fs/pnode.c - kernel/msm-4.9 - Gitiles

 /*
  *  linux/fs/pnode.c
  *
  * (C) Copyright IBM Corporation 2005.
  *	Released under GPL v2.
  *	Author : Ram Pai (linuxram@us.ibm.com)
  *
  */
 #include <linux/mnt_namespace.h>
 #include <linux/mount.h>
 #include <linux/fs.h>
 #include <linux/nsproxy.h>
 #include "internal.h"
 #include "pnode.h"

 /* return the next shared peer mount of @p */
 static inline struct mount *next_peer(struct mount *p)
 {
 	return list_entry(p->mnt_share.next, struct mount, mnt_share);
 }

 static inline struct mount *first_slave(struct mount *p)
 {
 	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
 }

 static inline struct mount *last_slave(struct mount *p)
 {
 	return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
 }

 static inline struct mount *next_slave(struct mount *p)
 {
 	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
 }

 static struct mount *get_peer_under_root(struct mount *mnt,
 					 struct mnt_namespace *ns,
 					 const struct path *root)
 {
 	struct mount *m = mnt;

 	do {
 		/* Check the namespace first for optimization */
 		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
 			return m;

 		m = next_peer(m);
 	} while (m != mnt);

 	return NULL;
 }

 /*
  * Get ID of closest dominating peer group having a representative
  * under the given root.
  *
  * Caller must hold namespace_sem
  */
 int get_dominating_id(struct mount *mnt, const struct path *root)
 {
 	struct mount *m;

 	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
 		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
 		if (d)
 			return d->mnt_group_id;
 	}

 	return 0;
 }

 static int do_make_slave(struct mount *mnt)
 {
 	struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
 	struct mount *slave_mnt;

 	/*
 	 * slave 'mnt' to a peer mount that has the
 	 * same root dentry. If none is available then
 	 * slave it to anything that is available.
 	 */
 	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
 	       peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;

 	if (peer_mnt == mnt) {
 		peer_mnt = next_peer(mnt);
 		if (peer_mnt == mnt)
 			peer_mnt = NULL;
 	}
 	if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
 	    list_empty(&mnt->mnt_share))
 		mnt_release_group_id(mnt);

 	list_del_init(&mnt->mnt_share);
 	mnt->mnt_group_id = 0;

 	if (peer_mnt)
 		master = peer_mnt;

 	if (master) {
 		list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
 			slave_mnt->mnt_master = master;
 		list_move(&mnt->mnt_slave, &master->mnt_slave_list);
 		list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
 		INIT_LIST_HEAD(&mnt->mnt_slave_list);
 	} else {
 		struct list_head *p = &mnt->mnt_slave_list;
 		while (!list_empty(p)) {
                         slave_mnt = list_first_entry(p,
 					struct mount, mnt_slave);
 			list_del_init(&slave_mnt->mnt_slave);
 			slave_mnt->mnt_master = NULL;
 		}
 	}
 	mnt->mnt_master = master;
 	CLEAR_MNT_SHARED(mnt);
 	return 0;
 }

 /*
  * vfsmount lock must be held for write
  */
 void change_mnt_propagation(struct mount *mnt, int type)
 {
 	if (type == MS_SHARED) {
 		set_mnt_shared(mnt);
 		return;
 	}
 	do_make_slave(mnt);
 	if (type != MS_SLAVE) {
 		list_del_init(&mnt->mnt_slave);
 		mnt->mnt_master = NULL;
 		if (type == MS_UNBINDABLE)
 			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
 		else
 			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
 	}
 }

 /*
  * get the next mount in the propagation tree.
  * @m: the mount seen last
  * @origin: the original mount from where the tree walk initiated
  *
  * Note that peer groups form contiguous segments of slave lists.
  * We rely on that in get_source() to be able to find out if
  * vfsmount found while iterating with propagation_next() is
  * a peer of one we'd found earlier.
  */
 static struct mount *propagation_next(struct mount *m,
 					 struct mount *origin)
 {
 	/* are there any slaves of this mount? */
 	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 		return first_slave(m);

 	while (1) {
 		struct mount *master = m->mnt_master;

 		if (master == origin->mnt_master) {
 			struct mount *next = next_peer(m);
 			return (next == origin) ? NULL : next;
 		} else if (m->mnt_slave.next != &master->mnt_slave_list)
 			return next_slave(m);

 		/* back at master */
 		m = master;
 	}
 }

 static struct mount *skip_propagation_subtree(struct mount *m,
 						struct mount *origin)
 {
 	/*
 	 * Advance m such that propagation_next will not return
 	 * the slaves of m.
 	 */
 	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 		m = last_slave(m);

 	return m;
 }

 static struct mount *next_group(struct mount *m, struct mount *origin)
 {
 	while (1) {
 		while (1) {
 			struct mount *next;
 			if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 				return first_slave(m);
 			next = next_peer(m);
 			if (m->mnt_group_id == origin->mnt_group_id) {
 				if (next == origin)
 					return NULL;
 			} else if (m->mnt_slave.next != &next->mnt_slave)
 				break;
 			m = next;
 		}
 		/* m is the last peer */
 		while (1) {
 			struct mount *master = m->mnt_master;
 			if (m->mnt_slave.next != &master->mnt_slave_list)
 				return next_slave(m);
 			m = next_peer(master);
 			if (master->mnt_group_id == origin->mnt_group_id)
 				break;
 			if (master->mnt_slave.next == &m->mnt_slave)
 				break;
 			m = master;
 		}
 		if (m == origin)
 			return NULL;
 	}
 }

 /* all accesses are serialized by namespace_sem */
 static struct user_namespace *user_ns;
 static struct mount *last_dest, *first_source, *last_source, *dest_master;
 static struct mountpoint *mp;
 static struct hlist_head *list;

 static inline bool peers(struct mount *m1, struct mount *m2)
 {
 	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
 }

 static int propagate_one(struct mount *m)
 {
 	struct mount *child;
 	int type;
 	/* skip ones added by this propagate_mnt() */
 	if (IS_MNT_NEW(m))
 		return 0;
 	/* skip if mountpoint isn't covered by it */
 	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
 		return 0;
 	if (peers(m, last_dest)) {
 		type = CL_MAKE_SHARED;
 	} else {
 		struct mount *n, *p;
 		bool done;
 		for (n = m; ; n = p) {
 			p = n->mnt_master;
 			if (p == dest_master || IS_MNT_MARKED(p))
 				break;
 		}
 		do {
 			struct mount *parent = last_source->mnt_parent;
 			if (last_source == first_source)
 				break;
 			done = parent->mnt_master == p;
 			if (done && peers(n, parent))
 				break;
 			last_source = last_source->mnt_master;
 		} while (!done);

 		type = CL_SLAVE;
 		/* beginning of peer group among the slaves? */
 		if (IS_MNT_SHARED(m))
 			type |= CL_MAKE_SHARED;
 	}

 	/* Notice when we are propagating across user namespaces */
 	if (m->mnt_ns->user_ns != user_ns)
 		type |= CL_UNPRIVILEGED;
 	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
 	if (IS_ERR(child))
 		return PTR_ERR(child);
 	child->mnt.mnt_flags &= ~MNT_LOCKED;
 	mnt_set_mountpoint(m, mp, child);
 	last_dest = m;
 	last_source = child;
 	if (m->mnt_master != dest_master) {
 		read_seqlock_excl(&mount_lock);
 		SET_MNT_MARK(m->mnt_master);
 		read_sequnlock_excl(&mount_lock);
 	}
 	hlist_add_head(&child->mnt_hash, list);
 	return count_mounts(m->mnt_ns, child);
 }

 /*
  * mount 'source_mnt' under the destination 'dest_mnt' at
  * dentry 'dest_dentry'. And propagate that mount to
  * all the peer and slave mounts of 'dest_mnt'.
  * Link all the new mounts into a propagation tree headed at
  * source_mnt. Also link all the new mounts using ->mnt_list
  * headed at source_mnt's ->mnt_list
  *
  * @dest_mnt: destination mount.
  * @dest_dentry: destination dentry.
  * @source_mnt: source mount.
  * @tree_list : list of heads of trees to be attached.
  */
 int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
 		    struct mount *source_mnt, struct hlist_head *tree_list)
 {
 	struct mount *m, *n;
 	int ret = 0;

 	/*
 	 * we don't want to bother passing tons of arguments to
 	 * propagate_one(); everything is serialized by namespace_sem,
 	 * so globals will do just fine.
 	 */
 	user_ns = current->nsproxy->mnt_ns->user_ns;
 	last_dest = dest_mnt;
 	first_source = source_mnt;
 	last_source = source_mnt;
 	mp = dest_mp;
 	list = tree_list;
 	dest_master = dest_mnt->mnt_master;

 	/* all peers of dest_mnt, except dest_mnt itself */
 	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
 		ret = propagate_one(n);
 		if (ret)
 			goto out;
 	}

 	/* all slave groups */
 	for (m = next_group(dest_mnt, dest_mnt); m;
 			m = next_group(m, dest_mnt)) {
 		/* everything in that slave group */
 		n = m;
 		do {
 			ret = propagate_one(n);
 			if (ret)
 				goto out;
 			n = next_peer(n);
 		} while (n != m);
 	}
 out:
 	read_seqlock_excl(&mount_lock);
 	hlist_for_each_entry(n, tree_list, mnt_hash) {
 		m = n->mnt_parent;
 		if (m->mnt_master != dest_mnt->mnt_master)
 			CLEAR_MNT_MARK(m->mnt_master);
 	}
 	read_sequnlock_excl(&mount_lock);
 	return ret;
 }

 static struct mount *find_topper(struct mount *mnt)
 {
 	/* If there is exactly one mount covering mnt completely return it. */
 	struct mount *child;

 	if (!list_is_singular(&mnt->mnt_mounts))
 		return NULL;

 	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
 	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
 		return NULL;

 	return child;
 }

 /*
  * return true if the refcount is greater than count
  */
 static inline int do_refcount_check(struct mount *mnt, int count)
 {
 	return mnt_get_count(mnt) > count;
 }

 /*
  * check if the mount 'mnt' can be unmounted successfully.
  * @mnt: the mount to be checked for unmount
  * NOTE: unmounting 'mnt' would naturally propagate to all
  * other mounts its parent propagates to.
  * Check if any of these mounts that **do not have submounts**
  * have more references than 'refcnt'. If so return busy.
  *
  * vfsmount lock must be held for write
  */
 int propagate_mount_busy(struct mount *mnt, int refcnt)
 {
 	struct mount *m, *child, *topper;
 	struct mount *parent = mnt->mnt_parent;

 	if (mnt == parent)
 		return do_refcount_check(mnt, refcnt);

 	/*
 	 * quickly check if the current mount can be unmounted.
 	 * If not, we don't have to go checking for all other
 	 * mounts
 	 */
 	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 		return 1;

 	for (m = propagation_next(parent, parent); m;
 	     		m = propagation_next(m, parent)) {
 		int count = 1;
 		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
 		if (!child)
 			continue;

 		/* Is there exactly one mount on the child that covers
 		 * it completely whose reference should be ignored?
 		 */
 		topper = find_topper(child);
 		if (topper)
 			count += 1;
 		else if (!list_empty(&child->mnt_mounts))
 			continue;

 		if (do_refcount_check(child, count))
 			return 1;
 	}
 	return 0;
 }

 /*
  * Clear MNT_LOCKED when it can be shown to be safe.
  *
  * mount_lock lock must be held for write
  */
 void propagate_mount_unlock(struct mount *mnt)
 {
 	struct mount *parent = mnt->mnt_parent;
 	struct mount *m, *child;

 	BUG_ON(parent == mnt);

 	for (m = propagation_next(parent, parent); m;
 			m = propagation_next(m, parent)) {
 		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
 		if (child)
 			child->mnt.mnt_flags &= ~MNT_LOCKED;
 	}
 }

 static void umount_one(struct mount *mnt, struct list_head *to_umount)
 {
 	CLEAR_MNT_MARK(mnt);
 	mnt->mnt.mnt_flags |= MNT_UMOUNT;
 	list_del_init(&mnt->mnt_child);
 	list_del_init(&mnt->mnt_umounting);
 	list_move_tail(&mnt->mnt_list, to_umount);
 }

 /*
  * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
  * parent propagates to.
  */
 static bool __propagate_umount(struct mount *mnt,
 			       struct list_head *to_umount,
 			       struct list_head *to_restore)
 {
 	bool progress = false;
 	struct mount *child;

 	/*
 	 * The state of the parent won't change if this mount is
 	 * already unmounted or marked as without children.
 	 */
 	if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
 		goto out;

 	/* Verify topper is the only grandchild that has not been
 	 * speculatively unmounted.
 	 */
 	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
 		if (child->mnt_mountpoint == mnt->mnt.mnt_root)
 			continue;
 		if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
 			continue;
 		/* Found a mounted child */
 		goto children;
 	}

 	/* Mark mounts that can be unmounted if not locked */
 	SET_MNT_MARK(mnt);
 	progress = true;

 	/* If a mount is without children and not locked umount it. */
 	if (!IS_MNT_LOCKED(mnt)) {
 		umount_one(mnt, to_umount);
 	} else {
 children:
 		list_move_tail(&mnt->mnt_umounting, to_restore);
 	}
 out:
 	return progress;
 }

 static void umount_list(struct list_head *to_umount,
 			struct list_head *to_restore)
 {
 	struct mount *mnt, *child, *tmp;
 	list_for_each_entry(mnt, to_umount, mnt_list) {
 		list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
 			/* topper? */
 			if (child->mnt_mountpoint == mnt->mnt.mnt_root)
 				list_move_tail(&child->mnt_umounting, to_restore);
 			else
 				umount_one(child, to_umount);
 		}
 	}
 }

 static void restore_mounts(struct list_head *to_restore)
 {
 	/* Restore mounts to a clean working state */
 	while (!list_empty(to_restore)) {
 		struct mount *mnt, *parent;
 		struct mountpoint *mp;

 		mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
 		CLEAR_MNT_MARK(mnt);
 		list_del_init(&mnt->mnt_umounting);

 		/* Should this mount be reparented? */
 		mp = mnt->mnt_mp;
 		parent = mnt->mnt_parent;
 		while (parent->mnt.mnt_flags & MNT_UMOUNT) {
 			mp = parent->mnt_mp;
 			parent = parent->mnt_parent;
 		}
 		if (parent != mnt->mnt_parent)
 			mnt_change_mountpoint(parent, mp, mnt);
 	}
 }

 static void cleanup_umount_visitations(struct list_head *visited)
 {
 	while (!list_empty(visited)) {
 		struct mount *mnt =
 			list_first_entry(visited, struct mount, mnt_umounting);
 		list_del_init(&mnt->mnt_umounting);
 	}
 }

 /*
  * collect all mounts that receive propagation from the mount in @list,
  * and return these additional mounts in the same list.
  * @list: the list of mounts to be unmounted.
  *
  * vfsmount lock must be held for write
  */
 int propagate_umount(struct list_head *list)
 {
 	struct mount *mnt;
 	LIST_HEAD(to_restore);
 	LIST_HEAD(to_umount);
 	LIST_HEAD(visited);

 	/* Find candidates for unmounting */
 	list_for_each_entry_reverse(mnt, list, mnt_list) {
 		struct mount *parent = mnt->mnt_parent;
 		struct mount *m;

 		/*
 		 * If this mount has already been visited it is known that it's
 		 * entire peer group and all of their slaves in the propagation
 		 * tree for the mountpoint has already been visited and there is
 		 * no need to visit them again.
 		 */
 		if (!list_empty(&mnt->mnt_umounting))
 			continue;

 		list_add_tail(&mnt->mnt_umounting, &visited);
 		for (m = propagation_next(parent, parent); m;
 		     m = propagation_next(m, parent)) {
 			struct mount *child = __lookup_mnt(&m->mnt,
 							   mnt->mnt_mountpoint);
 			if (!child)
 				continue;

 			if (!list_empty(&child->mnt_umounting)) {
 				/*
 				 * If the child has already been visited it is
 				 * know that it's entire peer group and all of
 				 * their slaves in the propgation tree for the
 				 * mountpoint has already been visited and there
 				 * is no need to visit this subtree again.
 				 */
 				m = skip_propagation_subtree(m, parent);
 				continue;
 			} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
 				/*
 				 * We have come accross an partially unmounted
 				 * mount in list that has not been visited yet.
 				 * Remember it has been visited and continue
 				 * about our merry way.
 				 */
 				list_add_tail(&child->mnt_umounting, &visited);
 				continue;
 			}

 			/* Check the child and parents while progress is made */
 			while (__propagate_umount(child,
 						  &to_umount, &to_restore)) {
 				/* Is the parent a umount candidate? */
 				child = child->mnt_parent;
 				if (list_empty(&child->mnt_umounting))
 					break;
 			}
 		}
 	}

 	umount_list(&to_umount, &to_restore);
 	restore_mounts(&to_restore);
 	cleanup_umount_visitations(&visited);
 	list_splice_tail(&to_umount, list);

 	return 0;
 }

 /*
  *  Iterates over all slaves, and slaves of slaves.
  */
 static struct mount *next_descendent(struct mount *root, struct mount *cur)
 {
 	if (!IS_MNT_NEW(cur) && !list_empty(&cur->mnt_slave_list))
 		return first_slave(cur);
 	do {
 		struct mount *master = cur->mnt_master;

 		if (!master || cur->mnt_slave.next != &master->mnt_slave_list) {
 			struct mount *next = next_slave(cur);

 			return (next == root) ? NULL : next;
 		}
 		cur = master;
 	} while (cur != root);
 	return NULL;
 }

 void propagate_remount(struct mount *mnt)
 {
 	struct mount *m = mnt;
 	struct super_block *sb = mnt->mnt.mnt_sb;

 	if (sb->s_op->copy_mnt_data) {
 		m = next_descendent(mnt, m);
 		while (m) {
 			sb->s_op->copy_mnt_data(m->mnt.data, mnt->mnt.data);
 			m = next_descendent(mnt, m);
 		}
 	}
 }
	/*
	* linux/fs/pnode.c
	*
	* (C) Copyright IBM Corporation 2005.
	* Released under GPL v2.
	* Author : Ram Pai (linuxram@us.ibm.com)
	*
	*/
	#include <linux/mnt_namespace.h>
	#include <linux/mount.h>
	#include <linux/fs.h>
	#include <linux/nsproxy.h>
	#include "internal.h"
	#include "pnode.h"

	/* return the next shared peer mount of @p */
	static inline struct mount next_peer(struct mount p)
	{
	return list_entry(p->mnt_share.next, struct mount, mnt_share);
	}

	static inline struct mount first_slave(struct mount p)
	{
	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
	}

	static inline struct mount last_slave(struct mount p)
	{
	return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
	}

	static inline struct mount next_slave(struct mount p)
	{
	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
	}

	static struct mount get_peer_under_root(struct mount mnt,
	struct mnt_namespace *ns,
	const struct path *root)
	{
	struct mount *m = mnt;

	do {
	/* Check the namespace first for optimization */
	if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
	return m;

	m = next_peer(m);
	} while (m != mnt);

	return NULL;
	}

	/*
	* Get ID of closest dominating peer group having a representative
	* under the given root.
	*
	* Caller must hold namespace_sem
	*/
	int get_dominating_id(struct mount mnt, const struct path root)
	{
	struct mount *m;

	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
	struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
	if (d)
	return d->mnt_group_id;
	}

	return 0;
	}

	static int do_make_slave(struct mount *mnt)
	{
	struct mount peer_mnt = mnt, master = mnt->mnt_master;
	struct mount *slave_mnt;

	/*
	* slave 'mnt' to a peer mount that has the
	* same root dentry. If none is available then
	* slave it to anything that is available.
	*/
	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
	peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;

	if (peer_mnt == mnt) {
	peer_mnt = next_peer(mnt);
	if (peer_mnt == mnt)
	peer_mnt = NULL;
	}
	if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
	list_empty(&mnt->mnt_share))
	mnt_release_group_id(mnt);

	list_del_init(&mnt->mnt_share);
	mnt->mnt_group_id = 0;

	if (peer_mnt)
	master = peer_mnt;

	if (master) {
	list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
	slave_mnt->mnt_master = master;
	list_move(&mnt->mnt_slave, &master->mnt_slave_list);
	list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
	INIT_LIST_HEAD(&mnt->mnt_slave_list);
	} else {
	struct list_head *p = &mnt->mnt_slave_list;
	while (!list_empty(p)) {
	slave_mnt = list_first_entry(p,
	struct mount, mnt_slave);
	list_del_init(&slave_mnt->mnt_slave);
	slave_mnt->mnt_master = NULL;
	}
	}
	mnt->mnt_master = master;
	CLEAR_MNT_SHARED(mnt);
	return 0;
	}

	/*
	* vfsmount lock must be held for write
	*/
	void change_mnt_propagation(struct mount *mnt, int type)
	{
	if (type == MS_SHARED) {
	set_mnt_shared(mnt);
	return;
	}
	do_make_slave(mnt);
	if (type != MS_SLAVE) {
	list_del_init(&mnt->mnt_slave);
	mnt->mnt_master = NULL;
	if (type == MS_UNBINDABLE)
	mnt->mnt.mnt_flags \|= MNT_UNBINDABLE;
	else
	mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
	}
	}

	/*
	* get the next mount in the propagation tree.
	* @m: the mount seen last
	* @origin: the original mount from where the tree walk initiated
	*
	* Note that peer groups form contiguous segments of slave lists.
	* We rely on that in get_source() to be able to find out if
	* vfsmount found while iterating with propagation_next() is
	* a peer of one we'd found earlier.
	*/
	static struct mount propagation_next(struct mount m,
	struct mount *origin)
	{
	/* are there any slaves of this mount? */
	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
	return first_slave(m);

	while (1) {
	struct mount *master = m->mnt_master;

	if (master == origin->mnt_master) {
	struct mount *next = next_peer(m);
	return (next == origin) ? NULL : next;
	} else if (m->mnt_slave.next != &master->mnt_slave_list)
	return next_slave(m);

	/* back at master */
	m = master;
	}
	}

	static struct mount skip_propagation_subtree(struct mount m,
	struct mount *origin)
	{
	/*
	* Advance m such that propagation_next will not return
	* the slaves of m.
	*/
	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
	m = last_slave(m);

	return m;
	}

	static struct mount next_group(struct mount m, struct mount *origin)
	{
	while (1) {
	while (1) {
	struct mount *next;
	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
	return first_slave(m);
	next = next_peer(m);
	if (m->mnt_group_id == origin->mnt_group_id) {
	if (next == origin)
	return NULL;
	} else if (m->mnt_slave.next != &next->mnt_slave)
	break;
	m = next;
	}
	/* m is the last peer */
	while (1) {
	struct mount *master = m->mnt_master;
	if (m->mnt_slave.next != &master->mnt_slave_list)
	return next_slave(m);
	m = next_peer(master);
	if (master->mnt_group_id == origin->mnt_group_id)
	break;
	if (master->mnt_slave.next == &m->mnt_slave)
	break;
	m = master;
	}
	if (m == origin)
	return NULL;
	}
	}

	/* all accesses are serialized by namespace_sem */
	static struct user_namespace *user_ns;
	static struct mount last_dest, first_source, last_source, dest_master;
	static struct mountpoint *mp;
	static struct hlist_head *list;

	static inline bool peers(struct mount m1, struct mount m2)
	{
	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
	}

	static int propagate_one(struct mount *m)
	{
	struct mount *child;
	int type;
	/* skip ones added by this propagate_mnt() */
	if (IS_MNT_NEW(m))
	return 0;
	/* skip if mountpoint isn't covered by it */
	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
	return 0;
	if (peers(m, last_dest)) {
	type = CL_MAKE_SHARED;
	} else {
	struct mount n, p;
	bool done;
	for (n = m; ; n = p) {
	p = n->mnt_master;
	if (p == dest_master \|\| IS_MNT_MARKED(p))
	break;
	}
	do {
	struct mount *parent = last_source->mnt_parent;
	if (last_source == first_source)
	break;
	done = parent->mnt_master == p;
	if (done && peers(n, parent))
	break;
	last_source = last_source->mnt_master;
	} while (!done);

	type = CL_SLAVE;
	/* beginning of peer group among the slaves? */
	if (IS_MNT_SHARED(m))
	type \|= CL_MAKE_SHARED;
	}

	/* Notice when we are propagating across user namespaces */
	if (m->mnt_ns->user_ns != user_ns)
	type \|= CL_UNPRIVILEGED;
	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
	if (IS_ERR(child))
	return PTR_ERR(child);
	child->mnt.mnt_flags &= ~MNT_LOCKED;
	mnt_set_mountpoint(m, mp, child);
	last_dest = m;
	last_source = child;
	if (m->mnt_master != dest_master) {
	read_seqlock_excl(&mount_lock);
	SET_MNT_MARK(m->mnt_master);
	read_sequnlock_excl(&mount_lock);
	}
	hlist_add_head(&child->mnt_hash, list);
	return count_mounts(m->mnt_ns, child);
	}

	/*
	* mount 'source_mnt' under the destination 'dest_mnt' at
	* dentry 'dest_dentry'. And propagate that mount to
	* all the peer and slave mounts of 'dest_mnt'.
	* Link all the new mounts into a propagation tree headed at
	* source_mnt. Also link all the new mounts using ->mnt_list
	* headed at source_mnt's ->mnt_list
	*
	* @dest_mnt: destination mount.
	* @dest_dentry: destination dentry.
	* @source_mnt: source mount.
	* @tree_list : list of heads of trees to be attached.
	*/
	int propagate_mnt(struct mount dest_mnt, struct mountpoint dest_mp,
	struct mount source_mnt, struct hlist_head tree_list)
	{
	struct mount m, n;
	int ret = 0;

	/*
	* we don't want to bother passing tons of arguments to
	* propagate_one(); everything is serialized by namespace_sem,
	* so globals will do just fine.
	*/
	user_ns = current->nsproxy->mnt_ns->user_ns;
	last_dest = dest_mnt;
	first_source = source_mnt;
	last_source = source_mnt;
	mp = dest_mp;
	list = tree_list;
	dest_master = dest_mnt->mnt_master;

	/* all peers of dest_mnt, except dest_mnt itself */
	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
	ret = propagate_one(n);
	if (ret)
	goto out;
	}

	/* all slave groups */
	for (m = next_group(dest_mnt, dest_mnt); m;
	m = next_group(m, dest_mnt)) {
	/* everything in that slave group */
	n = m;
	do {
	ret = propagate_one(n);
	if (ret)
	goto out;
	n = next_peer(n);
	} while (n != m);
	}
	out:
	read_seqlock_excl(&mount_lock);
	hlist_for_each_entry(n, tree_list, mnt_hash) {
	m = n->mnt_parent;
	if (m->mnt_master != dest_mnt->mnt_master)
	CLEAR_MNT_MARK(m->mnt_master);
	}
	read_sequnlock_excl(&mount_lock);
	return ret;
	}

	static struct mount find_topper(struct mount mnt)
	{
	/* If there is exactly one mount covering mnt completely return it. */
	struct mount *child;

	if (!list_is_singular(&mnt->mnt_mounts))
	return NULL;

	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
	return NULL;

	return child;
	}

	/*
	* return true if the refcount is greater than count
	*/
	static inline int do_refcount_check(struct mount *mnt, int count)
	{
	return mnt_get_count(mnt) > count;
	}

	/*
	* check if the mount 'mnt' can be unmounted successfully.
	* @mnt: the mount to be checked for unmount
	* NOTE: unmounting 'mnt' would naturally propagate to all
	* other mounts its parent propagates to.
	* Check if any of these mounts that do not have submounts
	* have more references than 'refcnt'. If so return busy.
	*
	* vfsmount lock must be held for write
	*/
	int propagate_mount_busy(struct mount *mnt, int refcnt)
	{
	struct mount m, child, *topper;
	struct mount *parent = mnt->mnt_parent;

	if (mnt == parent)
	return do_refcount_check(mnt, refcnt);

	/*
	* quickly check if the current mount can be unmounted.
	* If not, we don't have to go checking for all other
	* mounts
	*/
	if (!list_empty(&mnt->mnt_mounts) \|\| do_refcount_check(mnt, refcnt))
	return 1;

	for (m = propagation_next(parent, parent); m;
	m = propagation_next(m, parent)) {
	int count = 1;
	child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
	if (!child)
	continue;

	/* Is there exactly one mount on the child that covers
	* it completely whose reference should be ignored?
	*/
	topper = find_topper(child);
	if (topper)
	count += 1;
	else if (!list_empty(&child->mnt_mounts))
	continue;

	if (do_refcount_check(child, count))
	return 1;
	}
	return 0;
	}

	/*
	* Clear MNT_LOCKED when it can be shown to be safe.
	*
	* mount_lock lock must be held for write
	*/
	void propagate_mount_unlock(struct mount *mnt)
	{
	struct mount *parent = mnt->mnt_parent;
	struct mount m, child;

	BUG_ON(parent == mnt);

	for (m = propagation_next(parent, parent); m;
	m = propagation_next(m, parent)) {
	child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
	if (child)
	child->mnt.mnt_flags &= ~MNT_LOCKED;
	}
	}

	static void umount_one(struct mount mnt, struct list_head to_umount)
	{
	CLEAR_MNT_MARK(mnt);
	mnt->mnt.mnt_flags \|= MNT_UMOUNT;
	list_del_init(&mnt->mnt_child);
	list_del_init(&mnt->mnt_umounting);
	list_move_tail(&mnt->mnt_list, to_umount);
	}

	/*
	* NOTE: unmounting 'mnt' naturally propagates to all other mounts its
	* parent propagates to.
	*/
	static bool __propagate_umount(struct mount *mnt,
	struct list_head *to_umount,
	struct list_head *to_restore)
	{
	bool progress = false;
	struct mount *child;

	/*
	* The state of the parent won't change if this mount is
	* already unmounted or marked as without children.
	*/
	if (mnt->mnt.mnt_flags & (MNT_UMOUNT \| MNT_MARKED))
	goto out;

	/* Verify topper is the only grandchild that has not been
	* speculatively unmounted.
	*/
	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
	if (child->mnt_mountpoint == mnt->mnt.mnt_root)
	continue;
	if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
	continue;
	/* Found a mounted child */
	goto children;
	}

	/* Mark mounts that can be unmounted if not locked */
	SET_MNT_MARK(mnt);
	progress = true;

	/* If a mount is without children and not locked umount it. */
	if (!IS_MNT_LOCKED(mnt)) {
	umount_one(mnt, to_umount);
	} else {
	children:
	list_move_tail(&mnt->mnt_umounting, to_restore);
	}
	out:
	return progress;
	}

	static void umount_list(struct list_head *to_umount,
	struct list_head *to_restore)
	{
	struct mount mnt, child, *tmp;
	list_for_each_entry(mnt, to_umount, mnt_list) {
	list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
	/* topper? */
	if (child->mnt_mountpoint == mnt->mnt.mnt_root)
	list_move_tail(&child->mnt_umounting, to_restore);
	else
	umount_one(child, to_umount);
	}
	}
	}

	static void restore_mounts(struct list_head *to_restore)
	{
	/* Restore mounts to a clean working state */
	while (!list_empty(to_restore)) {
	struct mount mnt, parent;
	struct mountpoint *mp;

	mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
	CLEAR_MNT_MARK(mnt);
	list_del_init(&mnt->mnt_umounting);

	/* Should this mount be reparented? */
	mp = mnt->mnt_mp;
	parent = mnt->mnt_parent;
	while (parent->mnt.mnt_flags & MNT_UMOUNT) {
	mp = parent->mnt_mp;
	parent = parent->mnt_parent;
	}
	if (parent != mnt->mnt_parent)
	mnt_change_mountpoint(parent, mp, mnt);
	}
	}

	static void cleanup_umount_visitations(struct list_head *visited)
	{
	while (!list_empty(visited)) {
	struct mount *mnt =
	list_first_entry(visited, struct mount, mnt_umounting);
	list_del_init(&mnt->mnt_umounting);
	}
	}

	/*
	* collect all mounts that receive propagation from the mount in @list,
	* and return these additional mounts in the same list.
	* @list: the list of mounts to be unmounted.
	*
	* vfsmount lock must be held for write
	*/
	int propagate_umount(struct list_head *list)
	{
	struct mount *mnt;
	LIST_HEAD(to_restore);
	LIST_HEAD(to_umount);
	LIST_HEAD(visited);

	/* Find candidates for unmounting */
	list_for_each_entry_reverse(mnt, list, mnt_list) {
	struct mount *parent = mnt->mnt_parent;
	struct mount *m;

	/*
	* If this mount has already been visited it is known that it's
	* entire peer group and all of their slaves in the propagation
	* tree for the mountpoint has already been visited and there is
	* no need to visit them again.
	*/
	if (!list_empty(&mnt->mnt_umounting))
	continue;

	list_add_tail(&mnt->mnt_umounting, &visited);
	for (m = propagation_next(parent, parent); m;
	m = propagation_next(m, parent)) {
	struct mount *child = __lookup_mnt(&m->mnt,
	mnt->mnt_mountpoint);
	if (!child)
	continue;

	if (!list_empty(&child->mnt_umounting)) {
	/*
	* If the child has already been visited it is
	* know that it's entire peer group and all of
	* their slaves in the propgation tree for the
	* mountpoint has already been visited and there
	* is no need to visit this subtree again.
	*/
	m = skip_propagation_subtree(m, parent);
	continue;
	} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
	/*
	* We have come accross an partially unmounted
	* mount in list that has not been visited yet.
	* Remember it has been visited and continue
	* about our merry way.
	*/
	list_add_tail(&child->mnt_umounting, &visited);
	continue;
	}

	/* Check the child and parents while progress is made */
	while (__propagate_umount(child,
	&to_umount, &to_restore)) {
	/* Is the parent a umount candidate? */
	child = child->mnt_parent;
	if (list_empty(&child->mnt_umounting))
	break;
	}
	}
	}

	umount_list(&to_umount, &to_restore);
	restore_mounts(&to_restore);
	cleanup_umount_visitations(&visited);
	list_splice_tail(&to_umount, list);

	return 0;
	}

	/*
	* Iterates over all slaves, and slaves of slaves.
	*/
	static struct mount next_descendent(struct mount root, struct mount *cur)
	{
	if (!IS_MNT_NEW(cur) && !list_empty(&cur->mnt_slave_list))
	return first_slave(cur);
	do {
	struct mount *master = cur->mnt_master;

	if (!master \|\| cur->mnt_slave.next != &master->mnt_slave_list) {
	struct mount *next = next_slave(cur);

	return (next == root) ? NULL : next;
	}
	cur = master;
	} while (cur != root);
	return NULL;
	}

	void propagate_remount(struct mount *mnt)
	{
	struct mount *m = mnt;
	struct super_block *sb = mnt->mnt.mnt_sb;

	if (sb->s_op->copy_mnt_data) {
	m = next_descendent(mnt, m);
	while (m) {
	sb->s_op->copy_mnt_data(m->mnt.data, mnt->mnt.data);
	m = next_descendent(mnt, m);
	}
	}
	}