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>

drivers/input/keyboard/atkbd.c

@@ -225,8 +225,10 @@ struct atkbd {
 
 	struct delayed_work event_work;
 	unsigned long event_jiffies;
-	struct mutex event_mutex;
 	unsigned long event_mask;
+
+	/* Serializes reconnect(), attr->set() and event work */
+	struct mutex mutex;
 };
 
 /*
@@ -577,7 +579,7 @@ static void atkbd_event_work(struct work_struct *work)
 {
 	struct atkbd *atkbd = container_of(work, struct atkbd, event_work.work);
 
-	mutex_lock(&atkbd->event_mutex);
+	mutex_lock(&atkbd->mutex);
 
 	if (!atkbd->enabled) {
 		/*
@@ -596,7 +598,7 @@ static void atkbd_event_work(struct work_struct *work)
 			atkbd_set_repeat_rate(atkbd);
 	}
 
-	mutex_unlock(&atkbd->event_mutex);
+	mutex_unlock(&atkbd->mutex);
 }
 
 /*
@@ -612,7 +614,7 @@ static void atkbd_schedule_event_work(struct atkbd *atkbd, int event_bit)
 
 	atkbd->event_jiffies = jiffies;
 	set_bit(event_bit, &atkbd->event_mask);
-	wmb();
+	mb();
 	schedule_delayed_work(&atkbd->event_work, delay);
 }
 
@@ -849,12 +851,13 @@ static void atkbd_disconnect(struct serio *serio)
 {
 	struct atkbd *atkbd = serio_get_drvdata(serio);
 
+	sysfs_remove_group(&serio->dev.kobj, &atkbd_attribute_group);
+
 	atkbd_disable(atkbd);
 
 	/* make sure we don't have a command in flight */
 	cancel_delayed_work_sync(&atkbd->event_work);
 
-	sysfs_remove_group(&serio->dev.kobj, &atkbd_attribute_group);
 	input_unregister_device(atkbd->dev);
 	serio_close(serio);
 	serio_set_drvdata(serio, NULL);
@@ -1087,7 +1090,7 @@ static int atkbd_connect(struct serio *serio, struct serio_driver *drv)
 	atkbd->dev = dev;
 	ps2_init(&atkbd->ps2dev, serio);
 	INIT_DELAYED_WORK(&atkbd->event_work, atkbd_event_work);
-	mutex_init(&atkbd->event_mutex);
+	mutex_init(&atkbd->mutex);
 
 	switch (serio->id.type) {
 
@@ -1160,19 +1163,23 @@ static int atkbd_reconnect(struct serio *serio)
 {
 	struct atkbd *atkbd = serio_get_drvdata(serio);
 	struct serio_driver *drv = serio->drv;
+	int retval = -1;
 
 	if (!atkbd || !drv) {
 		printk(KERN_DEBUG "atkbd: reconnect request, but serio is disconnected, ignoring...\n");
 		return -1;
 	}
 
+	mutex_lock(&atkbd->mutex);
+
 	atkbd_disable(atkbd);
 
 	if (atkbd->write) {
 		if (atkbd_probe(atkbd))
-			return -1;
+			goto out;
+
 		if (atkbd->set != atkbd_select_set(atkbd, atkbd->set, atkbd->extra))
-			return -1;
+			goto out;
 
 		atkbd_activate(atkbd);
 
@@ -1190,8 +1197,11 @@ static int atkbd_reconnect(struct serio *serio)
 	}
 
 	atkbd_enable(atkbd);
+	retval = 0;
 
-	return 0;
+ out:
+	mutex_unlock(&atkbd->mutex);
+	return retval;
 }
 
 static struct serio_device_id atkbd_serio_ids[] = {
@@ -1235,47 +1245,28 @@ static ssize_t atkbd_attr_show_helper(struct device *dev, char *buf,
 				ssize_t (*handler)(struct atkbd *, char *))
 {
 	struct serio *serio = to_serio_port(dev);
-	int retval;
+	struct atkbd *atkbd = serio_get_drvdata(serio);
 
-	retval = serio_pin_driver(serio);
-	if (retval)
-		return retval;
-
-	if (serio->drv != &atkbd_drv) {
-		retval = -ENODEV;
-		goto out;
-	}
-
-	retval = handler((struct atkbd *)serio_get_drvdata(serio), buf);
-
-out:
-	serio_unpin_driver(serio);
-	return retval;
+	return handler(atkbd, buf);
 }
 
 static ssize_t atkbd_attr_set_helper(struct device *dev, const char *buf, size_t count,
 				ssize_t (*handler)(struct atkbd *, const char *, size_t))
 {
 	struct serio *serio = to_serio_port(dev);
-	struct atkbd *atkbd;
+	struct atkbd *atkbd = serio_get_drvdata(serio);
 	int retval;
 
-	retval = serio_pin_driver(serio);
+	retval = mutex_lock_interruptible(&atkbd->mutex);
 	if (retval)
 		return retval;
 
-	if (serio->drv != &atkbd_drv) {
-		retval = -ENODEV;
-		goto out;
-	}
-
-	atkbd = serio_get_drvdata(serio);
 	atkbd_disable(atkbd);
 	retval = handler(atkbd, buf, count);
 	atkbd_enable(atkbd);
 
-out:
-	serio_unpin_driver(serio);
+	mutex_unlock(&atkbd->mutex);
+
 	return retval;
 }