linux/fs/pnode.c
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   1/*
   2 *  linux/fs/pnode.c
   3 *
   4 * (C) Copyright IBM Corporation 2005.
   5 *      Released under GPL v2.
   6 *      Author : Ram Pai (linuxram@us.ibm.com)
   7 *
   8 */
   9#include <linux/mnt_namespace.h>
  10#include <linux/mount.h>
  11#include <linux/fs.h>
  12#include <linux/nsproxy.h>
  13#include "internal.h"
  14#include "pnode.h"
  15
  16/* return the next shared peer mount of @p */
  17static inline struct mount *next_peer(struct mount *p)
  18{
  19        return list_entry(p->mnt_share.next, struct mount, mnt_share);
  20}
  21
  22static inline struct mount *first_slave(struct mount *p)
  23{
  24        return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
  25}
  26
  27static inline struct mount *next_slave(struct mount *p)
  28{
  29        return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
  30}
  31
  32static struct mount *get_peer_under_root(struct mount *mnt,
  33                                         struct mnt_namespace *ns,
  34                                         const struct path *root)
  35{
  36        struct mount *m = mnt;
  37
  38        do {
  39                /* Check the namespace first for optimization */
  40                if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
  41                        return m;
  42
  43                m = next_peer(m);
  44        } while (m != mnt);
  45
  46        return NULL;
  47}
  48
  49/*
  50 * Get ID of closest dominating peer group having a representative
  51 * under the given root.
  52 *
  53 * Caller must hold namespace_sem
  54 */
  55int get_dominating_id(struct mount *mnt, const struct path *root)
  56{
  57        struct mount *m;
  58
  59        for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
  60                struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
  61                if (d)
  62                        return d->mnt_group_id;
  63        }
  64
  65        return 0;
  66}
  67
  68static int do_make_slave(struct mount *mnt)
  69{
  70        struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
  71        struct mount *slave_mnt;
  72
  73        /*
  74         * slave 'mnt' to a peer mount that has the
  75         * same root dentry. If none is available then
  76         * slave it to anything that is available.
  77         */
  78        while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  79               peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
  80
  81        if (peer_mnt == mnt) {
  82                peer_mnt = next_peer(mnt);
  83                if (peer_mnt == mnt)
  84                        peer_mnt = NULL;
  85        }
  86        if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
  87            list_empty(&mnt->mnt_share))
  88                mnt_release_group_id(mnt);
  89
  90        list_del_init(&mnt->mnt_share);
  91        mnt->mnt_group_id = 0;
  92
  93        if (peer_mnt)
  94                master = peer_mnt;
  95
  96        if (master) {
  97                list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
  98                        slave_mnt->mnt_master = master;
  99                list_move(&mnt->mnt_slave, &master->mnt_slave_list);
 100                list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
 101                INIT_LIST_HEAD(&mnt->mnt_slave_list);
 102        } else {
 103                struct list_head *p = &mnt->mnt_slave_list;
 104                while (!list_empty(p)) {
 105                        slave_mnt = list_first_entry(p,
 106                                        struct mount, mnt_slave);
 107                        list_del_init(&slave_mnt->mnt_slave);
 108                        slave_mnt->mnt_master = NULL;
 109                }
 110        }
 111        mnt->mnt_master = master;
 112        CLEAR_MNT_SHARED(mnt);
 113        return 0;
 114}
 115
 116/*
 117 * vfsmount lock must be held for write
 118 */
 119void change_mnt_propagation(struct mount *mnt, int type)
 120{
 121        if (type == MS_SHARED) {
 122                set_mnt_shared(mnt);
 123                return;
 124        }
 125        do_make_slave(mnt);
 126        if (type != MS_SLAVE) {
 127                list_del_init(&mnt->mnt_slave);
 128                mnt->mnt_master = NULL;
 129                if (type == MS_UNBINDABLE)
 130                        mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
 131                else
 132                        mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
 133        }
 134}
 135
 136/*
 137 * get the next mount in the propagation tree.
 138 * @m: the mount seen last
 139 * @origin: the original mount from where the tree walk initiated
 140 *
 141 * Note that peer groups form contiguous segments of slave lists.
 142 * We rely on that in get_source() to be able to find out if
 143 * vfsmount found while iterating with propagation_next() is
 144 * a peer of one we'd found earlier.
 145 */
 146static struct mount *propagation_next(struct mount *m,
 147                                         struct mount *origin)
 148{
 149        /* are there any slaves of this mount? */
 150        if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 151                return first_slave(m);
 152
 153        while (1) {
 154                struct mount *master = m->mnt_master;
 155
 156                if (master == origin->mnt_master) {
 157                        struct mount *next = next_peer(m);
 158                        return (next == origin) ? NULL : next;
 159                } else if (m->mnt_slave.next != &master->mnt_slave_list)
 160                        return next_slave(m);
 161
 162                /* back at master */
 163                m = master;
 164        }
 165}
 166
 167static struct mount *next_group(struct mount *m, struct mount *origin)
 168{
 169        while (1) {
 170                while (1) {
 171                        struct mount *next;
 172                        if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
 173                                return first_slave(m);
 174                        next = next_peer(m);
 175                        if (m->mnt_group_id == origin->mnt_group_id) {
 176                                if (next == origin)
 177                                        return NULL;
 178                        } else if (m->mnt_slave.next != &next->mnt_slave)
 179                                break;
 180                        m = next;
 181                }
 182                /* m is the last peer */
 183                while (1) {
 184                        struct mount *master = m->mnt_master;
 185                        if (m->mnt_slave.next != &master->mnt_slave_list)
 186                                return next_slave(m);
 187                        m = next_peer(master);
 188                        if (master->mnt_group_id == origin->mnt_group_id)
 189                                break;
 190                        if (master->mnt_slave.next == &m->mnt_slave)
 191                                break;
 192                        m = master;
 193                }
 194                if (m == origin)
 195                        return NULL;
 196        }
 197}
 198
 199/* all accesses are serialized by namespace_sem */
 200static struct user_namespace *user_ns;
 201static struct mount *last_dest, *first_source, *last_source, *dest_master;
 202static struct mountpoint *mp;
 203static struct hlist_head *list;
 204
 205static inline bool peers(struct mount *m1, struct mount *m2)
 206{
 207        return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
 208}
 209
 210static int propagate_one(struct mount *m)
 211{
 212        struct mount *child;
 213        int type;
 214        /* skip ones added by this propagate_mnt() */
 215        if (IS_MNT_NEW(m))
 216                return 0;
 217        /* skip if mountpoint isn't covered by it */
 218        if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
 219                return 0;
 220        if (peers(m, last_dest)) {
 221                type = CL_MAKE_SHARED;
 222        } else {
 223                struct mount *n, *p;
 224                bool done;
 225                for (n = m; ; n = p) {
 226                        p = n->mnt_master;
 227                        if (p == dest_master || IS_MNT_MARKED(p))
 228                                break;
 229                }
 230                do {
 231                        struct mount *parent = last_source->mnt_parent;
 232                        if (last_source == first_source)
 233                                break;
 234                        done = parent->mnt_master == p;
 235                        if (done && peers(n, parent))
 236                                break;
 237                        last_source = last_source->mnt_master;
 238                } while (!done);
 239
 240                type = CL_SLAVE;
 241                /* beginning of peer group among the slaves? */
 242                if (IS_MNT_SHARED(m))
 243                        type |= CL_MAKE_SHARED;
 244        }
 245                
 246        /* Notice when we are propagating across user namespaces */
 247        if (m->mnt_ns->user_ns != user_ns)
 248                type |= CL_UNPRIVILEGED;
 249        child = copy_tree(last_source, last_source->mnt.mnt_root, type);
 250        if (IS_ERR(child))
 251                return PTR_ERR(child);
 252        child->mnt.mnt_flags &= ~MNT_LOCKED;
 253        mnt_set_mountpoint(m, mp, child);
 254        last_dest = m;
 255        last_source = child;
 256        if (m->mnt_master != dest_master) {
 257                read_seqlock_excl(&mount_lock);
 258                SET_MNT_MARK(m->mnt_master);
 259                read_sequnlock_excl(&mount_lock);
 260        }
 261        hlist_add_head(&child->mnt_hash, list);
 262        return count_mounts(m->mnt_ns, child);
 263}
 264
 265/*
 266 * mount 'source_mnt' under the destination 'dest_mnt' at
 267 * dentry 'dest_dentry'. And propagate that mount to
 268 * all the peer and slave mounts of 'dest_mnt'.
 269 * Link all the new mounts into a propagation tree headed at
 270 * source_mnt. Also link all the new mounts using ->mnt_list
 271 * headed at source_mnt's ->mnt_list
 272 *
 273 * @dest_mnt: destination mount.
 274 * @dest_dentry: destination dentry.
 275 * @source_mnt: source mount.
 276 * @tree_list : list of heads of trees to be attached.
 277 */
 278int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
 279                    struct mount *source_mnt, struct hlist_head *tree_list)
 280{
 281        struct mount *m, *n;
 282        int ret = 0;
 283
 284        /*
 285         * we don't want to bother passing tons of arguments to
 286         * propagate_one(); everything is serialized by namespace_sem,
 287         * so globals will do just fine.
 288         */
 289        user_ns = current->nsproxy->mnt_ns->user_ns;
 290        last_dest = dest_mnt;
 291        first_source = source_mnt;
 292        last_source = source_mnt;
 293        mp = dest_mp;
 294        list = tree_list;
 295        dest_master = dest_mnt->mnt_master;
 296
 297        /* all peers of dest_mnt, except dest_mnt itself */
 298        for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
 299                ret = propagate_one(n);
 300                if (ret)
 301                        goto out;
 302        }
 303
 304        /* all slave groups */
 305        for (m = next_group(dest_mnt, dest_mnt); m;
 306                        m = next_group(m, dest_mnt)) {
 307                /* everything in that slave group */
 308                n = m;
 309                do {
 310                        ret = propagate_one(n);
 311                        if (ret)
 312                                goto out;
 313                        n = next_peer(n);
 314                } while (n != m);
 315        }
 316out:
 317        read_seqlock_excl(&mount_lock);
 318        hlist_for_each_entry(n, tree_list, mnt_hash) {
 319                m = n->mnt_parent;
 320                if (m->mnt_master != dest_mnt->mnt_master)
 321                        CLEAR_MNT_MARK(m->mnt_master);
 322        }
 323        read_sequnlock_excl(&mount_lock);
 324        return ret;
 325}
 326
 327/*
 328 * return true if the refcount is greater than count
 329 */
 330static inline int do_refcount_check(struct mount *mnt, int count)
 331{
 332        return mnt_get_count(mnt) > count;
 333}
 334
 335/*
 336 * check if the mount 'mnt' can be unmounted successfully.
 337 * @mnt: the mount to be checked for unmount
 338 * NOTE: unmounting 'mnt' would naturally propagate to all
 339 * other mounts its parent propagates to.
 340 * Check if any of these mounts that **do not have submounts**
 341 * have more references than 'refcnt'. If so return busy.
 342 *
 343 * vfsmount lock must be held for write
 344 */
 345int propagate_mount_busy(struct mount *mnt, int refcnt)
 346{
 347        struct mount *m, *child;
 348        struct mount *parent = mnt->mnt_parent;
 349        int ret = 0;
 350
 351        if (mnt == parent)
 352                return do_refcount_check(mnt, refcnt);
 353
 354        /*
 355         * quickly check if the current mount can be unmounted.
 356         * If not, we don't have to go checking for all other
 357         * mounts
 358         */
 359        if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
 360                return 1;
 361
 362        for (m = propagation_next(parent, parent); m;
 363                        m = propagation_next(m, parent)) {
 364                child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
 365                if (child && list_empty(&child->mnt_mounts) &&
 366                    (ret = do_refcount_check(child, 1)))
 367                        break;
 368        }
 369        return ret;
 370}
 371
 372/*
 373 * Clear MNT_LOCKED when it can be shown to be safe.
 374 *
 375 * mount_lock lock must be held for write
 376 */
 377void propagate_mount_unlock(struct mount *mnt)
 378{
 379        struct mount *parent = mnt->mnt_parent;
 380        struct mount *m, *child;
 381
 382        BUG_ON(parent == mnt);
 383
 384        for (m = propagation_next(parent, parent); m;
 385                        m = propagation_next(m, parent)) {
 386                child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
 387                if (child)
 388                        child->mnt.mnt_flags &= ~MNT_LOCKED;
 389        }
 390}
 391
 392/*
 393 * Mark all mounts that the MNT_LOCKED logic will allow to be unmounted.
 394 */
 395static void mark_umount_candidates(struct mount *mnt)
 396{
 397        struct mount *parent = mnt->mnt_parent;
 398        struct mount *m;
 399
 400        BUG_ON(parent == mnt);
 401
 402        for (m = propagation_next(parent, parent); m;
 403                        m = propagation_next(m, parent)) {
 404                struct mount *child = __lookup_mnt_last(&m->mnt,
 405                                                mnt->mnt_mountpoint);
 406                if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
 407                        SET_MNT_MARK(child);
 408                }
 409        }
 410}
 411
 412/*
 413 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 414 * parent propagates to.
 415 */
 416static void __propagate_umount(struct mount *mnt)
 417{
 418        struct mount *parent = mnt->mnt_parent;
 419        struct mount *m;
 420
 421        BUG_ON(parent == mnt);
 422
 423        for (m = propagation_next(parent, parent); m;
 424                        m = propagation_next(m, parent)) {
 425
 426                struct mount *child = __lookup_mnt_last(&m->mnt,
 427                                                mnt->mnt_mountpoint);
 428                /*
 429                 * umount the child only if the child has no children
 430                 * and the child is marked safe to unmount.
 431                 */
 432                if (!child || !IS_MNT_MARKED(child))
 433                        continue;
 434                CLEAR_MNT_MARK(child);
 435                if (list_empty(&child->mnt_mounts)) {
 436                        list_del_init(&child->mnt_child);
 437                        child->mnt.mnt_flags |= MNT_UMOUNT;
 438                        list_move_tail(&child->mnt_list, &mnt->mnt_list);
 439                }
 440        }
 441}
 442
 443/*
 444 * collect all mounts that receive propagation from the mount in @list,
 445 * and return these additional mounts in the same list.
 446 * @list: the list of mounts to be unmounted.
 447 *
 448 * vfsmount lock must be held for write
 449 */
 450int propagate_umount(struct list_head *list)
 451{
 452        struct mount *mnt;
 453
 454        list_for_each_entry_reverse(mnt, list, mnt_list)
 455                mark_umount_candidates(mnt);
 456
 457        list_for_each_entry(mnt, list, mnt_list)
 458                __propagate_umount(mnt);
 459        return 0;
 460}
 461