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TOMOYO Linux Cross Reference
Linux/fs/dcache.c

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

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