Linux 5.8-rc4

[linux/fpc-iii.git] / fs / pnode.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/pnode.c
 *
 * (C) Copyright IBM Corporation 2005.
 *      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 <uapi/linux/mount.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 *master, *slave_mnt;

        if (list_empty(&mnt->mnt_share)) {
                if (IS_MNT_SHARED(mnt)) {
                        mnt_release_group_id(mnt);
                        CLEAR_MNT_SHARED(mnt);
                }
                master = mnt->mnt_master;
                if (!master) {
                        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;
                        }
                        return 0;
                }
        } else {
                struct mount *m;
                /*
                 * slave 'mnt' to a peer mount that has the
                 * same root dentry. If none is available then
                 * slave it to anything that is available.
                 */
                for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
                        if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
                                master = m;
                                break;
                        }
                }
                list_del_init(&mnt->mnt_share);
                mnt->mnt_group_id = 0;
                CLEAR_MNT_SHARED(mnt);
        }
        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);
        mnt->mnt_master = master;
        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 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;
        }
                
        child = copy_tree(last_source, last_source->mnt.mnt_root, type);
        if (IS_ERR(child))
                return PTR_ERR(child);
        read_seqlock_excl(&mount_lock);
        mnt_set_mountpoint(m, mp, child);
        if (m->mnt_master != dest_master)
                SET_MNT_MARK(m->mnt_master);
        read_sequnlock_excl(&mount_lock);
        last_dest = m;
        last_source = child;
        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.
         */
        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;
}