[PATCH 4.9 046/153] mm balloon: umount balloon_mnt when removing vb device

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yisheng Xie <xieyisheng1@xxxxxxxxxx>

commit 9c57b5808c625f4fc93da330b932647eaff321f7 upstream.

With CONFIG_BALLOON_COMPACTION=y the kernel will mount balloon_mnt for
balloon page migration when we probe a virtio_balloon device.  However
we do not unmount it when removing the device.  Fix this.

Fixes: b1123ea6d3b3 ("mm: balloon: use general non-lru movable page feature")
Link: http://lkml.kernel.org/r/1486531318-35189-1-git-send-email-xieyisheng1@xxxxxxxxxx
Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Jason Wang <jasowang@xxxxxxxxxx>
Cc: Hanjun Guo <guohanjun@xxxxxxxxxx>
Cc: Xishi Qiu <qiuxishi@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/virtio/virtio_balloon.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -615,8 +615,12 @@ static void virtballoon_remove(struct vi
 	cancel_work_sync(&vb->update_balloon_stats_work);
 
 	remove_common(vb);
+#ifdef CONFIG_BALLOON_COMPACTION
 	if (vb->vb_dev_info.inode)
 		iput(vb->vb_dev_info.inode);
+
+	kern_unmount(balloon_mnt);
+#endif
 	kfree(vb);
 }