+ /*
+ * Ensure MNT_SHRINKABLE is set on snapshots to ensure they are
+ * unmounted automatically with the parent file system. This
+ * is done on the first getattr because it's not easy to get the
+ * vfsmount structure at mount time. This call path is explicitly
+ * marked unlikely to avoid any performance impact. FWIW, ext4
+ * resorts to a similar trick for sysadmin convenience.
+ */
+ if (unlikely(issnap && !(mnt->mnt_flags & MNT_SHRINKABLE)))
+ mnt->mnt_flags |= MNT_SHRINKABLE;
+