liu.z@gmail.com>
Closes: https://lore.kernel.org/platform-driver-x86/20240505130800.2546640-1-weifeng.liu.z@gmail.com/
Tested-by: Weifeng Liu <weifeng.liu.z@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
Cc: Tony Lindgren <tony.lindgren@linux.intel.com>
Cc: Maximilian Luz <luzmaximilian@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/tty/serial/serial_core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index c476d884356d..b47a277978a0 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3211,6 +3211,9 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	if (uport->attr_group)
 		uport->tty_groups[1] = uport->attr_group;
 
+	/* Ensure serdev drivers can call serdev_device_open() right away */
+	uport->flags &= ~UPF_DEAD;
+
 	/*
 	 * Register the port whether it's detected or not.  This allows
 	 * setserial to be used to alter this port's parameters.
@@ -3221,6 +3224,7 @@ static int serial_core_add_one_port(struct uart_driver *drv, struct uart_port *u
 	if (!IS_ERR(tty_dev)) {
 		device_set_wakeup_capable(tty_dev, 1);
 	} else {
+		uport->flags |= UPF_DEAD;
 		dev_err(uport->dev, "Cannot register tty device on line %d\n",
 		       uport->line);
 	}
@@ -3426,8 +3430,6 @@ int serial_core_register_port(struct uart_driver *drv, struct uart_port *port)
 	if (ret)
 		goto err_unregister_port_dev;
 
-	port->flags &= ~UPF_DEAD;
-
 	mutex_unlock(&port_mutex);
 
 	return 0;
-- 
2.44.0

Re: [PATCH] serial: Clear UPF_DEAD before calling tty_port_register_device_attr_serdev()

[Tony Lindgren]

On Thu, May 09, 2024 at 04:15:49PM +0200, Hans de Goede wrote:
> If a serdev_device_driver is already loaded for a serdev_tty_port when it
> gets registered by tty_port_register_device_attr_serdev() then that
> driver's probe() method will be called immediately.
> 
> The serdev_device_driver's probe() method should then be able to call
> serdev_device_open() successfully, but because UPF_DEAD is still dead
> serdev_device_open() will fail with -ENXIO in this scenario:
> 
>   serdev_device_open()
>   ctrl->ops->open()	/* this callback being ttyport_open() */
>   tty->ops->open()	/* this callback being uart_open() */
>   tty_port_open()
>   port->ops->activate()	/* this callback being uart_port_activate() */
>   Find bit UPF_DEAD is set in uport->flags and fail with errno -ENXIO.
> 
> Fix this be clearing UPF_DEAD before tty_port_register_device_attr_serdev()

Looks OK to me:

Reviewed-by: Tony Lindgren <tony.lindgren@linux.intel.com>

Re: [PATCH] serial: Clear UPF_DEAD before calling tty_port_register_device_attr_serdev()

[Andy Shevchenko]

On Thu, May 9, 2024 at 5:16 PM Hans de Goede <hdegoede@redhat.com> wrote:
>
> If a serdev_device_driver is already loaded for a serdev_tty_port when it
> gets registered by tty_port_register_device_attr_serdev() then that
> driver's probe() method will be called immediately.
>
> The serdev_device_driver's probe() method should then be able to call
> serdev_device_open() successfully, but because UPF_DEAD is still dead
> serdev_device_open() will fail with -ENXIO in this scenario:
>
>   serdev_device_open()
>   ctrl->ops->open()     /* this callback being ttyport_open() */
>   tty->ops->open()      /* this callback being uart_open() */
>   tty_port_open()
>   port->ops->activate() /* this callback being uart_port_activate() */
>   Find bit UPF_DEAD is set in uport->flags and fail with errno -ENXIO.
>
> Fix this be clearing UPF_DEAD before tty_port_register_device_attr_serdev()
> note this only moves up the UPD_DEAD clearing a small bit, before:
>
>   tty_port_register_device_attr_serdev();
>   mutex_unlock(&tty_port.mutex);
>   uart_port.flags &= ~UPF_DEAD;
>   mutex_unlock(&port_mutex);
>
> after:
>
>   uart_port.flags &= ~UPF_DEAD;
>   tty_port_register_device_attr_serdev();
>   mutex_unlock(&tty_port.mutex);
>   mutex_unlock(&port_mutex);

I guess I have given the tag, anyway since Tony OK with this, no more questions:
Reviewed-by: Andy Shevchenko <andy@kernel.org>

-- 
With Best Regards,
Andy Shevchenko