UIO: hold a reference to the device's owner while the device is open

Otherwise the device might just disappear while /dev/uioX is being used
which results in an Oops.

Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
Signed-off-by: Hans J Koch <hjk@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/uio/uio.c

@@ -301,23 +301,33 @@ static int uio_open(struct inode *inode, struct file *filep)
 	if (!idev)
 		return -ENODEV;
 
+	if (!try_module_get(idev->owner))
+		return -ENODEV;
+
 	listener = kmalloc(sizeof(*listener), GFP_KERNEL);
-	if (!listener)
-		return -ENOMEM;
+	if (!listener) {
+		ret = -ENOMEM;
+		goto err_alloc_listener;
+	}
 
 	listener->dev = idev;
 	listener->event_count = atomic_read(&idev->event);
 	filep->private_data = listener;
 
 	if (idev->info->open) {
-		if (!try_module_get(idev->owner))
-			return -ENODEV;
 		ret = idev->info->open(idev->info, inode);
-		module_put(idev->owner);
+		if (ret)
+			goto err_infoopen;
 	}
 
-	if (ret)
-		kfree(listener);
+	return 0;
+
+err_infoopen:
+
+	kfree(listener);
+err_alloc_listener:
+
+	module_put(idev->owner);
 
 	return ret;
 }
@@ -336,12 +346,11 @@ static int uio_release(struct inode *inode, struct file *filep)
 	struct uio_listener *listener = filep->private_data;
 	struct uio_device *idev = listener->dev;
 
-	if (idev->info->release) {
-		if (!try_module_get(idev->owner))
-			return -ENODEV;
+	if (idev->info->release)
 		ret = idev->info->release(idev->info, inode);
-		module_put(idev->owner);
-	}
+
+	module_put(idev->owner);
+
 	if (filep->f_flags & FASYNC)
 		ret = uio_fasync(-1, filep, 0);
 	kfree(listener);
@@ -510,10 +519,7 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 		return -EINVAL;
 
 	if (idev->info->mmap) {
-		if (!try_module_get(idev->owner))
-			return -ENODEV;
 		ret = idev->info->mmap(idev->info, vma);
-		module_put(idev->owner);
 		return ret;
 	}