summaryrefslogtreecommitdiff
path: root/lib/rhashtable.c
blob: 50abe4fec4b8e87bb6d2870577a19f8f4445e6a0 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
/*
 * Resizable, Scalable, Concurrent Hash Table
 *
 * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
 * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
 * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
 *
 * Code partially derived from nft_hash
 * Rewritten with rehash code from br_multicast plus single list
 * pointer as suggested by Josh Triplett
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/log2.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <linux/rhashtable.h>
#include <linux/err.h>

#define HASH_DEFAULT_SIZE	64UL
#define HASH_MIN_SIZE		4U
#define BUCKET_LOCKS_PER_CPU   128UL

static u32 head_hashfn(struct rhashtable *ht,
		       const struct bucket_table *tbl,
		       const struct rhash_head *he)
{
	return rht_head_hashfn(ht, tbl, he, ht->p);
}

#ifdef CONFIG_PROVE_LOCKING
#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))

int lockdep_rht_mutex_is_held(struct rhashtable *ht)
{
	return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
}
EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);

int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
{
	spinlock_t *lock = rht_bucket_lock(tbl, hash);

	return (debug_locks) ? lockdep_is_held(lock) : 1;
}
EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
#else
#define ASSERT_RHT_MUTEX(HT)
#endif


static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
			      gfp_t gfp)
{
	unsigned int i, size;
#if defined(CONFIG_PROVE_LOCKING)
	unsigned int nr_pcpus = 2;
#else
	unsigned int nr_pcpus = num_possible_cpus();
#endif

	nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
	size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);

	/* Never allocate more than 0.5 locks per bucket */
	size = min_t(unsigned int, size, tbl->size >> 1);

	if (sizeof(spinlock_t) != 0) {
#ifdef CONFIG_NUMA
		if (size * sizeof(spinlock_t) > PAGE_SIZE &&
		    gfp == GFP_KERNEL)
			tbl->locks = vmalloc(size * sizeof(spinlock_t));
		else
#endif
		tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
					   gfp);
		if (!tbl->locks)
			return -ENOMEM;
		for (i = 0; i < size; i++)
			spin_lock_init(&tbl->locks[i]);
	}
	tbl->locks_mask = size - 1;

	return 0;
}

static void bucket_table_free(const struct bucket_table *tbl)
{
	if (tbl)
		kvfree(tbl->locks);

	kvfree(tbl);
}

static void bucket_table_free_rcu(struct rcu_head *head)
{
	bucket_table_free(container_of(head, struct bucket_table, rcu));
}

static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
					       size_t nbuckets,
					       gfp_t gfp)
{
	struct bucket_table *tbl = NULL;
	size_t size;
	int i;

	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
	if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
	    gfp != GFP_KERNEL)
		tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
	if (tbl == NULL && gfp == GFP_KERNEL)
		tbl = vzalloc(size);
	if (tbl == NULL)
		return NULL;

	tbl->size = nbuckets;

	if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
		bucket_table_free(tbl);
		return NULL;
	}

	INIT_LIST_HEAD(&tbl->walkers);

	get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));

	for (i = 0; i < nbuckets; i++)
		INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);

	return tbl;
}

static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
						  struct bucket_table *tbl)
{
	struct bucket_table *new_tbl;

	do {
		new_tbl = tbl;
		tbl = rht_dereference_rcu(tbl->future_tbl, ht);
	} while (tbl);

	return new_tbl;
}

static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
{
	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
	struct bucket_table *new_tbl = rhashtable_last_table(ht,
		rht_dereference_rcu(old_tbl->future_tbl, ht));
	struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
	int err = -ENOENT;
	struct rhash_head *head, *next, *entry;
	spinlock_t *new_bucket_lock;
	unsigned int new_hash;

	rht_for_each(entry, old_tbl, old_hash) {
		err = 0;
		next = rht_dereference_bucket(entry->next, old_tbl, old_hash);

		if (rht_is_a_nulls(next))
			break;

		pprev = &entry->next;
	}

	if (err)
		goto out;

	new_hash = head_hashfn(ht, new_tbl, entry);

	new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);

	spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
	head = rht_dereference_bucket(new_tbl->buckets[new_hash],
				      new_tbl, new_hash);

	if (rht_is_a_nulls(head))
		INIT_RHT_NULLS_HEAD(entry->next, ht, new_hash);
	else
		RCU_INIT_POINTER(entry->next, head);

	rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
	spin_unlock(new_bucket_lock);

	rcu_assign_pointer(*pprev, next);

out:
	return err;
}

static void rhashtable_rehash_chain(struct rhashtable *ht,
				    unsigned int old_hash)
{
	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
	spinlock_t *old_bucket_lock;

	old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);

	spin_lock_bh(old_bucket_lock);
	while (!rhashtable_rehash_one(ht, old_hash))
		;
	old_tbl->rehash++;
	spin_unlock_bh(old_bucket_lock);
}

static int rhashtable_rehash_attach(struct rhashtable *ht,
				    struct bucket_table *old_tbl,
				    struct bucket_table *new_tbl)
{
	/* Protect future_tbl using the first bucket lock. */
	spin_lock_bh(old_tbl->locks);

	/* Did somebody beat us to it? */
	if (rcu_access_pointer(old_tbl->future_tbl)) {
		spin_unlock_bh(old_tbl->locks);
		return -EEXIST;
	}

	/* Make insertions go into the new, empty table right away. Deletions
	 * and lookups will be attempted in both tables until we synchronize.
	 */
	rcu_assign_pointer(old_tbl->future_tbl, new_tbl);

	/* Ensure the new table is visible to readers. */
	smp_wmb();

	spin_unlock_bh(old_tbl->locks);

	return 0;
}

static int rhashtable_rehash_table(struct rhashtable *ht)
{
	struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
	struct bucket_table *new_tbl;
	struct rhashtable_walker *walker;
	unsigned int old_hash;

	new_tbl = rht_dereference(old_tbl->future_tbl, ht);
	if (!new_tbl)
		return 0;

	for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
		rhashtable_rehash_chain(ht, old_hash);

	/* Publish the new table pointer. */
	rcu_assign_pointer(ht->tbl, new_tbl);

	spin_lock(&ht->lock);
	list_for_each_entry(walker, &old_tbl->walkers, list)
		walker->tbl = NULL;
	spin_unlock(&ht->lock);

	/* Wait for readers. All new readers will see the new
	 * table, and thus no references to the old table will
	 * remain.
	 */
	call_rcu(&old_tbl->rcu, bucket_table_free_rcu);

	return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
}

/**
 * rhashtable_expand - Expand hash table while allowing concurrent lookups
 * @ht:		the hash table to expand
 *
 * A secondary bucket array is allocated and the hash entries are migrated.
 *
 * This function may only be called in a context where it is safe to call
 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 *
 * The caller must ensure that no concurrent resizing occurs by holding
 * ht->mutex.
 *
 * It is valid to have concurrent insertions and deletions protected by per
 * bucket locks or concurrent RCU protected lookups and traversals.
 */
static int rhashtable_expand(struct rhashtable *ht)
{
	struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
	int err;

	ASSERT_RHT_MUTEX(ht);

	old_tbl = rhashtable_last_table(ht, old_tbl);

	new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
	if (new_tbl == NULL)
		return -ENOMEM;

	err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
	if (err)
		bucket_table_free(new_tbl);

	return err;
}

/**
 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 * @ht:		the hash table to shrink
 *
 * This function shrinks the hash table to fit, i.e., the smallest
 * size would not cause it to expand right away automatically.
 *
 * The caller must ensure that no concurrent resizing occurs by holding
 * ht->mutex.
 *
 * The caller must ensure that no concurrent table mutations take place.
 * It is however valid to have concurrent lookups if they are RCU protected.
 *
 * It is valid to have concurrent insertions and deletions protected by per
 * bucket locks or concurrent RCU protected lookups and traversals.
 */
static int rhashtable_shrink(struct rhashtable *ht)
{
	struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
	unsigned int size;
	int err;

	ASSERT_RHT_MUTEX(ht);

	size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2);
	if (size < ht->p.min_size)
		size = ht->p.min_size;

	if (old_tbl->size <= size)
		return 0;

	if (rht_dereference(old_tbl->future_tbl, ht))
		return -EEXIST;

	new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
	if (new_tbl == NULL)
		return -ENOMEM;

	err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
	if (err)
		bucket_table_free(new_tbl);

	return err;
}

static void rht_deferred_worker(struct work_struct *work)
{
	struct rhashtable *ht;
	struct bucket_table *tbl;
	int err = 0;

	ht = container_of(work, struct rhashtable, run_work);
	mutex_lock(&ht->mutex);
	if (ht->being_destroyed)
		goto unlock;

	tbl = rht_dereference(ht->tbl, ht);
	tbl = rhashtable_last_table(ht, tbl);

	if (rht_grow_above_75(ht, tbl))
		rhashtable_expand(ht);
	else if (rht_shrink_below_30(ht, tbl))
		rhashtable_shrink(ht);

	err = rhashtable_rehash_table(ht);

unlock:
	mutex_unlock(&ht->mutex);

	if (err)
		schedule_work(&ht->run_work);
}

static bool rhashtable_check_elasticity(struct rhashtable *ht,
					struct bucket_table *tbl,
					unsigned int hash)
{
	unsigned int elasticity = ht->elasticity;
	struct rhash_head *head;

	rht_for_each(head, tbl, hash)
		if (!--elasticity)
			return true;

	return false;
}

int rhashtable_insert_rehash(struct rhashtable *ht)
{
	struct bucket_table *old_tbl;
	struct bucket_table *new_tbl;
	struct bucket_table *tbl;
	unsigned int size;
	int err;

	old_tbl = rht_dereference_rcu(ht->tbl, ht);
	tbl = rhashtable_last_table(ht, old_tbl);

	size = tbl->size;

	if (rht_grow_above_75(ht, tbl))
		size *= 2;
	/* More than two rehashes (not resizes) detected. */
	else if (WARN_ON(old_tbl != tbl && old_tbl->size == size))
		return -EBUSY;

	new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
	if (new_tbl == NULL)
		return -ENOMEM;

	err = rhashtable_rehash_attach(ht, tbl, new_tbl);
	if (err) {
		bucket_table_free(new_tbl);
		if (err == -EEXIST)
			err = 0;
	} else
		schedule_work(&ht->run_work);

	return err;
}
EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);

int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
			   struct rhash_head *obj,
			   struct bucket_table *tbl)
{
	struct rhash_head *head;
	unsigned int hash;
	int err;

	tbl = rhashtable_last_table(ht, tbl);
	hash = head_hashfn(ht, tbl, obj);
	spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);

	err = -EEXIST;
	if (key && rhashtable_lookup_fast(ht, key, ht->p))
		goto exit;

	err = -EAGAIN;
	if (rhashtable_check_elasticity(ht, tbl, hash) ||
	    rht_grow_above_100(ht, tbl))
		goto exit;

	err = 0;

	head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);

	RCU_INIT_POINTER(obj->next, head);

	rcu_assign_pointer(tbl->buckets[hash], obj);

	atomic_inc(&ht->nelems);

exit:
	spin_unlock(rht_bucket_lock(tbl, hash));

	return err;
}
EXPORT_SYMBOL_GPL(rhashtable_insert_slow);

/**
 * rhashtable_walk_init - Initialise an iterator
 * @ht:		Table to walk over
 * @iter:	Hash table Iterator
 *
 * This function prepares a hash table walk.
 *
 * Note that if you restart a walk after rhashtable_walk_stop you
 * may see the same object twice.  Also, you may miss objects if
 * there are removals in between rhashtable_walk_stop and the next
 * call to rhashtable_walk_start.
 *
 * For a completely stable walk you should construct your own data
 * structure outside the hash table.
 *
 * This function may sleep so you must not call it from interrupt
 * context or with spin locks held.
 *
 * You must call rhashtable_walk_exit if this function returns
 * successfully.
 */
int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
{
	iter->ht = ht;
	iter->p = NULL;
	iter->slot = 0;
	iter->skip = 0;

	iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
	if (!iter->walker)
		return -ENOMEM;

	mutex_lock(&ht->mutex);
	iter->walker->tbl = rht_dereference(ht->tbl, ht);
	list_add(&iter->walker->list, &iter->walker->tbl->walkers);
	mutex_unlock(&ht->mutex);

	return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_walk_init);

/**
 * rhashtable_walk_exit - Free an iterator
 * @iter:	Hash table Iterator
 *
 * This function frees resources allocated by rhashtable_walk_init.
 */
void rhashtable_walk_exit(struct rhashtable_iter *iter)
{
	mutex_lock(&iter->ht->mutex);
	if (iter->walker->tbl)
		list_del(&iter->walker->list);
	mutex_unlock(&iter->ht->mutex);
	kfree(iter->walker);
}
EXPORT_SYMBOL_GPL(rhashtable_walk_exit);

/**
 * rhashtable_walk_start - Start a hash table walk
 * @iter:	Hash table iterator
 *
 * Start a hash table walk.  Note that we take the RCU lock in all
 * cases including when we return an error.  So you must always call
 * rhashtable_walk_stop to clean up.
 *
 * Returns zero if successful.
 *
 * Returns -EAGAIN if resize event occured.  Note that the iterator
 * will rewind back to the beginning and you may use it immediately
 * by calling rhashtable_walk_next.
 */
int rhashtable_walk_start(struct rhashtable_iter *iter)
	__acquires(RCU)
{
	struct rhashtable *ht = iter->ht;

	mutex_lock(&ht->mutex);

	if (iter->walker->tbl)
		list_del(&iter->walker->list);

	rcu_read_lock();

	mutex_unlock(&ht->mutex);

	if (!iter->walker->tbl) {
		iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
		return -EAGAIN;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_walk_start);

/**
 * rhashtable_walk_next - Return the next object and advance the iterator
 * @iter:	Hash table iterator
 *
 * Note that you must call rhashtable_walk_stop when you are finished
 * with the walk.
 *
 * Returns the next object or NULL when the end of the table is reached.
 *
 * Returns -EAGAIN if resize event occured.  Note that the iterator
 * will rewind back to the beginning and you may continue to use it.
 */
void *rhashtable_walk_next(struct rhashtable_iter *iter)
{
	struct bucket_table *tbl = iter->walker->tbl;
	struct rhashtable *ht = iter->ht;
	struct rhash_head *p = iter->p;
	void *obj = NULL;

	if (p) {
		p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
		goto next;
	}

	for (; iter->slot < tbl->size; iter->slot++) {
		int skip = iter->skip;

		rht_for_each_rcu(p, tbl, iter->slot) {
			if (!skip)
				break;
			skip--;
		}

next:
		if (!rht_is_a_nulls(p)) {
			iter->skip++;
			iter->p = p;
			obj = rht_obj(ht, p);
			goto out;
		}

		iter->skip = 0;
	}

	/* Ensure we see any new tables. */
	smp_rmb();

	iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
	if (iter->walker->tbl) {
		iter->slot = 0;
		iter->skip = 0;
		return ERR_PTR(-EAGAIN);
	}

	iter->p = NULL;

out:

	return obj;
}
EXPORT_SYMBOL_GPL(rhashtable_walk_next);

/**
 * rhashtable_walk_stop - Finish a hash table walk
 * @iter:	Hash table iterator
 *
 * Finish a hash table walk.
 */
void rhashtable_walk_stop(struct rhashtable_iter *iter)
	__releases(RCU)
{
	struct rhashtable *ht;
	struct bucket_table *tbl = iter->walker->tbl;

	if (!tbl)
		goto out;

	ht = iter->ht;

	spin_lock(&ht->lock);
	if (tbl->rehash < tbl->size)
		list_add(&iter->walker->list, &tbl->walkers);
	else
		iter->walker->tbl = NULL;
	spin_unlock(&ht->lock);

	iter->p = NULL;

out:
	rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(rhashtable_walk_stop);

static size_t rounded_hashtable_size(const struct rhashtable_params *params)
{
	return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
		   (unsigned long)params->min_size);
}

static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
{
	return jhash2(key, length, seed);
}

/**
 * rhashtable_init - initialize a new hash table
 * @ht:		hash table to be initialized
 * @params:	configuration parameters
 *
 * Initializes a new hash table based on the provided configuration
 * parameters. A table can be configured either with a variable or
 * fixed length key:
 *
 * Configuration Example 1: Fixed length keys
 * struct test_obj {
 *	int			key;
 *	void *			my_member;
 *	struct rhash_head	node;
 * };
 *
 * struct rhashtable_params params = {
 *	.head_offset = offsetof(struct test_obj, node),
 *	.key_offset = offsetof(struct test_obj, key),
 *	.key_len = sizeof(int),
 *	.hashfn = jhash,
 *	.nulls_base = (1U << RHT_BASE_SHIFT),
 * };
 *
 * Configuration Example 2: Variable length keys
 * struct test_obj {
 *	[...]
 *	struct rhash_head	node;
 * };
 *
 * u32 my_hash_fn(const void *data, u32 seed)
 * {
 *	struct test_obj *obj = data;
 *
 *	return [... hash ...];
 * }
 *
 * struct rhashtable_params params = {
 *	.head_offset = offsetof(struct test_obj, node),
 *	.hashfn = jhash,
 *	.obj_hashfn = my_hash_fn,
 * };
 */
int rhashtable_init(struct rhashtable *ht,
		    const struct rhashtable_params *params)
{
	struct bucket_table *tbl;
	size_t size;

	size = HASH_DEFAULT_SIZE;

	if ((!params->key_len && !params->obj_hashfn) ||
	    (params->obj_hashfn && !params->obj_cmpfn))
		return -EINVAL;

	if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
		return -EINVAL;

	if (params->nelem_hint)
		size = rounded_hashtable_size(params);

	memset(ht, 0, sizeof(*ht));
	mutex_init(&ht->mutex);
	spin_lock_init(&ht->lock);
	memcpy(&ht->p, params, sizeof(*params));

	if (params->min_size)
		ht->p.min_size = roundup_pow_of_two(params->min_size);

	if (params->max_size)
		ht->p.max_size = rounddown_pow_of_two(params->max_size);

	ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);

	/* The maximum (not average) chain length grows with the
	 * size of the hash table, at a rate of (log N)/(log log N).
	 * The value of 16 is selected so that even if the hash
	 * table grew to 2^32 you would not expect the maximum
	 * chain length to exceed it unless we are under attack
	 * (or extremely unlucky).
	 *
	 * As this limit is only to detect attacks, we don't need
	 * to set it to a lower value as you'd need the chain
	 * length to vastly exceed 16 to have any real effect
	 * on the system.
	 */
	if (!params->insecure_elasticity)
		ht->elasticity = 16;

	if (params->locks_mul)
		ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
	else
		ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;

	ht->key_len = ht->p.key_len;
	if (!params->hashfn) {
		ht->p.hashfn = jhash;

		if (!(ht->key_len & (sizeof(u32) - 1))) {
			ht->key_len /= sizeof(u32);
			ht->p.hashfn = rhashtable_jhash2;
		}
	}

	tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
	if (tbl == NULL)
		return -ENOMEM;

	atomic_set(&ht->nelems, 0);

	RCU_INIT_POINTER(ht->tbl, tbl);

	INIT_WORK(&ht->run_work, rht_deferred_worker);

	return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_init);

/**
 * rhashtable_destroy - destroy hash table
 * @ht:		the hash table to destroy
 *
 * Frees the bucket array. This function is not rcu safe, therefore the caller
 * has to make sure that no resizing may happen by unpublishing the hashtable
 * and waiting for the quiescent cycle before releasing the bucket array.
 */
void rhashtable_destroy(struct rhashtable *ht)
{
	ht->being_destroyed = true;

	cancel_work_sync(&ht->run_work);

	mutex_lock(&ht->mutex);
	bucket_table_free(rht_dereference(ht->tbl, ht));
	mutex_unlock(&ht->mutex);
}
EXPORT_SYMBOL_GPL(rhashtable_destroy);