UMOUNT_SYNC
if (how & UMOUNT_SYNC)
if (how & UMOUNT_SYNC)
umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
umount_tree(res, UMOUNT_SYNC);
umount_tree(child, UMOUNT_SYNC);
umount_tree(mnt, UMOUNT_SYNC);
umount_tree(mnt, UMOUNT_PROPAGATE|UMOUNT_SYNC);
umount_tree(m, UMOUNT_PROPAGATE|UMOUNT_SYNC);