개념 설명 전체 · v6.6 / fs/dcache.c

    1 // SPDX-License-Identifier: GPL-2.0-only
    2 /*
    3  * fs/dcache.c
    4  *
    5  * Complete reimplementation
    6  * (C) 1997 Thomas Schoebel-Theuer,
    7  * with heavy changes by Linus Torvalds
    8  */
    9 
   10 /*
   11  * Notes on the allocation strategy:
   12  *
   13  * The dcache is a master of the icache - whenever a dcache entry
   14  * exists, the inode will always exist. "iput()" is done either when
   15  * the dcache entry is deleted or garbage collected.
   16  */
   17 
   18 #include <linux/ratelimit.h>
   19 #include <linux/string.h>
   20 #include <linux/mm.h>
   21 #include <linux/fs.h>
   22 #include <linux/fscrypt.h>
   23 #include <linux/fsnotify.h>
   24 #include <linux/slab.h>
   25 #include <linux/init.h>
   26 #include <linux/hash.h>
   27 #include <linux/cache.h>
   28 #include <linux/export.h>
   29 #include <linux/security.h>
   30 #include <linux/seqlock.h>
   31 #include <linux/memblock.h>
   32 #include <linux/bit_spinlock.h>
   33 #include <linux/rculist_bl.h>
   34 #include <linux/list_lru.h>
   35 #include "internal.h"
   36 #include "mount.h"
   37 
   38 /*
   39  * Usage:
   40  * dcache->d_inode->i_lock protects:
   41  *   - i_dentry, d_u.d_alias, d_inode of aliases
   42  * dcache_hash_bucket lock protects:
   43  *   - the dcache hash table
   44  * s_roots bl list spinlock protects:
   45  *   - the s_roots list (see __d_drop)
   46  * dentry->d_sb->s_dentry_lru_lock protects:
   47  *   - the dcache lru lists and counters
   48  * d_lock protects:
   49  *   - d_flags
   50  *   - d_name
   51  *   - d_lru
   52  *   - d_count
   53  *   - d_unhashed()
   54  *   - d_parent and d_subdirs
   55  *   - childrens' d_child and d_parent
   56  *   - d_u.d_alias, d_inode
   57  *
   58  * Ordering:
   59  * dentry->d_inode->i_lock
   60  *   dentry->d_lock
   61  *     dentry->d_sb->s_dentry_lru_lock
   62  *     dcache_hash_bucket lock
   63  *     s_roots lock
   64  *
   65  * If there is an ancestor relationship:
   66  * dentry->d_parent->...->d_parent->d_lock
   67  *   ...
   68  *     dentry->d_parent->d_lock
   69  *       dentry->d_lock
   70  *
   71  * If no ancestor relationship:
   72  * arbitrary, since it's serialized on rename_lock
   73  */
   74 int sysctl_vfs_cache_pressure __read_mostly = 100;
   75 EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);
   76 
   77 __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);
   78 
   79 EXPORT_SYMBOL(rename_lock);
   80 
   81 static struct kmem_cache *dentry_cache __read_mostly;
   82 
   83 const struct qstr empty_name = QSTR_INIT("", 0);
   84 EXPORT_SYMBOL(empty_name);
   85 const struct qstr slash_name = QSTR_INIT("/", 1);
   86 EXPORT_SYMBOL(slash_name);
   87 const struct qstr dotdot_name = QSTR_INIT("..", 2);
   88 EXPORT_SYMBOL(dotdot_name);
   89 
   90 /*
   91  * This is the single most critical data structure when it comes
   92  * to the dcache: the hashtable for lookups. Somebody should try
   93  * to make this good - I've just made it work.
   94  *
   95  * This hash-function tries to avoid losing too many bits of hash
   96  * information, yet avoid using a prime hash-size or similar.
   97  */
   98 
   99 static unsigned int d_hash_shift __read_mostly;
  100 
  101 static struct hlist_bl_head *dentry_hashtable __read_mostly;
  102 
  103 static inline struct hlist_bl_head *d_hash(unsigned int hash)
  104 {
  105 	return dentry_hashtable + (hash >> d_hash_shift);
  106 }
  107 
  108 #define IN_LOOKUP_SHIFT 10
  109 static struct hlist_bl_head in_lookup_hashtable[1 << IN_LOOKUP_SHIFT];
  110 
  111 static inline struct hlist_bl_head *in_lookup_hash(const struct dentry *parent,
  112 					unsigned int hash)
  113 {
  114 	hash += (unsigned long) parent / L1_CACHE_BYTES;
  115 	return in_lookup_hashtable + hash_32(hash, IN_LOOKUP_SHIFT);
  116 }
  117 
  118 struct dentry_stat_t {
  119 	long nr_dentry;
  120 	long nr_unused;
  121 	long age_limit;		/* age in seconds */
  122 	long want_pages;	/* pages requested by system */
  123 	long nr_negative;	/* # of unused negative dentries */
  124 	long dummy;		/* Reserved for future use */
  125 };
  126 
  127 static DEFINE_PER_CPU(long, nr_dentry);
  128 static DEFINE_PER_CPU(long, nr_dentry_unused);
  129 static DEFINE_PER_CPU(long, nr_dentry_negative);
  130 
  131 #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
  132 /* Statistics gathering. */
  133 static struct dentry_stat_t dentry_stat = {
  134 	.age_limit = 45,
  135 };
  136 
  137 /*
  138  * Here we resort to our own counters instead of using generic per-cpu counters
  139  * for consistency with what the vfs inode code does. We are expected to harvest
  140  * better code and performance by having our own specialized counters.
  141  *
  142  * Please note that the loop is done over all possible CPUs, not over all online
  143  * CPUs. The reason for this is that we don't want to play games with CPUs going
  144  * on and off. If one of them goes off, we will just keep their counters.
  145  *
  146  * glommer: See cffbc8a for details, and if you ever intend to change this,
  147  * please update all vfs counters to match.
  148  */
  149 static long get_nr_dentry(void)
  150 {
  151 	int i;
  152 	long sum = 0;
  153 	for_each_possible_cpu(i)
  154 		sum += per_cpu(nr_dentry, i);
  155 	return sum < 0 ? 0 : sum;
  156 }
  157 
  158 static long get_nr_dentry_unused(void)
  159 {
  160 	int i;
  161 	long sum = 0;
  162 	for_each_possible_cpu(i)
  163 		sum += per_cpu(nr_dentry_unused, i);
  164 	return sum < 0 ? 0 : sum;
  165 }
  166 
  167 static long get_nr_dentry_negative(void)
  168 {
  169 	int i;
  170 	long sum = 0;
  171 
  172 	for_each_possible_cpu(i)
  173 		sum += per_cpu(nr_dentry_negative, i);
  174 	return sum < 0 ? 0 : sum;
  175 }
  176 
  177 static int proc_nr_dentry(struct ctl_table *table, int write, void *buffer,
  178 			  size_t *lenp, loff_t *ppos)
  179 {
  180 	dentry_stat.nr_dentry = get_nr_dentry();
  181 	dentry_stat.nr_unused = get_nr_dentry_unused();
  182 	dentry_stat.nr_negative = get_nr_dentry_negative();
  183 	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
  184 }
  185 
  186 static struct ctl_table fs_dcache_sysctls[] = {
  187 	{
  188 		.procname	= "dentry-state",
  189 		.data		= &dentry_stat,
  190 		.maxlen		= 6*sizeof(long),
  191 		.mode		= 0444,
  192 		.proc_handler	= proc_nr_dentry,
  193 	},
  194 	{ }
  195 };
  196 
  197 static int __init init_fs_dcache_sysctls(void)
  198 {
  199 	register_sysctl_init("fs", fs_dcache_sysctls);
  200 	return 0;
  201 }
  202 fs_initcall(init_fs_dcache_sysctls);
  203 #endif
  204 
  205 /*
  206  * Compare 2 name strings, return 0 if they match, otherwise non-zero.
  207  * The strings are both count bytes long, and count is non-zero.
  208  */
  209 #ifdef CONFIG_DCACHE_WORD_ACCESS
  210 
  211 #include <asm/word-at-a-time.h>
  212 /*
  213  * NOTE! 'cs' and 'scount' come from a dentry, so it has a
  214  * aligned allocation for this particular component. We don't
  215  * strictly need the load_unaligned_zeropad() safety, but it
  216  * doesn't hurt either.
  217  *
  218  * In contrast, 'ct' and 'tcount' can be from a pathname, and do
  219  * need the careful unaligned handling.
  220  */
  221 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
  222 {
  223 	unsigned long a,b,mask;
  224 
  225 	for (;;) {
  226 		a = read_word_at_a_time(cs);
  227 		b = load_unaligned_zeropad(ct);
  228 		if (tcount < sizeof(unsigned long))
  229 			break;
  230 		if (unlikely(a != b))
  231 			return 1;
  232 		cs += sizeof(unsigned long);
  233 		ct += sizeof(unsigned long);
  234 		tcount -= sizeof(unsigned long);
  235 		if (!tcount)
  236 			return 0;
  237 	}
  238 	mask = bytemask_from_count(tcount);
  239 	return unlikely(!!((a ^ b) & mask));
  240 }
  241 
  242 #else
  243 
  244 static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char *ct, unsigned tcount)
  245 {
  246 	do {
  247 		if (*cs != *ct)
  248 			return 1;
  249 		cs++;
  250 		ct++;
  251 		tcount--;
  252 	} while (tcount);
  253 	return 0;
  254 }
  255 
  256 #endif
  257 
  258 static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount)
  259 {
  260 	/*
  261 	 * Be careful about RCU walk racing with rename:
  262 	 * use 'READ_ONCE' to fetch the name pointer.
  263 	 *
  264 	 * NOTE! Even if a rename will mean that the length
  265 	 * was not loaded atomically, we don't care. The
  266 	 * RCU walk will check the sequence count eventually,
  267 	 * and catch it. And we won't overrun the buffer,
  268 	 * because we're reading the name pointer atomically,
  269 	 * and a dentry name is guaranteed to be properly
  270 	 * terminated with a NUL byte.
  271 	 *
  272 	 * End result: even if 'len' is wrong, we'll exit
  273 	 * early because the data cannot match (there can
  274 	 * be no NUL in the ct/tcount data)
  275 	 */
  276 	const unsigned char *cs = READ_ONCE(dentry->d_name.name);
  277 
  278 	return dentry_string_cmp(cs, ct, tcount);
  279 }
  280 
  281 struct external_name {
  282 	union {
  283 		atomic_t count;
  284 		struct rcu_head head;
  285 	} u;
  286 	unsigned char name[];
  287 };
  288 
  289 static inline struct external_name *external_name(struct dentry *dentry)
  290 {
  291 	return container_of(dentry->d_name.name, struct external_name, name[0]);
  292 }
  293 
  294 static void __d_free(struct rcu_head *head)
  295 {
  296 	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
  297 
  298 	kmem_cache_free(dentry_cache, dentry); 
  299 }
  300 
  301 static void __d_free_external(struct rcu_head *head)
  302 {
  303 	struct dentry *dentry = container_of(head, struct dentry, d_u.d_rcu);
  304 	kfree(external_name(dentry));
  305 	kmem_cache_free(dentry_cache, dentry);
  306 }
  307 
  308 static inline int dname_external(const struct dentry *dentry)
  309 {
  310 	return dentry->d_name.name != dentry->d_iname;
  311 }
  312 
  313 void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry)
  314 {
  315 	spin_lock(&dentry->d_lock);
  316 	name->name = dentry->d_name;
  317 	if (unlikely(dname_external(dentry))) {
  318 		atomic_inc(&external_name(dentry)->u.count);
  319 	} else {
  320 		memcpy(name->inline_name, dentry->d_iname,
  321 		       dentry->d_name.len + 1);
  322 		name->name.name = name->inline_name;
  323 	}
  324 	spin_unlock(&dentry->d_lock);
  325 }
  326 EXPORT_SYMBOL(take_dentry_name_snapshot);
  327 
  328 void release_dentry_name_snapshot(struct name_snapshot *name)
  329 {
  330 	if (unlikely(name->name.name != name->inline_name)) {
  331 		struct external_name *p;
  332 		p = container_of(name->name.name, struct external_name, name[0]);
  333 		if (unlikely(atomic_dec_and_test(&p->u.count)))
  334 			kfree_rcu(p, u.head);
  335 	}
  336 }
  337 EXPORT_SYMBOL(release_dentry_name_snapshot);
  338 
  339 static inline void __d_set_inode_and_type(struct dentry *dentry,
  340 					  struct inode *inode,
  341 					  unsigned type_flags)
  342 {
  343 	unsigned flags;
  344 
  345 	dentry->d_inode = inode;
  346 	flags = READ_ONCE(dentry->d_flags);
  347 	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
  348 	flags |= type_flags;
  349 	smp_store_release(&dentry->d_flags, flags);
  350 }
  351 
  352 static inline void __d_clear_type_and_inode(struct dentry *dentry)
  353 {
  354 	unsigned flags = READ_ONCE(dentry->d_flags);
  355 
  356 	flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU);
  357 	WRITE_ONCE(dentry->d_flags, flags);
  358 	dentry->d_inode = NULL;
  359 	if (dentry->d_flags & DCACHE_LRU_LIST)
  360 		this_cpu_inc(nr_dentry_negative);
  361 }
  362 
  363 static void dentry_free(struct dentry *dentry)
  364 {
  365 	WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
  366 	if (unlikely(dname_external(dentry))) {
  367 		struct external_name *p = external_name(dentry);
  368 		if (likely(atomic_dec_and_test(&p->u.count))) {
  369 			call_rcu(&dentry->d_u.d_rcu, __d_free_external);
  370 			return;
  371 		}
  372 	}
  373 	/* if dentry was never visible to RCU, immediate free is OK */
  374 	if (dentry->d_flags & DCACHE_NORCU)
  375 		__d_free(&dentry->d_u.d_rcu);
  376 	else
  377 		call_rcu(&dentry->d_u.d_rcu, __d_free);
  378 }
  379 
  380 /*
  381  * Release the dentry's inode, using the filesystem
  382  * d_iput() operation if defined.
  383  */
  384 static void dentry_unlink_inode(struct dentry * dentry)
  385 	__releases(dentry->d_lock)
  386 	__releases(dentry->d_inode->i_lock)
  387 {
  388 	struct inode *inode = dentry->d_inode;
  389 
  390 	raw_write_seqcount_begin(&dentry->d_seq);
  391 	__d_clear_type_and_inode(dentry);
  392 	hlist_del_init(&dentry->d_u.d_alias);
  393 	raw_write_seqcount_end(&dentry->d_seq);
  394 	spin_unlock(&dentry->d_lock);
  395 	spin_unlock(&inode->i_lock);
  396 	if (!inode->i_nlink)
  397 		fsnotify_inoderemove(inode);
  398 	if (dentry->d_op && dentry->d_op->d_iput)
  399 		dentry->d_op->d_iput(dentry, inode);
  400 	else
  401 		iput(inode);
  402 }
  403 
  404 /*
  405  * The DCACHE_LRU_LIST bit is set whenever the 'd_lru' entry
  406  * is in use - which includes both the "real" per-superblock
  407  * LRU list _and_ the DCACHE_SHRINK_LIST use.
  408  *
  409  * The DCACHE_SHRINK_LIST bit is set whenever the dentry is
  410  * on the shrink list (ie not on the superblock LRU list).
  411  *
  412  * The per-cpu "nr_dentry_unused" counters are updated with
  413  * the DCACHE_LRU_LIST bit.
  414  *
  415  * The per-cpu "nr_dentry_negative" counters are only updated
  416  * when deleted from or added to the per-superblock LRU list, not
  417  * from/to the shrink list. That is to avoid an unneeded dec/inc
  418  * pair when moving from LRU to shrink list in select_collect().
  419  *
  420  * These helper functions make sure we always follow the
  421  * rules. d_lock must be held by the caller.
  422  */
  423 #define D_FLAG_VERIFY(dentry,x) WARN_ON_ONCE(((dentry)->d_flags & (DCACHE_LRU_LIST | DCACHE_SHRINK_LIST)) != (x))
  424 static void d_lru_add(struct dentry *dentry)
  425 {
  426 	D_FLAG_VERIFY(dentry, 0);
  427 	dentry->d_flags |= DCACHE_LRU_LIST;
  428 	this_cpu_inc(nr_dentry_unused);
  429 	if (d_is_negative(dentry))
  430 		this_cpu_inc(nr_dentry_negative);
  431 	WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
  432 }
  433 
  434 static void d_lru_del(struct dentry *dentry)
  435 {
  436 	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
  437 	dentry->d_flags &= ~DCACHE_LRU_LIST;
  438 	this_cpu_dec(nr_dentry_unused);
  439 	if (d_is_negative(dentry))
  440 		this_cpu_dec(nr_dentry_negative);
  441 	WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru));
  442 }
  443 
  444 static void d_shrink_del(struct dentry *dentry)
  445 {
  446 	D_FLAG_VERIFY(dentry, DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
  447 	list_del_init(&dentry->d_lru);
  448 	dentry->d_flags &= ~(DCACHE_SHRINK_LIST | DCACHE_LRU_LIST);
  449 	this_cpu_dec(nr_dentry_unused);
  450 }
  451 
  452 static void d_shrink_add(struct dentry *dentry, struct list_head *list)
  453 {
  454 	D_FLAG_VERIFY(dentry, 0);
  455 	list_add(&dentry->d_lru, list);
  456 	dentry->d_flags |= DCACHE_SHRINK_LIST | DCACHE_LRU_LIST;
  457 	this_cpu_inc(nr_dentry_unused);
  458 }
  459 
  460 /*
  461  * These can only be called under the global LRU lock, ie during the
  462  * callback for freeing the LRU list. "isolate" removes it from the
  463  * LRU lists entirely, while shrink_move moves it to the indicated
  464  * private list.
  465  */
  466 static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry)
  467 {
  468 	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
  469 	dentry->d_flags &= ~DCACHE_LRU_LIST;
  470 	this_cpu_dec(nr_dentry_unused);
  471 	if (d_is_negative(dentry))
  472 		this_cpu_dec(nr_dentry_negative);
  473 	list_lru_isolate(lru, &dentry->d_lru);
  474 }
  475 
  476 static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry,
  477 			      struct list_head *list)
  478 {
  479 	D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST);
  480 	dentry->d_flags |= DCACHE_SHRINK_LIST;
  481 	if (d_is_negative(dentry))
  482 		this_cpu_dec(nr_dentry_negative);
  483 	list_lru_isolate_move(lru, &dentry->d_lru, list);
  484 }
  485 
  486 static void ___d_drop(struct dentry *dentry)
  487 {
  488 	struct hlist_bl_head *b;
  489 	/*
  490 	 * Hashed dentries are normally on the dentry hashtable,
  491 	 * with the exception of those newly allocated by
  492 	 * d_obtain_root, which are always IS_ROOT:
  493 	 */
  494 	if (unlikely(IS_ROOT(dentry)))
  495 		b = &dentry->d_sb->s_roots;
  496 	else
  497 		b = d_hash(dentry->d_name.hash);
  498 
  499 	hlist_bl_lock(b);
  500 	__hlist_bl_del(&dentry->d_hash);
  501 	hlist_bl_unlock(b);
  502 }
  503 
  504 void __d_drop(struct dentry *dentry)
  505 {
  506 	if (!d_unhashed(dentry)) {
  507 		___d_drop(dentry);
  508 		dentry->d_hash.pprev = NULL;
  509 		write_seqcount_invalidate(&dentry->d_seq);
  510 	}
  511 }
  512 EXPORT_SYMBOL(__d_drop);
  513 
  514 /**
  515  * d_drop - drop a dentry
  516  * @dentry: dentry to drop
  517  *
  518  * d_drop() unhashes the entry from the parent dentry hashes, so that it won't
  519  * be found through a VFS lookup any more. Note that this is different from
  520  * deleting the dentry - d_delete will try to mark the dentry negative if
  521  * possible, giving a successful _negative_ lookup, while d_drop will
  522  * just make the cache lookup fail.
  523  *
  524  * d_drop() is used mainly for stuff that wants to invalidate a dentry for some
  525  * reason (NFS timeouts or autofs deletes).
  526  *
  527  * __d_drop requires dentry->d_lock
  528  *
  529  * ___d_drop doesn't mark dentry as "unhashed"
  530  * (dentry->d_hash.pprev will be LIST_POISON2, not NULL).
  531  */
  532 void d_drop(struct dentry *dentry)
  533 {
  534 	spin_lock(&dentry->d_lock);
  535 	__d_drop(dentry);
  536 	spin_unlock(&dentry->d_lock);
  537 }
  538 EXPORT_SYMBOL(d_drop);
  539 
  540 static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
  541 {
  542 	struct dentry *next;
  543 	/*
  544 	 * Inform d_walk() and shrink_dentry_list() that we are no longer
  545 	 * attached to the dentry tree
  546 	 */
  547 	dentry->d_flags |= DCACHE_DENTRY_KILLED;
  548 	if (unlikely(list_empty(&dentry->d_child)))
  549 		return;
  550 	__list_del_entry(&dentry->d_child);
  551 	/*
  552 	 * Cursors can move around the list of children.  While we'd been
  553 	 * a normal list member, it didn't matter - ->d_child.next would've
  554 	 * been updated.  However, from now on it won't be and for the
  555 	 * things like d_walk() it might end up with a nasty surprise.
  556 	 * Normally d_walk() doesn't care about cursors moving around -
  557 	 * ->d_lock on parent prevents that and since a cursor has no children
  558 	 * of its own, we get through it without ever unlocking the parent.
  559 	 * There is one exception, though - if we ascend from a child that
  560 	 * gets killed as soon as we unlock it, the next sibling is found
  561 	 * using the value left in its ->d_child.next.  And if _that_
  562 	 * pointed to a cursor, and cursor got moved (e.g. by lseek())
  563 	 * before d_walk() regains parent->d_lock, we'll end up skipping
  564 	 * everything the cursor had been moved past.
  565 	 *
  566 	 * Solution: make sure that the pointer left behind in ->d_child.next
  567 	 * points to something that won't be moving around.  I.e. skip the
  568 	 * cursors.
  569 	 */
  570 	while (dentry->d_child.next != &parent->d_subdirs) {
  571 		next = list_entry(dentry->d_child.next, struct dentry, d_child);
  572 		if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
  573 			break;
  574 		dentry->d_child.next = next->d_child.next;
  575 	}
  576 }
  577 
  578 static void __dentry_kill(struct dentry *dentry)
  579 {
  580 	struct dentry *parent = NULL;
  581 	bool can_free = true;
  582 	if (!IS_ROOT(dentry))
  583 		parent = dentry->d_parent;
  584 
  585 	/*
  586 	 * The dentry is now unrecoverably dead to the world.
  587 	 */
  588 	lockref_mark_dead(&dentry->d_lockref);
  589 
  590 	/*
  591 	 * inform the fs via d_prune that this dentry is about to be
  592 	 * unhashed and destroyed.
  593 	 */
  594 	if (dentry->d_flags & DCACHE_OP_PRUNE)
  595 		dentry->d_op->d_prune(dentry);
  596 
  597 	if (dentry->d_flags & DCACHE_LRU_LIST) {
  598 		if (!(dentry->d_flags & DCACHE_SHRINK_LIST))
  599 			d_lru_del(dentry);
  600 	}
  601 	/* if it was on the hash then remove it */
  602 	__d_drop(dentry);
  603 	dentry_unlist(dentry, parent);
  604 	if (parent)
  605 		spin_unlock(&parent->d_lock);
  606 	if (dentry->d_inode)
  607 		dentry_unlink_inode(dentry);
  608 	else
  609 		spin_unlock(&dentry->d_lock);
  610 	this_cpu_dec(nr_dentry);
  611 	if (dentry->d_op && dentry->d_op->d_release)
  612 		dentry->d_op->d_release(dentry);
  613 
  614 	spin_lock(&dentry->d_lock);
  615 	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
  616 		dentry->d_flags |= DCACHE_MAY_FREE;
  617 		can_free = false;
  618 	}
  619 	spin_unlock(&dentry->d_lock);
  620 	if (likely(can_free))
  621 		dentry_free(dentry);
  622 	cond_resched();
  623 }
  624 
  625 static struct dentry *__lock_parent(struct dentry *dentry)
  626 {
  627 	struct dentry *parent;
  628 	rcu_read_lock();
  629 	spin_unlock(&dentry->d_lock);
  630 again:
  631 	parent = READ_ONCE(dentry->d_parent);
  632 	spin_lock(&parent->d_lock);
  633 	/*
  634 	 * We can't blindly lock dentry until we are sure
  635 	 * that we won't violate the locking order.
  636 	 * Any changes of dentry->d_parent must have
  637 	 * been done with parent->d_lock held, so
  638 	 * spin_lock() above is enough of a barrier
  639 	 * for checking if it's still our child.
  640 	 */
  641 	if (unlikely(parent != dentry->d_parent)) {
  642 		spin_unlock(&parent->d_lock);
  643 		goto again;
  644 	}
  645 	rcu_read_unlock();
  646 	if (parent != dentry)
  647 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
  648 	else
  649 		parent = NULL;
  650 	return parent;
  651 }
  652 
  653 static inline struct dentry *lock_parent(struct dentry *dentry)
  654 {
  655 	struct dentry *parent = dentry->d_parent;
  656 	if (IS_ROOT(dentry))
  657 		return NULL;
  658 	if (likely(spin_trylock(&parent->d_lock)))
  659 		return parent;
  660 	return __lock_parent(dentry);
  661 }
  662 
  663 static inline bool retain_dentry(struct dentry *dentry)
  664 {
  665 	WARN_ON(d_in_lookup(dentry));
  666 
  667 	/* Unreachable? Get rid of it */
  668 	if (unlikely(d_unhashed(dentry)))
  669 		return false;
  670 
  671 	if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
  672 		return false;
  673 
  674 	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) {
  675 		if (dentry->d_op->d_delete(dentry))
  676 			return false;
  677 	}
  678 
  679 	if (unlikely(dentry->d_flags & DCACHE_DONTCACHE))
  680 		return false;
  681 
  682 	/* retain; LRU fodder */
  683 	dentry->d_lockref.count--;
  684 	if (unlikely(!(dentry->d_flags & DCACHE_LRU_LIST)))
  685 		d_lru_add(dentry);
  686 	else if (unlikely(!(dentry->d_flags & DCACHE_REFERENCED)))
  687 		dentry->d_flags |= DCACHE_REFERENCED;
  688 	return true;
  689 }
  690 
  691 void d_mark_dontcache(struct inode *inode)
  692 {
  693 	struct dentry *de;
  694 
  695 	spin_lock(&inode->i_lock);
  696 	hlist_for_each_entry(de, &inode->i_dentry, d_u.d_alias) {
  697 		spin_lock(&de->d_lock);
  698 		de->d_flags |= DCACHE_DONTCACHE;
  699 		spin_unlock(&de->d_lock);
  700 	}
  701 	inode->i_state |= I_DONTCACHE;
  702 	spin_unlock(&inode->i_lock);
  703 }
  704 EXPORT_SYMBOL(d_mark_dontcache);
  705 
  706 /*
  707  * Finish off a dentry we've decided to kill.
  708  * dentry->d_lock must be held, returns with it unlocked.
  709  * Returns dentry requiring refcount drop, or NULL if we're done.
  710  */
  711 static struct dentry *dentry_kill(struct dentry *dentry)
  712 	__releases(dentry->d_lock)
  713 {
  714 	struct inode *inode = dentry->d_inode;
  715 	struct dentry *parent = NULL;
  716 
  717 	if (inode && unlikely(!spin_trylock(&inode->i_lock)))
  718 		goto slow_positive;
  719 
  720 	if (!IS_ROOT(dentry)) {
  721 		parent = dentry->d_parent;
  722 		if (unlikely(!spin_trylock(&parent->d_lock))) {
  723 			parent = __lock_parent(dentry);
  724 			if (likely(inode || !dentry->d_inode))
  725 				goto got_locks;
  726 			/* negative that became positive */
  727 			if (parent)
  728 				spin_unlock(&parent->d_lock);
  729 			inode = dentry->d_inode;
  730 			goto slow_positive;
  731 		}
  732 	}
  733 	__dentry_kill(dentry);
  734 	return parent;
  735 
  736 slow_positive:
  737 	spin_unlock(&dentry->d_lock);
  738 	spin_lock(&inode->i_lock);
  739 	spin_lock(&dentry->d_lock);
  740 	parent = lock_parent(dentry);
  741 got_locks:
  742 	if (unlikely(dentry->d_lockref.count != 1)) {
  743 		dentry->d_lockref.count--;
  744 	} else if (likely(!retain_dentry(dentry))) {
  745 		__dentry_kill(dentry);
  746 		return parent;
  747 	}
  748 	/* we are keeping it, after all */
  749 	if (inode)
  750 		spin_unlock(&inode->i_lock);
  751 	if (parent)
  752 		spin_unlock(&parent->d_lock);
  753 	spin_unlock(&dentry->d_lock);
  754 	return NULL;
  755 }
  756 
  757 /*
  758  * Try to do a lockless dput(), and return whether that was successful.
  759  *
  760  * If unsuccessful, we return false, having already taken the dentry lock.
  761  *
  762  * The caller needs to hold the RCU read lock, so that the dentry is
  763  * guaranteed to stay around even if the refcount goes down to zero!
  764  */
  765 static inline bool fast_dput(struct dentry *dentry)
  766 {
  767 	int ret;
  768 	unsigned int d_flags;
  769 
  770 	/*
  771 	 * If we have a d_op->d_delete() operation, we sould not
  772 	 * let the dentry count go to zero, so use "put_or_lock".
  773 	 */
  774 	if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
  775 		return lockref_put_or_lock(&dentry->d_lockref);
  776 
  777 	/*
  778 	 * .. otherwise, we can try to just decrement the
  779 	 * lockref optimistically.
  780 	 */
  781 	ret = lockref_put_return(&dentry->d_lockref);
  782 
  783 	/*
  784 	 * If the lockref_put_return() failed due to the lock being held
  785 	 * by somebody else, the fast path has failed. We will need to
  786 	 * get the lock, and then check the count again.
  787 	 */
  788 	if (unlikely(ret < 0)) {
  789 		spin_lock(&dentry->d_lock);
  790 		if (dentry->d_lockref.count > 1) {
  791 			dentry->d_lockref.count--;
  792 			spin_unlock(&dentry->d_lock);
  793 			return true;
  794 		}
  795 		return false;
  796 	}
  797 
  798 	/*
  799 	 * If we weren't the last ref, we're done.
  800 	 */
  801 	if (ret)
  802 		return true;
  803 
  804 	/*
  805 	 * Careful, careful. The reference count went down
  806 	 * to zero, but we don't hold the dentry lock, so
  807 	 * somebody else could get it again, and do another
  808 	 * dput(), and we need to not race with that.
  809 	 *
  810 	 * However, there is a very special and common case
  811 	 * where we don't care, because there is nothing to
  812 	 * do: the dentry is still hashed, it does not have
  813 	 * a 'delete' op, and it's referenced and already on
  814 	 * the LRU list.
  815 	 *
  816 	 * NOTE! Since we aren't locked, these values are
  817 	 * not "stable". However, it is sufficient that at
  818 	 * some point after we dropped the reference the
  819 	 * dentry was hashed and the flags had the proper
  820 	 * value. Other dentry users may have re-gotten
  821 	 * a reference to the dentry and change that, but
  822 	 * our work is done - we can leave the dentry
  823 	 * around with a zero refcount.
  824 	 *
  825 	 * Nevertheless, there are two cases that we should kill
  826 	 * the dentry anyway.
  827 	 * 1. free disconnected dentries as soon as their refcount
  828 	 *    reached zero.
  829 	 * 2. free dentries if they should not be cached.
  830 	 */
  831 	smp_rmb();
  832 	d_flags = READ_ONCE(dentry->d_flags);
  833 	d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST |
  834 			DCACHE_DISCONNECTED | DCACHE_DONTCACHE;
  835 
  836 	/* Nothing to do? Dropping the reference was all we needed? */
  837 	if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry))
  838 		return true;
  839 
  840 	/*
  841 	 * Not the fast normal case? Get the lock. We've already decremented
  842 	 * the refcount, but we'll need to re-check the situation after
  843 	 * getting the lock.
  844 	 */
  845 	spin_lock(&dentry->d_lock);
  846 
  847 	/*
  848 	 * Did somebody else grab a reference to it in the meantime, and
  849 	 * we're no longer the last user after all? Alternatively, somebody
  850 	 * else could have killed it and marked it dead. Either way, we
  851 	 * don't need to do anything else.
  852 	 */
  853 	if (dentry->d_lockref.count) {
  854 		spin_unlock(&dentry->d_lock);
  855 		return true;
  856 	}
  857 
  858 	/*
  859 	 * Re-get the reference we optimistically dropped. We hold the
  860 	 * lock, and we just tested that it was zero, so we can just
  861 	 * set it to 1.
  862 	 */
  863 	dentry->d_lockref.count = 1;
  864 	return false;
  865 }
  866 
  867 
  868 /* 
  869  * This is dput
  870  *
  871  * This is complicated by the fact that we do not want to put
  872  * dentries that are no longer on any hash chain on the unused
  873  * list: we'd much rather just get rid of them immediately.
  874  *
  875  * However, that implies that we have to traverse the dentry
  876  * tree upwards to the parents which might _also_ now be
  877  * scheduled for deletion (it may have been only waiting for
  878  * its last child to go away).
  879  *
  880  * This tail recursion is done by hand as we don't want to depend
  881  * on the compiler to always get this right (gcc generally doesn't).
  882  * Real recursion would eat up our stack space.
  883  */
  884 
  885 /*
  886  * dput - release a dentry
  887  * @dentry: dentry to release 
  888  *
  889  * Release a dentry. This will drop the usage count and if appropriate
  890  * call the dentry unlink method as well as removing it from the queues and
  891  * releasing its resources. If the parent dentries were scheduled for release
  892  * they too may now get deleted.
  893  */
  894 void dput(struct dentry *dentry)
  895 {
  896 	while (dentry) {
  897 		might_sleep();
  898 
  899 		rcu_read_lock();
  900 		if (likely(fast_dput(dentry))) {
  901 			rcu_read_unlock();
  902 			return;
  903 		}
  904 
  905 		/* Slow case: now with the dentry lock held */
  906 		rcu_read_unlock();
  907 
  908 		if (likely(retain_dentry(dentry))) {
  909 			spin_unlock(&dentry->d_lock);
  910 			return;
  911 		}
  912 
  913 		dentry = dentry_kill(dentry);
  914 	}
  915 }
  916 EXPORT_SYMBOL(dput);
  917 
  918 static void __dput_to_list(struct dentry *dentry, struct list_head *list)
  919 __must_hold(&dentry->d_lock)
  920 {
  921 	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
  922 		/* let the owner of the list it's on deal with it */
  923 		--dentry->d_lockref.count;
  924 	} else {
  925 		if (dentry->d_flags & DCACHE_LRU_LIST)
  926 			d_lru_del(dentry);
  927 		if (!--dentry->d_lockref.count)
  928 			d_shrink_add(dentry, list);
  929 	}
  930 }
  931 
  932 void dput_to_list(struct dentry *dentry, struct list_head *list)
  933 {
  934 	rcu_read_lock();
  935 	if (likely(fast_dput(dentry))) {
  936 		rcu_read_unlock();
  937 		return;
  938 	}
  939 	rcu_read_unlock();
  940 	if (!retain_dentry(dentry))
  941 		__dput_to_list(dentry, list);
  942 	spin_unlock(&dentry->d_lock);
  943 }
  944 
  945 /* This must be called with d_lock held */
  946 static inline void __dget_dlock(struct dentry *dentry)
  947 {
  948 	dentry->d_lockref.count++;
  949 }
  950 
  951 static inline void __dget(struct dentry *dentry)
  952 {
  953 	lockref_get(&dentry->d_lockref);
  954 }
  955 
  956 struct dentry *dget_parent(struct dentry *dentry)
  957 {
  958 	int gotref;
  959 	struct dentry *ret;
  960 	unsigned seq;
  961 
  962 	/*
  963 	 * Do optimistic parent lookup without any
  964 	 * locking.
  965 	 */
  966 	rcu_read_lock();
  967 	seq = raw_seqcount_begin(&dentry->d_seq);
  968 	ret = READ_ONCE(dentry->d_parent);
  969 	gotref = lockref_get_not_zero(&ret->d_lockref);
  970 	rcu_read_unlock();
  971 	if (likely(gotref)) {
  972 		if (!read_seqcount_retry(&dentry->d_seq, seq))
  973 			return ret;
  974 		dput(ret);
  975 	}
  976 
  977 repeat:
  978 	/*
  979 	 * Don't need rcu_dereference because we re-check it was correct under
  980 	 * the lock.
  981 	 */
  982 	rcu_read_lock();
  983 	ret = dentry->d_parent;
  984 	spin_lock(&ret->d_lock);
  985 	if (unlikely(ret != dentry->d_parent)) {
  986 		spin_unlock(&ret->d_lock);
  987 		rcu_read_unlock();
  988 		goto repeat;
  989 	}
  990 	rcu_read_unlock();
  991 	BUG_ON(!ret->d_lockref.count);
  992 	ret->d_lockref.count++;
  993 	spin_unlock(&ret->d_lock);
  994 	return ret;
  995 }
  996 EXPORT_SYMBOL(dget_parent);
  997 
  998 static struct dentry * __d_find_any_alias(struct inode *inode)
  999 {
 1000 	struct dentry *alias;
 1001 
 1002 	if (hlist_empty(&inode->i_dentry))
 1003 		return NULL;
 1004 	alias = hlist_entry(inode->i_dentry.first, struct dentry, d_u.d_alias);
 1005 	__dget(alias);
 1006 	return alias;
 1007 }
 1008 
 1009 /**
 1010  * d_find_any_alias - find any alias for a given inode
 1011  * @inode: inode to find an alias for
 1012  *
 1013  * If any aliases exist for the given inode, take and return a
 1014  * reference for one of them.  If no aliases exist, return %NULL.
 1015  */
 1016 struct dentry *d_find_any_alias(struct inode *inode)
 1017 {
 1018 	struct dentry *de;
 1019 
 1020 	spin_lock(&inode->i_lock);
 1021 	de = __d_find_any_alias(inode);
 1022 	spin_unlock(&inode->i_lock);
 1023 	return de;
 1024 }
 1025 EXPORT_SYMBOL(d_find_any_alias);
 1026 
 1027 static struct dentry *__d_find_alias(struct inode *inode)
 1028 {
 1029 	struct dentry *alias;
 1030 
 1031 	if (S_ISDIR(inode->i_mode))
 1032 		return __d_find_any_alias(inode);
 1033 
 1034 	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
 1035 		spin_lock(&alias->d_lock);
 1036  		if (!d_unhashed(alias)) {
 1037 			__dget_dlock(alias);
 1038 			spin_unlock(&alias->d_lock);
 1039 			return alias;
 1040 		}
 1041 		spin_unlock(&alias->d_lock);
 1042 	}
 1043 	return NULL;
 1044 }
 1045 
 1046 /**
 1047  * d_find_alias - grab a hashed alias of inode
 1048  * @inode: inode in question
 1049  *
 1050  * If inode has a hashed alias, or is a directory and has any alias,
 1051  * acquire the reference to alias and return it. Otherwise return NULL.
 1052  * Notice that if inode is a directory there can be only one alias and
 1053  * it can be unhashed only if it has no children, or if it is the root
 1054  * of a filesystem, or if the directory was renamed and d_revalidate
 1055  * was the first vfs operation to notice.
 1056  *
 1057  * If the inode has an IS_ROOT, DCACHE_DISCONNECTED alias, then prefer
 1058  * any other hashed alias over that one.
 1059  */
 1060 struct dentry *d_find_alias(struct inode *inode)
 1061 {
 1062 	struct dentry *de = NULL;
 1063 
 1064 	if (!hlist_empty(&inode->i_dentry)) {
 1065 		spin_lock(&inode->i_lock);
 1066 		de = __d_find_alias(inode);
 1067 		spin_unlock(&inode->i_lock);
 1068 	}
 1069 	return de;
 1070 }
 1071 EXPORT_SYMBOL(d_find_alias);
 1072 
 1073 /*
 1074  *  Caller MUST be holding rcu_read_lock() and be guaranteed
 1075  *  that inode won't get freed until rcu_read_unlock().
 1076  */
 1077 struct dentry *d_find_alias_rcu(struct inode *inode)
 1078 {
 1079 	struct hlist_head *l = &inode->i_dentry;
 1080 	struct dentry *de = NULL;
 1081 
 1082 	spin_lock(&inode->i_lock);
 1083 	// ->i_dentry and ->i_rcu are colocated, but the latter won't be
 1084 	// used without having I_FREEING set, which means no aliases left
 1085 	if (likely(!(inode->i_state & I_FREEING) && !hlist_empty(l))) {
 1086 		if (S_ISDIR(inode->i_mode)) {
 1087 			de = hlist_entry(l->first, struct dentry, d_u.d_alias);
 1088 		} else {
 1089 			hlist_for_each_entry(de, l, d_u.d_alias)
 1090 				if (!d_unhashed(de))
 1091 					break;
 1092 		}
 1093 	}
 1094 	spin_unlock(&inode->i_lock);
 1095 	return de;
 1096 }
 1097 
 1098 /*
 1099  *	Try to kill dentries associated with this inode.
 1100  * WARNING: you must own a reference to inode.
 1101  */
 1102 void d_prune_aliases(struct inode *inode)
 1103 {
 1104 	struct dentry *dentry;
 1105 restart:
 1106 	spin_lock(&inode->i_lock);
 1107 	hlist_for_each_entry(dentry, &inode->i_dentry, d_u.d_alias) {
 1108 		spin_lock(&dentry->d_lock);
 1109 		if (!dentry->d_lockref.count) {
 1110 			struct dentry *parent = lock_parent(dentry);
 1111 			if (likely(!dentry->d_lockref.count)) {
 1112 				__dentry_kill(dentry);
 1113 				dput(parent);
 1114 				goto restart;
 1115 			}
 1116 			if (parent)
 1117 				spin_unlock(&parent->d_lock);
 1118 		}
 1119 		spin_unlock(&dentry->d_lock);
 1120 	}
 1121 	spin_unlock(&inode->i_lock);
 1122 }
 1123 EXPORT_SYMBOL(d_prune_aliases);
 1124 
 1125 /*
 1126  * Lock a dentry from shrink list.
 1127  * Called under rcu_read_lock() and dentry->d_lock; the former
 1128  * guarantees that nothing we access will be freed under us.
 1129  * Note that dentry is *not* protected from concurrent dentry_kill(),
 1130  * d_delete(), etc.
 1131  *
 1132  * Return false if dentry has been disrupted or grabbed, leaving
 1133  * the caller to kick it off-list.  Otherwise, return true and have
 1134  * that dentry's inode and parent both locked.
 1135  */
 1136 static bool shrink_lock_dentry(struct dentry *dentry)
 1137 {
 1138 	struct inode *inode;
 1139 	struct dentry *parent;
 1140 
 1141 	if (dentry->d_lockref.count)
 1142 		return false;
 1143 
 1144 	inode = dentry->d_inode;
 1145 	if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
 1146 		spin_unlock(&dentry->d_lock);
 1147 		spin_lock(&inode->i_lock);
 1148 		spin_lock(&dentry->d_lock);
 1149 		if (unlikely(dentry->d_lockref.count))
 1150 			goto out;
 1151 		/* changed inode means that somebody had grabbed it */
 1152 		if (unlikely(inode != dentry->d_inode))
 1153 			goto out;
 1154 	}
 1155 
 1156 	parent = dentry->d_parent;
 1157 	if (IS_ROOT(dentry) || likely(spin_trylock(&parent->d_lock)))
 1158 		return true;
 1159 
 1160 	spin_unlock(&dentry->d_lock);
 1161 	spin_lock(&parent->d_lock);
 1162 	if (unlikely(parent != dentry->d_parent)) {
 1163 		spin_unlock(&parent->d_lock);
 1164 		spin_lock(&dentry->d_lock);
 1165 		goto out;
 1166 	}
 1167 	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 1168 	if (likely(!dentry->d_lockref.count))
 1169 		return true;
 1170 	spin_unlock(&parent->d_lock);
 1171 out:
 1172 	if (inode)
 1173 		spin_unlock(&inode->i_lock);
 1174 	return false;
 1175 }
 1176 
 1177 void shrink_dentry_list(struct list_head *list)
 1178 {
 1179 	while (!list_empty(list)) {
 1180 		struct dentry *dentry, *parent;
 1181 
 1182 		dentry = list_entry(list->prev, struct dentry, d_lru);
 1183 		spin_lock(&dentry->d_lock);
 1184 		rcu_read_lock();
 1185 		if (!shrink_lock_dentry(dentry)) {
 1186 			bool can_free = false;
 1187 			rcu_read_unlock();
 1188 			d_shrink_del(dentry);
 1189 			if (dentry->d_lockref.count < 0)
 1190 				can_free = dentry->d_flags & DCACHE_MAY_FREE;
 1191 			spin_unlock(&dentry->d_lock);
 1192 			if (can_free)
 1193 				dentry_free(dentry);
 1194 			continue;
 1195 		}
 1196 		rcu_read_unlock();
 1197 		d_shrink_del(dentry);
 1198 		parent = dentry->d_parent;
 1199 		if (parent != dentry)
 1200 			__dput_to_list(parent, list);
 1201 		__dentry_kill(dentry);
 1202 	}
 1203 }
 1204 
 1205 static enum lru_status dentry_lru_isolate(struct list_head *item,
 1206 		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 1207 {
 1208 	struct list_head *freeable = arg;
 1209 	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
 1210 
 1211 
 1212 	/*
 1213 	 * we are inverting the lru lock/dentry->d_lock here,
 1214 	 * so use a trylock. If we fail to get the lock, just skip
 1215 	 * it
 1216 	 */
 1217 	if (!spin_trylock(&dentry->d_lock))
 1218 		return LRU_SKIP;
 1219 
 1220 	/*
 1221 	 * Referenced dentries are still in use. If they have active
 1222 	 * counts, just remove them from the LRU. Otherwise give them
 1223 	 * another pass through the LRU.
 1224 	 */
 1225 	if (dentry->d_lockref.count) {
 1226 		d_lru_isolate(lru, dentry);
 1227 		spin_unlock(&dentry->d_lock);
 1228 		return LRU_REMOVED;
 1229 	}
 1230 
 1231 	if (dentry->d_flags & DCACHE_REFERENCED) {
 1232 		dentry->d_flags &= ~DCACHE_REFERENCED;
 1233 		spin_unlock(&dentry->d_lock);
 1234 
 1235 		/*
 1236 		 * The list move itself will be made by the common LRU code. At
 1237 		 * this point, we've dropped the dentry->d_lock but keep the
 1238 		 * lru lock. This is safe to do, since every list movement is
 1239 		 * protected by the lru lock even if both locks are held.
 1240 		 *
 1241 		 * This is guaranteed by the fact that all LRU management
 1242 		 * functions are intermediated by the LRU API calls like
 1243 		 * list_lru_add and list_lru_del. List movement in this file
 1244 		 * only ever occur through this functions or through callbacks
 1245 		 * like this one, that are called from the LRU API.
 1246 		 *
 1247 		 * The only exceptions to this are functions like
 1248 		 * shrink_dentry_list, and code that first checks for the
 1249 		 * DCACHE_SHRINK_LIST flag.  Those are guaranteed to be
 1250 		 * operating only with stack provided lists after they are
 1251 		 * properly isolated from the main list.  It is thus, always a
 1252 		 * local access.
 1253 		 */
 1254 		return LRU_ROTATE;
 1255 	}
 1256 
 1257 	d_lru_shrink_move(lru, dentry, freeable);
 1258 	spin_unlock(&dentry->d_lock);
 1259 
 1260 	return LRU_REMOVED;
 1261 }
 1262 
 1263 /**
 1264  * prune_dcache_sb - shrink the dcache
 1265  * @sb: superblock
 1266  * @sc: shrink control, passed to list_lru_shrink_walk()
 1267  *
 1268  * Attempt to shrink the superblock dcache LRU by @sc->nr_to_scan entries. This
 1269  * is done when we need more memory and called from the superblock shrinker
 1270  * function.
 1271  *
 1272  * This function may fail to free any resources if all the dentries are in
 1273  * use.
 1274  */
 1275 long prune_dcache_sb(struct super_block *sb, struct shrink_control *sc)
 1276 {
 1277 	LIST_HEAD(dispose);
 1278 	long freed;
 1279 
 1280 	freed = list_lru_shrink_walk(&sb->s_dentry_lru, sc,
 1281 				     dentry_lru_isolate, &dispose);
 1282 	shrink_dentry_list(&dispose);
 1283 	return freed;
 1284 }
 1285 
 1286 static enum lru_status dentry_lru_isolate_shrink(struct list_head *item,
 1287 		struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
 1288 {
 1289 	struct list_head *freeable = arg;
 1290 	struct dentry	*dentry = container_of(item, struct dentry, d_lru);
 1291 
 1292 	/*
 1293 	 * we are inverting the lru lock/dentry->d_lock here,
 1294 	 * so use a trylock. If we fail to get the lock, just skip
 1295 	 * it
 1296 	 */
 1297 	if (!spin_trylock(&dentry->d_lock))
 1298 		return LRU_SKIP;
 1299 
 1300 	d_lru_shrink_move(lru, dentry, freeable);
 1301 	spin_unlock(&dentry->d_lock);
 1302 
 1303 	return LRU_REMOVED;
 1304 }
 1305 
 1306 
 1307 /**
 1308  * shrink_dcache_sb - shrink dcache for a superblock
 1309  * @sb: superblock
 1310  *
 1311  * Shrink the dcache for the specified super block. This is used to free
 1312  * the dcache before unmounting a file system.
 1313  */
 1314 void shrink_dcache_sb(struct super_block *sb)
 1315 {
 1316 	do {
 1317 		LIST_HEAD(dispose);
 1318 
 1319 		list_lru_walk(&sb->s_dentry_lru,
 1320 			dentry_lru_isolate_shrink, &dispose, 1024);
 1321 		shrink_dentry_list(&dispose);
 1322 	} while (list_lru_count(&sb->s_dentry_lru) > 0);
 1323 }
 1324 EXPORT_SYMBOL(shrink_dcache_sb);
 1325 
 1326 /**
 1327  * enum d_walk_ret - action to talke during tree walk
 1328  * @D_WALK_CONTINUE:	contrinue walk
 1329  * @D_WALK_QUIT:	quit walk
 1330  * @D_WALK_NORETRY:	quit when retry is needed
 1331  * @D_WALK_SKIP:	skip this dentry and its children
 1332  */
 1333 enum d_walk_ret {
 1334 	D_WALK_CONTINUE,
 1335 	D_WALK_QUIT,
 1336 	D_WALK_NORETRY,
 1337 	D_WALK_SKIP,
 1338 };
 1339 
 1340 /**
 1341  * d_walk - walk the dentry tree
 1342  * @parent:	start of walk
 1343  * @data:	data passed to @enter() and @finish()
 1344  * @enter:	callback when first entering the dentry
 1345  *
 1346  * The @enter() callbacks are called with d_lock held.
 1347  */
 1348 static void d_walk(struct dentry *parent, void *data,
 1349 		   enum d_walk_ret (*enter)(void *, struct dentry *))
 1350 {
 1351 	struct dentry *this_parent;
 1352 	struct list_head *next;
 1353 	unsigned seq = 0;
 1354 	enum d_walk_ret ret;
 1355 	bool retry = true;
 1356 
 1357 again:
 1358 	read_seqbegin_or_lock(&rename_lock, &seq);
 1359 	this_parent = parent;
 1360 	spin_lock(&this_parent->d_lock);
 1361 
 1362 	ret = enter(data, this_parent);
 1363 	switch (ret) {
 1364 	case D_WALK_CONTINUE:
 1365 		break;
 1366 	case D_WALK_QUIT:
 1367 	case D_WALK_SKIP:
 1368 		goto out_unlock;
 1369 	case D_WALK_NORETRY:
 1370 		retry = false;
 1371 		break;
 1372 	}
 1373 repeat:
 1374 	next = this_parent->d_subdirs.next;
 1375 resume:
 1376 	while (next != &this_parent->d_subdirs) {
 1377 		struct list_head *tmp = next;
 1378 		struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
 1379 		next = tmp->next;
 1380 
 1381 		if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
 1382 			continue;
 1383 
 1384 		spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 1385 
 1386 		ret = enter(data, dentry);
 1387 		switch (ret) {
 1388 		case D_WALK_CONTINUE:
 1389 			break;
 1390 		case D_WALK_QUIT:
 1391 			spin_unlock(&dentry->d_lock);
 1392 			goto out_unlock;
 1393 		case D_WALK_NORETRY:
 1394 			retry = false;
 1395 			break;
 1396 		case D_WALK_SKIP:
 1397 			spin_unlock(&dentry->d_lock);
 1398 			continue;
 1399 		}
 1400 
 1401 		if (!list_empty(&dentry->d_subdirs)) {
 1402 			spin_unlock(&this_parent->d_lock);
 1403 			spin_release(&dentry->d_lock.dep_map, _RET_IP_);
 1404 			this_parent = dentry;
 1405 			spin_acquire(&this_parent->d_lock.dep_map, 0, 1, _RET_IP_);
 1406 			goto repeat;
 1407 		}
 1408 		spin_unlock(&dentry->d_lock);
 1409 	}
 1410 	/*
 1411 	 * All done at this level ... ascend and resume the search.
 1412 	 */
 1413 	rcu_read_lock();
 1414 ascend:
 1415 	if (this_parent != parent) {
 1416 		struct dentry *child = this_parent;
 1417 		this_parent = child->d_parent;
 1418 
 1419 		spin_unlock(&child->d_lock);
 1420 		spin_lock(&this_parent->d_lock);
 1421 
 1422 		/* might go back up the wrong parent if we have had a rename. */
 1423 		if (need_seqretry(&rename_lock, seq))
 1424 			goto rename_retry;
 1425 		/* go into the first sibling still alive */
 1426 		do {
 1427 			next = child->d_child.next;
 1428 			if (next == &this_parent->d_subdirs)
 1429 				goto ascend;
 1430 			child = list_entry(next, struct dentry, d_child);
 1431 		} while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
 1432 		rcu_read_unlock();
 1433 		goto resume;
 1434 	}
 1435 	if (need_seqretry(&rename_lock, seq))
 1436 		goto rename_retry;
 1437 	rcu_read_unlock();
 1438 
 1439 out_unlock:
 1440 	spin_unlock(&this_parent->d_lock);
 1441 	done_seqretry(&rename_lock, seq);
 1442 	return;
 1443 
 1444 rename_retry:
 1445 	spin_unlock(&this_parent->d_lock);
 1446 	rcu_read_unlock();
 1447 	BUG_ON(seq & 1);
 1448 	if (!retry)
 1449 		return;
 1450 	seq = 1;
 1451 	goto again;
 1452 }
 1453 
 1454 struct check_mount {
 1455 	struct vfsmount *mnt;
 1456 	unsigned int mounted;
 1457 };
 1458 
 1459 static enum d_walk_ret path_check_mount(void *data, struct dentry *dentry)
 1460 {
 1461 	struct check_mount *info = data;
 1462 	struct path path = { .mnt = info->mnt, .dentry = dentry };
 1463 
 1464 	if (likely(!d_mountpoint(dentry)))
 1465 		return D_WALK_CONTINUE;
 1466 	if (__path_is_mountpoint(&path)) {
 1467 		info->mounted = 1;
 1468 		return D_WALK_QUIT;
 1469 	}
 1470 	return D_WALK_CONTINUE;
 1471 }
 1472 
 1473 /**
 1474  * path_has_submounts - check for mounts over a dentry in the
 1475  *                      current namespace.
 1476  * @parent: path to check.
 1477  *
 1478  * Return true if the parent or its subdirectories contain
 1479  * a mount point in the current namespace.
 1480  */
 1481 int path_has_submounts(const struct path *parent)
 1482 {
 1483 	struct check_mount data = { .mnt = parent->mnt, .mounted = 0 };
 1484 
 1485 	read_seqlock_excl(&mount_lock);
 1486 	d_walk(parent->dentry, &data, path_check_mount);
 1487 	read_sequnlock_excl(&mount_lock);
 1488 
 1489 	return data.mounted;
 1490 }
 1491 EXPORT_SYMBOL(path_has_submounts);
 1492 
 1493 /*
 1494  * Called by mount code to set a mountpoint and check if the mountpoint is
 1495  * reachable (e.g. NFS can unhash a directory dentry and then the complete
 1496  * subtree can become unreachable).
 1497  *
 1498  * Only one of d_invalidate() and d_set_mounted() must succeed.  For
 1499  * this reason take rename_lock and d_lock on dentry and ancestors.
 1500  */
 1501 int d_set_mounted(struct dentry *dentry)
 1502 {
 1503 	struct dentry *p;
 1504 	int ret = -ENOENT;
 1505 	write_seqlock(&rename_lock);
 1506 	for (p = dentry->d_parent; !IS_ROOT(p); p = p->d_parent) {
 1507 		/* Need exclusion wrt. d_invalidate() */
 1508 		spin_lock(&p->d_lock);
 1509 		if (unlikely(d_unhashed(p))) {
 1510 			spin_unlock(&p->d_lock);
 1511 			goto out;
 1512 		}
 1513 		spin_unlock(&p->d_lock);
 1514 	}
 1515 	spin_lock(&dentry->d_lock);
 1516 	if (!d_unlinked(dentry)) {
 1517 		ret = -EBUSY;
 1518 		if (!d_mountpoint(dentry)) {
 1519 			dentry->d_flags |= DCACHE_MOUNTED;
 1520 			ret = 0;
 1521 		}
 1522 	}
 1523  	spin_unlock(&dentry->d_lock);
 1524 out:
 1525 	write_sequnlock(&rename_lock);
 1526 	return ret;
 1527 }
 1528 
 1529 /*
 1530  * Search the dentry child list of the specified parent,
 1531  * and move any unused dentries to the end of the unused
 1532  * list for prune_dcache(). We descend to the next level
 1533  * whenever the d_subdirs list is non-empty and continue
 1534  * searching.
 1535  *
 1536  * It returns zero iff there are no unused children,
 1537  * otherwise  it returns the number of children moved to
 1538  * the end of the unused list. This may not be the total
 1539  * number of unused children, because select_parent can
 1540  * drop the lock and return early due to latency
 1541  * constraints.
 1542  */
 1543 
 1544 struct select_data {
 1545 	struct dentry *start;
 1546 	union {
 1547 		long found;
 1548 		struct dentry *victim;
 1549 	};
 1550 	struct list_head dispose;
 1551 };
 1552 
 1553 static enum d_walk_ret select_collect(void *_data, struct dentry *dentry)
 1554 {
 1555 	struct select_data *data = _data;
 1556 	enum d_walk_ret ret = D_WALK_CONTINUE;
 1557 
 1558 	if (data->start == dentry)
 1559 		goto out;
 1560 
 1561 	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
 1562 		data->found++;
 1563 	} else {
 1564 		if (dentry->d_flags & DCACHE_LRU_LIST)
 1565 			d_lru_del(dentry);
 1566 		if (!dentry->d_lockref.count) {
 1567 			d_shrink_add(dentry, &data->dispose);
 1568 			data->found++;
 1569 		}
 1570 	}
 1571 	/*
 1572 	 * We can return to the caller if we have found some (this
 1573 	 * ensures forward progress). We'll be coming back to find
 1574 	 * the rest.
 1575 	 */
 1576 	if (!list_empty(&data->dispose))
 1577 		ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
 1578 out:
 1579 	return ret;
 1580 }
 1581 
 1582 static enum d_walk_ret select_collect2(void *_data, struct dentry *dentry)
 1583 {
 1584 	struct select_data *data = _data;
 1585 	enum d_walk_ret ret = D_WALK_CONTINUE;
 1586 
 1587 	if (data->start == dentry)
 1588 		goto out;
 1589 
 1590 	if (dentry->d_flags & DCACHE_SHRINK_LIST) {
 1591 		if (!dentry->d_lockref.count) {
 1592 			rcu_read_lock();
 1593 			data->victim = dentry;
 1594 			return D_WALK_QUIT;
 1595 		}
 1596 	} else {
 1597 		if (dentry->d_flags & DCACHE_LRU_LIST)
 1598 			d_lru_del(dentry);
 1599 		if (!dentry->d_lockref.count)
 1600 			d_shrink_add(dentry, &data->dispose);
 1601 	}
 1602 	/*
 1603 	 * We can return to the caller if we have found some (this
 1604 	 * ensures forward progress). We'll be coming back to find
 1605 	 * the rest.
 1606 	 */
 1607 	if (!list_empty(&data->dispose))
 1608 		ret = need_resched() ? D_WALK_QUIT : D_WALK_NORETRY;
 1609 out:
 1610 	return ret;
 1611 }
 1612 
 1613 /**
 1614  * shrink_dcache_parent - prune dcache
 1615  * @parent: parent of entries to prune
 1616  *
 1617  * Prune the dcache to remove unused children of the parent dentry.
 1618  */
 1619 void shrink_dcache_parent(struct dentry *parent)
 1620 {
 1621 	for (;;) {
 1622 		struct select_data data = {.start = parent};
 1623 
 1624 		INIT_LIST_HEAD(&data.dispose);
 1625 		d_walk(parent, &data, select_collect);
 1626 
 1627 		if (!list_empty(&data.dispose)) {
 1628 			shrink_dentry_list(&data.dispose);
 1629 			continue;
 1630 		}
 1631 
 1632 		cond_resched();
 1633 		if (!data.found)
 1634 			break;
 1635 		data.victim = NULL;
 1636 		d_walk(parent, &data, select_collect2);
 1637 		if (data.victim) {
 1638 			struct dentry *parent;
 1639 			spin_lock(&data.victim->d_lock);
 1640 			if (!shrink_lock_dentry(data.victim)) {
 1641 				spin_unlock(&data.victim->d_lock);
 1642 				rcu_read_unlock();
 1643 			} else {
 1644 				rcu_read_unlock();
 1645 				parent = data.victim->d_parent;
 1646 				if (parent != data.victim)
 1647 					__dput_to_list(parent, &data.dispose);
 1648 				__dentry_kill(data.victim);
 1649 			}
 1650 		}
 1651 		if (!list_empty(&data.dispose))
 1652 			shrink_dentry_list(&data.dispose);
 1653 	}
 1654 }
 1655 EXPORT_SYMBOL(shrink_dcache_parent);
 1656 
 1657 static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
 1658 {
 1659 	/* it has busy descendents; complain about those instead */
 1660 	if (!list_empty(&dentry->d_subdirs))
 1661 		return D_WALK_CONTINUE;
 1662 
 1663 	/* root with refcount 1 is fine */
 1664 	if (dentry == _data && dentry->d_lockref.count == 1)
 1665 		return D_WALK_CONTINUE;
 1666 
 1667 	WARN(1, "BUG: Dentry %p{i=%lx,n=%pd} "
 1668 			" still in use (%d) [unmount of %s %s]\n",
 1669 		       dentry,
 1670 		       dentry->d_inode ?
 1671 		       dentry->d_inode->i_ino : 0UL,
 1672 		       dentry,
 1673 		       dentry->d_lockref.count,
 1674 		       dentry->d_sb->s_type->name,
 1675 		       dentry->d_sb->s_id);
 1676 	return D_WALK_CONTINUE;
 1677 }
 1678 
 1679 static void do_one_tree(struct dentry *dentry)
 1680 {
 1681 	shrink_dcache_parent(dentry);
 1682 	d_walk(dentry, dentry, umount_check);
 1683 	d_drop(dentry);
 1684 	dput(dentry);
 1685 }
 1686 
 1687 /*
 1688  * destroy the dentries attached to a superblock on unmounting
 1689  */
 1690 void shrink_dcache_for_umount(struct super_block *sb)
 1691 {
 1692 	struct dentry *dentry;
 1693 
 1694 	WARN(down_read_trylock(&sb->s_umount), "s_umount should've been locked");
 1695 
 1696 	dentry = sb->s_root;
 1697 	sb->s_root = NULL;
 1698 	do_one_tree(dentry);
 1699 
 1700 	while (!hlist_bl_empty(&sb->s_roots)) {
 1701 		dentry = dget(hlist_bl_entry(hlist_bl_first(&sb->s_roots), struct dentry, d_hash));
 1702 		do_one_tree(dentry);
 1703 	}
 1704 }
 1705 
 1706 static enum d_walk_ret find_submount(void *_data, struct dentry *dentry)
 1707 {
 1708 	struct dentry **victim = _data;
 1709 	if (d_mountpoint(dentry)) {
 1710 		__dget_dlock(dentry);
 1711 		*victim = dentry;
 1712 		return D_WALK_QUIT;
 1713 	}
 1714 	return D_WALK_CONTINUE;
 1715 }
 1716 
 1717 /**
 1718  * d_invalidate - detach submounts, prune dcache, and drop
 1719  * @dentry: dentry to invalidate (aka detach, prune and drop)
 1720  */
 1721 void d_invalidate(struct dentry *dentry)
 1722 {
 1723 	bool had_submounts = false;
 1724 	spin_lock(&dentry->d_lock);
 1725 	if (d_unhashed(dentry)) {
 1726 		spin_unlock(&dentry->d_lock);
 1727 		return;
 1728 	}
 1729 	__d_drop(dentry);
 1730 	spin_unlock(&dentry->d_lock);
 1731 
 1732 	/* Negative dentries can be dropped without further checks */
 1733 	if (!dentry->d_inode)
 1734 		return;
 1735 
 1736 	shrink_dcache_parent(dentry);
 1737 	for (;;) {
 1738 		struct dentry *victim = NULL;
 1739 		d_walk(dentry, &victim, find_submount);
 1740 		if (!victim) {
 1741 			if (had_submounts)
 1742 				shrink_dcache_parent(dentry);
 1743 			return;
 1744 		}
 1745 		had_submounts = true;
 1746 		detach_mounts(victim);
 1747 		dput(victim);
 1748 	}
 1749 }
 1750 EXPORT_SYMBOL(d_invalidate);
 1751 
 1752 /**
 1753  * __d_alloc	-	allocate a dcache entry
 1754  * @sb: filesystem it will belong to
 1755  * @name: qstr of the name
 1756  *
 1757  * Allocates a dentry. It returns %NULL if there is insufficient memory
 1758  * available. On a success the dentry is returned. The name passed in is
 1759  * copied and the copy passed in may be reused after this call.
 1760  */
 1761  
 1762 static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 1763 {
 1764 	struct dentry *dentry;
 1765 	char *dname;
 1766 	int err;
 1767 
 1768 	dentry = kmem_cache_alloc_lru(dentry_cache, &sb->s_dentry_lru,
 1769 				      GFP_KERNEL);
 1770 	if (!dentry)
 1771 		return NULL;
 1772 
 1773 	/*
 1774 	 * We guarantee that the inline name is always NUL-terminated.
 1775 	 * This way the memcpy() done by the name switching in rename
 1776 	 * will still always have a NUL at the end, even if we might
 1777 	 * be overwriting an internal NUL character
 1778 	 */
 1779 	dentry->d_iname[DNAME_INLINE_LEN-1] = 0;
 1780 	if (unlikely(!name)) {
 1781 		name = &slash_name;
 1782 		dname = dentry->d_iname;
 1783 	} else if (name->len > DNAME_INLINE_LEN-1) {
 1784 		size_t size = offsetof(struct external_name, name[1]);
 1785 		struct external_name *p = kmalloc(size + name->len,
 1786 						  GFP_KERNEL_ACCOUNT |
 1787 						  __GFP_RECLAIMABLE);
 1788 		if (!p) {
 1789 			kmem_cache_free(dentry_cache, dentry); 
 1790 			return NULL;
 1791 		}
 1792 		atomic_set(&p->u.count, 1);
 1793 		dname = p->name;
 1794 	} else  {
 1795 		dname = dentry->d_iname;
 1796 	}	
 1797 
 1798 	dentry->d_name.len = name->len;
 1799 	dentry->d_name.hash = name->hash;
 1800 	memcpy(dname, name->name, name->len);
 1801 	dname[name->len] = 0;
 1802 
 1803 	/* Make sure we always see the terminating NUL character */
 1804 	smp_store_release(&dentry->d_name.name, dname); /* ^^^ */
 1805 
 1806 	dentry->d_lockref.count = 1;
 1807 	dentry->d_flags = 0;
 1808 	spin_lock_init(&dentry->d_lock);
 1809 	seqcount_spinlock_init(&dentry->d_seq, &dentry->d_lock);
 1810 	dentry->d_inode = NULL;
 1811 	dentry->d_parent = dentry;
 1812 	dentry->d_sb = sb;
 1813 	dentry->d_op = NULL;
 1814 	dentry->d_fsdata = NULL;
 1815 	INIT_HLIST_BL_NODE(&dentry->d_hash);
 1816 	INIT_LIST_HEAD(&dentry->d_lru);
 1817 	INIT_LIST_HEAD(&dentry->d_subdirs);
 1818 	INIT_HLIST_NODE(&dentry->d_u.d_alias);
 1819 	INIT_LIST_HEAD(&dentry->d_child);
 1820 	d_set_d_op(dentry, dentry->d_sb->s_d_op);
 1821 
 1822 	if (dentry->d_op && dentry->d_op->d_init) {
 1823 		err = dentry->d_op->d_init(dentry);
 1824 		if (err) {
 1825 			if (dname_external(dentry))
 1826 				kfree(external_name(dentry));
 1827 			kmem_cache_free(dentry_cache, dentry);
 1828 			return NULL;
 1829 		}
 1830 	}
 1831 
 1832 	this_cpu_inc(nr_dentry);
 1833 
 1834 	return dentry;
 1835 }
 1836 
 1837 /**
 1838  * d_alloc	-	allocate a dcache entry
 1839  * @parent: parent of entry to allocate
 1840  * @name: qstr of the name
 1841  *
 1842  * Allocates a dentry. It returns %NULL if there is insufficient memory
 1843  * available. On a success the dentry is returned. The name passed in is
 1844  * copied and the copy passed in may be reused after this call.
 1845  */
 1846 struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 1847 {
 1848 	struct dentry *dentry = __d_alloc(parent->d_sb, name);
 1849 	if (!dentry)
 1850 		return NULL;
 1851 	spin_lock(&parent->d_lock);
 1852 	/*
 1853 	 * don't need child lock because it is not subject
 1854 	 * to concurrency here
 1855 	 */
 1856 	__dget_dlock(parent);
 1857 	dentry->d_parent = parent;
 1858 	list_add(&dentry->d_child, &parent->d_subdirs);
 1859 	spin_unlock(&parent->d_lock);
 1860 
 1861 	return dentry;
 1862 }
 1863 EXPORT_SYMBOL(d_alloc);
 1864 
 1865 struct dentry *d_alloc_anon(struct super_block *sb)
 1866 {
 1867 	return __d_alloc(sb, NULL);
 1868 }
 1869 EXPORT_SYMBOL(d_alloc_anon);
 1870 
 1871 struct dentry *d_alloc_cursor(struct dentry * parent)
 1872 {
 1873 	struct dentry *dentry = d_alloc_anon(parent->d_sb);
 1874 	if (dentry) {
 1875 		dentry->d_flags |= DCACHE_DENTRY_CURSOR;
 1876 		dentry->d_parent = dget(parent);
 1877 	}
 1878 	return dentry;
 1879 }
 1880 
 1881 /**
 1882  * d_alloc_pseudo - allocate a dentry (for lookup-less filesystems)
 1883  * @sb: the superblock
 1884  * @name: qstr of the name
 1885  *
 1886  * For a filesystem that just pins its dentries in memory and never
 1887  * performs lookups at all, return an unhashed IS_ROOT dentry.
 1888  * This is used for pipes, sockets et.al. - the stuff that should
 1889  * never be anyone's children or parents.  Unlike all other
 1890  * dentries, these will not have RCU delay between dropping the
 1891  * last reference and freeing them.
 1892  *
 1893  * The only user is alloc_file_pseudo() and that's what should
 1894  * be considered a public interface.  Don't use directly.
 1895  */
 1896 struct dentry *d_alloc_pseudo(struct super_block *sb, const struct qstr *name)
 1897 {
 1898 	struct dentry *dentry = __d_alloc(sb, name);
 1899 	if (likely(dentry))
 1900 		dentry->d_flags |= DCACHE_NORCU;
 1901 	return dentry;
 1902 }
 1903 
 1904 struct dentry *d_alloc_name(struct dentry *parent, const char *name)
 1905 {
 1906 	struct qstr q;
 1907 
 1908 	q.name = name;
 1909 	q.hash_len = hashlen_string(parent, name);
 1910 	return d_alloc(parent, &q);
 1911 }
 1912 EXPORT_SYMBOL(d_alloc_name);
 1913 
 1914 void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
 1915 {
 1916 	WARN_ON_ONCE(dentry->d_op);
 1917 	WARN_ON_ONCE(dentry->d_flags & (DCACHE_OP_HASH	|
 1918 				DCACHE_OP_COMPARE	|
 1919 				DCACHE_OP_REVALIDATE	|
 1920 				DCACHE_OP_WEAK_REVALIDATE	|
 1921 				DCACHE_OP_DELETE	|
 1922 				DCACHE_OP_REAL));
 1923 	dentry->d_op = op;
 1924 	if (!op)
 1925 		return;
 1926 	if (op->d_hash)
 1927 		dentry->d_flags |= DCACHE_OP_HASH;
 1928 	if (op->d_compare)
 1929 		dentry->d_flags |= DCACHE_OP_COMPARE;
 1930 	if (op->d_revalidate)
 1931 		dentry->d_flags |= DCACHE_OP_REVALIDATE;
 1932 	if (op->d_weak_revalidate)
 1933 		dentry->d_flags |= DCACHE_OP_WEAK_REVALIDATE;
 1934 	if (op->d_delete)
 1935 		dentry->d_flags |= DCACHE_OP_DELETE;
 1936 	if (op->d_prune)
 1937 		dentry->d_flags |= DCACHE_OP_PRUNE;
 1938 	if (op->d_real)
 1939 		dentry->d_flags |= DCACHE_OP_REAL;
 1940 
 1941 }
 1942 EXPORT_SYMBOL(d_set_d_op);
 1943 
 1944 
 1945 /*
 1946  * d_set_fallthru - Mark a dentry as falling through to a lower layer
 1947  * @dentry - The dentry to mark
 1948  *
 1949  * Mark a dentry as falling through to the lower layer (as set with
 1950  * d_pin_lower()).  This flag may be recorded on the medium.
 1951  */
 1952 void d_set_fallthru(struct dentry *dentry)
 1953 {
 1954 	spin_lock(&dentry->d_lock);
 1955 	dentry->d_flags |= DCACHE_FALLTHRU;
 1956 	spin_unlock(&dentry->d_lock);
 1957 }
 1958 EXPORT_SYMBOL(d_set_fallthru);
 1959 
 1960 static unsigned d_flags_for_inode(struct inode *inode)
 1961 {
 1962 	unsigned add_flags = DCACHE_REGULAR_TYPE;
 1963 
 1964 	if (!inode)
 1965 		return DCACHE_MISS_TYPE;
 1966 
 1967 	if (S_ISDIR(inode->i_mode)) {
 1968 		add_flags = DCACHE_DIRECTORY_TYPE;
 1969 		if (unlikely(!(inode->i_opflags & IOP_LOOKUP))) {
 1970 			if (unlikely(!inode->i_op->lookup))
 1971 				add_flags = DCACHE_AUTODIR_TYPE;
 1972 			else
 1973 				inode->i_opflags |= IOP_LOOKUP;
 1974 		}
 1975 		goto type_determined;
 1976 	}
 1977 
 1978 	if (unlikely(!(inode->i_opflags & IOP_NOFOLLOW))) {
 1979 		if (unlikely(inode->i_op->get_link)) {
 1980 			add_flags = DCACHE_SYMLINK_TYPE;
 1981 			goto type_determined;
 1982 		}
 1983 		inode->i_opflags |= IOP_NOFOLLOW;
 1984 	}
 1985 
 1986 	if (unlikely(!S_ISREG(inode->i_mode)))
 1987 		add_flags = DCACHE_SPECIAL_TYPE;
 1988 
 1989 type_determined:
 1990 	if (unlikely(IS_AUTOMOUNT(inode)))
 1991 		add_flags |= DCACHE_NEED_AUTOMOUNT;
 1992 	return add_flags;
 1993 }
 1994 
 1995 static void __d_instantiate(struct dentry *dentry, struct inode *inode)
 1996 {
 1997 	unsigned add_flags = d_flags_for_inode(inode);
 1998 	WARN_ON(d_in_lookup(dentry));
 1999 
 2000 	spin_lock(&dentry->d_lock);
 2001 	/*
 2002 	 * Decrement negative dentry count if it was in the LRU list.
 2003 	 */
 2004 	if (dentry->d_flags & DCACHE_LRU_LIST)
 2005 		this_cpu_dec(nr_dentry_negative);
 2006 	hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
 2007 	raw_write_seqcount_begin(&dentry->d_seq);
 2008 	__d_set_inode_and_type(dentry, inode, add_flags);
 2009 	raw_write_seqcount_end(&dentry->d_seq);
 2010 	fsnotify_update_flags(dentry);
 2011 	spin_unlock(&dentry->d_lock);
 2012 }
 2013 
 2014 /**
 2015  * d_instantiate - fill in inode information for a dentry
 2016  * @entry: dentry to complete
 2017  * @inode: inode to attach to this dentry
 2018  *
 2019  * Fill in inode information in the entry.
 2020  *
 2021  * This turns negative dentries into productive full members
 2022  * of society.
 2023  *
 2024  * NOTE! This assumes that the inode count has been incremented
 2025  * (or otherwise set) by the caller to indicate that it is now
 2026  * in use by the dcache.
 2027  */
 2028  
 2029 void d_instantiate(struct dentry *entry, struct inode * inode)
 2030 {
 2031 	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
 2032 	if (inode) {
 2033 		security_d_instantiate(entry, inode);
 2034 		spin_lock(&inode->i_lock);
 2035 		__d_instantiate(entry, inode);
 2036 		spin_unlock(&inode->i_lock);
 2037 	}
 2038 }
 2039 EXPORT_SYMBOL(d_instantiate);
 2040 
 2041 /*
 2042  * This should be equivalent to d_instantiate() + unlock_new_inode(),
 2043  * with lockdep-related part of unlock_new_inode() done before
 2044  * anything else.  Use that instead of open-coding d_instantiate()/
 2045  * unlock_new_inode() combinations.
 2046  */
 2047 void d_instantiate_new(struct dentry *entry, struct inode *inode)
 2048 {
 2049 	BUG_ON(!hlist_unhashed(&entry->d_u.d_alias));
 2050 	BUG_ON(!inode);
 2051 	lockdep_annotate_inode_mutex_key(inode);
 2052 	security_d_instantiate(entry, inode);
 2053 	spin_lock(&inode->i_lock);
 2054 	__d_instantiate(entry, inode);
 2055 	WARN_ON(!(inode->i_state & I_NEW));
 2056 	inode->i_state &= ~I_NEW & ~I_CREATING;
 2057 	smp_mb();
 2058 	wake_up_bit(&inode->i_state, __I_NEW);
 2059 	spin_unlock(&inode->i_lock);
 2060 }
 2061 EXPORT_SYMBOL(d_instantiate_new);
 2062 
 2063 struct dentry *d_make_root(struct inode *root_inode)
 2064 {
 2065 	struct dentry *res = NULL;
 2066 
 2067 	if (root_inode) {
 2068 		res = d_alloc_anon(root_inode->i_sb);
 2069 		if (res)
 2070 			d_instantiate(res, root_inode);
 2071 		else
 2072 			iput(root_inode);
 2073 	}
 2074 	return res;
 2075 }
 2076 EXPORT_SYMBOL(d_make_root);
 2077 
 2078 static struct dentry *__d_instantiate_anon(struct dentry *dentry,
 2079 					   struct inode *inode,
 2080 					   bool disconnected)
 2081 {
 2082 	struct dentry *res;
 2083 	unsigned add_flags;
 2084 
 2085 	security_d_instantiate(dentry, inode);
 2086 	spin_lock(&inode->i_lock);
 2087 	res = __d_find_any_alias(inode);
 2088 	if (res) {
 2089 		spin_unlock(&inode->i_lock);
 2090 		dput(dentry);
 2091 		goto out_iput;
 2092 	}
 2093 
 2094 	/* attach a disconnected dentry */
 2095 	add_flags = d_flags_for_inode(inode);
 2096 
 2097 	if (disconnected)
 2098 		add_flags |= DCACHE_DISCONNECTED;
 2099 
 2100 	spin_lock(&dentry->d_lock);
 2101 	__d_set_inode_and_type(dentry, inode, add_flags);
 2102 	hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
 2103 	if (!disconnected) {
 2104 		hlist_bl_lock(&dentry->d_sb->s_roots);
 2105 		hlist_bl_add_head(&dentry->d_hash, &dentry->d_sb->s_roots);
 2106 		hlist_bl_unlock(&dentry->d_sb->s_roots);
 2107 	}
 2108 	spin_unlock(&dentry->d_lock);
 2109 	spin_unlock(&inode->i_lock);
 2110 
 2111 	return dentry;
 2112 
 2113  out_iput:
 2114 	iput(inode);
 2115 	return res;
 2116 }
 2117 
 2118 struct dentry *d_instantiate_anon(struct dentry *dentry, struct inode *inode)
 2119 {
 2120 	return __d_instantiate_anon(dentry, inode, true);
 2121 }
 2122 EXPORT_SYMBOL(d_instantiate_anon);
 2123 
 2124 static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected)
 2125 {
 2126 	struct dentry *tmp;
 2127 	struct dentry *res;
 2128 
 2129 	if (!inode)
 2130 		return ERR_PTR(-ESTALE);
 2131 	if (IS_ERR(inode))
 2132 		return ERR_CAST(inode);
 2133 
 2134 	res = d_find_any_alias(inode);
 2135 	if (res)
 2136 		goto out_iput;
 2137 
 2138 	tmp = d_alloc_anon(inode->i_sb);
 2139 	if (!tmp) {
 2140 		res = ERR_PTR(-ENOMEM);
 2141 		goto out_iput;
 2142 	}
 2143 
 2144 	return __d_instantiate_anon(tmp, inode, disconnected);
 2145 
 2146 out_iput:
 2147 	iput(inode);
 2148 	return res;
 2149 }
 2150 
 2151 /**
 2152  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
 2153  * @inode: inode to allocate the dentry for
 2154  *
 2155  * Obtain a dentry for an inode resulting from NFS filehandle conversion or
 2156  * similar open by handle operations.  The returned dentry may be anonymous,
 2157  * or may have a full name (if the inode was already in the cache).
 2158  *
 2159  * When called on a directory inode, we must ensure that the inode only ever
 2160  * has one dentry.  If a dentry is found, that is returned instead of
 2161  * allocating a new one.
 2162  *
 2163  * On successful return, the reference to the inode has been transferred
 2164  * to the dentry.  In case of an error the reference on the inode is released.
 2165  * To make it easier to use in export operations a %NULL or IS_ERR inode may
 2166  * be passed in and the error will be propagated to the return value,
 2167  * with a %NULL @inode replaced by ERR_PTR(-ESTALE).
 2168  */
 2169 struct dentry *d_obtain_alias(struct inode *inode)
 2170 {
 2171 	return __d_obtain_alias(inode, true);
 2172 }
 2173 EXPORT_SYMBOL(d_obtain_alias);
 2174 
 2175 /**
 2176  * d_obtain_root - find or allocate a dentry for a given inode
 2177  * @inode: inode to allocate the dentry for
 2178  *
 2179  * Obtain an IS_ROOT dentry for the root of a filesystem.
 2180  *
 2181  * We must ensure that directory inodes only ever have one dentry.  If a
 2182  * dentry is found, that is returned instead of allocating a new one.
 2183  *
 2184  * On successful return, the reference to the inode has been transferred
 2185  * to the dentry.  In case of an error the reference on the inode is
 2186  * released.  A %NULL or IS_ERR inode may be passed in and will be the
 2187  * error will be propagate to the return value, with a %NULL @inode
 2188  * replaced by ERR_PTR(-ESTALE).
 2189  */
 2190 struct dentry *d_obtain_root(struct inode *inode)
 2191 {
 2192 	return __d_obtain_alias(inode, false);
 2193 }
 2194 EXPORT_SYMBOL(d_obtain_root);
 2195 
 2196 /**
 2197  * d_add_ci - lookup or allocate new dentry with case-exact name
 2198  * @inode:  the inode case-insensitive lookup has found
 2199  * @dentry: the negative dentry that was passed to the parent's lookup func
 2200  * @name:   the case-exact name to be associated with the returned dentry
 2201  *
 2202  * This is to avoid filling the dcache with case-insensitive names to the
 2203  * same inode, only the actual correct case is stored in the dcache for
 2204  * case-insensitive filesystems.
 2205  *
 2206  * For a case-insensitive lookup match and if the case-exact dentry
 2207  * already exists in the dcache, use it and return it.
 2208  *
 2209  * If no entry exists with the exact case name, allocate new dentry with
 2210  * the exact case, and return the spliced entry.
 2211  */
 2212 struct dentry *d_add_ci(struct dentry *dentry, struct inode *inode,
 2213 			struct qstr *name)
 2214 {
 2215 	struct dentry *found, *res;
 2216 
 2217 	/*
 2218 	 * First check if a dentry matching the name already exists,
 2219 	 * if not go ahead and create it now.
 2220 	 */
 2221 	found = d_hash_and_lookup(dentry->d_parent, name);
 2222 	if (found) {
 2223 		iput(inode);
 2224 		return found;
 2225 	}
 2226 	if (d_in_lookup(dentry)) {
 2227 		found = d_alloc_parallel(dentry->d_parent, name,
 2228 					dentry->d_wait);
 2229 		if (IS_ERR(found) || !d_in_lookup(found)) {
 2230 			iput(inode);
 2231 			return found;
 2232 		}
 2233 	} else {
 2234 		found = d_alloc(dentry->d_parent, name);
 2235 		if (!found) {
 2236 			iput(inode);
 2237 			return ERR_PTR(-ENOMEM);
 2238 		} 
 2239 	}
 2240 	res = d_splice_alias(inode, found);
 2241 	if (res) {
 2242 		d_lookup_done(found);
 2243 		dput(found);
 2244 		return res;
 2245 	}
 2246 	return found;
 2247 }
 2248 EXPORT_SYMBOL(d_add_ci);
 2249 
 2250 /**
 2251  * d_same_name - compare dentry name with case-exact name
 2252  * @parent: parent dentry
 2253  * @dentry: the negative dentry that was passed to the parent's lookup func
 2254  * @name:   the case-exact name to be associated with the returned dentry
 2255  *
 2256  * Return: true if names are same, or false
 2257  */
 2258 bool d_same_name(const struct dentry *dentry, const struct dentry *parent,
 2259 		 const struct qstr *name)
 2260 {
 2261 	if (likely(!(parent->d_flags & DCACHE_OP_COMPARE))) {
 2262 		if (dentry->d_name.len != name->len)
 2263 			return false;
 2264 		return dentry_cmp(dentry, name->name, name->len) == 0;
 2265 	}
 2266 	return parent->d_op->d_compare(dentry,
 2267 				       dentry->d_name.len, dentry->d_name.name,
 2268 				       name) == 0;
 2269 }
 2270 EXPORT_SYMBOL_GPL(d_same_name);
 2271 
 2272 /*
 2273  * This is __d_lookup_rcu() when the parent dentry has
 2274  * DCACHE_OP_COMPARE, which makes things much nastier.
 2275  */
 2276 static noinline struct dentry *__d_lookup_rcu_op_compare(
 2277 	const struct dentry *parent,
 2278 	const struct qstr *name,
 2279 	unsigned *seqp)
 2280 {
 2281 	u64 hashlen = name->hash_len;
 2282 	struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
 2283 	struct hlist_bl_node *node;
 2284 	struct dentry *dentry;
 2285 
 2286 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 2287 		int tlen;
 2288 		const char *tname;
 2289 		unsigned seq;
 2290 
 2291 seqretry:
 2292 		seq = raw_seqcount_begin(&dentry->d_seq);
 2293 		if (dentry->d_parent != parent)
 2294 			continue;
 2295 		if (d_unhashed(dentry))
 2296 			continue;
 2297 		if (dentry->d_name.hash != hashlen_hash(hashlen))
 2298 			continue;
 2299 		tlen = dentry->d_name.len;
 2300 		tname = dentry->d_name.name;
 2301 		/* we want a consistent (name,len) pair */
 2302 		if (read_seqcount_retry(&dentry->d_seq, seq)) {
 2303 			cpu_relax();
 2304 			goto seqretry;
 2305 		}
 2306 		if (parent->d_op->d_compare(dentry, tlen, tname, name) != 0)
 2307 			continue;
 2308 		*seqp = seq;
 2309 		return dentry;
 2310 	}
 2311 	return NULL;
 2312 }
 2313 
 2314 /**
 2315  * __d_lookup_rcu - search for a dentry (racy, store-free)
 2316  * @parent: parent dentry
 2317  * @name: qstr of name we wish to find
 2318  * @seqp: returns d_seq value at the point where the dentry was found
 2319  * Returns: dentry, or NULL
 2320  *
 2321  * __d_lookup_rcu is the dcache lookup function for rcu-walk name
 2322  * resolution (store-free path walking) design described in
 2323  * Documentation/filesystems/path-lookup.txt.
 2324  *
 2325  * This is not to be used outside core vfs.
 2326  *
 2327  * __d_lookup_rcu must only be used in rcu-walk mode, ie. with vfsmount lock
 2328  * held, and rcu_read_lock held. The returned dentry must not be stored into
 2329  * without taking d_lock and checking d_seq sequence count against @seq
 2330  * returned here.
 2331  *
 2332  * A refcount may be taken on the found dentry with the d_rcu_to_refcount
 2333  * function.
 2334  *
 2335  * Alternatively, __d_lookup_rcu may be called again to look up the child of
 2336  * the returned dentry, so long as its parent's seqlock is checked after the
 2337  * child is looked up. Thus, an interlocking stepping of sequence lock checks
 2338  * is formed, giving integrity down the path walk.
 2339  *
 2340  * NOTE! The caller *has* to check the resulting dentry against the sequence
 2341  * number we've returned before using any of the resulting dentry state!
 2342  */
 2343 struct dentry *__d_lookup_rcu(const struct dentry *parent,
 2344 				const struct qstr *name,
 2345 				unsigned *seqp)
 2346 {
 2347 	u64 hashlen = name->hash_len;
 2348 	const unsigned char *str = name->name;
 2349 	struct hlist_bl_head *b = d_hash(hashlen_hash(hashlen));
 2350 	struct hlist_bl_node *node;
 2351 	struct dentry *dentry;
 2352 
 2353 	/*
 2354 	 * Note: There is significant duplication with __d_lookup_rcu which is
 2355 	 * required to prevent single threaded performance regressions
 2356 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
 2357 	 * Keep the two functions in sync.
 2358 	 */
 2359 
 2360 	if (unlikely(parent->d_flags & DCACHE_OP_COMPARE))
 2361 		return __d_lookup_rcu_op_compare(parent, name, seqp);
 2362 
 2363 	/*
 2364 	 * The hash list is protected using RCU.
 2365 	 *
 2366 	 * Carefully use d_seq when comparing a candidate dentry, to avoid
 2367 	 * races with d_move().
 2368 	 *
 2369 	 * It is possible that concurrent renames can mess up our list
 2370 	 * walk here and result in missing our dentry, resulting in the
 2371 	 * false-negative result. d_lookup() protects against concurrent
 2372 	 * renames using rename_lock seqlock.
 2373 	 *
 2374 	 * See Documentation/filesystems/path-lookup.txt for more details.
 2375 	 */
 2376 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 2377 		unsigned seq;
 2378 
 2379 		/*
 2380 		 * The dentry sequence count protects us from concurrent
 2381 		 * renames, and thus protects parent and name fields.
 2382 		 *
 2383 		 * The caller must perform a seqcount check in order
 2384 		 * to do anything useful with the returned dentry.
 2385 		 *
 2386 		 * NOTE! We do a "raw" seqcount_begin here. That means that
 2387 		 * we don't wait for the sequence count to stabilize if it
 2388 		 * is in the middle of a sequence change. If we do the slow
 2389 		 * dentry compare, we will do seqretries until it is stable,
 2390 		 * and if we end up with a successful lookup, we actually
 2391 		 * want to exit RCU lookup anyway.
 2392 		 *
 2393 		 * Note that raw_seqcount_begin still *does* smp_rmb(), so
 2394 		 * we are still guaranteed NUL-termination of ->d_name.name.
 2395 		 */
 2396 		seq = raw_seqcount_begin(&dentry->d_seq);
 2397 		if (dentry->d_parent != parent)
 2398 			continue;
 2399 		if (d_unhashed(dentry))
 2400 			continue;
 2401 		if (dentry->d_name.hash_len != hashlen)
 2402 			continue;
 2403 		if (dentry_cmp(dentry, str, hashlen_len(hashlen)) != 0)
 2404 			continue;
 2405 		*seqp = seq;
 2406 		return dentry;
 2407 	}
 2408 	return NULL;
 2409 }
 2410 
 2411 /**
 2412  * d_lookup - search for a dentry
 2413  * @parent: parent dentry
 2414  * @name: qstr of name we wish to find
 2415  * Returns: dentry, or NULL
 2416  *
 2417  * d_lookup searches the children of the parent dentry for the name in
 2418  * question. If the dentry is found its reference count is incremented and the
 2419  * dentry is returned. The caller must use dput to free the entry when it has
 2420  * finished using it. %NULL is returned if the dentry does not exist.
 2421  */
 2422 struct dentry *d_lookup(const struct dentry *parent, const struct qstr *name)
 2423 {
 2424 	struct dentry *dentry;
 2425 	unsigned seq;
 2426 
 2427 	do {
 2428 		seq = read_seqbegin(&rename_lock);
 2429 		dentry = __d_lookup(parent, name);
 2430 		if (dentry)
 2431 			break;
 2432 	} while (read_seqretry(&rename_lock, seq));
 2433 	return dentry;
 2434 }
 2435 EXPORT_SYMBOL(d_lookup);
 2436 
 2437 /**
 2438  * __d_lookup - search for a dentry (racy)
 2439  * @parent: parent dentry
 2440  * @name: qstr of name we wish to find
 2441  * Returns: dentry, or NULL
 2442  *
 2443  * __d_lookup is like d_lookup, however it may (rarely) return a
 2444  * false-negative result due to unrelated rename activity.
 2445  *
 2446  * __d_lookup is slightly faster by avoiding rename_lock read seqlock,
 2447  * however it must be used carefully, eg. with a following d_lookup in
 2448  * the case of failure.
 2449  *
 2450  * __d_lookup callers must be commented.
 2451  */
 2452 struct dentry *__d_lookup(const struct dentry *parent, const struct qstr *name)
 2453 {
 2454 	unsigned int hash = name->hash;
 2455 	struct hlist_bl_head *b = d_hash(hash);
 2456 	struct hlist_bl_node *node;
 2457 	struct dentry *found = NULL;
 2458 	struct dentry *dentry;
 2459 
 2460 	/*
 2461 	 * Note: There is significant duplication with __d_lookup_rcu which is
 2462 	 * required to prevent single threaded performance regressions
 2463 	 * especially on architectures where smp_rmb (in seqcounts) are costly.
 2464 	 * Keep the two functions in sync.
 2465 	 */
 2466 
 2467 	/*
 2468 	 * The hash list is protected using RCU.
 2469 	 *
 2470 	 * Take d_lock when comparing a candidate dentry, to avoid races
 2471 	 * with d_move().
 2472 	 *
 2473 	 * It is possible that concurrent renames can mess up our list
 2474 	 * walk here and result in missing our dentry, resulting in the
 2475 	 * false-negative result. d_lookup() protects against concurrent
 2476 	 * renames using rename_lock seqlock.
 2477 	 *
 2478 	 * See Documentation/filesystems/path-lookup.txt for more details.
 2479 	 */
 2480 	rcu_read_lock();
 2481 	
 2482 	hlist_bl_for_each_entry_rcu(dentry, node, b, d_hash) {
 2483 
 2484 		if (dentry->d_name.hash != hash)
 2485 			continue;
 2486 
 2487 		spin_lock(&dentry->d_lock);
 2488 		if (dentry->d_parent != parent)
 2489 			goto next;
 2490 		if (d_unhashed(dentry))
 2491 			goto next;
 2492 
 2493 		if (!d_same_name(dentry, parent, name))
 2494 			goto next;
 2495 
 2496 		dentry->d_lockref.count++;
 2497 		found = dentry;
 2498 		spin_unlock(&dentry->d_lock);
 2499 		break;
 2500 next:
 2501 		spin_unlock(&dentry->d_lock);
 2502  	}
 2503  	rcu_read_unlock();
 2504 
 2505  	return found;
 2506 }
 2507 
 2508 /**
 2509  * d_hash_and_lookup - hash the qstr then search for a dentry
 2510  * @dir: Directory to search in
 2511  * @name: qstr of name we wish to find
 2512  *
 2513  * On lookup failure NULL is returned; on bad name - ERR_PTR(-error)
 2514  */
 2515 struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
 2516 {
 2517 	/*
 2518 	 * Check for a fs-specific hash function. Note that we must
 2519 	 * calculate the standard hash first, as the d_op->d_hash()
 2520 	 * routine may choose to leave the hash value unchanged.
 2521 	 */
 2522 	name->hash = full_name_hash(dir, name->name, name->len);
 2523 	if (dir->d_flags & DCACHE_OP_HASH) {
 2524 		int err = dir->d_op->d_hash(dir, name);
 2525 		if (unlikely(err < 0))
 2526 			return ERR_PTR(err);
 2527 	}
 2528 	return d_lookup(dir, name);
 2529 }
 2530 EXPORT_SYMBOL(d_hash_and_lookup);
 2531 
 2532 /*
 2533  * When a file is deleted, we have two options:
 2534  * - turn this dentry into a negative dentry
 2535  * - unhash this dentry and free it.
 2536  *
 2537  * Usually, we want to just turn this into
 2538  * a negative dentry, but if anybody else is
 2539  * currently using the dentry or the inode
 2540  * we can't do that and we fall back on removing
 2541  * it from the hash queues and waiting for
 2542  * it to be deleted later when it has no users
 2543  */
 2544  
 2545 /**
 2546  * d_delete - delete a dentry
 2547  * @dentry: The dentry to delete
 2548  *
 2549  * Turn the dentry into a negative dentry if possible, otherwise
 2550  * remove it from the hash queues so it can be deleted later
 2551  */
 2552  
 2553 void d_delete(struct dentry * dentry)
 2554 {
 2555 	struct inode *inode = dentry->d_inode;
 2556 
 2557 	spin_lock(&inode->i_lock);
 2558 	spin_lock(&dentry->d_lock);
 2559 	/*
 2560 	 * Are we the only user?
 2561 	 */
 2562 	if (dentry->d_lockref.count == 1) {
 2563 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
 2564 		dentry_unlink_inode(dentry);
 2565 	} else {
 2566 		__d_drop(dentry);
 2567 		spin_unlock(&dentry->d_lock);
 2568 		spin_unlock(&inode->i_lock);
 2569 	}
 2570 }
 2571 EXPORT_SYMBOL(d_delete);
 2572 
 2573 static void __d_rehash(struct dentry *entry)
 2574 {
 2575 	struct hlist_bl_head *b = d_hash(entry->d_name.hash);
 2576 
 2577 	hlist_bl_lock(b);
 2578 	hlist_bl_add_head_rcu(&entry->d_hash, b);
 2579 	hlist_bl_unlock(b);
 2580 }
 2581 
 2582 /**
 2583  * d_rehash	- add an entry back to the hash
 2584  * @entry: dentry to add to the hash
 2585  *
 2586  * Adds a dentry to the hash according to its name.
 2587  */
 2588  
 2589 void d_rehash(struct dentry * entry)
 2590 {
 2591 	spin_lock(&entry->d_lock);
 2592 	__d_rehash(entry);
 2593 	spin_unlock(&entry->d_lock);
 2594 }
 2595 EXPORT_SYMBOL(d_rehash);
 2596 
 2597 static inline unsigned start_dir_add(struct inode *dir)
 2598 {
 2599 	preempt_disable_nested();
 2600 	for (;;) {
 2601 		unsigned n = dir->i_dir_seq;
 2602 		if (!(n & 1) && cmpxchg(&dir->i_dir_seq, n, n + 1) == n)
 2603 			return n;
 2604 		cpu_relax();
 2605 	}
 2606 }
 2607 
 2608 static inline void end_dir_add(struct inode *dir, unsigned int n,
 2609 			       wait_queue_head_t *d_wait)
 2610 {
 2611 	smp_store_release(&dir->i_dir_seq, n + 2);
 2612 	preempt_enable_nested();
 2613 	wake_up_all(d_wait);
 2614 }
 2615 
 2616 static void d_wait_lookup(struct dentry *dentry)
 2617 {
 2618 	if (d_in_lookup(dentry)) {
 2619 		DECLARE_WAITQUEUE(wait, current);
 2620 		add_wait_queue(dentry->d_wait, &wait);
 2621 		do {
 2622 			set_current_state(TASK_UNINTERRUPTIBLE);
 2623 			spin_unlock(&dentry->d_lock);
 2624 			schedule();
 2625 			spin_lock(&dentry->d_lock);
 2626 		} while (d_in_lookup(dentry));
 2627 	}
 2628 }
 2629 
 2630 struct dentry *d_alloc_parallel(struct dentry *parent,
 2631 				const struct qstr *name,
 2632 				wait_queue_head_t *wq)
 2633 {
 2634 	unsigned int hash = name->hash;
 2635 	struct hlist_bl_head *b = in_lookup_hash(parent, hash);
 2636 	struct hlist_bl_node *node;
 2637 	struct dentry *new = d_alloc(parent, name);
 2638 	struct dentry *dentry;
 2639 	unsigned seq, r_seq, d_seq;
 2640 
 2641 	if (unlikely(!new))
 2642 		return ERR_PTR(-ENOMEM);
 2643 
 2644 retry:
 2645 	rcu_read_lock();
 2646 	seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
 2647 	r_seq = read_seqbegin(&rename_lock);
 2648 	dentry = __d_lookup_rcu(parent, name, &d_seq);
 2649 	if (unlikely(dentry)) {
 2650 		if (!lockref_get_not_dead(&dentry->d_lockref)) {
 2651 			rcu_read_unlock();
 2652 			goto retry;
 2653 		}
 2654 		if (read_seqcount_retry(&dentry->d_seq, d_seq)) {
 2655 			rcu_read_unlock();
 2656 			dput(dentry);
 2657 			goto retry;
 2658 		}
 2659 		rcu_read_unlock();
 2660 		dput(new);
 2661 		return dentry;
 2662 	}
 2663 	if (unlikely(read_seqretry(&rename_lock, r_seq))) {
 2664 		rcu_read_unlock();
 2665 		goto retry;
 2666 	}
 2667 
 2668 	if (unlikely(seq & 1)) {
 2669 		rcu_read_unlock();
 2670 		goto retry;
 2671 	}
 2672 
 2673 	hlist_bl_lock(b);
 2674 	if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
 2675 		hlist_bl_unlock(b);
 2676 		rcu_read_unlock();
 2677 		goto retry;
 2678 	}
 2679 	/*
 2680 	 * No changes for the parent since the beginning of d_lookup().
 2681 	 * Since all removals from the chain happen with hlist_bl_lock(),
 2682 	 * any potential in-lookup matches are going to stay here until
 2683 	 * we unlock the chain.  All fields are stable in everything
 2684 	 * we encounter.
 2685 	 */
 2686 	hlist_bl_for_each_entry(dentry, node, b, d_u.d_in_lookup_hash) {
 2687 		if (dentry->d_name.hash != hash)
 2688 			continue;
 2689 		if (dentry->d_parent != parent)
 2690 			continue;
 2691 		if (!d_same_name(dentry, parent, name))
 2692 			continue;
 2693 		hlist_bl_unlock(b);
 2694 		/* now we can try to grab a reference */
 2695 		if (!lockref_get_not_dead(&dentry->d_lockref)) {
 2696 			rcu_read_unlock();
 2697 			goto retry;
 2698 		}
 2699 
 2700 		rcu_read_unlock();
 2701 		/*
 2702 		 * somebody is likely to be still doing lookup for it;
 2703 		 * wait for them to finish
 2704 		 */
 2705 		spin_lock(&dentry->d_lock);
 2706 		d_wait_lookup(dentry);
 2707 		/*
 2708 		 * it's not in-lookup anymore; in principle we should repeat
 2709 		 * everything from dcache lookup, but it's likely to be what
 2710 		 * d_lookup() would've found anyway.  If it is, just return it;
 2711 		 * otherwise we really have to repeat the whole thing.
 2712 		 */
 2713 		if (unlikely(dentry->d_name.hash != hash))
 2714 			goto mismatch;
 2715 		if (unlikely(dentry->d_parent != parent))
 2716 			goto mismatch;
 2717 		if (unlikely(d_unhashed(dentry)))
 2718 			goto mismatch;
 2719 		if (unlikely(!d_same_name(dentry, parent, name)))
 2720 			goto mismatch;
 2721 		/* OK, it *is* a hashed match; return it */
 2722 		spin_unlock(&dentry->d_lock);
 2723 		dput(new);
 2724 		return dentry;
 2725 	}
 2726 	rcu_read_unlock();
 2727 	/* we can't take ->d_lock here; it's OK, though. */
 2728 	new->d_flags |= DCACHE_PAR_LOOKUP;
 2729 	new->d_wait = wq;
 2730 	hlist_bl_add_head_rcu(&new->d_u.d_in_lookup_hash, b);
 2731 	hlist_bl_unlock(b);
 2732 	return new;
 2733 mismatch:
 2734 	spin_unlock(&dentry->d_lock);
 2735 	dput(dentry);
 2736 	goto retry;
 2737 }
 2738 EXPORT_SYMBOL(d_alloc_parallel);
 2739 
 2740 /*
 2741  * - Unhash the dentry
 2742  * - Retrieve and clear the waitqueue head in dentry
 2743  * - Return the waitqueue head
 2744  */
 2745 static wait_queue_head_t *__d_lookup_unhash(struct dentry *dentry)
 2746 {
 2747 	wait_queue_head_t *d_wait;
 2748 	struct hlist_bl_head *b;
 2749 
 2750 	lockdep_assert_held(&dentry->d_lock);
 2751 
 2752 	b = in_lookup_hash(dentry->d_parent, dentry->d_name.hash);
 2753 	hlist_bl_lock(b);
 2754 	dentry->d_flags &= ~DCACHE_PAR_LOOKUP;
 2755 	__hlist_bl_del(&dentry->d_u.d_in_lookup_hash);
 2756 	d_wait = dentry->d_wait;
 2757 	dentry->d_wait = NULL;
 2758 	hlist_bl_unlock(b);
 2759 	INIT_HLIST_NODE(&dentry->d_u.d_alias);
 2760 	INIT_LIST_HEAD(&dentry->d_lru);
 2761 	return d_wait;
 2762 }
 2763 
 2764 void __d_lookup_unhash_wake(struct dentry *dentry)
 2765 {
 2766 	spin_lock(&dentry->d_lock);
 2767 	wake_up_all(__d_lookup_unhash(dentry));
 2768 	spin_unlock(&dentry->d_lock);
 2769 }
 2770 EXPORT_SYMBOL(__d_lookup_unhash_wake);
 2771 
 2772 /* inode->i_lock held if inode is non-NULL */
 2773 
 2774 static inline void __d_add(struct dentry *dentry, struct inode *inode)
 2775 {
 2776 	wait_queue_head_t *d_wait;
 2777 	struct inode *dir = NULL;
 2778 	unsigned n;
 2779 	spin_lock(&dentry->d_lock);
 2780 	if (unlikely(d_in_lookup(dentry))) {
 2781 		dir = dentry->d_parent->d_inode;
 2782 		n = start_dir_add(dir);
 2783 		d_wait = __d_lookup_unhash(dentry);
 2784 	}
 2785 	if (inode) {
 2786 		unsigned add_flags = d_flags_for_inode(inode);
 2787 		hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
 2788 		raw_write_seqcount_begin(&dentry->d_seq);
 2789 		__d_set_inode_and_type(dentry, inode, add_flags);
 2790 		raw_write_seqcount_end(&dentry->d_seq);
 2791 		fsnotify_update_flags(dentry);
 2792 	}
 2793 	__d_rehash(dentry);
 2794 	if (dir)
 2795 		end_dir_add(dir, n, d_wait);
 2796 	spin_unlock(&dentry->d_lock);
 2797 	if (inode)
 2798 		spin_unlock(&inode->i_lock);
 2799 }
 2800 
 2801 /**
 2802  * d_add - add dentry to hash queues
 2803  * @entry: dentry to add
 2804  * @inode: The inode to attach to this dentry
 2805  *
 2806  * This adds the entry to the hash queues and initializes @inode.
 2807  * The entry was actually filled in earlier during d_alloc().
 2808  */
 2809 
 2810 void d_add(struct dentry *entry, struct inode *inode)
 2811 {
 2812 	if (inode) {
 2813 		security_d_instantiate(entry, inode);
 2814 		spin_lock(&inode->i_lock);
 2815 	}
 2816 	__d_add(entry, inode);
 2817 }
 2818 EXPORT_SYMBOL(d_add);
 2819 
 2820 /**
 2821  * d_exact_alias - find and hash an exact unhashed alias
 2822  * @entry: dentry to add
 2823  * @inode: The inode to go with this dentry
 2824  *
 2825  * If an unhashed dentry with the same name/parent and desired
 2826  * inode already exists, hash and return it.  Otherwise, return
 2827  * NULL.
 2828  *
 2829  * Parent directory should be locked.
 2830  */
 2831 struct dentry *d_exact_alias(struct dentry *entry, struct inode *inode)
 2832 {
 2833 	struct dentry *alias;
 2834 	unsigned int hash = entry->d_name.hash;
 2835 
 2836 	spin_lock(&inode->i_lock);
 2837 	hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
 2838 		/*
 2839 		 * Don't need alias->d_lock here, because aliases with
 2840 		 * d_parent == entry->d_parent are not subject to name or
 2841 		 * parent changes, because the parent inode i_mutex is held.
 2842 		 */
 2843 		if (alias->d_name.hash != hash)
 2844 			continue;
 2845 		if (alias->d_parent != entry->d_parent)
 2846 			continue;
 2847 		if (!d_same_name(alias, entry->d_parent, &entry->d_name))
 2848 			continue;
 2849 		spin_lock(&alias->d_lock);
 2850 		if (!d_unhashed(alias)) {
 2851 			spin_unlock(&alias->d_lock);
 2852 			alias = NULL;
 2853 		} else {
 2854 			__dget_dlock(alias);
 2855 			__d_rehash(alias);
 2856 			spin_unlock(&alias->d_lock);
 2857 		}
 2858 		spin_unlock(&inode->i_lock);
 2859 		return alias;
 2860 	}
 2861 	spin_unlock(&inode->i_lock);
 2862 	return NULL;
 2863 }
 2864 EXPORT_SYMBOL(d_exact_alias);
 2865 
 2866 static void swap_names(struct dentry *dentry, struct dentry *target)
 2867 {
 2868 	if (unlikely(dname_external(target))) {
 2869 		if (unlikely(dname_external(dentry))) {
 2870 			/*
 2871 			 * Both external: swap the pointers
 2872 			 */
 2873 			swap(target->d_name.name, dentry->d_name.name);
 2874 		} else {
 2875 			/*
 2876 			 * dentry:internal, target:external.  Steal target's
 2877 			 * storage and make target internal.
 2878 			 */
 2879 			memcpy(target->d_iname, dentry->d_name.name,
 2880 					dentry->d_name.len + 1);
 2881 			dentry->d_name.name = target->d_name.name;
 2882 			target->d_name.name = target->d_iname;
 2883 		}
 2884 	} else {
 2885 		if (unlikely(dname_external(dentry))) {
 2886 			/*
 2887 			 * dentry:external, target:internal.  Give dentry's
 2888 			 * storage to target and make dentry internal
 2889 			 */
 2890 			memcpy(dentry->d_iname, target->d_name.name,
 2891 					target->d_name.len + 1);
 2892 			target->d_name.name = dentry->d_name.name;
 2893 			dentry->d_name.name = dentry->d_iname;
 2894 		} else {
 2895 			/*
 2896 			 * Both are internal.
 2897 			 */
 2898 			unsigned int i;
 2899 			BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
 2900 			for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
 2901 				swap(((long *) &dentry->d_iname)[i],
 2902 				     ((long *) &target->d_iname)[i]);
 2903 			}
 2904 		}
 2905 	}
 2906 	swap(dentry->d_name.hash_len, target->d_name.hash_len);
 2907 }
 2908 
 2909 static void copy_name(struct dentry *dentry, struct dentry *target)
 2910 {
 2911 	struct external_name *old_name = NULL;
 2912 	if (unlikely(dname_external(dentry)))
 2913 		old_name = external_name(dentry);
 2914 	if (unlikely(dname_external(target))) {
 2915 		atomic_inc(&external_name(target)->u.count);
 2916 		dentry->d_name = target->d_name;
 2917 	} else {
 2918 		memcpy(dentry->d_iname, target->d_name.name,
 2919 				target->d_name.len + 1);
 2920 		dentry->d_name.name = dentry->d_iname;
 2921 		dentry->d_name.hash_len = target->d_name.hash_len;
 2922 	}
 2923 	if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
 2924 		kfree_rcu(old_name, u.head);
 2925 }
 2926 
 2927 /*
 2928  * __d_move - move a dentry
 2929  * @dentry: entry to move
 2930  * @target: new dentry
 2931  * @exchange: exchange the two dentries
 2932  *
 2933  * Update the dcache to reflect the move of a file name. Negative
 2934  * dcache entries should not be moved in this way. Caller must hold
 2935  * rename_lock, the i_mutex of the source and target directories,
 2936  * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
 2937  */
 2938 static void __d_move(struct dentry *dentry, struct dentry *target,
 2939 		     bool exchange)
 2940 {
 2941 	struct dentry *old_parent, *p;
 2942 	wait_queue_head_t *d_wait;
 2943 	struct inode *dir = NULL;
 2944 	unsigned n;
 2945 
 2946 	WARN_ON(!dentry->d_inode);
 2947 	if (WARN_ON(dentry == target))
 2948 		return;
 2949 
 2950 	BUG_ON(d_ancestor(target, dentry));
 2951 	old_parent = dentry->d_parent;
 2952 	p = d_ancestor(old_parent, target);
 2953 	if (IS_ROOT(dentry)) {
 2954 		BUG_ON(p);
 2955 		spin_lock(&target->d_parent->d_lock);
 2956 	} else if (!p) {
 2957 		/* target is not a descendent of dentry->d_parent */
 2958 		spin_lock(&target->d_parent->d_lock);
 2959 		spin_lock_nested(&old_parent->d_lock, DENTRY_D_LOCK_NESTED);
 2960 	} else {
 2961 		BUG_ON(p == dentry);
 2962 		spin_lock(&old_parent->d_lock);
 2963 		if (p != target)
 2964 			spin_lock_nested(&target->d_parent->d_lock,
 2965 					DENTRY_D_LOCK_NESTED);
 2966 	}
 2967 	spin_lock_nested(&dentry->d_lock, 2);
 2968 	spin_lock_nested(&target->d_lock, 3);
 2969 
 2970 	if (unlikely(d_in_lookup(target))) {
 2971 		dir = target->d_parent->d_inode;
 2972 		n = start_dir_add(dir);
 2973 		d_wait = __d_lookup_unhash(target);
 2974 	}
 2975 
 2976 	write_seqcount_begin(&dentry->d_seq);
 2977 	write_seqcount_begin_nested(&target->d_seq, DENTRY_D_LOCK_NESTED);
 2978 
 2979 	/* unhash both */
 2980 	if (!d_unhashed(dentry))
 2981 		___d_drop(dentry);
 2982 	if (!d_unhashed(target))
 2983 		___d_drop(target);
 2984 
 2985 	/* ... and switch them in the tree */
 2986 	dentry->d_parent = target->d_parent;
 2987 	if (!exchange) {
 2988 		copy_name(dentry, target);
 2989 		target->d_hash.pprev = NULL;
 2990 		dentry->d_parent->d_lockref.count++;
 2991 		if (dentry != old_parent) /* wasn't IS_ROOT */
 2992 			WARN_ON(!--old_parent->d_lockref.count);
 2993 	} else {
 2994 		target->d_parent = old_parent;
 2995 		swap_names(dentry, target);
 2996 		list_move(&target->d_child, &target->d_parent->d_subdirs);
 2997 		__d_rehash(target);
 2998 		fsnotify_update_flags(target);
 2999 	}
 3000 	list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
 3001 	__d_rehash(dentry);
 3002 	fsnotify_update_flags(dentry);
 3003 	fscrypt_handle_d_move(dentry);
 3004 
 3005 	write_seqcount_end(&target->d_seq);
 3006 	write_seqcount_end(&dentry->d_seq);
 3007 
 3008 	if (dir)
 3009 		end_dir_add(dir, n, d_wait);
 3010 
 3011 	if (dentry->d_parent != old_parent)
 3012 		spin_unlock(&dentry->d_parent->d_lock);
 3013 	if (dentry != old_parent)
 3014 		spin_unlock(&old_parent->d_lock);
 3015 	spin_unlock(&target->d_lock);
 3016 	spin_unlock(&dentry->d_lock);
 3017 }
 3018 
 3019 /*
 3020  * d_move - move a dentry
 3021  * @dentry: entry to move
 3022  * @target: new dentry
 3023  *
 3024  * Update the dcache to reflect the move of a file name. Negative
 3025  * dcache entries should not be moved in this way. See the locking
 3026  * requirements for __d_move.
 3027  */
 3028 void d_move(struct dentry *dentry, struct dentry *target)
 3029 {
 3030 	write_seqlock(&rename_lock);
 3031 	__d_move(dentry, target, false);
 3032 	write_sequnlock(&rename_lock);
 3033 }
 3034 EXPORT_SYMBOL(d_move);
 3035 
 3036 /*
 3037  * d_exchange - exchange two dentries
 3038  * @dentry1: first dentry
 3039  * @dentry2: second dentry
 3040  */
 3041 void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
 3042 {
 3043 	write_seqlock(&rename_lock);
 3044 
 3045 	WARN_ON(!dentry1->d_inode);
 3046 	WARN_ON(!dentry2->d_inode);
 3047 	WARN_ON(IS_ROOT(dentry1));
 3048 	WARN_ON(IS_ROOT(dentry2));
 3049 
 3050 	__d_move(dentry1, dentry2, true);
 3051 
 3052 	write_sequnlock(&rename_lock);
 3053 }
 3054 
 3055 /**
 3056  * d_ancestor - search for an ancestor
 3057  * @p1: ancestor dentry
 3058  * @p2: child dentry
 3059  *
 3060  * Returns the ancestor dentry of p2 which is a child of p1, if p1 is
 3061  * an ancestor of p2, else NULL.
 3062  */
 3063 struct dentry *d_ancestor(struct dentry *p1, struct dentry *p2)
 3064 {
 3065 	struct dentry *p;
 3066 
 3067 	for (p = p2; !IS_ROOT(p); p = p->d_parent) {
 3068 		if (p->d_parent == p1)
 3069 			return p;
 3070 	}
 3071 	return NULL;
 3072 }
 3073 
 3074 /*
 3075  * This helper attempts to cope with remotely renamed directories
 3076  *
 3077  * It assumes that the caller is already holding
 3078  * dentry->d_parent->d_inode->i_mutex, and rename_lock
 3079  *
 3080  * Note: If ever the locking in lock_rename() changes, then please
 3081  * remember to update this too...
 3082  */
 3083 static int __d_unalias(struct inode *inode,
 3084 		struct dentry *dentry, struct dentry *alias)
 3085 {
 3086 	struct mutex *m1 = NULL;
 3087 	struct rw_semaphore *m2 = NULL;
 3088 	int ret = -ESTALE;
 3089 
 3090 	/* If alias and dentry share a parent, then no extra locks required */
 3091 	if (alias->d_parent == dentry->d_parent)
 3092 		goto out_unalias;
 3093 
 3094 	/* See lock_rename() */
 3095 	if (!mutex_trylock(&dentry->d_sb->s_vfs_rename_mutex))
 3096 		goto out_err;
 3097 	m1 = &dentry->d_sb->s_vfs_rename_mutex;
 3098 	if (!inode_trylock_shared(alias->d_parent->d_inode))
 3099 		goto out_err;
 3100 	m2 = &alias->d_parent->d_inode->i_rwsem;
 3101 out_unalias:
 3102 	__d_move(alias, dentry, false);
 3103 	ret = 0;
 3104 out_err:
 3105 	if (m2)
 3106 		up_read(m2);
 3107 	if (m1)
 3108 		mutex_unlock(m1);
 3109 	return ret;
 3110 }
 3111 
 3112 /**
 3113  * d_splice_alias - splice a disconnected dentry into the tree if one exists
 3114  * @inode:  the inode which may have a disconnected dentry
 3115  * @dentry: a negative dentry which we want to point to the inode.
 3116  *
 3117  * If inode is a directory and has an IS_ROOT alias, then d_move that in
 3118  * place of the given dentry and return it, else simply d_add the inode
 3119  * to the dentry and return NULL.
 3120  *
 3121  * If a non-IS_ROOT directory is found, the filesystem is corrupt, and
 3122  * we should error out: directories can't have multiple aliases.
 3123  *
 3124  * This is needed in the lookup routine of any filesystem that is exportable
 3125  * (via knfsd) so that we can build dcache paths to directories effectively.
 3126  *
 3127  * If a dentry was found and moved, then it is returned.  Otherwise NULL
 3128  * is returned.  This matches the expected return value of ->lookup.
 3129  *
 3130  * Cluster filesystems may call this function with a negative, hashed dentry.
 3131  * In that case, we know that the inode will be a regular file, and also this
 3132  * will only occur during atomic_open. So we need to check for the dentry
 3133  * being already hashed only in the final case.
 3134  */
 3135 struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 3136 {
 3137 	if (IS_ERR(inode))
 3138 		return ERR_CAST(inode);
 3139 
 3140 	BUG_ON(!d_unhashed(dentry));
 3141 
 3142 	if (!inode)
 3143 		goto out;
 3144 
 3145 	security_d_instantiate(dentry, inode);
 3146 	spin_lock(&inode->i_lock);
 3147 	if (S_ISDIR(inode->i_mode)) {
 3148 		struct dentry *new = __d_find_any_alias(inode);
 3149 		if (unlikely(new)) {
 3150 			/* The reference to new ensures it remains an alias */
 3151 			spin_unlock(&inode->i_lock);
 3152 			write_seqlock(&rename_lock);
 3153 			if (unlikely(d_ancestor(new, dentry))) {
 3154 				write_sequnlock(&rename_lock);
 3155 				dput(new);
 3156 				new = ERR_PTR(-ELOOP);
 3157 				pr_warn_ratelimited(
 3158 					"VFS: Lookup of '%s' in %s %s"
 3159 					" would have caused loop\n",
 3160 					dentry->d_name.name,
 3161 					inode->i_sb->s_type->name,
 3162 					inode->i_sb->s_id);
 3163 			} else if (!IS_ROOT(new)) {
 3164 				struct dentry *old_parent = dget(new->d_parent);
 3165 				int err = __d_unalias(inode, dentry, new);
 3166 				write_sequnlock(&rename_lock);
 3167 				if (err) {
 3168 					dput(new);
 3169 					new = ERR_PTR(err);
 3170 				}
 3171 				dput(old_parent);
 3172 			} else {
 3173 				__d_move(new, dentry, false);
 3174 				write_sequnlock(&rename_lock);
 3175 			}
 3176 			iput(inode);
 3177 			return new;
 3178 		}
 3179 	}
 3180 out:
 3181 	__d_add(dentry, inode);
 3182 	return NULL;
 3183 }
 3184 EXPORT_SYMBOL(d_splice_alias);
 3185 
 3186 /*
 3187  * Test whether new_dentry is a subdirectory of old_dentry.
 3188  *
 3189  * Trivially implemented using the dcache structure
 3190  */
 3191 
 3192 /**
 3193  * is_subdir - is new dentry a subdirectory of old_dentry
 3194  * @new_dentry: new dentry
 3195  * @old_dentry: old dentry
 3196  *
 3197  * Returns true if new_dentry is a subdirectory of the parent (at any depth).
 3198  * Returns false otherwise.
 3199  * Caller must ensure that "new_dentry" is pinned before calling is_subdir()
 3200  */
 3201   
 3202 bool is_subdir(struct dentry *new_dentry, struct dentry *old_dentry)
 3203 {
 3204 	bool result;
 3205 	unsigned seq;
 3206 
 3207 	if (new_dentry == old_dentry)
 3208 		return true;
 3209 
 3210 	do {
 3211 		/* for restarting inner loop in case of seq retry */
 3212 		seq = read_seqbegin(&rename_lock);
 3213 		/*
 3214 		 * Need rcu_readlock to protect against the d_parent trashing
 3215 		 * due to d_move
 3216 		 */
 3217 		rcu_read_lock();
 3218 		if (d_ancestor(old_dentry, new_dentry))
 3219 			result = true;
 3220 		else
 3221 			result = false;
 3222 		rcu_read_unlock();
 3223 	} while (read_seqretry(&rename_lock, seq));
 3224 
 3225 	return result;
 3226 }
 3227 EXPORT_SYMBOL(is_subdir);
 3228 
 3229 static enum d_walk_ret d_genocide_kill(void *data, struct dentry *dentry)
 3230 {
 3231 	struct dentry *root = data;
 3232 	if (dentry != root) {
 3233 		if (d_unhashed(dentry) || !dentry->d_inode)
 3234 			return D_WALK_SKIP;
 3235 
 3236 		if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
 3237 			dentry->d_flags |= DCACHE_GENOCIDE;
 3238 			dentry->d_lockref.count--;
 3239 		}
 3240 	}
 3241 	return D_WALK_CONTINUE;
 3242 }
 3243 
 3244 void d_genocide(struct dentry *parent)
 3245 {
 3246 	d_walk(parent, parent, d_genocide_kill);
 3247 }
 3248 
 3249 void d_tmpfile(struct file *file, struct inode *inode)
 3250 {
 3251 	struct dentry *dentry = file->f_path.dentry;
 3252 
 3253 	inode_dec_link_count(inode);
 3254 	BUG_ON(dentry->d_name.name != dentry->d_iname ||
 3255 		!hlist_unhashed(&dentry->d_u.d_alias) ||
 3256 		!d_unlinked(dentry));
 3257 	spin_lock(&dentry->d_parent->d_lock);
 3258 	spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
 3259 	dentry->d_name.len = sprintf(dentry->d_iname, "#%llu",
 3260 				(unsigned long long)inode->i_ino);
 3261 	spin_unlock(&dentry->d_lock);
 3262 	spin_unlock(&dentry->d_parent->d_lock);
 3263 	d_instantiate(dentry, inode);
 3264 }
 3265 EXPORT_SYMBOL(d_tmpfile);
 3266 
 3267 static __initdata unsigned long dhash_entries;
 3268 static int __init set_dhash_entries(char *str)
 3269 {
 3270 	if (!str)
 3271 		return 0;
 3272 	dhash_entries = simple_strtoul(str, &str, 0);
 3273 	return 1;
 3274 }
 3275 __setup("dhash_entries=", set_dhash_entries);
 3276 
 3277 static void __init dcache_init_early(void)
 3278 {
 3279 	/* If hashes are distributed across NUMA nodes, defer
 3280 	 * hash allocation until vmalloc space is available.
 3281 	 */
 3282 	if (hashdist)
 3283 		return;
 3284 
 3285 	dentry_hashtable =
 3286 		alloc_large_system_hash("Dentry cache",
 3287 					sizeof(struct hlist_bl_head),
 3288 					dhash_entries,
 3289 					13,
 3290 					HASH_EARLY | HASH_ZERO,
 3291 					&d_hash_shift,
 3292 					NULL,
 3293 					0,
 3294 					0);
 3295 	d_hash_shift = 32 - d_hash_shift;
 3296 }
 3297 
 3298 static void __init dcache_init(void)
 3299 {
 3300 	/*
 3301 	 * A constructor could be added for stable state like the lists,
 3302 	 * but it is probably not worth it because of the cache nature
 3303 	 * of the dcache.
 3304 	 */
 3305 	dentry_cache = KMEM_CACHE_USERCOPY(dentry,
 3306 		SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
 3307 		d_iname);
 3308 
 3309 	/* Hash may have been set up in dcache_init_early */
 3310 	if (!hashdist)
 3311 		return;
 3312 
 3313 	dentry_hashtable =
 3314 		alloc_large_system_hash("Dentry cache",
 3315 					sizeof(struct hlist_bl_head),
 3316 					dhash_entries,
 3317 					13,
 3318 					HASH_ZERO,
 3319 					&d_hash_shift,
 3320 					NULL,
 3321 					0,
 3322 					0);
 3323 	d_hash_shift = 32 - d_hash_shift;
 3324 }
 3325 
 3326 /* SLAB cache for __getname() consumers */
 3327 struct kmem_cache *names_cachep __read_mostly;
 3328 EXPORT_SYMBOL(names_cachep);
 3329 
 3330 void __init vfs_caches_init_early(void)
 3331 {
 3332 	int i;
 3333 
 3334 	for (i = 0; i < ARRAY_SIZE(in_lookup_hashtable); i++)
 3335 		INIT_HLIST_BL_HEAD(&in_lookup_hashtable[i]);
 3336 
 3337 	dcache_init_early();
 3338 	inode_init_early();
 3339 }
 3340 
 3341 void __init vfs_caches_init(void)
 3342 {
 3343 	names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
 3344 			SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
 3345 
 3346 	dcache_init();
 3347 	inode_init();
 3348 	files_init();
 3349 	files_maxfiles_init();
 3350 	mnt_init();
 3351 	bdev_cache_init();
 3352 	chrdev_init();
 3353 }