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