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).
 340 */
 341static int grab_super(struct super_block *s) __releases(sb_lock)
 342{
 343        if (atomic_inc_not_zero(&s->s_active)) {
 344                spin_unlock(&sb_lock);
 345                return 1;
 346        }
 347        /* it's going away */
 348        s->s_count++;
 349        spin_unlock(&sb_lock);
 350        /* wait for it to die */
 351        down_write(&s->s_umount);
 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 hlist_node *node;
 451        struct super_block *old;
 452        int err;
 453
 454retry:
 455        spin_lock(&sb_lock);
 456        if (test) {
 457                hlist_for_each_entry(old, node, &type->fs_supers, s_instances) {
 458                        if (!test(old, data))
 459                                continue;
 460                        if (!grab_super(old))
 461                                goto retry;
 462                        if (s) {
 463                                up_write(&s->s_umount);
 464                                destroy_super(s);
 465                                s = NULL;
 466                        }
 467                        down_write(&old->s_umount);
 468                        if (unlikely(!(old->s_flags & MS_BORN))) {
 469                                deactivate_locked_super(old);
 470                                goto retry;
 471                        }
 472                        return old;
 473                }
 474        }
 475        if (!s) {
 476                spin_unlock(&sb_lock);
 477                s = alloc_super(type, flags);
 478                if (!s)
 479                        return ERR_PTR(-ENOMEM);
 480                goto retry;
 481        }
 482                
 483        err = set(s, data);
 484        if (err) {
 485                spin_unlock(&sb_lock);
 486                up_write(&s->s_umount);
 487                destroy_super(s);
 488                return ERR_PTR(err);
 489        }
 490        s->s_type = type;
 491        strlcpy(s->s_id, type->name, sizeof(s->s_id));
 492        list_add_tail(&s->s_list, &super_blocks);
 493        hlist_add_head(&s->s_instances, &type->fs_supers);
 494        spin_unlock(&sb_lock);
 495        get_filesystem(type);
 496        register_shrinker(&s->s_shrink);
 497        return s;
 498}
 499
 500EXPORT_SYMBOL(sget);
 501
 502void drop_super(struct super_block *sb)
 503{
 504        up_read(&sb->s_umount);
 505        put_super(sb);
 506}
 507
 508EXPORT_SYMBOL(drop_super);
 509
 510/**
 511 *      iterate_supers - call function for all active superblocks
 512 *      @f: function to call
 513 *      @arg: argument to pass to it
 514 *
 515 *      Scans the superblock list and calls given function, passing it
 516 *      locked superblock and given argument.
 517 */
 518void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
 519{
 520        struct super_block *sb, *p = NULL;
 521
 522        spin_lock(&sb_lock);
 523        list_for_each_entry(sb, &super_blocks, s_list) {
 524                if (hlist_unhashed(&sb->s_instances))
 525                        continue;
 526                sb->s_count++;
 527                spin_unlock(&sb_lock);
 528
 529                down_read(&sb->s_umount);
 530                if (sb->s_root && (sb->s_flags & MS_BORN))
 531                        f(sb, arg);
 532                up_read(&sb->s_umount);
 533
 534                spin_lock(&sb_lock);
 535                if (p)
 536                        __put_super(p);
 537                p = sb;
 538        }
 539        if (p)
 540                __put_super(p);
 541        spin_unlock(&sb_lock);
 542}
 543
 544/**
 545 *      iterate_supers_type - call function for superblocks of given type
 546 *      @type: fs type
 547 *      @f: function to call
 548 *      @arg: argument to pass to it
 549 *
 550 *      Scans the superblock list and calls given function, passing it
 551 *      locked superblock and given argument.
 552 */
 553void iterate_supers_type(struct file_system_type *type,
 554        void (*f)(struct super_block *, void *), void *arg)
 555{
 556        struct super_block *sb, *p = NULL;
 557        struct hlist_node *node;
 558
 559        spin_lock(&sb_lock);
 560        hlist_for_each_entry(sb, node, &type->fs_supers, s_instances) {
 561                sb->s_count++;
 562                spin_unlock(&sb_lock);
 563
 564                down_read(&sb->s_umount);
 565                if (sb->s_root && (sb->s_flags & MS_BORN))
 566                        f(sb, arg);
 567                up_read(&sb->s_umount);
 568
 569                spin_lock(&sb_lock);
 570                if (p)
 571                        __put_super(p);
 572                p = sb;
 573        }
 574        if (p)
 575                __put_super(p);
 576        spin_unlock(&sb_lock);
 577}
 578
 579EXPORT_SYMBOL(iterate_supers_type);
 580
 581/**
 582 *      get_super - get the superblock of a device
 583 *      @bdev: device to get the superblock for
 584 *      
 585 *      Scans the superblock list and finds the superblock of the file system
 586 *      mounted on the device given. %NULL is returned if no match is found.
 587 */
 588
 589struct super_block *get_super(struct block_device *bdev)
 590{
 591        struct super_block *sb;
 592
 593        if (!bdev)
 594                return NULL;
 595
 596        spin_lock(&sb_lock);
 597rescan:
 598        list_for_each_entry(sb, &super_blocks, s_list) {
 599                if (hlist_unhashed(&sb->s_instances))
 600                        continue;
 601                if (sb->s_bdev == bdev) {
 602                        sb->s_count++;
 603                        spin_unlock(&sb_lock);
 604                        down_read(&sb->s_umount);
 605                        /* still alive? */
 606                        if (sb->s_root && (sb->s_flags & MS_BORN))
 607                                return sb;
 608                        up_read(&sb->s_umount);
 609                        /* nope, got unmounted */
 610                        spin_lock(&sb_lock);
 611                        __put_super(sb);
 612                        goto rescan;
 613                }
 614        }
 615        spin_unlock(&sb_lock);
 616        return NULL;
 617}
 618
 619EXPORT_SYMBOL(get_super);
 620
 621/**
 622 *      get_super_thawed - get thawed superblock of a device
 623 *      @bdev: device to get the superblock for
 624 *
 625 *      Scans the superblock list and finds the superblock of the file system
 626 *      mounted on the device. The superblock is returned once it is thawed
 627 *      (or immediately if it was not frozen). %NULL is returned if no match
 628 *      is found.
 629 */
 630struct super_block *get_super_thawed(struct block_device *bdev)
 631{
 632        while (1) {
 633                struct super_block *s = get_super(bdev);
 634                if (!s || s->s_writers.frozen == SB_UNFROZEN)
 635                        return s;
 636                up_read(&s->s_umount);
 637                wait_event(s->s_writers.wait_unfrozen,
 638                           s->s_writers.frozen == SB_UNFROZEN);
 639                put_super(s);
 640        }
 641}
 642EXPORT_SYMBOL(get_super_thawed);
 643
 644/**
 645 * get_active_super - get an active reference to the superblock of a device
 646 * @bdev: device to get the superblock for
 647 *
 648 * Scans the superblock list and finds the superblock of the file system
 649 * mounted on the device given.  Returns the superblock with an active
 650 * reference or %NULL if none was found.
 651 */
 652struct super_block *get_active_super(struct block_device *bdev)
 653{
 654        struct super_block *sb;
 655
 656        if (!bdev)
 657                return NULL;
 658
 659restart:
 660        spin_lock(&sb_lock);
 661        list_for_each_entry(sb, &super_blocks, s_list) {
 662                if (hlist_unhashed(&sb->s_instances))
 663                        continue;
 664                if (sb->s_bdev == bdev) {
 665                        if (grab_super(sb)) /* drops sb_lock */
 666                                return sb;
 667                        else
 668                                goto restart;
 669                }
 670        }
 671        spin_unlock(&sb_lock);
 672        return NULL;
 673}
 674 
 675struct super_block *user_get_super(dev_t dev)
 676{
 677        struct super_block *sb;
 678
 679        spin_lock(&sb_lock);
 680rescan:
 681        list_for_each_entry(sb, &super_blocks, s_list) {
 682                if (hlist_unhashed(&sb->s_instances))
 683                        continue;
 684                if (sb->s_dev ==  dev) {
 685                        sb->s_count++;
 686                        spin_unlock(&sb_lock);
 687                        down_read(&sb->s_umount);
 688                        /* still alive? */
 689                        if (sb->s_root && (sb->s_flags & MS_BORN))
 690                                return sb;
 691                        up_read(&sb->s_umount);
 692                        /* nope, got unmounted */
 693                        spin_lock(&sb_lock);
 694                        __put_super(sb);
 695                        goto rescan;
 696                }
 697        }
 698        spin_unlock(&sb_lock);
 699        return NULL;
 700}
 701
 702/**
 703 *      do_remount_sb - asks filesystem to change mount options.
 704 *      @sb:    superblock in question
 705 *      @flags: numeric part of options
 706 *      @data:  the rest of options
 707 *      @force: whether or not to force the change
 708 *
 709 *      Alters the mount options of a mounted file system.
 710 */
 711int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 712{
 713        int retval;
 714        int remount_ro;
 715
 716        if (sb->s_writers.frozen != SB_UNFROZEN)
 717                return -EBUSY;
 718
 719#ifdef CONFIG_BLOCK
 720        if (!(flags & MS_RDONLY) && bdev_read_only(sb->s_bdev))
 721                return -EACCES;
 722#endif
 723
 724        if (flags & MS_RDONLY)
 725                acct_auto_close(sb);
 726        shrink_dcache_sb(sb);
 727        sync_filesystem(sb);
 728
 729        remount_ro = (flags & MS_RDONLY) && !(sb->s_flags & MS_RDONLY);
 730
 731        /* If we are remounting RDONLY and current sb is read/write,
 732           make sure there are no rw files opened */
 733        if (remount_ro) {
 734                if (force) {
 735                        mark_files_ro(sb);
 736                } else {
 737                        retval = sb_prepare_remount_readonly(sb);
 738                        if (retval)
 739                                return retval;
 740                }
 741        }
 742
 743        if (sb->s_op->remount_fs) {
 744                retval = sb->s_op->remount_fs(sb, &flags, data);
 745                if (retval) {
 746                        if (!force)
 747                                goto cancel_readonly;
 748                        /* If forced remount, go ahead despite any errors */
 749                        WARN(1, "forced remount of a %s fs returned %i\n",
 750                             sb->s_type->name, retval);
 751                }
 752        }
 753        sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (flags & MS_RMT_MASK);
 754        /* Needs to be ordered wrt mnt_is_readonly() */
 755        smp_wmb();
 756        sb->s_readonly_remount = 0;
 757
 758        /*
 759         * Some filesystems modify their metadata via some other path than the
 760         * bdev buffer cache (eg. use a private mapping, or directories in
 761         * pagecache, etc). Also file data modifications go via their own
 762         * mappings. So If we try to mount readonly then copy the filesystem
 763         * from bdev, we could get stale data, so invalidate it to give a best
 764         * effort at coherency.
 765         */
 766        if (remount_ro && sb->s_bdev)
 767                invalidate_bdev(sb->s_bdev);
 768        return 0;
 769
 770cancel_readonly:
 771        sb->s_readonly_remount = 0;
 772        return retval;
 773}
 774
 775static void do_emergency_remount(struct work_struct *work)
 776{
 777        struct super_block *sb, *p = NULL;
 778
 779        spin_lock(&sb_lock);
 780        list_for_each_entry(sb, &super_blocks, s_list) {
 781                if (hlist_unhashed(&sb->s_instances))
 782                        continue;
 783                sb->s_count++;
 784                spin_unlock(&sb_lock);
 785                down_write(&sb->s_umount);
 786                if (sb->s_root && sb->s_bdev && (sb->s_flags & MS_BORN) &&
 787                    !(sb->s_flags & MS_RDONLY)) {
 788                        /*
 789                         * What lock protects sb->s_flags??
 790                         */
 791                        do_remount_sb(sb, MS_RDONLY, NULL, 1);
 792                }
 793                up_write(&sb->s_umount);
 794                spin_lock(&sb_lock);
 795                if (p)
 796                        __put_super(p);
 797                p = sb;
 798        }
 799        if (p)
 800                __put_super(p);
 801        spin_unlock(&sb_lock);
 802        kfree(work);
 803        printk("Emergency Remount complete\n");
 804}
 805
 806void emergency_remount(void)
 807{
 808        struct work_struct *work;
 809
 810        work = kmalloc(sizeof(*work), GFP_ATOMIC);
 811        if (work) {
 812                INIT_WORK(work, do_emergency_remount);
 813                schedule_work(work);
 814        }
 815}
 816
 817/*
 818 * Unnamed block devices are dummy devices used by virtual
 819 * filesystems which don't use real block-devices.  -- jrs
 820 */
 821
 822static DEFINE_IDA(unnamed_dev_ida);
 823static DEFINE_SPINLOCK(unnamed_dev_lock);/* protects the above */
 824static int unnamed_dev_start = 0; /* don't bother trying below it */
 825
 826int get_anon_bdev(dev_t *p)
 827{
 828        int dev;
 829        int error;
 830
 831 retry:
 832        if (ida_pre_get(&unnamed_dev_ida, GFP_ATOMIC) == 0)
 833                return -ENOMEM;
 834        spin_lock(&unnamed_dev_lock);
 835        error = ida_get_new_above(&unnamed_dev_ida, unnamed_dev_start, &dev);
 836        if (!error)
 837                unnamed_dev_start = dev + 1;
 838        spin_unlock(&unnamed_dev_lock);
 839        if (error == -EAGAIN)
 840                /* We raced and lost with another CPU. */
 841                goto retry;
 842        else if (error)
 843                return -EAGAIN;
 844
 845        if ((dev & MAX_IDR_MASK) == (1 << MINORBITS)) {
 846                spin_lock(&unnamed_dev_lock);
 847                ida_remove(&unnamed_dev_ida, dev);
 848                if (unnamed_dev_start > dev)
 849                        unnamed_dev_start = dev;
 850                spin_unlock(&unnamed_dev_lock);
 851                return -EMFILE;
 852        }
 853        *p = MKDEV(0, dev & MINORMASK);
 854        return 0;
 855}
 856EXPORT_SYMBOL(get_anon_bdev);
 857
 858void free_anon_bdev(dev_t dev)
 859{
 860        int slot = MINOR(dev);
 861        spin_lock(&unnamed_dev_lock);
 862        ida_remove(&unnamed_dev_ida, slot);
 863        if (slot < unnamed_dev_start)
 864                unnamed_dev_start = slot;
 865        spin_unlock(&unnamed_dev_lock);
 866}
 867EXPORT_SYMBOL(free_anon_bdev);
 868
 869int set_anon_super(struct super_block *s, void *data)
 870{
 871        int error = get_anon_bdev(&s->s_dev);
 872        if (!error)
 873                s->s_bdi = &noop_backing_dev_info;
 874        return error;
 875}
 876
 877EXPORT_SYMBOL(set_anon_super);
 878
 879void kill_anon_super(struct super_block *sb)
 880{
 881        dev_t dev = sb->s_dev;
 882        generic_shutdown_super(sb);
 883        free_anon_bdev(dev);
 884}
 885
 886EXPORT_SYMBOL(kill_anon_super);
 887
 888void kill_litter_super(struct super_block *sb)
 889{
 890        if (sb->s_root)
 891                d_genocide(sb->s_root);
 892        kill_anon_super(sb);
 893}
 894
 895EXPORT_SYMBOL(kill_litter_super);
 896
 897static int ns_test_super(struct super_block *sb, void *data)
 898{
 899        return sb->s_fs_info == data;
 900}
 901
 902static int ns_set_super(struct super_block *sb, void *data)
 903{
 904        sb->s_fs_info = data;
 905        return set_anon_super(sb, NULL);
 906}
 907
 908struct dentry *mount_ns(struct file_system_type *fs_type, int flags,
 909        void *data, int (*fill_super)(struct super_block *, void *, int))
 910{
 911        struct super_block *sb;
 912
 913        sb = sget(fs_type, ns_test_super, ns_set_super, flags, data);
 914        if (IS_ERR(sb))
 915                return ERR_CAST(sb);
 916
 917        if (!sb->s_root) {
 918                int err;
 919                err = fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 920                if (err) {
 921                        deactivate_locked_super(sb);
 922                        return ERR_PTR(err);
 923                }
 924
 925                sb->s_flags |= MS_ACTIVE;
 926        }
 927
 928        return dget(sb->s_root);
 929}
 930
 931EXPORT_SYMBOL(mount_ns);
 932
 933#ifdef CONFIG_BLOCK
 934static int set_bdev_super(struct super_block *s, void *data)
 935{
 936        s->s_bdev = data;
 937        s->s_dev = s->s_bdev->bd_dev;
 938
 939        /*
 940         * We set the bdi here to the queue backing, file systems can
 941         * overwrite this in ->fill_super()
 942         */
 943        s->s_bdi = &bdev_get_queue(s->s_bdev)->backing_dev_info;
 944        return 0;
 945}
 946
 947static int test_bdev_super(struct super_block *s, void *data)
 948{
 949        return (void *)s->s_bdev == data;
 950}
 951
 952struct dentry *mount_bdev(struct file_system_type *fs_type,
 953        int flags, const char *dev_name, void *data,
 954        int (*fill_super)(struct super_block *, void *, int))
 955{
 956        struct block_device *bdev;
 957        struct super_block *s;
 958        fmode_t mode = FMODE_READ | FMODE_EXCL;
 959        int error = 0;
 960
 961        if (!(flags & MS_RDONLY))
 962                mode |= FMODE_WRITE;
 963
 964        bdev = blkdev_get_by_path(dev_name, mode, fs_type);
 965        if (IS_ERR(bdev))
 966                return ERR_CAST(bdev);
 967
 968        /*
 969         * once the super is inserted into the list by sget, s_umount
 970         * will protect the lockfs code from trying to start a snapshot
 971         * while we are mounting
 972         */
 973        mutex_lock(&bdev->bd_fsfreeze_mutex);
 974        if (bdev->bd_fsfreeze_count > 0) {
 975                mutex_unlock(&bdev->bd_fsfreeze_mutex);
 976                error = -EBUSY;
 977                goto error_bdev;
 978        }
 979        s = sget(fs_type, test_bdev_super, set_bdev_super, flags | MS_NOSEC,
 980                 bdev);
 981        mutex_unlock(&bdev->bd_fsfreeze_mutex);
 982        if (IS_ERR(s))
 983                goto error_s;
 984
 985        if (s->s_root) {
 986                if ((flags ^ s->s_flags) & MS_RDONLY) {
 987                        deactivate_locked_super(s);
 988                        error = -EBUSY;
 989                        goto error_bdev;
 990                }
 991
 992                /*
 993                 * s_umount nests inside bd_mutex during
 994                 * __invalidate_device().  blkdev_put() acquires
 995                 * bd_mutex and can't be called under s_umount.  Drop
 996                 * s_umount temporarily.  This is safe as we're
 997                 * holding an active reference.
 998                 */
 999                up_write(&s->s_umount);
1000                blkdev_put(bdev, mode);
1001                down_write(&s->s_umount);
1002        } else {
1003                char b[BDEVNAME_SIZE];
1004
1005                s->s_mode = mode;
1006                strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
1007                sb_set_blocksize(s, block_size(bdev));
1008                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1009                if (error) {
1010                        deactivate_locked_super(s);
1011                        goto error;
1012                }
1013
1014                s->s_flags |= MS_ACTIVE;
1015                bdev->bd_super = s;
1016        }
1017
1018        return dget(s->s_root);
1019
1020error_s:
1021        error = PTR_ERR(s);
1022error_bdev:
1023        blkdev_put(bdev, mode);
1024error:
1025        return ERR_PTR(error);
1026}
1027EXPORT_SYMBOL(mount_bdev);
1028
1029void kill_block_super(struct super_block *sb)
1030{
1031        struct block_device *bdev = sb->s_bdev;
1032        fmode_t mode = sb->s_mode;
1033
1034        bdev->bd_super = NULL;
1035        generic_shutdown_super(sb);
1036        sync_blockdev(bdev);
1037        WARN_ON_ONCE(!(mode & FMODE_EXCL));
1038        blkdev_put(bdev, mode | FMODE_EXCL);
1039}
1040
1041EXPORT_SYMBOL(kill_block_super);
1042#endif
1043
1044struct dentry *mount_nodev(struct file_system_type *fs_type,
1045        int flags, void *data,
1046        int (*fill_super)(struct super_block *, void *, int))
1047{
1048        int error;
1049        struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
1050
1051        if (IS_ERR(s))
1052                return ERR_CAST(s);
1053
1054        error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1055        if (error) {
1056                deactivate_locked_super(s);
1057                return ERR_PTR(error);
1058        }
1059        s->s_flags |= MS_ACTIVE;
1060        return dget(s->s_root);
1061}
1062EXPORT_SYMBOL(mount_nodev);
1063
1064static int compare_single(struct super_block *s, void *p)
1065{
1066        return 1;
1067}
1068
1069struct dentry *mount_single(struct file_system_type *fs_type,
1070        int flags, void *data,
1071        int (*fill_super)(struct super_block *, void *, int))
1072{
1073        struct super_block *s;
1074        int error;
1075
1076        s = sget(fs_type, compare_single, set_anon_super, flags, NULL);
1077        if (IS_ERR(s))
1078                return ERR_CAST(s);
1079        if (!s->s_root) {
1080                error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
1081                if (error) {
1082                        deactivate_locked_super(s);
1083                        return ERR_PTR(error);
1084                }
1085                s->s_flags |= MS_ACTIVE;
1086        } else {
1087                do_remount_sb(s, flags, data, 0);
1088        }
1089        return dget(s->s_root);
1090}
1091EXPORT_SYMBOL(mount_single);
1092
1093struct dentry *
1094mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
1095{
1096        struct dentry *root;
1097        struct super_block *sb;
1098        char *secdata = NULL;
1099        int error = -ENOMEM;
1100
1101        if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
1102                secdata = alloc_secdata();
1103                if (!secdata)
1104                        goto out;
1105
1106                error = security_sb_copy_data(data, secdata);
1107                if (error)
1108                        goto out_free_secdata;
1109        }
1110
1111        root = type->mount(type, flags, name, data);
1112        if (IS_ERR(root)) {
1113                error = PTR_ERR(root);
1114                goto out_free_secdata;
1115        }
1116        sb = root->d_sb;
1117        BUG_ON(!sb);
1118        WARN_ON(!sb->s_bdi);
1119        WARN_ON(sb->s_bdi == &default_backing_dev_info);
1120        sb->s_flags |= MS_BORN;
1121
1122        error = security_sb_kern_mount(sb, flags, secdata);
1123        if (error)
1124                goto out_sb;
1125
1126        /*
1127         * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE
1128         * but s_maxbytes was an unsigned long long for many releases. Throw
1129         * this warning for a little while to try and catch filesystems that
1130         * violate this rule.
1131         */
1132        WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
1133                "negative value (%lld)\n", type->name, sb->s_maxbytes);
1134
1135        up_write(&sb->s_umount);
1136        free_secdata(secdata);
1137        return root;
1138out_sb:
1139        dput(root);
1140        deactivate_locked_super(sb);
1141out_free_secdata:
1142        free_secdata(secdata);
1143out:
1144        return ERR_PTR(error);
1145}
1146
1147/*
1148 * This is an internal function, please use sb_end_{write,pagefault,intwrite}
1149 * instead.
1150 */
1151void __sb_end_write(struct super_block *sb, int level)
1152{
1153        percpu_counter_dec(&sb->s_writers.counter[level-1]);
1154        /*
1155         * Make sure s_writers are updated before we wake up waiters in
1156         * freeze_super().
1157         */
1158        smp_mb();
1159        if (waitqueue_active(&sb->s_writers.wait))
1160                wake_up(&sb->s_writers.wait);
1161        rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
1162}
1163EXPORT_SYMBOL(__sb_end_write);
1164
1165#ifdef CONFIG_LOCKDEP
1166/*
1167 * We want lockdep to tell us about possible deadlocks with freezing but
1168 * it's it bit tricky to properly instrument it. Getting a freeze protection
1169 * works as getting a read lock but there are subtle problems. XFS for example
1170 * gets freeze protection on internal level twice in some cases, which is OK
1171 * only because we already hold a freeze protection also on higher level. Due
1172 * to these cases we have to tell lockdep we are doing trylock when we
1173 * already hold a freeze protection for a higher freeze level.
1174 */
1175static void acquire_freeze_lock(struct super_block *sb, int level, bool trylock,
1176                                unsigned long ip)
1177{
1178        int i;
1179
1180        if (!trylock) {
1181                for (i = 0; i < level - 1; i++)
1182                        if (lock_is_held(&sb->s_writers.lock_map[i])) {
1183                                trylock = true;
1184                                break;
1185                        }
1186        }
1187        rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, trylock, ip);
1188}
1189#endif
1190
1191/*
1192 * This is an internal function, please use sb_start_{write,pagefault,intwrite}
1193 * instead.
1194 */
1195int __sb_start_write(struct super_block *sb, int level, bool wait)
1196{
1197retry:
1198        if (unlikely(sb->s_writers.frozen >= level)) {
1199                if (!wait)
1200                        return 0;
1201                wait_event(sb->s_writers.wait_unfrozen,
1202                           sb->s_writers.frozen < level);
1203        }
1204
1205#ifdef CONFIG_LOCKDEP
1206        acquire_freeze_lock(sb, level, !wait, _RET_IP_);
1207#endif
1208        percpu_counter_inc(&sb->s_writers.counter[level-1]);
1209        /*
1210         * Make sure counter is updated before we check for frozen.
1211         * freeze_super() first sets frozen and then checks the counter.
1212         */
1213        smp_mb();
1214        if (unlikely(sb->s_writers.frozen >= level)) {
1215                __sb_end_write(sb, level);
1216                goto retry;
1217        }
1218        return 1;
1219}
1220EXPORT_SYMBOL(__sb_start_write);
1221
1222/**
1223 * sb_wait_write - wait until all writers to given file system finish
1224 * @sb: the super for which we wait
1225 * @level: type of writers we wait for (normal vs page fault)
1226 *
1227 * This function waits until there are no writers of given type to given file
1228 * system. Caller of this function should make sure there can be no new writers
1229 * of type @level before calling this function. Otherwise this function can
1230 * livelock.
1231 */
1232static void sb_wait_write(struct super_block *sb, int level)
1233{
1234        s64 writers;
1235
1236        /*
1237         * We just cycle-through lockdep here so that it does not complain
1238         * about returning with lock to userspace
1239         */
1240        rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
1241        rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
1242
1243        do {
1244                DEFINE_WAIT(wait);
1245
1246                /*
1247                 * We use a barrier in prepare_to_wait() to separate setting
1248                 * of frozen and checking of the counter
1249                 */
1250                prepare_to_wait(&sb->s_writers.wait, &wait,
1251                                TASK_UNINTERRUPTIBLE);
1252
1253                writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
1254                if (writers)
1255                        schedule();
1256
1257                finish_wait(&sb->s_writers.wait, &wait);
1258        } while (writers);
1259}
1260
1261/**
1262 * freeze_super - lock the filesystem and force it into a consistent state
1263 * @sb: the super to lock
1264 *
1265 * Syncs the super to make sure the filesystem is consistent and calls the fs's
1266 * freeze_fs.  Subsequent calls to this without first thawing the fs will return
1267 * -EBUSY.
1268 *
1269 * During this function, sb->s_writers.frozen goes through these values:
1270 *
1271 * SB_UNFROZEN: File system is normal, all writes progress as usual.
1272 *
1273 * SB_FREEZE_WRITE: The file system is in the process of being frozen.  New
1274 * writes should be blocked, though page faults are still allowed. We wait for
1275 * all writes to complete and then proceed to the next stage.
1276 *
1277 * SB_FREEZE_PAGEFAULT: Freezing continues. Now also page faults are blocked
1278 * but internal fs threads can still modify the filesystem (although they
1279 * should not dirty new pages or inodes), writeback can run etc. After waiting
1280 * for all running page faults we sync the filesystem which will clean all
1281 * dirty pages and inodes (no new dirty pages or inodes can be created when
1282 * sync is running).
1283 *
1284 * SB_FREEZE_FS: The file system is frozen. Now all internal sources of fs
1285 * modification are blocked (e.g. XFS preallocation truncation on inode
1286 * reclaim). This is usually implemented by blocking new transactions for
1287 * filesystems that have them and need this additional guard. After all
1288 * internal writers are finished we call ->freeze_fs() to finish filesystem
1289 * freezing. Then we transition to SB_FREEZE_COMPLETE state. This state is
1290 * mostly auxiliary for filesystems to verify they do not modify frozen fs.
1291 *
1292 * sb->s_writers.frozen is protected by sb->s_umount.
1293 */
1294int freeze_super(struct super_block *sb)
1295{
1296        int ret;
1297
1298        atomic_inc(&sb->s_active);
1299        down_write(&sb->s_umount);
1300        if (sb->s_writers.frozen != SB_UNFROZEN) {
1301                deactivate_locked_super(sb);
1302                return -EBUSY;
1303        }
1304
1305        if (!(sb->s_flags & MS_BORN)) {
1306                up_write(&sb->s_umount);
1307                return 0;       /* sic - it's "nothing to do" */
1308        }
1309
1310        if (sb->s_flags & MS_RDONLY) {
1311                /* Nothing to do really... */
1312                sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1313                up_write(&sb->s_umount);
1314                return 0;
1315        }
1316
1317        /* From now on, no new normal writers can start */
1318        sb->s_writers.frozen = SB_FREEZE_WRITE;
1319        smp_wmb();
1320
1321        /* Release s_umount to preserve sb_start_write -> s_umount ordering */
1322        up_write(&sb->s_umount);
1323
1324        sb_wait_write(sb, SB_FREEZE_WRITE);
1325
1326        /* Now we go and block page faults... */
1327        down_write(&sb->s_umount);
1328        sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
1329        smp_wmb();
1330
1331        sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
1332
1333        /* All writers are done so after syncing there won't be dirty data */
1334        sync_filesystem(sb);
1335
1336        /* Now wait for internal filesystem counter */
1337        sb->s_writers.frozen = SB_FREEZE_FS;
1338        smp_wmb();
1339        sb_wait_write(sb, SB_FREEZE_FS);
1340
1341        if (sb->s_op->freeze_fs) {
1342                ret = sb->s_op->freeze_fs(sb);
1343                if (ret) {
1344                        printk(KERN_ERR
1345                                "VFS:Filesystem freeze failed\n");
1346                        sb->s_writers.frozen = SB_UNFROZEN;
1347                        smp_wmb();
1348                        wake_up(&sb->s_writers.wait_unfrozen);
1349                        deactivate_locked_super(sb);
1350                        return ret;
1351                }
1352        }
1353        /*
1354         * This is just for debugging purposes so that fs can warn if it
1355         * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
1356         */
1357        sb->s_writers.frozen = SB_FREEZE_COMPLETE;
1358        up_write(&sb->s_umount);
1359        return 0;
1360}
1361EXPORT_SYMBOL(freeze_super);
1362
1363/**
1364 * thaw_super -- unlock filesystem
1365 * @sb: the super to thaw
1366 *
1367 * Unlocks the filesystem and marks it writeable again after freeze_super().
1368 */
1369int thaw_super(struct super_block *sb)
1370{
1371        int error;
1372
1373        down_write(&sb->s_umount);
1374        if (sb->s_writers.frozen == SB_UNFROZEN) {
1375                up_write(&sb->s_umount);
1376                return -EINVAL;
1377        }
1378
1379        if (sb->s_flags & MS_RDONLY)
1380                goto out;
1381
1382        if (sb->s_op->unfreeze_fs) {
1383                error = sb->s_op->unfreeze_fs(sb);
1384                if (error) {
1385                        printk(KERN_ERR
1386                                "VFS:Filesystem thaw failed\n");
1387                        up_write(&sb->s_umount);
1388                        return error;
1389                }
1390        }
1391
1392out:
1393        sb->s_writers.frozen = SB_UNFROZEN;
1394        smp_wmb();
1395        wake_up(&sb->s_writers.wait_unfrozen);
1396        deactivate_locked_super(sb);
1397
1398        return 0;
1399}
1400EXPORT_SYMBOL(thaw_super);
1401
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