hwmon: (fschmd) Fix a memleak on multiple opens of /dev/watchdog

When /dev/watchdog gets opened a second time we return -EBUSY, but
we already have got a kref then, so we end up leaking our data struct.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: stable@kernel.org

drivers/hwmon/fschmd.c

@@ -768,6 +768,7 @@ leave:
 static int watchdog_open(struct inode *inode, struct file *filp)
 {
 	struct fschmd_data *pos, *data = NULL;
+	int watchdog_is_open;
 
 	/* We get called from drivers/char/misc.c with misc_mtx hold, and we
 	   call misc_register() from fschmd_probe() with watchdog_data_mutex
@@ -782,10 +783,12 @@ static int watchdog_open(struct inode *inode, struct file *filp)
 		}
 	}
 	/* Note we can never not have found data, so we don't check for this */
-	kref_get(&data->kref);
+	watchdog_is_open = test_and_set_bit(0, &data->watchdog_is_open);
+	if (!watchdog_is_open)
+		kref_get(&data->kref);
 	mutex_unlock(&watchdog_data_mutex);
 
-	if (test_and_set_bit(0, &data->watchdog_is_open))
+	if (watchdog_is_open)
 		return -EBUSY;
 
 	/* Start the watchdog */