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Linux/fs/dcache.c

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

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