serial: Clear UPF_DEAD before calling tty_port_register_device_attr_serdev()

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>
Link: https://lore.kernel.org/r/20240509141549.63704-1-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 84ae70d52b056aeeeb182c967e3a5dc7881c3b94..2c1a0254d3f4a9e4056b3a1b6ba2346e434ae353 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3207,6 +3207,9 @@ 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.
@@ -3217,6 +3220,7 @@ 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;