rhashtable.c 20.7 KB
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856
/*
 * 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/atomic.h>
#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>
#include <linux/export.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);

	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);

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

	if (rht_grow_above_75(ht, tbl))
		rhashtable_expand(ht);
	else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
		rhashtable_shrink(ht);

	err = rhashtable_rehash_table(ht);

	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 *tbl)
{
	struct bucket_table *old_tbl;
	struct bucket_table *new_tbl;
	unsigned int size;
	int err;

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

	size = tbl->size;

	err = -EBUSY;

	if (rht_grow_above_75(ht, tbl))
		size *= 2;
	/* Do not schedule more than one rehash */
	else if (old_tbl != tbl)
		goto fail;

	err = -ENOMEM;

	new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
	if (new_tbl == NULL)
		goto fail;

	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;

fail:
	/* Do not fail the insert if someone else did a rehash. */
	if (likely(rcu_dereference_raw(tbl->future_tbl)))
		return 0;

	/* Schedule async rehash to retry allocation in process context. */
	if (err == -ENOMEM)
		schedule_work(&ht->run_work);

	return err;
}
EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);

struct bucket_table *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 = -E2BIG;
	if (unlikely(rht_grow_above_max(ht, tbl)))
		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));

	if (err == 0)
		return NULL;
	else if (err == -EAGAIN)
		return tbl;
	else
		return ERR_PTR(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;

	spin_lock(&ht->lock);
	iter->walker->tbl =
		rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
	list_add(&iter->walker->list, &iter->walker->tbl->walkers);
	spin_unlock(&ht->lock);

	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)
{
	spin_lock(&iter->ht->lock);
	if (iter->walker->tbl)
		list_del(&iter->walker->list);
	spin_unlock(&iter->ht->lock);
	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;

	rcu_read_lock();

	spin_lock(&ht->lock);
	if (iter->walker->tbl)
		list_del(&iter->walker->list);
	spin_unlock(&ht->lock);

	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;

	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;
			return rht_obj(ht, p);
		}

		iter->skip = 0;
	}

	iter->p = NULL;

	/* 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);
	}

	return NULL;
}
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 len, 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;

	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);

	if (params->insecure_max_entries)
		ht->p.insecure_max_entries =
			rounddown_pow_of_two(params->insecure_max_entries);
	else
		ht->p.insecure_max_entries = ht->p.max_size * 2;

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

	if (params->nelem_hint)
		size = rounded_hashtable_size(&ht->p);

	/* 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_free_and_destroy - free elements and destroy hash table
 * @ht:		the hash table to destroy
 * @free_fn:	callback to release resources of element
 * @arg:	pointer passed to free_fn
 *
 * Stops an eventual async resize. If defined, invokes free_fn for each
 * element to releasal resources. Please note that RCU protected
 * readers may still be accessing the elements. Releasing of resources
 * must occur in a compatible manner. Then frees the bucket array.
 *
 * This function will eventually sleep to wait for an async resize
 * to complete. The caller is responsible that no further write operations
 * occurs in parallel.
 */
void rhashtable_free_and_destroy(struct rhashtable *ht,
				 void (*free_fn)(void *ptr, void *arg),
				 void *arg)
{
	const struct bucket_table *tbl;
	unsigned int i;

	cancel_work_sync(&ht->run_work);

	mutex_lock(&ht->mutex);
	tbl = rht_dereference(ht->tbl, ht);
	if (free_fn) {
		for (i = 0; i < tbl->size; i++) {
			struct rhash_head *pos, *next;

			for (pos = rht_dereference(tbl->buckets[i], ht),
			     next = !rht_is_a_nulls(pos) ?
					rht_dereference(pos->next, ht) : NULL;
			     !rht_is_a_nulls(pos);
			     pos = next,
			     next = !rht_is_a_nulls(pos) ?
					rht_dereference(pos->next, ht) : NULL)
				free_fn(rht_obj(ht, pos), arg);
		}
	}

	bucket_table_free(tbl);
	mutex_unlock(&ht->mutex);
}
EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);

void rhashtable_destroy(struct rhashtable *ht)
{
	return rhashtable_free_and_destroy(ht, NULL, NULL);
}
EXPORT_SYMBOL_GPL(rhashtable_destroy);