Input: serio - fix potential deadlock when unbinding drivers

sysfs_remove_group() waits for sysfs attributes to be removed, therefore
we do not need to worry about driver-specific attributes being accessed
after driver has been detached from the device. In fact, attempts to take
serio->drv_mutex in attribute methods may lead to the following deadlock:

                                          sysfs_read_file()
                                            fill_read_buffer()
                                              sysfs_get_active_two()
                                                psmouse_attr_show_helper()
                                                  serio_pin_driver()
serio_disconnect_driver()
  mutex_lock(&serio->drv_mutex);
                                <-------->        mutex_lock(&serio_drv_mutex);
    psmouse_disconnect()
      sysfs_remove_group(... psmouse_attr_group);
        ....
        sysfs_deactivate();
          wait_for_completion();

Fix this by removing calls to serio_[un]pin_driver() and functions themselves
and using driver-private mutexes to serialize access to attribute's set()
methods that may change device state.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 3 insertions, 29 deletions

diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
index 401ac6b..d59e18b 100644
--- a/drivers/input/mouse/psmouse-base.c
+++ b/drivers/input/mouse/psmouse-base.c
@@ -1450,24 +1450,10 @@ ssize_t psmouse_attr_show_helper(struct device *dev, struct device_attribute *de
 	struct serio *serio = to_serio_port(dev);
 	struct psmouse_attribute *attr = to_psmouse_attr(devattr);
 	struct psmouse *psmouse;
-	int retval;
-
-	retval = serio_pin_driver(serio);
-	if (retval)
-		return retval;
-
-	if (serio->drv != &psmouse_drv) {
-		retval = -ENODEV;
-		goto out;
-	}
 
 	psmouse = serio_get_drvdata(serio);
 
-	retval = attr->show(psmouse, attr->data, buf);
-
-out:
-	serio_unpin_driver(serio);
-	return retval;
+	return attr->show(psmouse, attr->data, buf);
 }
 
 ssize_t psmouse_attr_set_helper(struct device *dev, struct device_attribute *devattr,
@@ -1478,18 +1464,9 @@ ssize_t psmouse_attr_set_helper(struct device *dev, struct device_attribute *dev
 	struct psmouse *psmouse, *parent = NULL;
 	int retval;
 
-	retval = serio_pin_driver(serio);
-	if (retval)
-		return retval;
-
-	if (serio->drv != &psmouse_drv) {
-		retval = -ENODEV;
-		goto out_unpin;
-	}
-
 	retval = mutex_lock_interruptible(&psmouse_mutex);
 	if (retval)
-		goto out_unpin;
+		goto out;
 
 	psmouse = serio_get_drvdata(serio);
 
@@ -1519,8 +1496,7 @@ ssize_t psmouse_attr_set_helper(struct device *dev, struct device_attribute *dev
 
  out_unlock:
 	mutex_unlock(&psmouse_mutex);
- out_unpin:
-	serio_unpin_driver(serio);
+ out:
 	return retval;
 }
 
@@ -1582,9 +1558,7 @@ static ssize_t psmouse_attr_set_protocol(struct psmouse *psmouse, void *data, co
 		}
 
 		mutex_unlock(&psmouse_mutex);
-		serio_unpin_driver(serio);
 		serio_unregister_child_port(serio);
-		serio_pin_driver_uninterruptible(serio);
 		mutex_lock(&psmouse_mutex);
 
 		if (serio->drv != &psmouse_drv) {