linux/fs/dcache.c
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   1/*
   2 * fs/dcache.c
   3 *
   4 * Complete reimplementation
   5 * (C) 1997 Thomas Schoebel-Theuer,
   6 * with heavy changes by Linus Torvalds
   7 */
   8
   9/*
  10 * Notes on the allocation strategy:
  11 *
  12 * The dcache is a master of the icache - whenever a dcache entry
  13 * exists, the inode will always exist. "iput()" is done either when
  14 * the dcache entry is deleted or garbage collected.
  15 */
  16
  17#include <linux/ratelimit.h>
  18#include <linux/string.h>
  19#include <linux/mm.h>
  20#include <linux/fs.h>
  21#include <linux/fsnotify.h>
  22#include <linux/slab.h>
  23#include <linux/init.h>
  24#include <linux/hash.h>
  25#include <linux/cache.h>
  26#include <linux/export.h>
  27#include <linux/security.h>
  28#include <linux/seqlock.h>
  29#include <linux/memblock.h>
  30#include <linux/bit_spinlock.h>
  31#include <linux/rculist_bl.h>
  32#include <linux/list_lru.h>
  33#include "internal.h"
  34#include "mount.h"
  35
  36/*
  37 * Usage:
  38 * dcache->d_inode->i_lock protects:
  39 *   - i_dentry, d_u.d_alias, d_inode of aliases
  40 * dcache_hash_bucket lock protects:
  41 *   - the dcache hash table
  42 * s_roots bl list spinlock protects:
  43 *   - the s_roots list (see __d_drop)
  44 * dentry->d_sb->s_dentry_lru_lock protects:
  45 *   - the dcache lru lists and counters
  46 * d_lock protects:
  47 *   - d_flags
  48 *   - d_name
  49 *   - d_lru
  50 *   - d_count
  51 *   - d_unhashed()
  52 *   - d_parent and d_subdirs
  53 *   - childrens' d_child and d_parent
  54 *   - d_u.d_alias, d_inode
  55 *
  56 * Ordering:
  57 * dentry->d_inode->i_lock
  58 *   dentry->d_lock
  59 *     dentry->d_sb->s_dentry_lru_lock
  60 *     dcache_hash_bucket lock
  61 *     s_roots lock
  62 *
  63 * If there is an ancestor relationship:
  64 * dentry->d_parent->...->d_parent->d_lock
  65 *   ...
  66 *     dentry->d_parent->d_lock
  67 *       dentry->d_lock
  68 *
  69 * If no ancestor relationship:
  70 * arbitrary, since it's serialized on rename_lock
  71 */
  72int sysctl_vfs_cache_pressure __read_mostly = 100;
  73EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
  74
  75__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
  76
  77EXPORT_SYMBOL(rename_lock);
  78
  79static struct kmem_cache *dentry_cache __read_mostly;
  80
  81const struct qstr empty_name = QSTR_INIT("", 0);
  82EXPORT_SYMBOL(empty_name);
  83const struct qstr slash_name = QSTR_INIT("/", 1);
  84EXPORT_SYMBOL(slash_name);
  85
  86/*
  87 * This is the single most critical data structure when it comes
  88 * to the dcache: the hashtable for lookups. Somebody should try
  89 * to make this good - I've just made it work.
  90 *
  91 * This hash-function tries to avoid losing too many bits of hash
  92 * information, yet avoid using a prime hash-size or similar.
  93 */
  94
  95static unsigned int d_hash_shift __read_mostly;
  96
  97static struct hlist_bl_head *dentry_hashtable __read_mostly;
  98
  99static inline struct hlist_bl_head *d_hash(unsigned int hash)
 100{
 101        return dentry_hashtable + (hash >> d_hash_shift);
 102}
 103
 104#define IN_LOOKUP_SHIFT 10
 105static struct hlist_bl_head in_lookup_hashtable[1 << IN_LOOKUP_SHIFT];
 106
 107static inline struct hlist_bl_head *in_lookup_hash(const struct dentry *parent,
 108                                        unsigned int hash)
 109{
 110        hash += (unsigned long) parent / L1_CACHE_BYTES;
 111        return in_lookup_hashtable + hash_32(hash, IN_LOOKUP_SHIFT);
 112}
 113
 114
 115/* Statistics gathering. */
 116struct dentry_stat_t dentry_stat = {
 117        .age_limit = 45,
 118};
 119
 120static DEFINE_PER_CPU(long, nr_dentry);
 121static DEFINE_PER_CPU(long, nr_dentry_unused);
 122
 123#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
 124
 125/*
 126 * Here we resort to our own counters instead of using generic per-cpu counters
 127 * for consistency with what the vfs inode code does. We are expected to harvest
 128 * better code and performance by having our own specialized counters.
 129 *
 130 * Please note that the loop is done over all possible CPUs, not over all online
 131 * CPUs. The reason for this is that we don't want to play games with CPUs going
 132 * on and off. If one of them goes off, we will just keep their counters.
 133 *
 134 * glommer: See cffbc8a for details, and if you ever intend to change this,
 135 * please update all vfs counters to match.
 136 */
 137static long get_nr_dentry(void)
 138{
 139        int i;
 140        long sum = 0;
 141        for_each_possible_cpu(i)
 142                sum += per_cpu(nr_dentry, i);
 143        return sum < 0 ? 0 : sum;
 144}
 145
 146static long get_nr_dentry_unused(void)
 147{
 148        int i;
 149        long sum = 0;
 150        for_each_possible_cpu(i)
 151                sum += per_cpu(nr_dentry_unused, i);
 152        return sum < 0 ? 0 : sum;
 153}
 154
 155int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer,
 156                   size_t *lenp, loff_t *ppos)
 157{
 158        dentry_stat.nr_dentry = get_nr_dentry();
 159        dentry_stat.nr_unused = get_nr_dentry_unused();
 160        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 161}
 162#endif
 163
 164/*
 165 * Compare 2 name strings, return 0 if they match, otherwise non-zero.
 166 * The strings are both count bytes long, and count is non-zero.
 167 */
 168#ifdef CONFIG_DCACHE_WORD_ACCESS
 169
 170#include <asm/word-at-a-time.h>
 171/*
 172 * NOTE! 'cs' and 'scount' come from a dentry, so it has a
 173 * aligned allocation for this particular component. We don't
 174 * strictly need the load_unaligned_zeropad() safety, but it
 175 * doesn't hurt either.
 176 *
 177 * In contrast, 'ct' and 'tcount' can be from a pathname, and do
 178 * need the careful unaligned handling.
 179 */
 180static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
 181{
 182        unsigned long a,b,mask;
 183
 184        for (;;) {
 185                a = read_word_at_a_time(cs);
 186                b = load_unaligned_zeropad(ct);
 187                if (tcount < sizeof(unsigned long))
 188                        break;
 189                if (unlikely(a != b))
 190                        return 1;
 191                cs += sizeof(unsigned long);
 192                ct += sizeof(unsigned long);
 193                tcount -= sizeof(unsigned long);
 194                if (!tcount)
 195                        return 0;
 196        }
 197        mask = bytemask_from_count(tcount);
 198        return unlikely(!!((a ^ b) & mask));
 199}
 200
 201#else
 202
 203static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
 204{
 205        do {
 206                if (*cs != *ct)
 207                        return 1;
 208                cs++;
 209                ct++;
 210                tcount--;
 211        } while (tcount);
 212        return 0;
 213}
 214
 215#endif
 216
 217static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
 218{
 219        /*
 220         * Be careful about RCU walk racing with rename:
 221         * use 'READ_ONCE' to fetch the name pointer.
 222         *
 223         * NOTE! Even if a rename will mean that the length
 224         * was not loaded atomically, we don't care. The
 225         * RCU walk will check the sequence count eventually,
 226         * and catch it. And we won't overrun the buffer,
 227         * because we're reading the name pointer atomically,
 228         * and a dentry name is guaranteed to be properly
 229         * terminated with a NUL byte.
 230         *
 231         * End result: even if 'len' is wrong, we'll exit
 232         * early because the data cannot match (there can
 233         * be no NUL in the ct/tcount data)
 234         */
 235        const unsigned char *cs = READ_ONCE(dentry->d_name.name);
 236
 237        return dentry_string_cmp(cs, ct, tcount);
 238}
 239
 240struct external_name {
 241        union {
 242                atomic_t count;
 243                struct rcu_head head;
 244        } u;
 245        unsigned char name[];
 246};
 247
 248static inline struct external_name *external_name(struct dentry *dentry)
 249{
 250        return container_of(dentry->d_name.name, struct external_name, name[0]);
 251}
 252
 253static void __d_free(struct rcu_head *head)
 254{
 255        struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
 256
 257        kmem_cache_free(dentry_cache, dentry); 
 258}
 259
 260static void __d_free_external(struct rcu_head *head)
 261{
 262        struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
 263        kfree(external_name(dentry));
 264        kmem_cache_free(dentry_cache, dentry);
 265}
 266
 267static inline int dname_external(const struct dentry *dentry)
 268{
 269        return dentry->d_name.name != dentry->d_iname;
 270}
 271
 272void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
 273{
 274        spin_lock(&dentry->d_lock);
 275        if (unlikely(dname_external(dentry))) {
 276                struct external_name *p = external_name(dentry);
 277                atomic_inc(&p->u.count);
 278                spin_unlock(&dentry->d_lock);
 279                name->name = p->name;
 280        } else {
 281                memcpy(name->inline_name, dentry->d_iname,
 282                       dentry->d_name.len + 1);
 283                spin_unlock(&dentry->d_lock);
 284                name->name = name->inline_name;
 285        }
 286}
 287EXPORT_SYMBOL(take_dentry_name_snapshot);
 288
 289void release_dentry_name_snapshot(struct name_snapshot *name)
 290{
 291        if (unlikely(name->name != name->inline_name)) {
 292                struct external_name *p;
 293                p = container_of(name->name, struct external_name, name[0]);
 294                if (unlikely(atomic_dec_and_test(&p->u.count)))
 295                        kfree_rcu(p, u.head);
 296        }
 297}
 298EXPORT_SYMBOL(release_dentry_name_snapshot);
 299
 300static inline void __d_set_inode_and_type(struct dentry *dentry,
 301                                          struct inode *inode,
 302                                          unsigned type_flags)
 303{
 304        unsigned flags;
 305
 306        dentry->d_inode = inode;
 307        flags = READ_ONCE(dentry->d_flags);
 308        flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
 309        flags |= type_flags;
 310        WRITE_ONCE(dentry->d_flags, flags);
 311}
 312
 313static inline void __d_clear_type_and_inode(struct dentry *dentry)
 314{
 315        unsigned flags = READ_ONCE(dentry->d_flags);
 316
 317        flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
 318        WRITE_ONCE(dentry->d_flags, flags);
 319        dentry->d_inode = NULL;
 320}
 321
 322static void dentry_free(struct dentry *dentry)
 323{
 324        WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
 325        if (unlikely(dname_external(dentry))) {
 326                struct external_name *p = external_name(dentry);
 327                if (likely(atomic_dec_and_test(&p->u.count))) {
 328                        call_rcu(&dentry->d_u.d_rcu, __d_free_external);
 329                        return;
 330                }
 331        }
 332        /* if dentry was never visible to RCU, immediate free is OK */
 333        if (!(dentry->d_flags & DCACHE_RCUACCESS))
 334                __d_free(&dentry->d_u.d_rcu);
 335        else
 336                call_rcu(&dentry->d_u.d_rcu, __d_free);
 337}
 338
 339/*
 340 * Release the dentry's inode, using the filesystem
 341 * d_iput() operation if defined.
 342 */
 343static void dentry_unlink_inode(struct dentry * dentry)
 344        __releases(dentry->d_lock)
 345        __releases(dentry->d_inode->i_lock)
 346{
 347        struct inode *inode = dentry->d_inode;
 348
 349        raw_write_seqcount_begin(&dentry->d_seq);
 350        __d_clear_type_and_inode(dentry);
 351        hlist_del_init(&dentry->d_u.d_alias);
 352        raw_write_seqcount_end(&dentry->d_seq);
 353        spin_unlock(&dentry->d_lock);
 354        spin_unlock(&inode->i_lock);
 355        if (!inode->i_nlink)
 356                fsnotify_inoderemove(inode);
 357        if (dentry->d_op && dentry->d_op->d_iput)
 358                dentry->d_op->d_iput(dentry, inode);
 359        else
 360                iput(inode);
 361}
 362
 363/*
 364 * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
 365 * is in use - which includes both the "real" per-superblock
 366 * LRU list _and_ the DCACHE_SHRINK_LIST use.
 367 *
 368 * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
 369 * on the shrink list (ie not on the superblock LRU list).
 370 *
 371 * The per-cpu "nr_dentry_unused" counters are updated with
 372 * the DCACHE_LRU_LIST bit.
 373 *
 374 * These helper functions make sure we always follow the
 375 * rules. d_lock must be held by the caller.
 376 */
 377#define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
 378static void d_lru_add(struct dentry *dentry)
 379{
 380        D_FLAG_VERIFY(dentry, 0);
 381        dentry->d_flags |= DCACHE_LRU_LIST;
 382        this_cpu_inc(nr_dentry_unused);
 383        WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
 384}
 385
 386static void d_lru_del(struct dentry *dentry)
 387{
 388        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
 389        dentry->d_flags &= ~DCACHE_LRU_LIST;
 390        this_cpu_dec(nr_dentry_unused);
 391        WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
 392}
 393
 394static void d_shrink_del(struct dentry *dentry)
 395{
 396        D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
 397        list_del_init(&dentry->d_lru);
 398        dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
 399        this_cpu_dec(nr_dentry_unused);
 400}
 401
 402static void d_shrink_add(struct dentry *dentry, struct list_head *list)
 403{
 404        D_FLAG_VERIFY(dentry, 0);
 405        list_add(&dentry->d_lru, list);
 406        dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
 407        this_cpu_inc(nr_dentry_unused);
 408}
 409
 410/*
 411 * These can only be called under the global LRU lock, ie during the
 412 * callback for freeing the LRU list. "isolate" removes it from the
 413 * LRU lists entirely, while shrink_move moves it to the indicated
 414 * private list.
 415 */
 416static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
 417{
 418        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
 419        dentry->d_flags &= ~DCACHE_LRU_LIST;
 420        this_cpu_dec(nr_dentry_unused);
 421        list_lru_isolate(lru, &dentry->d_lru);
 422}
 423
 424static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
 425                              struct list_head *list)
 426{
 427        D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
 428        dentry->d_flags |= DCACHE_SHRINK_LIST;
 429        list_lru_isolate_move(lru, &dentry->d_lru, list);
 430}
 431
 432/**
 433 * d_drop - drop a dentry
 434 * @dentry: dentry to drop
 435 *
 436 * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
 437 * be found through a VFS lookup any more. Note that this is different from
 438 * deleting the dentry - d_delete will try to mark the dentry negative if
 439 * possible, giving a successful _negative_ lookup, while d_drop will
 440 * just make the cache lookup fail.
 441 *
 442 * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
 443 * reason (NFS timeouts or autofs deletes).
 444 *
 445 * __d_drop requires dentry->d_lock
 446 * ___d_drop doesn't mark dentry as "unhashed"
 447 *   (dentry->d_hash.pprev will be LIST_POISON2, not NULL).
 448 */
 449static void ___d_drop(struct dentry *dentry)
 450{
 451        struct hlist_bl_head *b;
 452        /*
 453         * Hashed dentries are normally on the dentry hashtable,
 454         * with the exception of those newly allocated by
 455         * d_obtain_root, which are always IS_ROOT:
 456         */
 457        if (unlikely(IS_ROOT(dentry)))
 458                b = &dentry->d_sb->s_roots;
 459        else
 460                b = d_hash(dentry->d_name.hash);
 461
 462        hlist_bl_lock(b);
 463        __hlist_bl_del(&dentry->d_hash);
 464        hlist_bl_unlock(b);
 465}
 466
 467void __d_drop(struct dentry *dentry)
 468{
 469        if (!d_unhashed(dentry)) {
 470                ___d_drop(dentry);
 471                dentry->d_hash.pprev = NULL;
 472                write_seqcount_invalidate(&dentry->d_seq);
 473        }
 474}
 475EXPORT_SYMBOL(__d_drop);
 476
 477void d_drop(struct dentry *dentry)
 478{
 479        spin_lock(&dentry->d_lock);
 480        __d_drop(dentry);
 481        spin_unlock(&dentry->d_lock);
 482}
 483EXPORT_SYMBOL(d_drop);
 484
 485static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
 486{
 487        struct dentry *next;
 488        /*
 489         * Inform d_walk() and shrink_dentry_list() that we are no longer
 490         * attached to the dentry tree
 491         */
 492        dentry->d_flags |= DCACHE_DENTRY_KILLED;
 493        if (unlikely(list_empty(&dentry->d_child)))
 494                return;
 495        __list_del_entry(&dentry->d_child);
 496        /*
 497         * Cursors can move around the list of children.  While we'd been
 498         * a normal list member, it didn't matter - ->d_child.next would've
 499         * been updated.  However, from now on it won't be and for the
 500         * things like d_walk() it might end up with a nasty surprise.
 501         * Normally d_walk() doesn't care about cursors moving around -
 502         * ->d_lock on parent prevents that and since a cursor has no children
 503         * of its own, we get through it without ever unlocking the parent.
 504         * There is one exception, though - if we ascend from a child that
 505         * gets killed as soon as we unlock it, the next sibling is found
 506         * using the value left in its ->d_child.next.  And if _that_
 507         * pointed to a cursor, and cursor got moved (e.g. by lseek())
 508         * before d_walk() regains parent->d_lock, we'll end up skipping
 509         * everything the cursor had been moved past.
 510         *
 511         * Solution: make sure that the pointer left behind in ->d_child.next
 512         * points to something that won't be moving around.  I.e. skip the
 513         * cursors.
 514         */
 515        while (dentry->d_child.next != &parent->d_subdirs) {
 516                next = list_entry(dentry->d_child.next, struct dentry, d_child);
 517                if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
 518                        break;
 519                dentry->d_child.next = next->d_child.next;
 520        }
 521}
 522
 523static void __dentry_kill(struct dentry *dentry)
 524{
 525        struct dentry *parent = NULL;
 526        bool can_free = true;
 527        if (!IS_ROOT(dentry))
 528                parent = dentry->d_parent;
 529
 530        /*
 531         * The dentry is now unrecoverably dead to the world.
 532         */
 533        lockref_mark_dead(&dentry->d_lockref);
 534
 535        /*
 536         * inform the fs via d_prune that this dentry is about to be
 537         * unhashed and destroyed.
 538         */
 539        if (dentry->d_flags & DCACHE_OP_PRUNE)
 540                dentry->d_op->d_prune(dentry);
 541
 542        if (dentry->d_flags & DCACHE_LRU_LIST) {
 543                if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
 544                        d_lru_del(dentry);
 545        }
 546        /* if it was on the hash then remove it */
 547        __d_drop(dentry);
 548        dentry_unlist(dentry, parent);
 549        if (parent)
 550                spin_unlock(&parent->d_lock);
 551        if (dentry->d_inode)
 552                dentry_unlink_inode(dentry);
 553        else
 554                spin_unlock(&dentry->d_lock);
 555        this_cpu_dec(nr_dentry);
 556        if (dentry->d_op && dentry->d_op->d_release)
 557                dentry->d_op->d_release(dentry);
 558
 559        spin_lock(&dentry->d_lock);
 560        if (dentry->d_flags & DCACHE_SHRINK_LIST) {
 561                dentry->d_flags |= DCACHE_MAY_FREE;
 562                can_free = false;
 563        }
 564        spin_unlock(&dentry->d_lock);
 565        if (likely(can_free))
 566                dentry_free(dentry);
 567        cond_resched();
 568}
 569
 570static struct dentry *__lock_parent(struct dentry *dentry)
 571{
 572        struct dentry *parent;
 573        rcu_read_lock();
 574        spin_unlock(&dentry->d_lock);
 575again:
 576        parent = READ_ONCE(dentry->d_parent);
 577        spin_lock(&parent->d_lock);
 578        /*
 579         * We can't blindly lock dentry until we are sure
 580         * that we won't violate the locking order.
 581         * Any changes of dentry->d_parent must have
 582         * been done with parent->d_lock held, so
 583         * spin_lock() above is enough of a barrier
 584         * for checking if it's still our child.
 585         */
 586        if (unlikely(parent != dentry->d_parent)) {
 587                spin_unlock(&parent->d_lock);
 588                goto again;
 589        }
 590        rcu_read_unlock();
 591        if (parent != dentry)
 592                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 593        else
 594                parent = NULL;
 595        return parent;
 596}
 597
 598static inline struct dentry *lock_parent(struct dentry *dentry)
 599{
 600        struct dentry *parent = dentry->d_parent;
 601        if (IS_ROOT(dentry))
 602                return NULL;
 603        if (likely(spin_trylock(&parent->d_lock)))
 604                return parent;
 605        return __lock_parent(dentry);
 606}
 607
 608static inline bool retain_dentry(struct dentry *dentry)
 609{
 610        WARN_ON(d_in_lookup(dentry));
 611
 612        /* Unreachable? Get rid of it */
 613        if (unlikely(d_unhashed(dentry)))
 614                return false;
 615
 616        if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
 617                return false;
 618
 619        if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
 620                if (dentry->d_op->d_delete(dentry))
 621                        return false;
 622        }
 623        /* retain; LRU fodder */
 624        dentry->d_lockref.count--;
 625        if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
 626                d_lru_add(dentry);
 627        else if (unlikely(!(dentry->d_flags & DCACHE_REFERENCED)))
 628                dentry->d_flags |= DCACHE_REFERENCED;
 629        return true;
 630}
 631
 632/*
 633 * Finish off a dentry we've decided to kill.
 634 * dentry->d_lock must be held, returns with it unlocked.
 635 * Returns dentry requiring refcount drop, or NULL if we're done.
 636 */
 637static struct dentry *dentry_kill(struct dentry *dentry)
 638        __releases(dentry->d_lock)
 639{
 640        struct inode *inode = dentry->d_inode;
 641        struct dentry *parent = NULL;
 642
 643        if (inode && unlikely(!spin_trylock(&inode->i_lock)))
 644                goto slow_positive;
 645
 646        if (!IS_ROOT(dentry)) {
 647                parent = dentry->d_parent;
 648                if (unlikely(!spin_trylock(&parent->d_lock))) {
 649                        parent = __lock_parent(dentry);
 650                        if (likely(inode || !dentry->d_inode))
 651                                goto got_locks;
 652                        /* negative that became positive */
 653                        if (parent)
 654                                spin_unlock(&parent->d_lock);
 655                        inode = dentry->d_inode;
 656                        goto slow_positive;
 657                }
 658        }
 659        __dentry_kill(dentry);
 660        return parent;
 661
 662slow_positive:
 663        spin_unlock(&dentry->d_lock);
 664        spin_lock(&inode->i_lock);
 665        spin_lock(&dentry->d_lock);
 666        parent = lock_parent(dentry);
 667got_locks:
 668        if (unlikely(dentry->d_lockref.count != 1)) {
 669                dentry->d_lockref.count--;
 670        } else if (likely(!retain_dentry(dentry))) {
 671                __dentry_kill(dentry);
 672                return parent;
 673        }
 674        /* we are keeping it, after all */
 675        if (inode)
 676                spin_unlock(&inode->i_lock);
 677        if (parent)
 678                spin_unlock(&parent->d_lock);
 679        spin_unlock(&dentry->d_lock);
 680        return NULL;
 681}
 682
 683/*
 684 * Try to do a lockless dput(), and return whether that was successful.
 685 *
 686 * If unsuccessful, we return false, having already taken the dentry lock.
 687 *
 688 * The caller needs to hold the RCU read lock, so that the dentry is
 689 * guaranteed to stay around even if the refcount goes down to zero!
 690 */
 691static inline bool fast_dput(struct dentry *dentry)
 692{
 693        int ret;
 694        unsigned int d_flags;
 695
 696        /*
 697         * If we have a d_op->d_delete() operation, we sould not
 698         * let the dentry count go to zero, so use "put_or_lock".
 699         */
 700        if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
 701                return lockref_put_or_lock(&dentry->d_lockref);
 702
 703        /*
 704         * .. otherwise, we can try to just decrement the
 705         * lockref optimistically.
 706         */
 707        ret = lockref_put_return(&dentry->d_lockref);
 708
 709        /*
 710         * If the lockref_put_return() failed due to the lock being held
 711         * by somebody else, the fast path has failed. We will need to
 712         * get the lock, and then check the count again.
 713         */
 714        if (unlikely(ret < 0)) {
 715                spin_lock(&dentry->d_lock);
 716                if (dentry->d_lockref.count > 1) {
 717                        dentry->d_lockref.count--;
 718                        spin_unlock(&dentry->d_lock);
 719                        return true;
 720                }
 721                return false;
 722        }
 723
 724        /*
 725         * If we weren't the last ref, we're done.
 726         */
 727        if (ret)
 728                return true;
 729
 730        /*
 731         * Careful, careful. The reference count went down
 732         * to zero, but we don't hold the dentry lock, so
 733         * somebody else could get it again, and do another
 734         * dput(), and we need to not race with that.
 735         *
 736         * However, there is a very special and common case
 737         * where we don't care, because there is nothing to
 738         * do: the dentry is still hashed, it does not have
 739         * a 'delete' op, and it's referenced and already on
 740         * the LRU list.
 741         *
 742         * NOTE! Since we aren't locked, these values are
 743         * not "stable". However, it is sufficient that at
 744         * some point after we dropped the reference the
 745         * dentry was hashed and the flags had the proper
 746         * value. Other dentry users may have re-gotten
 747         * a reference to the dentry and change that, but
 748         * our work is done - we can leave the dentry
 749         * around with a zero refcount.
 750         */
 751        smp_rmb();
 752        d_flags = READ_ONCE(dentry->d_flags);
 753        d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED;
 754
 755        /* Nothing to do? Dropping the reference was all we needed? */
 756        if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
 757                return true;
 758
 759        /*
 760         * Not the fast normal case? Get the lock. We've already decremented
 761         * the refcount, but we'll need to re-check the situation after
 762         * getting the lock.
 763         */
 764        spin_lock(&dentry->d_lock);
 765
 766        /*
 767         * Did somebody else grab a reference to it in the meantime, and
 768         * we're no longer the last user after all? Alternatively, somebody
 769         * else could have killed it and marked it dead. Either way, we
 770         * don't need to do anything else.
 771         */
 772        if (dentry->d_lockref.count) {
 773                spin_unlock(&dentry->d_lock);
 774                return true;
 775        }
 776
 777        /*
 778         * Re-get the reference we optimistically dropped. We hold the
 779         * lock, and we just tested that it was zero, so we can just
 780         * set it to 1.
 781         */
 782        dentry->d_lockref.count = 1;
 783        return false;
 784}
 785
 786
 787/* 
 788 * This is dput
 789 *
 790 * This is complicated by the fact that we do not want to put
 791 * dentries that are no longer on any hash chain on the unused
 792 * list: we'd much rather just get rid of them immediately.
 793 *
 794 * However, that implies that we have to traverse the dentry
 795 * tree upwards to the parents which might _also_ now be
 796 * scheduled for deletion (it may have been only waiting for
 797 * its last child to go away).
 798 *
 799 * This tail recursion is done by hand as we don't want to depend
 800 * on the compiler to always get this right (gcc generally doesn't).
 801 * Real recursion would eat up our stack space.
 802 */
 803
 804/*
 805 * dput - release a dentry
 806 * @dentry: dentry to release 
 807 *
 808 * Release a dentry. This will drop the usage count and if appropriate
 809 * call the dentry unlink method as well as removing it from the queues and
 810 * releasing its resources. If the parent dentries were scheduled for release
 811 * they too may now get deleted.
 812 */
 813void dput(struct dentry *dentry)
 814{
 815        while (dentry) {
 816                might_sleep();
 817
 818                rcu_read_lock();
 819                if (likely(fast_dput(dentry))) {
 820                        rcu_read_unlock();
 821                        return;
 822                }
 823
 824                /* Slow case: now with the dentry lock held */
 825                rcu_read_unlock();
 826
 827                if (likely(retain_dentry(dentry))) {
 828                        spin_unlock(&dentry->d_lock);
 829                        return;
 830                }
 831
 832                dentry = dentry_kill(dentry);
 833        }
 834}
 835EXPORT_SYMBOL(dput);
 836
 837
 838/* This must be called with d_lock held */
 839static inline void __dget_dlock(struct dentry *dentry)
 840{
 841        dentry->d_lockref.count++;
 842}
 843
 844static inline void __dget(struct dentry *dentry)
 845{
 846        lockref_get(&dentry->d_lockref);
 847}
 848
 849struct dentry *dget_parent(struct dentry *dentry)
 850{
 851        int gotref;
 852        struct dentry *ret;
 853
 854        /*
 855         * Do optimistic parent lookup without any
 856         * locking.
 857         */
 858        rcu_read_lock();
 859        ret = READ_ONCE(dentry->d_parent);
 860        gotref = lockref_get_not_zero(&ret->d_lockref);
 861        rcu_read_unlock();
 862        if (likely(gotref)) {
 863                if (likely(ret == READ_ONCE(dentry->d_parent)))
 864                        return ret;
 865                dput(ret);
 866        }
 867
 868repeat:
 869        /*
 870         * Don't need rcu_dereference because we re-check it was correct under
 871         * the lock.
 872         */
 873        rcu_read_lock();
 874        ret = dentry->d_parent;
 875        spin_lock(&ret->d_lock);
 876        if (unlikely(ret != dentry->d_parent)) {
 877                spin_unlock(&ret->d_lock);
 878                rcu_read_unlock();
 879                goto repeat;
 880        }
 881        rcu_read_unlock();
 882        BUG_ON(!ret->d_lockref.count);
 883        ret->d_lockref.count++;
 884        spin_unlock(&ret->d_lock);
 885        return ret;
 886}
 887EXPORT_SYMBOL(dget_parent);
 888
 889static struct dentry * __d_find_any_alias(struct inode *inode)
 890{
 891        struct dentry *alias;
 892
 893        if (hlist_empty(&inode->i_dentry))
 894                return NULL;
 895        alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
 896        __dget(alias);
 897        return alias;
 898}
 899
 900/**
 901 * d_find_any_alias - find any alias for a given inode
 902 * @inode: inode to find an alias for
 903 *
 904 * If any aliases exist for the given inode, take and return a
 905 * reference for one of them.  If no aliases exist, return %NULL.
 906 */
 907struct dentry *d_find_any_alias(struct inode *inode)
 908{
 909        struct dentry *de;
 910
 911        spin_lock(&inode->i_lock);
 912        de = __d_find_any_alias(inode);
 913        spin_unlock(&inode->i_lock);
 914        return de;
 915}
 916EXPORT_SYMBOL(d_find_any_alias);
 917
 918/**
 919 * d_find_alias - grab a hashed alias of inode
 920 * @inode: inode in question
 921 *
 922 * If inode has a hashed alias, or is a directory and has any alias,
 923 * acquire the reference to alias and return it. Otherwise return NULL.
 924 * Notice that if inode is a directory there can be only one alias and
 925 * it can be unhashed only if it has no children, or if it is the root
 926 * of a filesystem, or if the directory was renamed and d_revalidate
 927 * was the first vfs operation to notice.
 928 *
 929 * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
 930 * any other hashed alias over that one.
 931 */
 932static struct dentry *__d_find_alias(struct inode *inode)
 933{
 934        struct dentry *alias;
 935
 936        if (S_ISDIR(inode->i_mode))
 937                return __d_find_any_alias(inode);
 938
 939        hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
 940                spin_lock(&alias->d_lock);
 941                if (!d_unhashed(alias)) {
 942                        __dget_dlock(alias);
 943                        spin_unlock(&alias->d_lock);
 944                        return alias;
 945                }
 946                spin_unlock(&alias->d_lock);
 947        }
 948        return NULL;
 949}
 950
 951struct dentry *d_find_alias(struct inode *inode)
 952{
 953        struct dentry *de = NULL;
 954
 955        if (!hlist_empty(&inode->i_dentry)) {
 956                spin_lock(&inode->i_lock);
 957                de = __d_find_alias(inode);
 958                spin_unlock(&inode->i_lock);
 959        }
 960        return de;
 961}
 962EXPORT_SYMBOL(d_find_alias);
 963
 964/*
 965 *      Try to kill dentries associated with this inode.
 966 * WARNING: you must own a reference to inode.
 967 */
 968void d_prune_aliases(struct inode *inode)
 969{
 970        struct dentry *dentry;
 971restart:
 972        spin_lock(&inode->i_lock);
 973        hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
 974                spin_lock(&dentry->d_lock);
 975                if (!dentry->d_lockref.count) {
 976                        struct dentry *parent = lock_parent(dentry);
 977                        if (likely(!dentry->d_lockref.count)) {
 978                                __dentry_kill(dentry);
 979                                dput(parent);
 980                                goto restart;
 981                        }
 982                        if (parent)
 983                                spin_unlock(&parent->d_lock);
 984                }
 985                spin_unlock(&dentry->d_lock);
 986        }
 987        spin_unlock(&inode->i_lock);
 988}
 989EXPORT_SYMBOL(d_prune_aliases);
 990
 991/*
 992 * Lock a dentry from shrink list.
 993 * Called under rcu_read_lock() and dentry->d_lock; the former
 994 * guarantees that nothing we access will be freed under us.
 995 * Note that dentry is *not* protected from concurrent dentry_kill(),
 996 * d_delete(), etc.
 997 *
 998 * Return false if dentry has been disrupted or grabbed, leaving
 999 * the caller to kick it off-list.  Otherwise, return true and have
1000 * that dentry's inode and parent both locked.
1001 */
1002static bool shrink_lock_dentry(struct dentry *dentry)
1003{
1004        struct inode *inode;
1005        struct dentry *parent;
1006
1007        if (dentry->d_lockref.count)
1008                return false;
1009
1010        inode = dentry->d_inode;
1011        if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
1012                spin_unlock(&dentry->d_lock);
1013                spin_lock(&inode->i_lock);
1014                spin_lock(&dentry->d_lock);
1015                if (unlikely(dentry->d_lockref.count))
1016                        goto out;
1017                /* changed inode means that somebody had grabbed it */
1018                if (unlikely(inode != dentry->d_inode))
1019                        goto out;
1020        }
1021
1022        parent = dentry->d_parent;
1023        if (IS_ROOT(dentry) || likely(spin_trylock(&parent->d_lock)))
1024                return true;
1025
1026        spin_unlock(&dentry->d_lock);
1027        spin_lock(&parent->d_lock);
1028        if (unlikely(parent != dentry->d_parent)) {
1029                spin_unlock(&parent->d_lock);
1030                spin_lock(&dentry->d_lock);
1031                goto out;
1032        }
1033        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1034        if (likely(!dentry->d_lockref.count))
1035                return true;
1036        spin_unlock(&parent->d_lock);
1037out:
1038        if (inode)
1039                spin_unlock(&inode->i_lock);
1040        return false;
1041}
1042
1043static void shrink_dentry_list(struct list_head *list)
1044{
1045        while (!list_empty(list)) {
1046                struct dentry *dentry, *parent;
1047
1048                dentry = list_entry(list->prev, struct dentry, d_lru);
1049                spin_lock(&dentry->d_lock);
1050                rcu_read_lock();
1051                if (!shrink_lock_dentry(dentry)) {
1052                        bool can_free = false;
1053                        rcu_read_unlock();
1054                        d_shrink_del(dentry);
1055                        if (dentry->d_lockref.count < 0)
1056                                can_free = dentry->d_flags & DCACHE_MAY_FREE;
1057                        spin_unlock(&dentry->d_lock);
1058                        if (can_free)
1059                                dentry_free(dentry);
1060                        continue;
1061                }
1062                rcu_read_unlock();
1063                d_shrink_del(dentry);
1064                parent = dentry->d_parent;
1065                __dentry_kill(dentry);
1066                if (parent == dentry)
1067                        continue;
1068                /*
1069                 * We need to prune ancestors too. This is necessary to prevent
1070                 * quadratic behavior of shrink_dcache_parent(), but is also
1071                 * expected to be beneficial in reducing dentry cache
1072                 * fragmentation.
1073                 */
1074                dentry = parent;
1075                while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
1076                        dentry = dentry_kill(dentry);
1077        }
1078}
1079
1080static enum lru_status dentry_lru_isolate(struct list_head *item,
1081                struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1082{
1083        struct list_head *freeable = arg;
1084        struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1085
1086
1087        /*
1088         * we are inverting the lru lock/dentry->d_lock here,
1089         * so use a trylock. If we fail to get the lock, just skip
1090         * it
1091         */
1092        if (!spin_trylock(&dentry->d_lock))
1093                return LRU_SKIP;
1094
1095        /*
1096         * Referenced dentries are still in use. If they have active
1097         * counts, just remove them from the LRU. Otherwise give them
1098         * another pass through the LRU.
1099         */
1100        if (dentry->d_lockref.count) {
1101                d_lru_isolate(lru, dentry);
1102                spin_unlock(&dentry->d_lock);
1103                return LRU_REMOVED;
1104        }
1105
1106        if (dentry->d_flags & DCACHE_REFERENCED) {
1107                dentry->d_flags &= ~DCACHE_REFERENCED;
1108                spin_unlock(&dentry->d_lock);
1109
1110                /*
1111                 * The list move itself will be made by the common LRU code. At
1112                 * this point, we've dropped the dentry->d_lock but keep the
1113                 * lru lock. This is safe to do, since every list movement is
1114                 * protected by the lru lock even if both locks are held.
1115                 *
1116                 * This is guaranteed by the fact that all LRU management
1117                 * functions are intermediated by the LRU API calls like
1118                 * list_lru_add and list_lru_del. List movement in this file
1119                 * only ever occur through this functions or through callbacks
1120                 * like this one, that are called from the LRU API.
1121                 *
1122                 * The only exceptions to this are functions like
1123                 * shrink_dentry_list, and code that first checks for the
1124                 * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
1125                 * operating only with stack provided lists after they are
1126                 * properly isolated from the main list.  It is thus, always a
1127                 * local access.
1128                 */
1129                return LRU_ROTATE;
1130        }
1131
1132        d_lru_shrink_move(lru, dentry, freeable);
1133        spin_unlock(&dentry->d_lock);
1134
1135        return LRU_REMOVED;
1136}
1137
1138/**
1139 * prune_dcache_sb - shrink the dcache
1140 * @sb: superblock
1141 * @sc: shrink control, passed to list_lru_shrink_walk()
1142 *
1143 * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
1144 * is done when we need more memory and called from the superblock shrinker
1145 * function.
1146 *
1147 * This function may fail to free any resources if all the dentries are in
1148 * use.
1149 */
1150long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
1151{
1152        LIST_HEAD(dispose);
1153        long freed;
1154
1155        freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
1156                                     dentry_lru_isolate, &dispose);
1157        shrink_dentry_list(&dispose);
1158        return freed;
1159}
1160
1161static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
1162                struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
1163{
1164        struct list_head *freeable = arg;
1165        struct dentry   *dentry = container_of(item, struct dentry, d_lru);
1166
1167        /*
1168         * we are inverting the lru lock/dentry->d_lock here,
1169         * so use a trylock. If we fail to get the lock, just skip
1170         * it
1171         */
1172        if (!spin_trylock(&dentry->d_lock))
1173                return LRU_SKIP;
1174
1175        d_lru_shrink_move(lru, dentry, freeable);
1176        spin_unlock(&dentry->d_lock);
1177
1178        return LRU_REMOVED;
1179}
1180
1181
1182/**
1183 * shrink_dcache_sb - shrink dcache for a superblock
1184 * @sb: superblock
1185 *
1186 * Shrink the dcache for the specified super block. This is used to free
1187 * the dcache before unmounting a file system.
1188 */
1189void shrink_dcache_sb(struct super_block *sb)
1190{
1191        long freed;
1192
1193        do {
1194                LIST_HEAD(dispose);
1195
1196                freed = list_lru_walk(&sb->s_dentry_lru,
1197                        dentry_lru_isolate_shrink, &dispose, 1024);
1198
1199                this_cpu_sub(nr_dentry_unused, freed);
1200                shrink_dentry_list(&dispose);
1201        } while (list_lru_count(&sb->s_dentry_lru) > 0);
1202}
1203EXPORT_SYMBOL(shrink_dcache_sb);
1204
1205/**
1206 * enum d_walk_ret - action to talke during tree walk
1207 * @D_WALK_CONTINUE:    contrinue walk
1208 * @D_WALK_QUIT:        quit walk
1209 * @D_WALK_NORETRY:     quit when retry is needed
1210 * @D_WALK_SKIP:        skip this dentry and its children
1211 */
1212enum d_walk_ret {
1213        D_WALK_CONTINUE,
1214        D_WALK_QUIT,
1215        D_WALK_NORETRY,
1216        D_WALK_SKIP,
1217};
1218
1219/**
1220 * d_walk - walk the dentry tree
1221 * @parent:     start of walk
1222 * @data:       data passed to @enter() and @finish()
1223 * @enter:      callback when first entering the dentry
1224 *
1225 * The @enter() callbacks are called with d_lock held.
1226 */
1227static void d_walk(struct dentry *parent, void *data,
1228                   enum d_walk_ret (*enter)(void *, struct dentry *))
1229{
1230        struct dentry *this_parent;
1231        struct list_head *next;
1232        unsigned seq = 0;
1233        enum d_walk_ret ret;
1234        bool retry = true;
1235
1236again:
1237        read_seqbegin_or_lock(&rename_lock, &seq);
1238        this_parent = parent;
1239        spin_lock(&this_parent->d_lock);
1240
1241        ret = enter(data, this_parent);
1242        switch (ret) {
1243        case D_WALK_CONTINUE:
1244                break;
1245        case D_WALK_QUIT:
1246        case D_WALK_SKIP:
1247                goto out_unlock;
1248        case D_WALK_NORETRY:
1249                retry = false;
1250                break;
1251        }
1252repeat:
1253        next = this_parent->d_subdirs.next;
1254resume:
1255        while (next != &this_parent->d_subdirs) {
1256                struct list_head *tmp = next;
1257                struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
1258                next = tmp->next;
1259
1260                if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
1261                        continue;
1262
1263                spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
1264
1265                ret = enter(data, dentry);
1266                switch (ret) {
1267                case D_WALK_CONTINUE:
1268                        break;
1269                case D_WALK_QUIT:
1270                        spin_unlock(&dentry->d_lock);
1271                        goto out_unlock;
1272                case D_WALK_NORETRY:
1273                        retry = false;
1274                        break;
1275                case D_WALK_SKIP:
1276                        spin_unlock(&dentry->d_lock);
1277                        continue;
1278                }
1279
1280                if (!list_empty(&dentry->d_subdirs)) {
1281                        spin_unlock(&this_parent->d_lock);
1282                        spin_release(&dentry->d_lock.dep_map, 1, _RET_IP_);
1283                        this_parent = dentry;
1284                        spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
1285                        goto repeat;
1286                }
1287                spin_unlock(&dentry->d_lock);
1288        }
1289        /*
1290         * All done at this level ... ascend and resume the search.
1291         */
1292        rcu_read_lock();
1293ascend:
1294        if (this_parent != parent) {
1295                struct dentry *child = this_parent;
1296                this_parent = child->d_parent;
1297
1298                spin_unlock(&child->d_lock);
1299                spin_lock(&this_parent->d_lock);
1300
1301                /* might go back up the wrong parent if we have had a rename. */
1302                if (need_seqretry(&rename_lock, seq))
1303                        goto rename_retry;
1304                /* go into the first sibling still alive */
1305                do {
1306                        next = child->d_child.next;
1307                        if (next == &this_parent->d_subdirs)
1308                                goto ascend;
1309                        child = list_entry(next, struct dentry, d_child);
1310                } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
1311                rcu_read_unlock();
1312                goto resume;
1313        }
1314        if (need_seqretry(&rename_lock, seq))
1315                goto rename_retry;
1316        rcu_read_unlock();
1317
1318out_unlock:
1319        spin_unlock(&this_parent->d_lock);
1320        done_seqretry(&rename_lock, seq);
1321        return;
1322
1323rename_retry:
1324        spin_unlock(&this_parent->d_lock);
1325        rcu_read_unlock();
1326        BUG_ON(seq & 1);
1327        if (!retry)
1328                return;
1329        seq = 1;
1330        goto again;
1331}
1332
1333struct check_mount {
1334        struct vfsmount *mnt;
1335        unsigned int mounted;
1336};
1337
1338static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
1339{
1340        struct check_mount *info = data;
1341        struct path path = { .mnt = info->mnt, .dentry = dentry };
1342
1343        if (likely(!d_mountpoint(dentry)))
1344                return D_WALK_CONTINUE;
1345        if (__path_is_mountpoint(&path)) {
1346                info->mounted = 1;
1347                return D_WALK_QUIT;
1348        }
1349        return D_WALK_CONTINUE;
1350}
1351
1352/**
1353 * path_has_submounts - check for mounts over a dentry in the
1354 *                      current namespace.
1355 * @parent: path to check.
1356 *
1357 * Return true if the parent or its subdirectories contain
1358 * a mount point in the current namespace.
1359 */
1360int path_has_submounts(const struct path *parent)
1361{
1362        struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
1363
1364        read_seqlock_excl(&mount_lock);
1365        d_walk(parent->dentry, &data, path_check_mount);
1366        read_sequnlock_excl(&mount_lock);
1367
1368        return data.mounted;
1369}
1370EXPORT_SYMBOL(path_has_submounts);
1371
1372/*
1373 * Called by mount code to set a mountpoint and check if the mountpoint is
1374 * reachable (e.g. NFS can unhash a directory dentry and then the complete
1375 * subtree can become unreachable).
1376 *
1377 * Only one of d_invalidate() and d_set_mounted() must succeed.  For
1378 * this reason take rename_lock and d_lock on dentry and ancestors.
1379 */
1380int d_set_mounted(struct dentry *dentry)
1381{
1382        struct dentry *p;
1383        int ret = -ENOENT;
1384        write_seqlock(&rename_lock);
1385        for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
1386                /* Need exclusion wrt. d_invalidate() */
1387                spin_lock(&p->d_lock);
1388                if (unlikely(d_unhashed(p))) {
1389                        spin_unlock(&p->d_lock);
1390                        goto out;
1391                }
1392                spin_unlock(&p->d_lock);
1393        }
1394        spin_lock(&dentry->d_lock);
1395        if (!d_unlinked(dentry)) {
1396                ret = -EBUSY;
1397                if (!d_mountpoint(dentry)) {
1398                        dentry->d_flags |= DCACHE_MOUNTED;
1399                        ret = 0;
1400                }
1401        }
1402        spin_unlock(&dentry->d_lock);
1403out:
1404        write_sequnlock(&rename_lock);
1405        return ret;
1406}
1407
1408/*
1409 * Search the dentry child list of the specified parent,
1410 * and move any unused dentries to the end of the unused
1411 * list for prune_dcache(). We descend to the next level
1412 * whenever the d_subdirs list is non-empty and continue
1413 * searching.
1414 *
1415 * It returns zero iff there are no unused children,
1416 * otherwise  it returns the number of children moved to
1417 * the end of the unused list. This may not be the total
1418 * number of unused children, because select_parent can
1419 * drop the lock and return early due to latency
1420 * constraints.
1421 */
1422
1423struct select_data {
1424        struct dentry *start;
1425        struct list_head dispose;
1426        int found;
1427};
1428
1429static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
1430{
1431        struct select_data *data = _data;
1432        enum d_walk_ret ret = D_WALK_CONTINUE;
1433
1434        if (data->start == dentry)
1435                goto out;
1436
1437        if (dentry->d_flags & DCACHE_SHRINK_LIST) {
1438                data->found++;
1439        } else {
1440                if (dentry->d_flags & DCACHE_LRU_LIST)
1441                        d_lru_del(dentry);
1442                if (!dentry->d_lockref.count) {
1443                        d_shrink_add(dentry, &data->dispose);
1444                        data->found++;
1445                }
1446        }
1447        /*
1448         * We can return to the caller if we have found some (this
1449         * ensures forward progress). We'll be coming back to find
1450         * the rest.
1451         */
1452        if (!list_empty(&data->dispose))
1453                ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
1454out:
1455        return ret;
1456}
1457
1458/**
1459 * shrink_dcache_parent - prune dcache
1460 * @parent: parent of entries to prune
1461 *
1462 * Prune the dcache to remove unused children of the parent dentry.
1463 */
1464void shrink_dcache_parent(struct dentry *parent)
1465{
1466        for (;;) {
1467                struct select_data data;
1468
1469                INIT_LIST_HEAD(&data.dispose);
1470                data.start = parent;
1471                data.found = 0;
1472
1473                d_walk(parent, &data, select_collect);
1474
1475                if (!list_empty(&data.dispose)) {
1476                        shrink_dentry_list(&data.dispose);
1477                        continue;
1478                }
1479
1480                cond_resched();
1481                if (!data.found)
1482                        break;
1483        }
1484}
1485EXPORT_SYMBOL(shrink_dcache_parent);
1486
1487static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
1488{
1489        /* it has busy descendents; complain about those instead */
1490        if (!list_empty(&dentry->d_subdirs))
1491                return D_WALK_CONTINUE;
1492
1493        /* root with refcount 1 is fine */
1494        if (dentry == _data && dentry->d_lockref.count == 1)
1495                return D_WALK_CONTINUE;
1496
1497        printk(KERN_ERR "BUG: Dentry %p{i=%lx,n=%pd} "
1498                        " still in use (%d) [unmount of %s %s]\n",
1499                       dentry,
1500                       dentry->d_inode ?
1501                       dentry->d_inode->i_ino : 0UL,
1502                       dentry,
1503                       dentry->d_lockref.count,
1504                       dentry->d_sb->s_type->name,
1505                       dentry->d_sb->s_id);
1506        WARN_ON(1);
1507        return D_WALK_CONTINUE;
1508}
1509
1510static void do_one_tree(struct dentry *dentry)
1511{
1512        shrink_dcache_parent(dentry);
1513        d_walk(dentry, dentry, umount_check);
1514        d_drop(dentry);
1515        dput(dentry);
1516}
1517
1518/*
1519 * destroy the dentries attached to a superblock on unmounting
1520 */
1521void shrink_dcache_for_umount(struct super_block *sb)
1522{
1523        struct dentry *dentry;
1524
1525        WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
1526
1527        dentry = sb->s_root;
1528        sb->s_root = NULL;
1529        do_one_tree(dentry);
1530
1531        while (!hlist_bl_empty(&sb->s_roots)) {
1532                dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_roots), struct dentry, d_hash));
1533                do_one_tree(dentry);
1534        }
1535}
1536
1537static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
1538{
1539        struct dentry **victim = _data;
1540        if (d_mountpoint(dentry)) {
1541                __dget_dlock(dentry);
1542                *victim = dentry;
1543                return D_WALK_QUIT;
1544        }
1545        return D_WALK_CONTINUE;
1546}
1547
1548/**
1549 * d_invalidate - detach submounts, prune dcache, and drop
1550 * @dentry: dentry to invalidate (aka detach, prune and drop)
1551 */
1552void d_invalidate(struct dentry *dentry)
1553{
1554        bool had_submounts = false;
1555        spin_lock(&dentry->d_lock);
1556        if (d_unhashed(dentry)) {
1557                spin_unlock(&dentry->d_lock);
1558                return;
1559        }
1560        __d_drop(dentry);
1561        spin_unlock(&dentry->d_lock);
1562
1563        /* Negative dentries can be dropped without further checks */
1564        if (!dentry->d_inode)
1565                return;
1566
1567        shrink_dcache_parent(dentry);
1568        for (;;) {
1569                struct dentry *victim = NULL;
1570                d_walk(dentry, &victim, find_submount);
1571                if (!victim) {
1572                        if (had_submounts)
1573                                shrink_dcache_parent(dentry);
1574                        return;
1575                }
1576                had_submounts = true;
1577                detach_mounts(victim);
1578                dput(victim);
1579        }
1580}
1581EXPORT_SYMBOL(d_invalidate);
1582
1583/**
1584 * __d_alloc    -       allocate a dcache entry
1585 * @sb: filesystem it will belong to
1586 * @name: qstr of the name
1587 *
1588 * Allocates a dentry. It returns %NULL if there is insufficient memory
1589 * available. On a success the dentry is returned. The name passed in is
1590 * copied and the copy passed in may be reused after this call.
1591 */
1592 
1593struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
1594{
1595        struct dentry *dentry;
1596        char *dname;
1597        int err;
1598
1599        dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
1600        if (!dentry)
1601                return NULL;
1602
1603        /*
1604         * We guarantee that the inline name is always NUL-terminated.
1605         * This way the memcpy() done by the name switching in rename
1606         * will still always have a NUL at the end, even if we might
1607         * be overwriting an internal NUL character
1608         */
1609        dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
1610        if (unlikely(!name)) {
1611                name = &slash_name;
1612                dname = dentry->d_iname;
1613        } else if (name->len > DNAME_INLINE_LEN-1) {
1614                size_t size = offsetof(struct external_name, name[1]);
1615                struct external_name *p = kmalloc(size + name->len,
1616                                                  GFP_KERNEL_ACCOUNT |
1617                                                  __GFP_RECLAIMABLE);
1618                if (!p) {
1619                        kmem_cache_free(dentry_cache, dentry); 
1620                        return NULL;
1621                }
1622                atomic_set(&p->u.count, 1);
1623                dname = p->name;
1624        } else  {
1625                dname = dentry->d_iname;
1626        }       
1627
1628        dentry->d_name.len = name->len;
1629        dentry->d_name.hash = name->hash;
1630        memcpy(dname, name->name, name->len);
1631        dname[name->len] = 0;
1632
1633        /* Make sure we always see the terminating NUL character */
1634        smp_store_release(&dentry->d_name.name, dname); /* ^^^ */
1635
1636        dentry->d_lockref.count = 1;
1637        dentry->d_flags = 0;
1638        spin_lock_init(&dentry->d_lock);
1639        seqcount_init(&dentry->d_seq);
1640        dentry->d_inode = NULL;
1641        dentry->d_parent = dentry;
1642        dentry->d_sb = sb;
1643        dentry->d_op = NULL;
1644        dentry->d_fsdata = NULL;
1645        INIT_HLIST_BL_NODE(&dentry->d_hash);
1646        INIT_LIST_HEAD(&dentry->d_lru);
1647        INIT_LIST_HEAD(&dentry->d_subdirs);
1648        INIT_HLIST_NODE(&dentry->d_u.d_alias);
1649        INIT_LIST_HEAD(&dentry->d_child);
1650        d_set_d_op(dentry, dentry->d_sb->s_d_op);
1651
1652        if (dentry->d_op && dentry->d_op->d_init) {
1653                err = dentry->d_op->d_init(dentry);
1654                if (err) {
1655                        if (dname_external(dentry))
1656                                kfree(external_name(dentry));
1657                        kmem_cache_free(dentry_cache, dentry);
1658                        return NULL;
1659                }
1660        }
1661
1662        this_cpu_inc(nr_dentry);
1663
1664        return dentry;
1665}
1666
1667/**
1668 * d_alloc      -       allocate a dcache entry
1669 * @parent: parent of entry to allocate
1670 * @name: qstr of the name
1671 *
1672 * Allocates a dentry. It returns %NULL if there is insufficient memory
1673 * available. On a success the dentry is returned. The name passed in is
1674 * copied and the copy passed in may be reused after this call.
1675 */
1676struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
1677{
1678        struct dentry *dentry = __d_alloc(parent->d_sb, name);
1679        if (!dentry)
1680                return NULL;
1681        dentry->d_flags |= DCACHE_RCUACCESS;
1682        spin_lock(&parent->d_lock);
1683        /*
1684         * don't need child lock because it is not subject
1685         * to concurrency here
1686         */
1687        __dget_dlock(parent);
1688        dentry->d_parent = parent;
1689        list_add(&dentry->d_child, &parent->d_subdirs);
1690        spin_unlock(&parent->d_lock);
1691
1692        return dentry;
1693}
1694EXPORT_SYMBOL(d_alloc);
1695
1696struct dentry *d_alloc_anon(struct super_block *sb)
1697{
1698        return __d_alloc(sb, NULL);
1699}
1700EXPORT_SYMBOL(d_alloc_anon);
1701
1702struct dentry *d_alloc_cursor(struct dentry * parent)
1703{
1704        struct dentry *dentry = d_alloc_anon(parent->d_sb);
1705        if (dentry) {
1706                dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
1707                dentry->d_parent = dget(parent);
1708        }
1709        return dentry;
1710}
1711
1712/**
1713 * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
1714 * @sb: the superblock
1715 * @name: qstr of the name
1716 *
1717 * For a filesystem that just pins its dentries in memory and never
1718 * performs lookups at all, return an unhashed IS_ROOT dentry.
1719 */
1720struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
1721{
1722        return __d_alloc(sb, name);
1723}
1724EXPORT_SYMBOL(d_alloc_pseudo);
1725
1726struct dentry *d_alloc_name(struct dentry *parent, const char *name)
1727{
1728        struct qstr q;
1729
1730        q.name = name;
1731        q.hash_len = hashlen_string(parent, name);
1732        return d_alloc(parent, &q);
1733}
1734EXPORT_SYMBOL(d_alloc_name);
1735
1736void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
1737{
1738        WARN_ON_ONCE(dentry->d_op);
1739        WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH  |
1740                                DCACHE_OP_COMPARE       |
1741                                DCACHE_OP_REVALIDATE    |
1742                                DCACHE_OP_WEAK_REVALIDATE       |
1743                                DCACHE_OP_DELETE        |
1744                                DCACHE_OP_REAL));
1745        dentry->d_op = op;
1746        if (!op)
1747                return;
1748        if (op->d_hash)
1749                dentry->d_flags |= DCACHE_OP_HASH;
1750        if (op->d_compare)
1751                dentry->d_flags |= DCACHE_OP_COMPARE;
1752        if (op->d_revalidate)
1753                dentry->d_flags |= DCACHE_OP_REVALIDATE;
1754        if (op->d_weak_revalidate)
1755                dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
1756        if (op->d_delete)
1757                dentry->d_flags |= DCACHE_OP_DELETE;
1758        if (op->d_prune)
1759                dentry->d_flags |= DCACHE_OP_PRUNE;
1760        if (op->d_real)
1761                dentry->d_flags |= DCACHE_OP_REAL;
1762
1763}
1764EXPORT_SYMBOL(d_set_d_op);
1765
1766
1767/*
1768 * d_set_fallthru - Mark a dentry as falling through to a lower layer
1769 * @dentry - The dentry to mark
1770 *
1771 * Mark a dentry as falling through to the lower layer (as set with
1772 * d_pin_lower()).  This flag may be recorded on the medium.
1773 */
1774void d_set_fallthru(struct dentry *dentry)
1775{
1776        spin_lock(&dentry->d_lock);
1777        dentry->d_flags |= DCACHE_FALLTHRU;
1778        spin_unlock(&dentry->d_lock);
1779}
1780EXPORT_SYMBOL(d_set_fallthru);
1781
1782static unsigned d_flags_for_inode(struct inode *inode)
1783{
1784        unsigned add_flags = DCACHE_REGULAR_TYPE;
1785
1786        if (!inode)
1787                return DCACHE_MISS_TYPE;
1788
1789        if (S_ISDIR(inode->i_mode)) {
1790                add_flags = DCACHE_DIRECTORY_TYPE;
1791                if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
1792                        if (unlikely(!inode->i_op->lookup))
1793                                add_flags = DCACHE_AUTODIR_TYPE;
1794                        else
1795                                inode->i_opflags |= IOP_LOOKUP;
1796                }
1797                goto type_determined;
1798        }
1799
1800        if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
1801                if (unlikely(inode->i_op->get_link)) {
1802                        add_flags = DCACHE_SYMLINK_TYPE;
1803                        goto type_determined;
1804                }
1805                inode->i_opflags |= IOP_NOFOLLOW;
1806        }
1807
1808        if (unlikely(!S_ISREG(inode->i_mode)))
1809                add_flags = DCACHE_SPECIAL_TYPE;
1810
1811type_determined:
1812        if (unlikely(IS_AUTOMOUNT(inode)))
1813                add_flags |= DCACHE_NEED_AUTOMOUNT;
1814        return add_flags;
1815}
1816
1817static void __d_instantiate(struct dentry *dentry, struct inode *inode)
1818{
1819        unsigned add_flags = d_flags_for_inode(inode);
1820        WARN_ON(d_in_lookup(dentry));
1821
1822        spin_lock(&dentry->d_lock);
1823        hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1824        raw_write_seqcount_begin(&dentry->d_seq);
1825        __d_set_inode_and_type(dentry, inode, add_flags);
1826        raw_write_seqcount_end(&dentry->d_seq);
1827        fsnotify_update_flags(dentry);
1828        spin_unlock(&dentry->d_lock);
1829}
1830
1831/**
1832 * d_instantiate - fill in inode information for a dentry
1833 * @entry: dentry to complete
1834 * @inode: inode to attach to this dentry
1835 *
1836 * Fill in inode information in the entry.
1837 *
1838 * This turns negative dentries into productive full members
1839 * of society.
1840 *
1841 * NOTE! This assumes that the inode count has been incremented
1842 * (or otherwise set) by the caller to indicate that it is now
1843 * in use by the dcache.
1844 */
1845 
1846void d_instantiate(struct dentry *entry, struct inode * inode)
1847{
1848        BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1849        if (inode) {
1850                security_d_instantiate(entry, inode);
1851                spin_lock(&inode->i_lock);
1852                __d_instantiate(entry, inode);
1853                spin_unlock(&inode->i_lock);
1854        }
1855}
1856EXPORT_SYMBOL(d_instantiate);
1857
1858/*
1859 * This should be equivalent to d_instantiate() + unlock_new_inode(),
1860 * with lockdep-related part of unlock_new_inode() done before
1861 * anything else.  Use that instead of open-coding d_instantiate()/
1862 * unlock_new_inode() combinations.
1863 */
1864void d_instantiate_new(struct dentry *entry, struct inode *inode)
1865{
1866        BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
1867        BUG_ON(!inode);
1868        lockdep_annotate_inode_mutex_key(inode);
1869        security_d_instantiate(entry, inode);
1870        spin_lock(&inode->i_lock);
1871        __d_instantiate(entry, inode);
1872        WARN_ON(!(inode->i_state & I_NEW));
1873        inode->i_state &= ~I_NEW & ~I_CREATING;
1874        smp_mb();
1875        wake_up_bit(&inode->i_state, __I_NEW);
1876        spin_unlock(&inode->i_lock);
1877}
1878EXPORT_SYMBOL(d_instantiate_new);
1879
1880struct dentry *d_make_root(struct inode *root_inode)
1881{
1882        struct dentry *res = NULL;
1883
1884        if (root_inode) {
1885                res = d_alloc_anon(root_inode->i_sb);
1886                if (res) {
1887                        res->d_flags |= DCACHE_RCUACCESS;
1888                        d_instantiate(res, root_inode);
1889                } else {
1890                        iput(root_inode);
1891                }
1892        }
1893        return res;
1894}
1895EXPORT_SYMBOL(d_make_root);
1896
1897static struct dentry *__d_instantiate_anon(struct dentry *dentry,
1898                                           struct inode *inode,
1899                                           bool disconnected)
1900{
1901        struct dentry *res;
1902        unsigned add_flags;
1903
1904        security_d_instantiate(dentry, inode);
1905        spin_lock(&inode->i_lock);
1906        res = __d_find_any_alias(inode);
1907        if (res) {
1908                spin_unlock(&inode->i_lock);
1909                dput(dentry);
1910                goto out_iput;
1911        }
1912
1913        /* attach a disconnected dentry */
1914        add_flags = d_flags_for_inode(inode);
1915
1916        if (disconnected)
1917                add_flags |= DCACHE_DISCONNECTED;
1918
1919        spin_lock(&dentry->d_lock);
1920        __d_set_inode_and_type(dentry, inode, add_flags);
1921        hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
1922        if (!disconnected) {
1923                hlist_bl_lock(&dentry->d_sb->s_roots);
1924                hlist_bl_add_head(&dentry->d_hash, &dentry->d_sb->s_roots);
1925                hlist_bl_unlock(&dentry->d_sb->s_roots);
1926        }
1927        spin_unlock(&dentry->d_lock);
1928        spin_unlock(&inode->i_lock);
1929
1930        return dentry;
1931
1932 out_iput:
1933        iput(inode);
1934        return res;
1935}
1936
1937struct dentry *d_instantiate_anon(struct dentry *dentry, struct inode *inode)
1938{
1939        return __d_instantiate_anon(dentry, inode, true);
1940}
1941EXPORT_SYMBOL(d_instantiate_anon);
1942
1943static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected)
1944{
1945        struct dentry *tmp;
1946        struct dentry *res;
1947
1948        if (!inode)
1949                return ERR_PTR(-ESTALE);
1950        if (IS_ERR(inode))
1951                return ERR_CAST(inode);
1952
1953        res = d_find_any_alias(inode);
1954        if (res)
1955                goto out_iput;
1956
1957        tmp = d_alloc_anon(inode->i_sb);
1958        if (!tmp) {
1959                res = ERR_PTR(-ENOMEM);
1960                goto out_iput;
1961        }
1962
1963        return __d_instantiate_anon(tmp, inode, disconnected);
1964
1965out_iput:
1966        iput(inode);
1967        return res;
1968}
1969
1970/**
1971 * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
1972 * @inode: inode to allocate the dentry for
1973 *
1974 * Obtain a dentry for an inode resulting from NFS filehandle conversion or
1975 * similar open by handle operations.  The returned dentry may be anonymous,
1976 * or may have a full name (if the inode was already in the cache).
1977 *
1978 * When called on a directory inode, we must ensure that the inode only ever
1979 * has one dentry.  If a dentry is found, that is returned instead of
1980 * allocating a new one.
1981 *
1982 * On successful return, the reference to the inode has been transferred
1983 * to the dentry.  In case of an error the reference on the inode is released.
1984 * To make it easier to use in export operations a %NULL or IS_ERR inode may
1985 * be passed in and the error will be propagated to the return value,
1986 * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
1987 */
1988struct dentry *d_obtain_alias(struct inode *inode)
1989{
1990        return __d_obtain_alias(inode, true);
1991}
1992EXPORT_SYMBOL(d_obtain_alias);
1993
1994/**
1995 * d_obtain_root - find or allocate a dentry for a given inode
1996 * @inode: inode to allocate the dentry for
1997 *
1998 * Obtain an IS_ROOT dentry for the root of a filesystem.
1999 *
2000 * We must ensure that directory inodes only ever have one dentry.  If a
2001 * dentry is found, that is returned instead of allocating a new one.
2002 *
2003 * On successful return, the reference to the inode has been transferred
2004 * to the dentry.  In case of an error the reference on the inode is
2005 * released.  A %NULL or IS_ERR inode may be passed in and will be the
2006 * error will be propagate to the return value, with a %NULL @inode
2007 * replaced by ERR_PTR(-ESTALE).
2008 */
2009struct dentry *d_obtain_root(struct inode *inode)
2010{
2011        return __d_obtain_alias(inode, false);
2012}
2013EXPORT_SYMBOL(d_obtain_root);
2014
2015/**
2016 * d_add_ci - lookup or allocate new dentry with case-exact name
2017 * @inode:  the inode case-insensitive lookup has found
2018 * @dentry: the negative dentry that was passed to the parent's lookup func
2019 * @name:   the case-exact name to be associated with the returned dentry
2020 *
2021 * This is to avoid filling the dcache with case-insensitive names to the
2022 * same inode, only the actual correct case is stored in the dcache for
2023 * case-insensitive filesystems.
2024 *
2025 * For a case-insensitive lookup match and if the the case-exact dentry
2026 * already exists in in the dcache, use it and return it.
2027 *
2028 * If no entry exists with the exact case name, allocate new dentry with
2029 * the exact case, and return the spliced entry.
2030 */
2031struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
2032                        struct qstr *name)
2033{
2034        struct dentry *found, *res;
2035
2036        /*
2037         * First check if a dentry matching the name already exists,
2038         * if not go ahead and create it now.
2039         */
2040        found = d_hash_and_lookup(dentry->d_parent, name);
2041        if (found) {
2042                iput(inode);
2043                return found;
2044        }
2045        if (d_in_lookup(dentry)) {
2046                found = d_alloc_parallel(dentry->d_parent, name,
2047                                        dentry->d_wait);
2048                if (IS_ERR(found) || !d_in_lookup(found)) {
2049                        iput(inode);
2050                        return found;
2051                }
2052        } else {
2053                found = d_alloc(dentry->d_parent, name);
2054                if (!found) {
2055                        iput(inode);
2056                        return ERR_PTR(-ENOMEM);
2057                } 
2058        }
2059        res = d_splice_alias(inode, found);
2060        if (res) {
2061                dput(found);
2062                return res;
2063        }
2064        return found;
2065}
2066EXPORT_SYMBOL(d_add_ci);
2067
2068
2069static inline bool d_same_name(const struct dentry *dentry,
2070                                const struct dentry *parent,
2071                                const struct qstr *name)
2072{
2073        if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
2074                if (dentry->d_name.len != name->len)
2075                        return false;
2076                return dentry_cmp(dentry, name->name, name->len) == 0;
2077        }
2078        return parent->d_op->d_compare(dentry,
2079                                       dentry->d_name.len, dentry->d_name.name,
2080                                       name) == 0;
2081}
2082
2083/**
2084 * __d_lookup_rcu - search for a dentry (racy, store-free)
2085 * @parent: parent dentry
2086 * @name: qstr of name we wish to find
2087 * @seqp: returns d_seq value at the point where the dentry was found
2088 * Returns: dentry, or NULL
2089 *
2090 * __d_lookup_rcu is the dcache lookup function for rcu-walk name
2091 * resolution (store-free path walking) design described in
2092 * Documentation/filesystems/path-lookup.txt.
2093 *
2094 * This is not to be used outside core vfs.
2095 *
2096 * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
2097 * held, and rcu_read_lock held. The returned dentry must not be stored into
2098 * without taking d_lock and checking d_seq sequence count against @seq
2099 * returned here.
2100 *
2101 * A refcount may be taken on the found dentry with the d_rcu_to_refcount
2102 * function.
2103 *
2104 * Alternatively, __d_lookup_rcu may be called again to look up the child of
2105 * the returned dentry, so long as its parent's seqlock is checked after the
2106 * child is looked up. Thus, an interlocking stepping of sequence lock checks
2107 * is formed, giving integrity down the path walk.
2108 *
2109 * NOTE! The caller *has* to check the resulting dentry against the sequence
2110 * number we've returned before using any of the resulting dentry state!
2111 */
2112struct dentry *__d_lookup_rcu(const struct dentry *parent,
2113                                const struct qstr *name,
2114                                unsigned *seqp)
2115{
2116        u64 hashlen = name->hash_len;
2117        const unsigned char *str = name->name;
2118        struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
2119        struct hlist_bl_node *node;
2120        struct dentry *dentry;
2121
2122        /*
2123         * Note: There is significant duplication with __d_lookup_rcu which is
2124         * required to prevent single threaded performance regressions
2125         * especially on architectures where smp_rmb (in seqcounts) are costly.
2126         * Keep the two functions in sync.
2127         */
2128
2129        /*
2130         * The hash list is protected using RCU.
2131         *
2132         * Carefully use d_seq when comparing a candidate dentry, to avoid
2133         * races with d_move().
2134         *
2135         * It is possible that concurrent renames can mess up our list
2136         * walk here and result in missing our dentry, resulting in the
2137         * false-negative result. d_lookup() protects against concurrent
2138         * renames using rename_lock seqlock.
2139         *
2140         * See Documentation/filesystems/path-lookup.txt for more details.
2141         */
2142        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2143                unsigned seq;
2144
2145seqretry:
2146                /*
2147                 * The dentry sequence count protects us from concurrent
2148                 * renames, and thus protects parent and name fields.
2149                 *
2150                 * The caller must perform a seqcount check in order
2151                 * to do anything useful with the returned dentry.
2152                 *
2153                 * NOTE! We do a "raw" seqcount_begin here. That means that
2154                 * we don't wait for the sequence count to stabilize if it
2155                 * is in the middle of a sequence change. If we do the slow
2156                 * dentry compare, we will do seqretries until it is stable,
2157                 * and if we end up with a successful lookup, we actually
2158                 * want to exit RCU lookup anyway.
2159                 *
2160                 * Note that raw_seqcount_begin still *does* smp_rmb(), so
2161                 * we are still guaranteed NUL-termination of ->d_name.name.
2162                 */
2163                seq = raw_seqcount_begin(&dentry->d_seq);
2164                if (dentry->d_parent != parent)
2165                        continue;
2166                if (d_unhashed(dentry))
2167                        continue;
2168
2169                if (unlikely(parent->d_flags & DCACHE_OP_COMPARE)) {
2170                        int tlen;
2171                        const char *tname;
2172                        if (dentry->d_name.hash != hashlen_hash(hashlen))
2173                                continue;
2174                        tlen = dentry->d_name.len;
2175                        tname = dentry->d_name.name;
2176                        /* we want a consistent (name,len) pair */
2177                        if (read_seqcount_retry(&dentry->d_seq, seq)) {
2178                                cpu_relax();
2179                                goto seqretry;
2180                        }
2181                        if (parent->d_op->d_compare(dentry,
2182                                                    tlen, tname, name) != 0)
2183                                continue;
2184                } else {
2185                        if (dentry->d_name.hash_len != hashlen)
2186                                continue;
2187                        if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
2188                                continue;
2189                }
2190                *seqp = seq;
2191                return dentry;
2192        }
2193        return NULL;
2194}
2195
2196/**
2197 * d_lookup - search for a dentry
2198 * @parent: parent dentry
2199 * @name: qstr of name we wish to find
2200 * Returns: dentry, or NULL
2201 *
2202 * d_lookup searches the children of the parent dentry for the name in
2203 * question. If the dentry is found its reference count is incremented and the
2204 * dentry is returned. The caller must use dput to free the entry when it has
2205 * finished using it. %NULL is returned if the dentry does not exist.
2206 */
2207struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
2208{
2209        struct dentry *dentry;
2210        unsigned seq;
2211
2212        do {
2213                seq = read_seqbegin(&rename_lock);
2214                dentry = __d_lookup(parent, name);
2215                if (dentry)
2216                        break;
2217        } while (read_seqretry(&rename_lock, seq));
2218        return dentry;
2219}
2220EXPORT_SYMBOL(d_lookup);
2221
2222/**
2223 * __d_lookup - search for a dentry (racy)
2224 * @parent: parent dentry
2225 * @name: qstr of name we wish to find
2226 * Returns: dentry, or NULL
2227 *
2228 * __d_lookup is like d_lookup, however it may (rarely) return a
2229 * false-negative result due to unrelated rename activity.
2230 *
2231 * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
2232 * however it must be used carefully, eg. with a following d_lookup in
2233 * the case of failure.
2234 *
2235 * __d_lookup callers must be commented.
2236 */
2237struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
2238{
2239        unsigned int hash = name->hash;
2240        struct hlist_bl_head *b = d_hash(hash);
2241        struct hlist_bl_node *node;
2242        struct dentry *found = NULL;
2243        struct dentry *dentry;
2244
2245        /*
2246         * Note: There is significant duplication with __d_lookup_rcu which is
2247         * required to prevent single threaded performance regressions
2248         * especially on architectures where smp_rmb (in seqcounts) are costly.
2249         * Keep the two functions in sync.
2250         */
2251
2252        /*
2253         * The hash list is protected using RCU.
2254         *
2255         * Take d_lock when comparing a candidate dentry, to avoid races
2256         * with d_move().
2257         *
2258         * It is possible that concurrent renames can mess up our list
2259         * walk here and result in missing our dentry, resulting in the
2260         * false-negative result. d_lookup() protects against concurrent
2261         * renames using rename_lock seqlock.
2262         *
2263         * See Documentation/filesystems/path-lookup.txt for more details.
2264         */
2265        rcu_read_lock();
2266        
2267        hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
2268
2269                if (dentry->d_name.hash != hash)
2270                        continue;
2271
2272                spin_lock(&dentry->d_lock);
2273                if (dentry->d_parent != parent)
2274                        goto next;
2275                if (d_unhashed(dentry))
2276                        goto next;
2277
2278                if (!d_same_name(dentry, parent, name))
2279                        goto next;
2280
2281                dentry->d_lockref.count++;
2282                found = dentry;
2283                spin_unlock(&dentry->d_lock);
2284                break;
2285next:
2286                spin_unlock(&dentry->d_lock);
2287        }
2288        rcu_read_unlock();
2289
2290        return found;
2291}
2292
2293/**
2294 * d_hash_and_lookup - hash the qstr then search for a dentry
2295 * @dir: Directory to search in
2296 * @name: qstr of name we wish to find
2297 *
2298 * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
2299 */
2300struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
2301{
2302        /*
2303         * Check for a fs-specific hash function. Note that we must
2304         * calculate the standard hash first, as the d_op->d_hash()
2305         * routine may choose to leave the hash value unchanged.
2306         */
2307        name->hash = full_name_hash(dir, name->name, name->len);
2308        if (dir->d_flags & DCACHE_OP_HASH) {
2309                int err = dir->d_op->d_hash(dir, name);
2310                if (unlikely(err < 0))
2311                        return ERR_PTR(err);
2312        }
2313        return d_lookup(dir, name);
2314}
2315EXPORT_SYMBOL(d_hash_and_lookup);
2316
2317/*
2318 * When a file is deleted, we have two options:
2319 * - turn this dentry into a negative dentry
2320 * - unhash this dentry and free it.
2321 *
2322 * Usually, we want to just turn this into
2323 * a negative dentry, but if anybody else is
2324 * currently using the dentry or the inode
2325 * we can't do that and we fall back on removing
2326 * it from the hash queues and waiting for
2327 * it to be deleted later when it has no users
2328 */
2329 
2330/**
2331 * d_delete - delete a dentry
2332 * @dentry: The dentry to delete
2333 *
2334 * Turn the dentry into a negative dentry if possible, otherwise
2335 * remove it from the hash queues so it can be deleted later
2336 */
2337 
2338void d_delete(struct dentry * dentry)
2339{
2340        struct inode *inode = dentry->d_inode;
2341        int isdir = d_is_dir(dentry);
2342
2343        spin_lock(&inode->i_lock);
2344        spin_lock(&dentry->d_lock);
2345        /*
2346         * Are we the only user?
2347         */
2348        if (dentry->d_lockref.count == 1) {
2349                dentry->d_flags &= ~DCACHE_CANT_MOUNT;
2350                dentry_unlink_inode(dentry);
2351        } else {
2352                __d_drop(dentry);
2353                spin_unlock(&dentry->d_lock);
2354                spin_unlock(&inode->i_lock);
2355        }
2356        fsnotify_nameremove(dentry, isdir);
2357}
2358EXPORT_SYMBOL(d_delete);
2359
2360static void __d_rehash(struct dentry *entry)
2361{
2362        struct hlist_bl_head *b = d_hash(entry->d_name.hash);
2363
2364        hlist_bl_lock(b);
2365        hlist_bl_add_head_rcu(&entry->d_hash, b);
2366        hlist_bl_unlock(b);
2367}
2368
2369/**
2370 * d_rehash     - add an entry back to the hash
2371 * @entry: dentry to add to the hash
2372 *
2373 * Adds a dentry to the hash according to its name.
2374 */
2375 
2376void d_rehash(struct dentry * entry)
2377{
2378        spin_lock(&entry->d_lock);
2379        __d_rehash(entry);
2380        spin_unlock(&entry->d_lock);
2381}
2382EXPORT_SYMBOL(d_rehash);
2383
2384static inline unsigned start_dir_add(struct inode *dir)
2385{
2386
2387        for (;;) {
2388                unsigned n = dir->i_dir_seq;
2389                if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
2390                        return n;
2391                cpu_relax();
2392        }
2393}
2394
2395static inline void end_dir_add(struct inode *dir, unsigned n)
2396{
2397        smp_store_release(&dir->i_dir_seq, n + 2);
2398}
2399
2400static void d_wait_lookup(struct dentry *dentry)
2401{
2402        if (d_in_lookup(dentry)) {
2403                DECLARE_WAITQUEUE(wait, current);
2404                add_wait_queue(dentry->d_wait, &wait);
2405                do {
2406                        set_current_state(TASK_UNINTERRUPTIBLE);
2407                        spin_unlock(&dentry->d_lock);
2408                        schedule();
2409                        spin_lock(&dentry->d_lock);
2410                } while (d_in_lookup(dentry));
2411        }
2412}
2413
2414struct dentry *d_alloc_parallel(struct dentry *parent,
2415                                const struct qstr *name,
2416                                wait_queue_head_t *wq)
2417{
2418        unsigned int hash = name->hash;
2419        struct hlist_bl_head *b = in_lookup_hash(parent, hash);
2420        struct hlist_bl_node *node;
2421        struct dentry *new = d_alloc(parent, name);
2422        struct dentry *dentry;
2423        unsigned seq, r_seq, d_seq;
2424
2425        if (unlikely(!new))
2426                return ERR_PTR(-ENOMEM);
2427
2428retry:
2429        rcu_read_lock();
2430        seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
2431        r_seq = read_seqbegin(&rename_lock);
2432        dentry = __d_lookup_rcu(parent, name, &d_seq);
2433        if (unlikely(dentry)) {
2434                if (!lockref_get_not_dead(&dentry->d_lockref)) {
2435                        rcu_read_unlock();
2436                        goto retry;
2437                }
2438                if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
2439                        rcu_read_unlock();
2440                        dput(dentry);
2441                        goto retry;
2442                }
2443                rcu_read_unlock();
2444                dput(new);
2445                return dentry;
2446        }
2447        if (unlikely(read_seqretry(&rename_lock, r_seq))) {
2448                rcu_read_unlock();
2449                goto retry;
2450        }
2451
2452        if (unlikely(seq & 1)) {
2453                rcu_read_unlock();
2454                goto retry;
2455        }
2456
2457        hlist_bl_lock(b);
2458        if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
2459                hlist_bl_unlock(b);
2460                rcu_read_unlock();
2461                goto retry;
2462        }
2463        /*
2464         * No changes for the parent since the beginning of d_lookup().
2465         * Since all removals from the chain happen with hlist_bl_lock(),
2466         * any potential in-lookup matches are going to stay here until
2467         * we unlock the chain.  All fields are stable in everything
2468         * we encounter.
2469         */
2470        hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
2471                if (dentry->d_name.hash != hash)
2472                        continue;
2473                if (dentry->d_parent != parent)
2474                        continue;
2475                if (!d_same_name(dentry, parent, name))
2476                        continue;
2477                hlist_bl_unlock(b);
2478                /* now we can try to grab a reference */
2479                if (!lockref_get_not_dead(&dentry->d_lockref)) {
2480                        rcu_read_unlock();
2481                        goto retry;
2482                }
2483
2484                rcu_read_unlock();
2485                /*
2486                 * somebody is likely to be still doing lookup for it;
2487                 * wait for them to finish
2488                 */
2489                spin_lock(&dentry->d_lock);
2490                d_wait_lookup(dentry);
2491                /*
2492                 * it's not in-lookup anymore; in principle we should repeat
2493                 * everything from dcache lookup, but it's likely to be what
2494                 * d_lookup() would've found anyway.  If it is, just return it;
2495                 * otherwise we really have to repeat the whole thing.
2496                 */
2497                if (unlikely(dentry->d_name.hash != hash))
2498                        goto mismatch;
2499                if (unlikely(dentry->d_parent != parent))
2500                        goto mismatch;
2501                if (unlikely(d_unhashed(dentry)))
2502                        goto mismatch;
2503                if (unlikely(!d_same_name(dentry, parent, name)))
2504                        goto mismatch;
2505                /* OK, it *is* a hashed match; return it */
2506                spin_unlock(&dentry->d_lock);
2507                dput(new);
2508                return dentry;
2509        }
2510        rcu_read_unlock();
2511        /* we can't take ->d_lock here; it's OK, though. */
2512        new->d_flags |= DCACHE_PAR_LOOKUP;
2513        new->d_wait = wq;
2514        hlist_bl_add_head_rcu(&new->d_u.d_in_lookup_hash, b);
2515        hlist_bl_unlock(b);
2516        return new;
2517mismatch:
2518        spin_unlock(&dentry->d_lock);
2519        dput(dentry);
2520        goto retry;
2521}
2522EXPORT_SYMBOL(d_alloc_parallel);
2523
2524void __d_lookup_done(struct dentry *dentry)
2525{
2526        struct hlist_bl_head *b = in_lookup_hash(dentry->d_parent,
2527                                                 dentry->d_name.hash);
2528        hlist_bl_lock(b);
2529        dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
2530        __hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
2531        wake_up_all(dentry->d_wait);
2532        dentry->d_wait = NULL;
2533        hlist_bl_unlock(b);
2534        INIT_HLIST_NODE(&dentry->d_u.d_alias);
2535        INIT_LIST_HEAD(&dentry->d_lru);
2536}
2537EXPORT_SYMBOL(__d_lookup_done);
2538
2539/* inode->i_lock held if inode is non-NULL */
2540
2541static inline void __d_add(struct dentry *dentry, struct inode *inode)
2542{
2543        struct inode *dir = NULL;
2544        unsigned n;
2545        spin_lock(&dentry->d_lock);
2546        if (unlikely(d_in_lookup(dentry))) {
2547                dir = dentry->d_parent->d_inode;
2548                n = start_dir_add(dir);
2549                __d_lookup_done(dentry);
2550        }
2551        if (inode) {
2552                unsigned add_flags = d_flags_for_inode(inode);
2553                hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
2554                raw_write_seqcount_begin(&dentry->d_seq);
2555                __d_set_inode_and_type(dentry, inode, add_flags);
2556                raw_write_seqcount_end(&dentry->d_seq);
2557                fsnotify_update_flags(dentry);
2558        }
2559        __d_rehash(dentry);
2560        if (dir)
2561                end_dir_add(dir, n);
2562        spin_unlock(&dentry->d_lock);
2563        if (inode)
2564                spin_unlock(&inode->i_lock);
2565}
2566
2567/**
2568 * d_add - add dentry to hash queues
2569 * @entry: dentry to add
2570 * @inode: The inode to attach to this dentry
2571 *
2572 * This adds the entry to the hash queues and initializes @inode.
2573 * The entry was actually filled in earlier during d_alloc().
2574 */
2575
2576void d_add(struct dentry *entry, struct inode *inode)
2577{
2578        if (inode) {
2579                security_d_instantiate(entry, inode);
2580                spin_lock(&inode->i_lock);
2581        }
2582        __d_add(entry, inode);
2583}
2584EXPORT_SYMBOL(d_add);
2585
2586/**
2587 * d_exact_alias - find and hash an exact unhashed alias
2588 * @entry: dentry to add
2589 * @inode: The inode to go with this dentry
2590 *
2591 * If an unhashed dentry with the same name/parent and desired
2592 * inode already exists, hash and return it.  Otherwise, return
2593 * NULL.
2594 *
2595 * Parent directory should be locked.
2596 */
2597struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
2598{
2599        struct dentry *alias;
2600        unsigned int hash = entry->d_name.hash;
2601
2602        spin_lock(&inode->i_lock);
2603        hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
2604                /*
2605                 * Don't need alias->d_lock here, because aliases with
2606                 * d_parent == entry->d_parent are not subject to name or
2607                 * parent changes, because the parent inode i_mutex is held.
2608                 */
2609                if (alias->d_name.hash != hash)
2610                        continue;
2611                if (alias->d_parent != entry->d_parent)
2612                        continue;
2613                if (!d_same_name(alias, entry->d_parent, &entry->d_name))
2614                        continue;
2615                spin_lock(&alias->d_lock);
2616                if (!d_unhashed(alias)) {
2617                        spin_unlock(&alias->d_lock);
2618                        alias = NULL;
2619                } else {
2620                        __dget_dlock(alias);
2621                        __d_rehash(alias);
2622                        spin_unlock(&alias->d_lock);
2623                }
2624                spin_unlock(&inode->i_lock);
2625                return alias;
2626        }
2627        spin_unlock(&inode->i_lock);
2628        return NULL;
2629}
2630EXPORT_SYMBOL(d_exact_alias);
2631
2632static void swap_names(struct dentry *dentry, struct dentry *target)
2633{
2634        if (unlikely(dname_external(target))) {
2635                if (unlikely(dname_external(dentry))) {
2636                        /*
2637                         * Both external: swap the pointers
2638                         */
2639                        swap(target->d_name.name, dentry->d_name.name);
2640                } else {
2641                        /*
2642                         * dentry:internal, target:external.  Steal target's
2643                         * storage and make target internal.
2644                         */
2645                        memcpy(target->d_iname, dentry->d_name.name,
2646                                        dentry->d_name.len + 1);
2647                        dentry->d_name.name = target->d_name.name;
2648                        target->d_name.name = target->d_iname;
2649                }
2650        } else {
2651                if (unlikely(dname_external(dentry))) {
2652                        /*
2653                         * dentry:external, target:internal.  Give dentry's
2654                         * storage to target and make dentry internal
2655                         */
2656                        memcpy(dentry->d_iname, target->d_name.name,
2657                                        target->d_name.len + 1);
2658                        target->d_name.name = dentry->d_name.name;
2659                        dentry->d_name.name = dentry->d_iname;
2660                } else {
2661                        /*
2662                         * Both are internal.
2663                         */
2664                        unsigned int i;
2665                        BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
2666                        for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
2667                                swap(((long *) &dentry->d_iname)[i],
2668                                     ((long *) &target->d_iname)[i]);
2669                        }
2670                }
2671        }
2672        swap(dentry->d_name.hash_len, target->d_name.hash_len);
2673}
2674
2675static void copy_name(struct dentry *dentry, struct dentry *target)
2676{
2677        struct external_name *old_name = NULL;
2678        if (unlikely(dname_external(dentry)))
2679                old_name = external_name(dentry);
2680        if (unlikely(dname_external(target))) {
2681                atomic_inc(&external_name(target)->u.count);
2682                dentry->d_name = target->d_name;
2683        } else {
2684                memcpy(dentry->d_iname, target->d_name.name,
2685                                target->d_name.len + 1);
2686                dentry->d_name.name = dentry->d_iname;
2687                dentry->d_name.hash_len = target->d_name.hash_len;
2688        }
2689        if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
2690                kfree_rcu(old_name, u.head);
2691}
2692
2693/*
2694 * __d_move - move a dentry
2695 * @dentry: entry to move
2696 * @target: new dentry
2697 * @exchange: exchange the two dentries
2698 *
2699 * Update the dcache to reflect the move of a file name. Negative
2700 * dcache entries should not be moved in this way. Caller must hold
2701 * rename_lock, the i_mutex of the source and target directories,
2702 * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
2703 */
2704static void __d_move(struct dentry *dentry, struct dentry *target,
2705                     bool exchange)
2706{
2707        struct dentry *old_parent, *p;
2708        struct inode *dir = NULL;
2709        unsigned n;
2710
2711        WARN_ON(!dentry->d_inode);
2712        if (WARN_ON(dentry == target))
2713                return;
2714
2715        BUG_ON(d_ancestor(target, dentry));
2716        old_parent = dentry->d_parent;
2717        p = d_ancestor(old_parent, target);
2718        if (IS_ROOT(dentry)) {
2719                BUG_ON(p);
2720                spin_lock(&target->d_parent->d_lock);
2721        } else if (!p) {
2722                /* target is not a descendent of dentry->d_parent */
2723                spin_lock(&target->d_parent->d_lock);
2724                spin_lock_nested(&old_parent->d_lock, DENTRY_D_LOCK_NESTED);
2725        } else {
2726                BUG_ON(p == dentry);
2727                spin_lock(&old_parent->d_lock);
2728                if (p != target)
2729                        spin_lock_nested(&target->d_parent->d_lock,
2730                                        DENTRY_D_LOCK_NESTED);
2731        }
2732        spin_lock_nested(&dentry->d_lock, 2);
2733        spin_lock_nested(&target->d_lock, 3);
2734
2735        if (unlikely(d_in_lookup(target))) {
2736                dir = target->d_parent->d_inode;
2737                n = start_dir_add(dir);
2738                __d_lookup_done(target);
2739        }
2740
2741        write_seqcount_begin(&dentry->d_seq);
2742        write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
2743
2744        /* unhash both */
2745        if (!d_unhashed(dentry))
2746                ___d_drop(dentry);
2747        if (!d_unhashed(target))
2748                ___d_drop(target);
2749
2750        /* ... and switch them in the tree */
2751        dentry->d_parent = target->d_parent;
2752        if (!exchange) {
2753                copy_name(dentry, target);
2754                target->d_hash.pprev = NULL;
2755                dentry->d_parent->d_lockref.count++;
2756                if (dentry == old_parent)
2757                        dentry->d_flags |= DCACHE_RCUACCESS;
2758                else
2759                        WARN_ON(!--old_parent->d_lockref.count);
2760        } else {
2761                target->d_parent = old_parent;
2762                swap_names(dentry, target);
2763                list_move(&target->d_child, &target->d_parent->d_subdirs);
2764                __d_rehash(target);
2765                fsnotify_update_flags(target);
2766        }
2767        list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
2768        __d_rehash(dentry);
2769        fsnotify_update_flags(dentry);
2770
2771        write_seqcount_end(&target->d_seq);
2772        write_seqcount_end(&dentry->d_seq);
2773
2774        if (dir)
2775                end_dir_add(dir, n);
2776
2777        if (dentry->d_parent != old_parent)
2778                spin_unlock(&dentry->d_parent->d_lock);
2779        if (dentry != old_parent)
2780                spin_unlock(&old_parent->d_lock);
2781        spin_unlock(&target->d_lock);
2782        spin_unlock(&dentry->d_lock);
2783}
2784
2785/*
2786 * d_move - move a dentry
2787 * @dentry: entry to move
2788 * @target: new dentry
2789 *
2790 * Update the dcache to reflect the move of a file name. Negative
2791 * dcache entries should not be moved in this way. See the locking
2792 * requirements for __d_move.
2793 */
2794void d_move(struct dentry *dentry, struct dentry *target)
2795{
2796        write_seqlock(&rename_lock);
2797        __d_move(dentry, target, false);
2798        write_sequnlock(&rename_lock);
2799}
2800EXPORT_SYMBOL(d_move);
2801
2802/*
2803 * d_exchange - exchange two dentries
2804 * @dentry1: first dentry
2805 * @dentry2: second dentry
2806 */
2807void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
2808{
2809        write_seqlock(&rename_lock);
2810
2811        WARN_ON(!dentry1->d_inode);
2812        WARN_ON(!dentry2->d_inode);
2813        WARN_ON(IS_ROOT(dentry1));
2814        WARN_ON(IS_ROOT(dentry2));
2815
2816        __d_move(dentry1, dentry2, true);
2817
2818        write_sequnlock(&rename_lock);
2819}
2820
2821/**
2822 * d_ancestor - search for an ancestor
2823 * @p1: ancestor dentry
2824 * @p2: child dentry
2825 *
2826 * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
2827 * an ancestor of p2, else NULL.
2828 */
2829struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
2830{
2831        struct dentry *p;
2832
2833        for (p = p2; !IS_ROOT(p); p = p->d_parent) {
2834                if (p->d_parent == p1)
2835                        return p;
2836        }
2837        return NULL;
2838}
2839
2840/*
2841 * This helper attempts to cope with remotely renamed directories
2842 *
2843 * It assumes that the caller is already holding
2844 * dentry->d_parent->d_inode->i_mutex, and rename_lock
2845 *
2846 * Note: If ever the locking in lock_rename() changes, then please
2847 * remember to update this too...
2848 */
2849static int __d_unalias(struct inode *inode,
2850                struct dentry *dentry, struct dentry *alias)
2851{
2852        struct mutex *m1 = NULL;
2853        struct rw_semaphore *m2 = NULL;
2854        int ret = -ESTALE;
2855
2856        /* If alias and dentry share a parent, then no extra locks required */
2857        if (alias->d_parent == dentry->d_parent)
2858                goto out_unalias;
2859
2860        /* See lock_rename() */
2861        if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
2862                goto out_err;
2863        m1 = &dentry->d_sb->s_vfs_rename_mutex;
2864        if (!inode_trylock_shared(alias->d_parent->d_inode))
2865                goto out_err;
2866        m2 = &alias->d_parent->d_inode->i_rwsem;
2867out_unalias:
2868        __d_move(alias, dentry, false);
2869        ret = 0;
2870out_err:
2871        if (m2)
2872                up_read(m2);
2873        if (m1)
2874                mutex_unlock(m1);
2875        return ret;
2876}
2877
2878/**
2879 * d_splice_alias - splice a disconnected dentry into the tree if one exists
2880 * @inode:  the inode which may have a disconnected dentry
2881 * @dentry: a negative dentry which we want to point to the inode.
2882 *
2883 * If inode is a directory and has an IS_ROOT alias, then d_move that in
2884 * place of the given dentry and return it, else simply d_add the inode
2885 * to the dentry and return NULL.
2886 *
2887 * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
2888 * we should error out: directories can't have multiple aliases.
2889 *
2890 * This is needed in the lookup routine of any filesystem that is exportable
2891 * (via knfsd) so that we can build dcache paths to directories effectively.
2892 *
2893 * If a dentry was found and moved, then it is returned.  Otherwise NULL
2894 * is returned.  This matches the expected return value of ->lookup.
2895 *
2896 * Cluster filesystems may call this function with a negative, hashed dentry.
2897 * In that case, we know that the inode will be a regular file, and also this
2898 * will only occur during atomic_open. So we need to check for the dentry
2899 * being already hashed only in the final case.
2900 */
2901struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
2902{
2903        if (IS_ERR(inode))
2904                return ERR_CAST(inode);
2905
2906        BUG_ON(!d_unhashed(dentry));
2907
2908        if (!inode)
2909                goto out;
2910
2911        security_d_instantiate(dentry, inode);
2912        spin_lock(&inode->i_lock);
2913        if (S_ISDIR(inode->i_mode)) {
2914                struct dentry *new = __d_find_any_alias(inode);
2915                if (unlikely(new)) {
2916                        /* The reference to new ensures it remains an alias */
2917                        spin_unlock(&inode->i_lock);
2918                        write_seqlock(&rename_lock);
2919                        if (unlikely(d_ancestor(new, dentry))) {
2920                                write_sequnlock(&rename_lock);
2921                                dput(new);
2922                                new = ERR_PTR(-ELOOP);
2923                                pr_warn_ratelimited(
2924                                        "VFS: Lookup of '%s' in %s %s"
2925                                        " would have caused loop\n",
2926                                        dentry->d_name.name,
2927                                        inode->i_sb->s_type->name,
2928                                        inode->i_sb->s_id);
2929                        } else if (!IS_ROOT(new)) {
2930                                struct dentry *old_parent = dget(new->d_parent);
2931                                int err = __d_unalias(inode, dentry, new);
2932                                write_sequnlock(&rename_lock);
2933                                if (err) {
2934                                        dput(new);
2935                                        new = ERR_PTR(err);
2936                                }
2937                                dput(old_parent);
2938                        } else {
2939                                __d_move(new, dentry, false);
2940                                write_sequnlock(&rename_lock);
2941                        }
2942                        iput(inode);
2943                        return new;
2944                }
2945        }
2946out:
2947        __d_add(dentry, inode);
2948        return NULL;
2949}
2950EXPORT_SYMBOL(d_splice_alias);
2951
2952/*
2953 * Test whether new_dentry is a subdirectory of old_dentry.
2954 *
2955 * Trivially implemented using the dcache structure
2956 */
2957
2958/**
2959 * is_subdir - is new dentry a subdirectory of old_dentry
2960 * @new_dentry: new dentry
2961 * @old_dentry: old dentry
2962 *
2963 * Returns true if new_dentry is a subdirectory of the parent (at any depth).
2964 * Returns false otherwise.
2965 * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
2966 */
2967  
2968bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
2969{
2970        bool result;
2971        unsigned seq;
2972
2973        if (new_dentry == old_dentry)
2974                return true;
2975
2976        do {
2977                /* for restarting inner loop in case of seq retry */
2978                seq = read_seqbegin(&rename_lock);
2979                /*
2980                 * Need rcu_readlock to protect against the d_parent trashing
2981                 * due to d_move
2982                 */
2983                rcu_read_lock();
2984                if (d_ancestor(old_dentry, new_dentry))
2985                        result = true;
2986                else
2987                        result = false;
2988                rcu_read_unlock();
2989        } while (read_seqretry(&rename_lock, seq));
2990
2991        return result;
2992}
2993EXPORT_SYMBOL(is_subdir);
2994
2995static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
2996{
2997        struct dentry *root = data;
2998        if (dentry != root) {
2999                if (d_unhashed(dentry) || !dentry->d_inode)
3000                        return D_WALK_SKIP;
3001
3002                if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
3003                        dentry->d_flags |= DCACHE_GENOCIDE;
3004                        dentry->d_lockref.count--;
3005                }
3006        }
3007        return D_WALK_CONTINUE;
3008}
3009
3010void d_genocide(struct dentry *parent)
3011{
3012        d_walk(parent, parent, d_genocide_kill);
3013}
3014
3015EXPORT_SYMBOL(d_genocide);
3016
3017void d_tmpfile(struct dentry *dentry, struct inode *inode)
3018{
3019        inode_dec_link_count(inode);
3020        BUG_ON(dentry->d_name.name != dentry->d_iname ||
3021                !hlist_unhashed(&dentry->d_u.d_alias) ||
3022                !d_unlinked(dentry));
3023        spin_lock(&dentry->d_parent->d_lock);
3024        spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
3025        dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
3026                                (unsigned long long)inode->i_ino);
3027        spin_unlock(&dentry->d_lock);
3028        spin_unlock(&dentry->d_parent->d_lock);
3029        d_instantiate(dentry, inode);
3030}
3031EXPORT_SYMBOL(d_tmpfile);
3032
3033static __initdata unsigned long dhash_entries;
3034static int __init set_dhash_entries(char *str)
3035{
3036        if (!str)
3037                return 0;
3038        dhash_entries = simple_strtoul(str, &str, 0);
3039        return 1;
3040}
3041__setup("dhash_entries=", set_dhash_entries);
3042
3043static void __init dcache_init_early(void)
3044{
3045        /* If hashes are distributed across NUMA nodes, defer
3046         * hash allocation until vmalloc space is available.
3047         */
3048        if (hashdist)
3049                return;
3050
3051        dentry_hashtable =
3052                alloc_large_system_hash("Dentry cache",
3053                                        sizeof(struct hlist_bl_head),
3054                                        dhash_entries,
3055                                        13,
3056                                        HASH_EARLY | HASH_ZERO,
3057                                        &d_hash_shift,
3058                                        NULL,
3059                                        0,
3060                                        0);
3061        d_hash_shift = 32 - d_hash_shift;
3062}
3063
3064static void __init dcache_init(void)
3065{
3066        /*
3067         * A constructor could be added for stable state like the lists,
3068         * but it is probably not worth it because of the cache nature
3069         * of the dcache.
3070         */
3071        dentry_cache = KMEM_CACHE_USERCOPY(dentry,
3072                SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
3073                d_iname);
3074
3075        /* Hash may have been set up in dcache_init_early */
3076        if (!hashdist)
3077                return;
3078
3079        dentry_hashtable =
3080                alloc_large_system_hash("Dentry cache",
3081                                        sizeof(struct hlist_bl_head),
3082                                        dhash_entries,
3083                                        13,
3084                                        HASH_ZERO,
3085                                        &d_hash_shift,
3086                                        NULL,
3087                                        0,
3088                                        0);
3089        d_hash_shift = 32 - d_hash_shift;
3090}
3091
3092/* SLAB cache for __getname() consumers */
3093struct kmem_cache *names_cachep __read_mostly;
3094EXPORT_SYMBOL(names_cachep);
3095
3096void __init vfs_caches_init_early(void)
3097{
3098        int i;
3099
3100        for (i = 0; i < ARRAY_SIZE(in_lookup_hashtable); i++)
3101                INIT_HLIST_BL_HEAD(&in_lookup_hashtable[i]);
3102
3103        dcache_init_early();
3104        inode_init_early();
3105}
3106
3107void __init vfs_caches_init(void)
3108{
3109        names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
3110                        SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
3111
3112        dcache_init();
3113        inode_init();
3114        files_init();
3115        files_maxfiles_init();
3116        mnt_init();
3117        bdev_cache_init();
3118        chrdev_init();
3119}
3120