linux/fs/super.c
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   1/*
   2 *  linux/fs/super.c
   3 *
   4 *  Copyright (C) 1991, 1992  Linus Torvalds
   5 *
   6 *  super.c contains code to handle: - mount structures
   7 *                                   - super-block tables
   8 *                                   - filesystem drivers list
   9 *                                   - mount system call
  10 *                                   - umount system call
  11 *                                   - ustat system call
  12 *
  13 * GK 2/5/95  -  Changed to support mounting the root fs via NFS
  14 *
  15 *  Added kerneld support: Jacques Gelinas and Bjorn Ekwall
  16 *  Added change_root: Werner Almesberger & Hans Lermen, Feb '96
  17 *  Added options to /proc/mounts:
  18 *    Torbjörn Lindh (torbjorn.lindh@gopta.se), April 14, 1996.
  19 *  Added devfs support: Richard Gooch <rgooch@atnf.csiro.au>, 13-JAN-1998
  20 *  Heavily rewritten for 'one fs - one tree' dcache architecture. AV, Mar 2000
  21 */
  22
  23#include <linux/export.h>
  24#include <linux/slab.h>
  25#include <linux/acct.h>
  26#include <linux/blkdev.h>
  27#include <linux/mount.h>
  28#include <linux/security.h>
  29#include <linux/writeback.h>            /* for the emergency remount stuff */
  30#include <linux/idr.h>
  31#include <linux/mutex.h>
  32#include <linux/backing-dev.h>
  33#include <linux/rculist_bl.h>
  34#include <linux/cleancache.h>
  35#include <linux/fsnotify.h>
  36#include <linux/lockdep.h>
  37#include "internal.h"
  38
  39
  40LIST_HEAD(super_blocks);
  41DEFINE_SPINLOCK(sb_lock);
  42
  43static char *sb_writers_name[SB_FREEZE_LEVELS] = {
  44        "sb_writers",
  45        "sb_pagefaults",
  46        "sb_internal",
  47};
  48
  49/*
  50 * One thing we have to be careful of with a per-sb shrinker is that we don't
  51 * drop the last active reference to the superblock from within the shrinker.
  52 * If that happens we could trigger unregistering the shrinker from within the
  53 * shrinker path and that leads to deadlock on the shrinker_rwsem. Hence we
  54 * take a passive reference to the superblock to avoid this from occurring.
  55 */
  56static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
  57{
  58        struct super_block *sb;
  59        int     fs_objects = 0;
  60        int     total_objects;
  61
  62        sb = container_of(shrink, struct super_block, s_shrink);
  63
  64        /*
  65         * Deadlock avoidance.  We may hold various FS locks, and we don't want
  66         * to recurse into the FS that called us in clear_inode() and friends..
  67         */
  68        if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
  69                return -1;
  70
  71        if (!grab_super_passive(sb))
  72                return -1;
  73
  74        if (sb->s_op && sb->s_op->nr_cached_objects)
  75                fs_objects = sb->s_op->nr_cached_objects(sb);
  76
  77        total_objects = sb->s_nr_dentry_unused +
  78                        sb->s_nr_inodes_unused + fs_objects + 1;
  79
  80        if (sc->nr_to_scan) {
  81                int     dentries;
  82                int     inodes;
  83
  84                /* proportion the scan between the caches */
  85                dentries = (sc->nr_to_scan * sb->s_nr_dentry_unused) /
  86                                                        total_objects;
  87                inodes = (sc->nr_to_scan * sb->s_nr_inodes_unused) /
  88                                                        total_objects;
  89                if (fs_objects)
  90                        fs_objects = (sc->nr_to_scan * fs_objects) /
  91                                                        total_objects;
  92                /*
  93                 * prune the dcache first as the icache is pinned by it, then
  94                 * prune the icache, followed by the filesystem specific caches
  95                 */
  96                prune_dcache_sb(sb, dentries);
  97                prune_icache_sb(sb, inodes);
  98
  99                if (fs_objects && sb->s_op->free_cached_objects) {
 100                        sb->s_op->free_cached_objects(sb, fs_objects);
 101                        fs_objects = sb->s_op->nr_cached_objects(sb);
 102                }
 103                total_objects = sb->s_nr_dentry_unused +
 104                                sb->s_nr_inodes_unused + fs_objects;
 105        }
 106
 107        total_objects = (total_objects / 100) * sysctl_vfs_cache_pressure;
 108        drop_super(sb);
 109        return total_objects;
 110}
 111
 112static int init_sb_writers(struct super_block *s, struct file_system_type *type)
 113{
 114        int err;
 115        int i;
 116
 117        for (i = 0; i < SB_FREEZE_LEVELS; i++) {
 118                err = percpu_counter_init(&s->s_writers.counter[i], 0);
 119                if (err < 0)
 120                        goto err_out;
 121                lockdep_init_map(&s->s_writers.lock_map[i], sb_writers_name[i],
 122                                 &type->s_writers_key[i], 0);
 123        }
 124        init_waitqueue_head(&s->s_writers.wait);
 125        init_waitqueue_head(&s->s_writers.wait_unfrozen);
 126        return 0;
 127err_out:
 128        while (--i >= 0)
 129                percpu_counter_destroy(&s->s_writers.counter[i]);
 130        return err;
 131}
 132
 133static void destroy_sb_writers(struct super_block *s)
 134{
 135        int i;
 136
 137        for (i = 0; i < SB_FREEZE_LEVELS; i++)
 138                percpu_counter_destroy(&s->s_writers.counter[i]);
 139}
 140
 141/**
 142 *      alloc_super     -       create new superblock
 143 *      @type:  filesystem type superblock should belong to
 144 *      @flags: the mount flags
 145 *
 146 *      Allocates and initializes a new &struct super_block.  alloc_super()
 147 *      returns a pointer new superblock or %NULL if allocation had failed.
 148 */
 149static struct super_block *alloc_super(struct file_system_type *type, int flags)
 150{
 151        struct super_block *s = kzalloc(sizeof(struct super_block),  GFP_USER);
 152        static const struct super_operations default_op;
 153
 154        if (s) {
 155                if (security_sb_alloc(s)) {
 156                        /*
 157                         * We cannot call security_sb_free() without
 158                         * security_sb_alloc() succeeding. So bail out manually
 159                         */
 160                        kfree(s);
 161                        s = NULL;
 162                        goto out;
 163                }
 164#ifdef CONFIG_SMP
 165                s->s_files = alloc_percpu(struct list_head);
 166                if (!s->s_files)
 167                        goto err_out;
 168                else {
 169                        int i;
 170
 171                        for_each_possible_cpu(i)
 172                                INIT_LIST_HEAD(per_cpu_ptr(s->s_files, i));
 173                }
 174#else
 175                INIT_LIST_HEAD(&s->s_files);
 176#endif
 177                if (init_sb_writers(s, type))
 178                        goto err_out;
 179                s->s_flags = flags;
 180                s->s_bdi = &default_backing_dev_info;
 181                INIT_HLIST_NODE(&s->s_instances);
 182                INIT_HLIST_BL_HEAD(&s->s_anon);
 183                INIT_LIST_HEAD(&s->s_inodes);
 184                INIT_LIST_HEAD(&s->s_dentry_lru);
 185                INIT_LIST_HEAD(&s->s_inode_lru);
 186                spin_lock_init(&s->s_inode_lru_lock);
 187                INIT_LIST_HEAD(&s->s_mounts);
 188                init_rwsem(&s->s_umount);
 189                lockdep_set_class(&s->s_umount, &type->s_umount_key);
 190                /*
 191                 * sget() can have s_umount recursion.
 192                 *
 193                 * When it cannot find a suitable sb, it allocates a new
 194                 * one (this one), and tries again to find a suitable old
 195                 * one.
 196                 *
 197                 * In case that succeeds, it will acquire the s_umount
 198                 * lock of the old one. Since these are clearly distrinct
 199                 * locks, and this object isn't exposed yet, there's no
 200                 * risk of deadlocks.
 201                 *
 202                 * Annotate this by putting this lock in a different
 203                 * subclass.
 204                 */
 205                down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
 206                s->s_count = 1;
 207                atomic_set(&s->s_active, 1);
 208                mutex_init(&s->s_vfs_rename_mutex);
 209                lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
 210                mutex_init(&s->s_dquot.dqio_mutex);
 211                mutex_init(&s->s_dquot.dqonoff_mutex);
 212                init_rwsem(&s->s_dquot.dqptr_sem);
 213                s->s_maxbytes = MAX_NON_LFS;
 214                s->s_op = &default_op;
 215                s->s_time_gran = 1000000000;
 216                s->cleancache_poolid = -1;
 217
 218                s->s_shrink.seeks = DEFAULT_SEEKS;
 219                s->s_shrink.shrink = prune_super;
 220                s->s_shrink.batch = 1024;
 221        }
 222out:
 223        return s;
 224err_out:
 225        security_sb_free(s);
 226#ifdef CONFIG_SMP
 227        if (s->s_files)
 228                free_percpu(s->s_files);
 229#endif
 230        destroy_sb_writers(s);
 231        kfree(s);
 232        s = NULL;
 233        goto out;
 234}
 235
 236/**
 237 *      destroy_super   -       frees a superblock
 238 *      @s: superblock to free
 239 *
 240 *      Frees a superblock.
 241 */
 242static inline void destroy_super(struct super_block *s)
 243{
 244#ifdef CONFIG_SMP
 245        free_percpu(s->s_files);
 246#endif
 247        destroy_sb_writers(s);
 248        security_sb_free(s);
 249        WARN_ON(!list_empty(&s->s_mounts));
 250        kfree(s->s_subtype);
 251        kfree(s->s_options);
 252        kfree(s);
 253}
 254
 255/* Superblock refcounting  */
 256
 257/*
 258 * Drop a superblock's refcount.  The caller must hold sb_lock.
 259 */
 260static void __put_super(struct super_block *sb)
 261{
 262        if (!--sb->s_count) {
 263                list_del_init(&sb->s_list);
 264                destroy_super(sb);
 265        }
 266}
 267
 268/**
 269 *      put_super       -       drop a temporary reference to superblock
 270 *      @sb: superblock in question
 271 *
 272 *      Drops a temporary reference, frees superblock if there's no
 273 *      references left.
 274 */
 275static void put_super(struct super_block *sb)
 276{
 277        spin_lock(&sb_lock);
 278        __put_super(sb);
 279        spin_unlock(&sb_lock);
 280}
 281
 282
 283/**
 284 *      deactivate_locked_super -       drop an active reference to superblock
 285 *      @s: superblock to deactivate
 286 *
 287 *      Drops an active reference to superblock, converting it into a temprory
 288 *      one if there is no other active references left.  In that case we
 289 *      tell fs driver to shut it down and drop the temporary reference we
 290 *      had just acquired.
 291 *
 292 *      Caller holds exclusive lock on superblock; that lock is released.
 293 */
 294void deactivate_locked_super(struct super_block *s)
 295{
 296        struct file_system_type *fs = s->s_type;
 297        if (atomic_dec_and_test(&s->s_active)) {
 298                cleancache_invalidate_fs(s);
 299                fs->kill_sb(s);
 300
 301                /* caches are now gone, we can safely kill the shrinker now */
 302                unregister_shrinker(&s->s_shrink);
 303                put_filesystem(fs);
 304                put_super(s);
 305        } else {
 306                up_write(&s->s_umount);
 307        }
 308}
 309
 310EXPORT_SYMBOL(deactivate_locked_super);
 311
 312/**
 313 *      deactivate_super        -       drop an active reference to superblock
 314 *      @s: superblock to deactivate
 315 *
 316 *      Variant of deactivate_locked_super(), except that superblock is *not*
 317 *      locked by caller.  If we are going to drop the final active reference,
 318 *      lock will be acquired prior to that.
 319 */
 320void deactivate_super(struct super_block *s)
 321{
 322        if (!atomic_add_unless(&s->s_active, -1, 1)) {
 323                down_write(&s->s_umount);
 324                deactivate_locked_super(s);
 325        }
 326}
 327
 328EXPORT_SYMBOL(deactivate_super);
 329
 330/**
 331 *      grab_super - acquire an active reference
 332 *      @s: reference we are trying to make active
 333 *
 334 *      Tries to acquire an active reference.  grab_super() is used when we
 335 *      had just found a superblock in super_blocks or fs_type->fs_supers
 336 *      and want to turn it into a full-blown active reference.  grab_super()
 337 *      is called with sb_lock held and drops it.  Returns 1 in case of
 338 *      success, 0 if we had failed (superblock contents was already dead or
 339 *      dying when grab_super() had been called).  Note that this is only
 340 *      called for superblocks not in rundown mode (== ones still on ->fs_supers
 341 *      of their type), so increment of ->s_count is OK here.
 342 */
 343static int grab_super(struct super_block *s) __releases(sb_lock)
 344{
 345        s->s_count++;
 346        spin_unlock(&sb_lock);
 347        down_write(&s->s_umount);
 348        if ((s->s_flags & MS_BORN) && atomic_inc_not_zero(&s->s_active)) {
 349                put_super(s);
 350                return 1;
 351        }
 352        up_write(&s->s_umount);
 353        put_super(s);
 354        return 0;
 355}
 356
 357/*
 358 *      grab_super_passive - acquire a passive reference
 359 *      @sb: reference we are trying to grab
 360 *
 361 *      Tries to acquire a passive reference. This is used in places where we
 362 *      cannot take an active reference but we need to ensure that the
 363 *      superblock does not go away while we are working on it. It returns
 364 *      false if a reference was not gained, and returns true with the s_umount
 365 *      lock held in read mode if a reference is gained. On successful return,
 366 *      the caller must drop the s_umount lock and the passive reference when
 367 *      done.
 368 */
 369bool grab_super_passive(struct super_block *sb)
 370{
 371        spin_lock(&sb_lock);
 372        if (hlist_unhashed(&sb->s_instances)) {
 373                spin_unlock(&sb_lock);
 374                return false;
 375        }
 376
 377        sb->s_count++;
 378        spin_unlock(&sb_lock);
 379
 380        if (down_read_trylock(&sb->s_umount)) {
 381                if (sb->s_root && (sb->s_flags & MS_BORN))
 382                        return true;
 383                up_read(&sb->s_umount);
 384        }
 385
 386        put_super(sb);
 387        return false;
 388}
 389
 390/**
 391 *      generic_shutdown_super  -       common helper for ->kill_sb()
 392 *      @sb: superblock to kill
 393 *
 394 *      generic_shutdown_super() does all fs-independent work on superblock
 395 *      shutdown.  Typical ->kill_sb() should pick all fs-specific objects
 396 *      that need destruction out of superblock, call generic_shutdown_super()
 397 *      and release aforementioned objects.  Note: dentries and inodes _are_
 398 *      taken care of and do not need specific handling.
 399 *
 400 *      Upon calling this function, the filesystem may no longer alter or
 401 *      rearrange the set of dentries belonging to this super_block, nor may it
 402 *      change the attachments of dentries to inodes.
 403 */
 404void generic_shutdown_super(struct super_block *sb)
 405{
 406        const struct super_operations *sop = sb->s_op;
 407
 408        if (sb->s_root) {
 409                shrink_dcache_for_umount(sb);
 410                sync_filesystem(sb);
 411                sb->s_flags &= ~MS_ACTIVE;
 412
 413                fsnotify_unmount_inodes(&sb->s_inodes);
 414
 415                evict_inodes(sb);
 416
 417                if (sop->put_super)
 418                        sop->put_super(sb);
 419
 420                if (!list_empty(&sb->s_inodes)) {
 421                        printk("VFS: Busy inodes after unmount of %s. "
 422                           "Self-destruct in 5 seconds.  Have a nice day...\n",
 423                           sb->s_id);
 424                }
 425        }
 426        spin_lock(&sb_lock);
 427        /* should be initialized for __put_super_and_need_restart() */
 428        hlist_del_init(&sb->s_instances);
 429        spin_unlock(&sb_lock);
 430        up_write(&sb->s_umount);
 431}
 432
 433EXPORT_SYMBOL(generic_shutdown_super);
 434
 435/**
 436 *      sget    -       find or create a superblock
 437 *      @type:  filesystem type superblock should belong to
 438 *      @test:  comparison callback
 439 *      @set:   setup callback
 440 *      @flags: mount flags
 441 *      @data:  argument to each of them
 442 */
 443struct super_block *sget(struct file_system_type *type,
 444                        int (*test)(struct super_block *,void *),
 445                        int (*set)(struct super_block *,void *),
 446                        int flags,
 447                        void *data)
 448{
 449        struct super_block *s = NULL;
 450        struct super_block *old;
 451        int err;
 452
 453retry:
 454        spin_lock(&sb_lock);
 455        if (test) {
 456                hlist_for_each_entry(old, &type->fs_supers, s_instances) {
 457                        if (!test(old, data))
 458                                continue;
 459                        if (!grab_super(old))
 460                                goto retry;
 461                        if (s) {
 462                                up_write(&s->s_umount);
 463                                destroy_super(s);
 464                                s = NULL;
 465                        }
 466                        return old;
 467                }
 468        }
 469        if (!s) {
 470                spin_unlock(&sb_lock);
 471                s = alloc_super(type, flags);
 472                if (!s)
 473                        return ERR_PTR(-ENOMEM);
 474                goto retry;
 475        }
 476                
 477        err = set(s, data);
 478        if (err) {
 479                spin_unlock(&sb_lock);
 480                up_write(&s->s_umount);
 481                destroy_super(s);
 482                return ERR_PTR(err);
 483        }
 484        s->s_type = type;
 485        strlcpy(s->s_id, type->name, sizeof(s->s_id));
 486        list_add_tail(&s->s_list, &super_blocks);
 487        hlist_add_head(&s->s_instances, &type->fs_supers);
 488        spin_unlock(&sb_lock);
 489        get_filesystem(type);
 490        register_shrinker(&s->s_shrink);
 491        return s;
 492}
 493
 494EXPORT_SYMBOL(sget);
 495
 496void drop_super(struct super_block *sb)
 497{
 498        up_read(&sb->s_umount);
 499        put_super(sb);
 500}
 501
 502EXPORT_SYMBOL(drop_super);
 503
 504/**
 505 *      iterate_supers - call function for all active superblocks
 506 *      @f: function to call
 507 *      @arg: argument to pass to it
 508 *
 509 *      Scans the superblock list and calls given function, passing it
 510 *      locked superblock and given argument.
 511 */
 512void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 513{
 514        struct super_block *sb, *p = NULL;
 515
 516        spin_lock(&sb_lock);
 517        list_for_each_entry(sb, &super_blocks, s_list) {
 518                if (hlist_unhashed(&sb->s_instances))
 519                        continue;
 520                sb->s_count++;
 521                spin_unlock(&sb_lock);
 522
 523                down_read(&sb->s_umount);
 524                if (sb->s_root && (sb->s_flags & MS_BORN))
 525                        f(sb, arg);
 526                up_read(&sb->s_umount);
 527
 528                spin_lock(&sb_lock);
 529                if (p)
 530                        __put_super(p);
 531                p = sb;
 532        }
 533        if (p)
 534                __put_super(p);
 535        spin_unlock(&sb_lock);
 536}
 537
 538/**
 539 *      iterate_supers_type - call function for superblocks of given type
 540 *      @type: fs type
 541 *      @f: function to call
 542 *      @arg: argument to pass to it
 543 *
 544 *      Scans the superblock list and calls given function, passing it
 545 *      locked superblock and given argument.
 546 */
 547void iterate_supers_type(struct file_system_type *type,
 548        void (*f)(struct super_block *, void *), void *arg)
 549{
 550        struct super_block *sb, *p = NULL;
 551
 552        spin_lock(&sb_lock);
 553        hlist_for_each_entry(sb, &type->fs_supers, s_instances) {
 554                sb->s_count++;
 555                spin_unlock(&sb_lock);
 556
 557                down_read(&sb->s_umount);
 558                if (sb->s_root && (sb->s_flags & MS_BORN))
 559                        f(sb, arg);
 560                up_read(&sb->s_umount);
 561
 562                spin_lock(&sb_lock);
 563                if (p)
 564                        __put_super(p);
 565                p = sb;
 566        }
 567        if (p)
 568                __put_super(p);
 569        spin_unlock(&sb_lock);
 570}
 571
 572EXPORT_SYMBOL(iterate_supers_type);
 573
 574/**
 575 *      get_super - get the superblock of a device
 576 *      @bdev: device to get the superblock for
 577 *      
 578 *      Scans the superblock list and finds the superblock of the file system
 579 *      mounted on the device given. %NULL is returned if no match is found.
 580 */
 581
 582struct super_block *get_super(struct block_device *bdev)
 583{
 584        struct super_block *sb;
 585
 586        if (!bdev)
 587                return NULL;
 588
 589        spin_lock(&sb_lock);
 590rescan:
 591        list_for_each_entry(sb, &super_blocks, s_list) {
 592                if (hlist_unhashed(&sb->s_instances))
 593                        continue;
 594                if (sb->s_bdev == bdev) {
 595                        sb->s_count++;
 596                        spin_unlock(&sb_lock);
 597                        down_read(&sb->s_umount);
 598                        /* still alive? */
 599                        if (sb->s_root && (sb->s_flags & MS_BORN))
 600                                return sb;
 601                        up_read(&sb->s_umount);
 602                        /* nope, got unmounted */
 603                        spin_lock(&sb_lock);
 604                        __put_super(sb);
 605                        goto rescan;
 606                }
 607        }
 608        spin_unlock(&sb_lock);
 609        return NULL;
 610}
 611
 612EXPORT_SYMBOL(get_super);
 613
 614/**
 615 *      get_super_thawed - get thawed superblock of a device
 616 *      @bdev: device to get the superblock for
 617 *
 618 *      Scans the superblock list and finds the superblock of the file system
 619 *      mounted on the device. The superblock is returned once it is thawed
 620 *      (or immediately if it was not frozen). %NULL is returned if no match
 621 *      is found.
 622 */
 623struct super_block *get_super_thawed(struct block_device *bdev)
 624{
 625        while (1) {
 626                struct super_block *s = get_super(bdev);
 627                if (!s || s->s_writers.frozen == SB_UNFROZEN)
 628                        return s;
 629                up_read(&s->s_umount);
 630                wait_event(s->s_writers.wait_unfrozen,
 631                           s->s_writers.frozen == SB_UNFROZEN);
 632                put_super(s);
 633        }
 634}
 635EXPORT_SYMBOL(get_super_thawed);
 636
 637/**
 638 * get_active_super - get an active reference to the superblock of a device
 639 * @bdev: device to get the superblock for
 640 *
 641 * Scans the superblock list and finds the superblock of the file system
 642 * mounted on the device given.  Returns the superblock with an active
 643 * reference or %NULL if none was found.
 644 */
 645struct super_block *get_active_super(struct block_device *bdev)
 646{
 647        struct super_block *sb;
 648
 649        if (!bdev)
 650                return NULL;
 651
 652restart:
 653        spin_lock(&sb_lock);
 654        list_for_each_entry(sb, &super_blocks, s_list) {
 655                if (hlist_unhashed(&sb->s_instances))
 656                        continue;
 657                if (sb->s_bdev == bdev) {
 658                        if (!grab_super(sb))
 659                                goto restart;
 660                        up_write(&sb->s_umount);
 661                        return sb;
 662                }
 663        }
 664        spin_unlock(&sb_lock);
 665        return NULL;
 666}
 667 
 668struct super_block *user_get_super(dev_t dev)
 669{
 670        struct super_block *sb;
 671
 672        spin_lock(&sb_lock);
 673rescan:
 674        list_for_each_entry(sb, &super_blocks, s_list) {
 675                if (hlist_unhashed(&sb->s_instances))
 676                        continue;
 677                if (sb->s_dev ==  dev) {
 678                        sb->s_count++;
 679                        spin_unlock(&sb_lock);
 680                        down_read(&sb->s_umount);
 681                        /* still alive? */
 682                        if (sb->s_root && (sb->s_flags & MS_BORN))
 683                                return sb;
 684                        up_read(&sb->s_umount);
 685                        /* nope, got unmounted */
 686                        spin_lock(&sb_lock);
 687                        __put_super(sb);
 688                        goto rescan;
 689                }
 690        }
 691        spin_unlock(&sb_lock);
 692        return NULL;
 693}
 694
 695/**
 696 *      do_remount_sb - asks filesystem to change mount options.
 697 *      @sb:    superblock in question
 698 *      @flags: numeric part of options
 699 *      @data:  the rest of options
 700 *      @force: whether or not to force the change
 701 *
 702 *      Alters the mount options of a mounted file system.
 703 */
 704int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 705{
 706        int retval;
 707        int remount_ro;
 708
 709        if (sb->s_writers.frozen != SB_UNFROZEN)
 710                return -EBUSY;
 711
 712#ifdef CONFIG_BLOCK
 713        if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
 714                return -EACCES;
 715#endif
 716
 717        if (flags & MS_RDONLY)
 718                acct_auto_close(sb);
 719        shrink_dcache_sb(sb);
 720        sync_filesystem(sb);
 721
 722        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
 723
 724        /* If we are remounting RDONLY and current sb is read/write,
 725           make sure there are no rw files opened */
 726        if (remount_ro) {
 727                if (force) {
 728                        mark_files_ro(sb);
 729                } else {
 730                        retval = sb_prepare_remount_readonly(sb);
 731                        if (retval)
 732                                return retval;
 733                }
 734        }
 735
 736        if (sb->s_op->remount_fs) {
 737                retval = sb->s_op->remount_fs(sb, &flags, data);
 738                if (retval) {
 739                        if (!force)
 740                                goto cancel_readonly;
 741                        /* If forced remount, go ahead despite any errors */
 742                        WARN(1, "forced remount of a %s fs returned %i\n",
 743                             sb->s_type->name, retval);
 744                }
 745        }
 746        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
 747        /* Needs to be ordered wrt mnt_is_readonly() */
 748        smp_wmb();
 749        sb->s_readonly_remount = 0;
 750
 751        /*
 752         * Some filesystems modify their metadata via some other path than the
 753         * bdev buffer cache (eg. use a private mapping, or directories in
 754         * pagecache, etc). Also file data modifications go via their own
 755         * mappings. So If we try to mount readonly then copy the filesystem
 756         * from bdev, we could get stale data, so invalidate it to give a best
 757         * effort at coherency.
 758         */
 759        if (remount_ro && sb->s_bdev)
 760                invalidate_bdev(sb->s_bdev);
 761        return 0;
 762
 763cancel_readonly:
 764        sb->s_readonly_remount = 0;
 765        return retval;
 766}
 767
 768static void do_emergency_remount(struct work_struct *work)
 769{
 770        struct super_block *sb, *p = NULL;
 771
 772        spin_lock(&sb_lock);
 773        list_for_each_entry(sb, &super_blocks, s_list) {
 774                if (hlist_unhashed(&sb->s_instances))
 775                        continue;
 776                sb->s_count++;
 777                spin_unlock(&sb_lock);
 778                down_write(&sb->s_umount);
 779                if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
 780                    !(sb->s_flags & MS_RDONLY)) {
 781                        /*
 782                         * What lock protects sb->s_flags??
 783                         */
 784                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
 785                }
 786                up_write(&sb->s_umount);
 787                spin_lock(&sb_lock);
 788                if (p)
 789                        __put_super(p);
 790                p = sb;
 791        }
 792        if (p)
 793                __put_super(p);
 794        spin_unlock(&sb_lock);
 795        kfree(work);
 796        printk("Emergency Remount complete\n");
 797}
 798
 799void emergency_remount(void)
 800{
 801        struct work_struct *work;
 802
 803        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 804        if (work) {
 805                INIT_WORK(work, do_emergency_remount);
 806                schedule_work(work);
 807        }
 808}
 809
 810/*
 811 * Unnamed block devices are dummy devices used by virtual
 812 * filesystems which don't use real block-devices.  -- jrs
 813 */
 814
 815static DEFINE_IDA(unnamed_dev_ida);
 816static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
 817static int unnamed_dev_start = 0; /* don't bother trying below it */
 818
 819int get_anon_bdev(dev_t *p)
 820{
 821        int dev;
 822        int error;
 823
 824 retry:
 825        if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
 826                return -ENOMEM;
 827        spin_lock(&unnamed_dev_lock);
 828        error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
 829        if (!error)
 830                unnamed_dev_start = dev + 1;
 831        spin_unlock(&unnamed_dev_lock);
 832        if (error == -EAGAIN)
 833                /* We raced and lost with another CPU. */
 834                goto retry;
 835        else if (error)
 836                return -EAGAIN;
 837
 838        if (dev == (1 << MINORBITS)) {
 839                spin_lock(&unnamed_dev_lock);
 840                ida_remove(&unnamed_dev_ida, dev);
 841                if (unnamed_dev_start > dev)
 842                        unnamed_dev_start = dev;
 843                spin_unlock(&unnamed_dev_lock);
 844                return -EMFILE;
 845        }
 846        *p = MKDEV(0, dev & MINORMASK);
 847        return 0;
 848}
 849EXPORT_SYMBOL(get_anon_bdev);
 850
 851void free_anon_bdev(dev_t dev)
 852{
 853        int slot = MINOR(dev);
 854        spin_lock(&unnamed_dev_lock);
 855        ida_remove(&unnamed_dev_ida, slot);
 856        if (slot < unnamed_dev_start)
 857                unnamed_dev_start = slot;
 858        spin_unlock(&unnamed_dev_lock);
 859}
 860EXPORT_SYMBOL(free_anon_bdev);
 861
 862int set_anon_super(struct super_block *s, void *data)
 863{
 864        int error = get_anon_bdev(&s->s_dev);
 865        if (!error)
 866                s->s_bdi = &noop_backing_dev_info;
 867        return error;
 868}
 869
 870EXPORT_SYMBOL(set_anon_super);
 871
 872void kill_anon_super(struct super_block *sb)
 873{
 874        dev_t dev = sb->s_dev;
 875        generic_shutdown_super(sb);
 876        free_anon_bdev(dev);
 877}
 878
 879EXPORT_SYMBOL(kill_anon_super);
 880
 881void kill_litter_super(struct super_block *sb)
 882{
 883        if (sb->s_root)
 884                d_genocide(sb->s_root);
 885        kill_anon_super(sb);
 886}
 887
 888EXPORT_SYMBOL(kill_litter_super);
 889
 890static int ns_test_super(struct super_block *sb, void *data)
 891{
 892        return sb->s_fs_info == data;
 893}
 894
 895static int ns_set_super(struct super_block *sb, void *data)
 896{
 897        sb->s_fs_info = data;
 898        return set_anon_super(sb, NULL);
 899}
 900
 901struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
 902        void *data, int (*fill_super)(struct super_block *, void *, int))
 903{
 904        struct super_block *sb;
 905
 906        sb = sget(fs_type, ns_test_super, ns_set_super, flags, data);
 907        if (IS_ERR(sb))
 908                return ERR_CAST(sb);
 909
 910        if (!sb->s_root) {
 911                int err;
 912                err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 913                if (err) {
 914                        deactivate_locked_super(sb);
 915                        return ERR_PTR(err);
 916                }
 917
 918                sb->s_flags |= MS_ACTIVE;
 919        }
 920
 921        return dget(sb->s_root);
 922}
 923
 924EXPORT_SYMBOL(mount_ns);
 925
 926#ifdef CONFIG_BLOCK
 927static int set_bdev_super(struct super_block *s, void *data)
 928{
 929        s->s_bdev = data;
 930        s->s_dev = s->s_bdev->bd_dev;
 931
 932        /*
 933         * We set the bdi here to the queue backing, file systems can
 934         * overwrite this in ->fill_super()
 935         */
 936        s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
 937        return 0;
 938}
 939
 940static int test_bdev_super(struct super_block *s, void *data)
 941{
 942        return (void *)s->s_bdev == data;
 943}
 944
 945struct dentry *mount_bdev(struct file_system_type *fs_type,
 946        int flags, const char *dev_name, void *data,
 947        int (*fill_super)(struct super_block *, void *, int))
 948{
 949        struct block_device *bdev;
 950        struct super_block *s;
 951        fmode_t mode = FMODE_READ | FMODE_EXCL;
 952        int error = 0;
 953
 954        if (!(flags & MS_RDONLY))
 955                mode |= FMODE_WRITE;
 956
 957        bdev = blkdev_get_by_path(dev_name, mode, fs_type);
 958        if (IS_ERR(bdev))
 959                return ERR_CAST(bdev);
 960
 961        /*
 962         * once the super is inserted into the list by sget, s_umount
 963         * will protect the lockfs code from trying to start a snapshot
 964         * while we are mounting
 965         */
 966        mutex_lock(&bdev->bd_fsfreeze_mutex);
 967        if (bdev->bd_fsfreeze_count > 0) {
 968                mutex_unlock(&bdev->bd_fsfreeze_mutex);
 969                error = -EBUSY;
 970                goto error_bdev;
 971        }
 972        s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
 973                 bdev);
 974        mutex_unlock(&bdev->bd_fsfreeze_mutex);
 975        if (IS_ERR(s))
 976                goto error_s;
 977
 978        if (s->s_root) {
 979                if ((flags ^ s->s_flags) & MS_RDONLY) {
 980                        deactivate_locked_super(s);
 981                        error = -EBUSY;
 982                        goto error_bdev;
 983                }
 984
 985                /*
 986                 * s_umount nests inside bd_mutex during
 987                 * __invalidate_device().  blkdev_put() acquires
 988                 * bd_mutex and can't be called under s_umount.  Drop
 989                 * s_umount temporarily.  This is safe as we're
 990                 * holding an active reference.
 991                 */
 992                up_write(&s->s_umount);
 993                blkdev_put(bdev, mode);
 994                down_write(&s->s_umount);
 995        } else {
 996                char b[BDEVNAME_SIZE];
 997
 998                s->s_mode = mode;
 999                strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
1000                sb_set_blocksize(s, block_size(bdev));
1001                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1002                if (error) {
1003                        deactivate_locked_super(s);
1004                        goto error;
1005                }
1006
1007                s->s_flags |= MS_ACTIVE;
1008                bdev->bd_super = s;
1009        }
1010
1011        return dget(s->s_root);
1012
1013error_s:
1014        error = PTR_ERR(s);
1015error_bdev:
1016        blkdev_put(bdev, mode);
1017error:
1018        return ERR_PTR(error);
1019}
1020EXPORT_SYMBOL(mount_bdev);
1021
1022void kill_block_super(struct super_block *sb)
1023{
1024        struct block_device *bdev = sb->s_bdev;
1025        fmode_t mode = sb->s_mode;
1026
1027        bdev->bd_super = NULL;
1028        generic_shutdown_super(sb);
1029        sync_blockdev(bdev);
1030        WARN_ON_ONCE(!(mode & FMODE_EXCL));
1031        blkdev_put(bdev, mode | FMODE_EXCL);
1032}
1033
1034EXPORT_SYMBOL(kill_block_super);
1035#endif
1036
1037struct dentry *mount_nodev(struct file_system_type *fs_type,
1038        int flags, void *data,
1039        int (*fill_super)(struct super_block *, void *, int))
1040{
1041        int error;
1042        struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1043
1044        if (IS_ERR(s))
1045                return ERR_CAST(s);
1046
1047        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1048        if (error) {
1049                deactivate_locked_super(s);
1050                return ERR_PTR(error);
1051        }
1052        s->s_flags |= MS_ACTIVE;
1053        return dget(s->s_root);
1054}
1055EXPORT_SYMBOL(mount_nodev);
1056
1057static int compare_single(struct super_block *s, void *p)
1058{
1059        return 1;
1060}
1061
1062struct dentry *mount_single(struct file_system_type *fs_type,
1063        int flags, void *data,
1064        int (*fill_super)(struct super_block *, void *, int))
1065{
1066        struct super_block *s;
1067        int error;
1068
1069        s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1070        if (IS_ERR(s))
1071                return ERR_CAST(s);
1072        if (!s->s_root) {
1073                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1074                if (error) {
1075                        deactivate_locked_super(s);
1076                        return ERR_PTR(error);
1077                }
1078                s->s_flags |= MS_ACTIVE;
1079        } else {
1080                do_remount_sb(s, flags, data, 0);
1081        }
1082        return dget(s->s_root);
1083}
1084EXPORT_SYMBOL(mount_single);
1085
1086struct dentry *
1087mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1088{
1089        struct dentry *root;
1090        struct super_block *sb;
1091        char *secdata = NULL;
1092        int error = -ENOMEM;
1093
1094        if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1095                secdata = alloc_secdata();
1096                if (!secdata)
1097                        goto out;
1098
1099                error = security_sb_copy_data(data, secdata);
1100                if (error)
1101                        goto out_free_secdata;
1102        }
1103
1104        root = type->mount(type, flags, name, data);
1105        if (IS_ERR(root)) {
1106                error = PTR_ERR(root);
1107                goto out_free_secdata;
1108        }
1109        sb = root->d_sb;
1110        BUG_ON(!sb);
1111        WARN_ON(!sb->s_bdi);
1112        WARN_ON(sb->s_bdi == &default_backing_dev_info);
1113        sb->s_flags |= MS_BORN;
1114
1115        error = security_sb_kern_mount(sb, flags, secdata);
1116        if (error)
1117                goto out_sb;
1118
1119        /*
1120         * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1121         * but s_maxbytes was an unsigned long long for many releases. Throw
1122         * this warning for a little while to try and catch filesystems that
1123         * violate this rule.
1124         */
1125        WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1126                "negative value (%lld)\n", type->name, sb->s_maxbytes);
1127
1128        up_write(&sb->s_umount);
1129        free_secdata(secdata);
1130        return root;
1131out_sb:
1132        dput(root);
1133        deactivate_locked_super(sb);
1134out_free_secdata:
1135        free_secdata(secdata);
1136out:
1137        return ERR_PTR(error);
1138}
1139
1140/*
1141 * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1142 * instead.
1143 */
1144void __sb_end_write(struct super_block *sb, int level)
1145{
1146        percpu_counter_dec(&sb->s_writers.counter[level-1]);
1147        /*
1148         * Make sure s_writers are updated before we wake up waiters in
1149         * freeze_super().
1150         */
1151        smp_mb();
1152        if (waitqueue_active(&sb->s_writers.wait))
1153                wake_up(&sb->s_writers.wait);
1154        rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
1155}
1156EXPORT_SYMBOL(__sb_end_write);
1157
1158#ifdef CONFIG_LOCKDEP
1159/*
1160 * We want lockdep to tell us about possible deadlocks with freezing but
1161 * it's it bit tricky to properly instrument it. Getting a freeze protection
1162 * works as getting a read lock but there are subtle problems. XFS for example
1163 * gets freeze protection on internal level twice in some cases, which is OK
1164 * only because we already hold a freeze protection also on higher level. Due
1165 * to these cases we have to tell lockdep we are doing trylock when we
1166 * already hold a freeze protection for a higher freeze level.
1167 */
1168static void acquire_freeze_lock(struct super_block *sb, int level, bool trylock,
1169                                unsigned long ip)
1170{
1171        int i;
1172
1173        if (!trylock) {
1174                for (i = 0; i < level - 1; i++)
1175                        if (lock_is_held(&sb->s_writers.lock_map[i])) {
1176                                trylock = true;
1177                                break;
1178                        }
1179        }
1180        rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, trylock, ip);
1181}
1182#endif
1183
1184/*
1185 * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1186 * instead.
1187 */
1188int __sb_start_write(struct super_block *sb, int level, bool wait)
1189{
1190retry:
1191        if (unlikely(sb->s_writers.frozen >= level)) {
1192                if (!wait)
1193                        return 0;
1194                wait_event(sb->s_writers.wait_unfrozen,
1195                           sb->s_writers.frozen < level);
1196        }
1197
1198#ifdef CONFIG_LOCKDEP
1199        acquire_freeze_lock(sb, level, !wait, _RET_IP_);
1200#endif
1201        percpu_counter_inc(&sb->s_writers.counter[level-1]);
1202        /*
1203         * Make sure counter is updated before we check for frozen.
1204         * freeze_super() first sets frozen and then checks the counter.
1205         */
1206        smp_mb();
1207        if (unlikely(sb->s_writers.frozen >= level)) {
1208                __sb_end_write(sb, level);
1209                goto retry;
1210        }
1211        return 1;
1212}
1213EXPORT_SYMBOL(__sb_start_write);
1214
1215/**
1216 * sb_wait_write - wait until all writers to given file system finish
1217 * @sb: the super for which we wait
1218 * @level: type of writers we wait for (normal vs page fault)
1219 *
1220 * This function waits until there are no writers of given type to given file
1221 * system. Caller of this function should make sure there can be no new writers
1222 * of type @level before calling this function. Otherwise this function can
1223 * livelock.
1224 */
1225static void sb_wait_write(struct super_block *sb, int level)
1226{
1227        s64 writers;
1228
1229        /*
1230         * We just cycle-through lockdep here so that it does not complain
1231         * about returning with lock to userspace
1232         */
1233        rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
1234        rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
1235
1236        do {
1237                DEFINE_WAIT(wait);
1238
1239                /*
1240                 * We use a barrier in prepare_to_wait() to separate setting
1241                 * of frozen and checking of the counter
1242                 */
1243                prepare_to_wait(&sb->s_writers.wait, &wait,
1244                                TASK_UNINTERRUPTIBLE);
1245
1246                writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
1247                if (writers)
1248                        schedule();
1249
1250                finish_wait(&sb->s_writers.wait, &wait);
1251        } while (writers);
1252}
1253
1254/**
1255 * freeze_super - lock the filesystem and force it into a consistent state
1256 * @sb: the super to lock
1257 *
1258 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1259 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1260 * -EBUSY.
1261 *
1262 * During this function, sb->s_writers.frozen goes through these values:
1263 *
1264 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1265 *
1266 * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1267 * writes should be blocked, though page faults are still allowed. We wait for
1268 * all writes to complete and then proceed to the next stage.
1269 *
1270 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1271 * but internal fs threads can still modify the filesystem (although they
1272 * should not dirty new pages or inodes), writeback can run etc. After waiting
1273 * for all running page faults we sync the filesystem which will clean all
1274 * dirty pages and inodes (no new dirty pages or inodes can be created when
1275 * sync is running).
1276 *
1277 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1278 * modification are blocked (e.g. XFS preallocation truncation on inode
1279 * reclaim). This is usually implemented by blocking new transactions for
1280 * filesystems that have them and need this additional guard. After all
1281 * internal writers are finished we call ->freeze_fs() to finish filesystem
1282 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1283 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1284 *
1285 * sb->s_writers.frozen is protected by sb->s_umount.
1286 */
1287int freeze_super(struct super_block *sb)
1288{
1289        int ret;
1290
1291        atomic_inc(&sb->s_active);
1292        down_write(&sb->s_umount);
1293        if (sb->s_writers.frozen != SB_UNFROZEN) {
1294                deactivate_locked_super(sb);
1295                return -EBUSY;
1296        }
1297
1298        if (!(sb->s_flags & MS_BORN)) {
1299                up_write(&sb->s_umount);
1300                return 0;       /* sic - it's "nothing to do" */
1301        }
1302
1303        if (sb->s_flags & MS_RDONLY) {
1304                /* Nothing to do really... */
1305                sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1306                up_write(&sb->s_umount);
1307                return 0;
1308        }
1309
1310        /* From now on, no new normal writers can start */
1311        sb->s_writers.frozen = SB_FREEZE_WRITE;
1312        smp_wmb();
1313
1314        /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1315        up_write(&sb->s_umount);
1316
1317        sb_wait_write(sb, SB_FREEZE_WRITE);
1318
1319        /* Now we go and block page faults... */
1320        down_write(&sb->s_umount);
1321        sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1322        smp_wmb();
1323
1324        sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1325
1326        /* All writers are done so after syncing there won't be dirty data */
1327        sync_filesystem(sb);
1328
1329        /* Now wait for internal filesystem counter */
1330        sb->s_writers.frozen = SB_FREEZE_FS;
1331        smp_wmb();
1332        sb_wait_write(sb, SB_FREEZE_FS);
1333
1334        if (sb->s_op->freeze_fs) {
1335                ret = sb->s_op->freeze_fs(sb);
1336                if (ret) {
1337                        printk(KERN_ERR
1338                                "VFS:Filesystem freeze failed\n");
1339                        sb->s_writers.frozen = SB_UNFROZEN;
1340                        smp_wmb();
1341                        wake_up(&sb->s_writers.wait_unfrozen);
1342                        deactivate_locked_super(sb);
1343                        return ret;
1344                }
1345        }
1346        /*
1347         * This is just for debugging purposes so that fs can warn if it
1348         * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
1349         */
1350        sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1351        up_write(&sb->s_umount);
1352        return 0;
1353}
1354EXPORT_SYMBOL(freeze_super);
1355
1356/**
1357 * thaw_super -- unlock filesystem
1358 * @sb: the super to thaw
1359 *
1360 * Unlocks the filesystem and marks it writeable again after freeze_super().
1361 */
1362int thaw_super(struct super_block *sb)
1363{
1364        int error;
1365
1366        down_write(&sb->s_umount);
1367        if (sb->s_writers.frozen == SB_UNFROZEN) {
1368                up_write(&sb->s_umount);
1369                return -EINVAL;
1370        }
1371
1372        if (sb->s_flags & MS_RDONLY)
1373                goto out;
1374
1375        if (sb->s_op->unfreeze_fs) {
1376                error = sb->s_op->unfreeze_fs(sb);
1377                if (error) {
1378                        printk(KERN_ERR
1379                                "VFS:Filesystem thaw failed\n");
1380                        up_write(&sb->s_umount);
1381                        return error;
1382                }
1383        }
1384
1385out:
1386        sb->s_writers.frozen = SB_UNFROZEN;
1387        smp_wmb();
1388        wake_up(&sb->s_writers.wait_unfrozen);
1389        deactivate_locked_super(sb);
1390
1391        return 0;
1392}
1393EXPORT_SYMBOL(thaw_super);
1394
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