lib/rhashtable.c

   1 /*
   2  * Resizable, Scalable, Concurrent Hash Table
   3  *
   4  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
   5  * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
   6  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
   7  *
   8  * Code partially derived from nft_hash
   9  * Rewritten with rehash code from br_multicast plus single list
  10  * pointer as suggested by Josh Triplett
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License version 2 as
  14  * published by the Free Software Foundation.
  15  */
  16
  17 #include <linux/kernel.h>
  18 #include <linux/init.h>
  19 #include <linux/log2.h>
  20 #include <linux/sched.h>
  21 #include <linux/slab.h>
  22 #include <linux/vmalloc.h>
  23 #include <linux/mm.h>
  24 #include <linux/jhash.h>
  25 #include <linux/random.h>
  26 #include <linux/rhashtable.h>
  27 #include <linux/err.h>
  28
  29 #define HASH_DEFAULT_SIZE       64UL
  30 #define HASH_MIN_SIZE           4U
  31 #define BUCKET_LOCKS_PER_CPU   128UL
  32
  33 static u32 head_hashfn(struct rhashtable *ht,
  34                        const struct bucket_table *tbl,
  35                        const struct rhash_head *he)
  36 {
  37         return rht_head_hashfn(ht, tbl, he, ht->p);
  38 }
  39
  40 #ifdef CONFIG_PROVE_LOCKING
  41 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
  42
  43 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
  44 {
  45         return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
  46 }
  47 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
  48
  49 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
  50 {
  51         spinlock_t *lock = rht_bucket_lock(tbl, hash);
  52
  53         return (debug_locks) ? lockdep_is_held(lock) : 1;
  54 }
  55 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
  56 #else
  57 #define ASSERT_RHT_MUTEX(HT)
  58 #endif
  59
  60
  61 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
  62                               gfp_t gfp)
  63 {
  64         unsigned int i, size;
  65 #if defined(CONFIG_PROVE_LOCKING)
  66         unsigned int nr_pcpus = 2;
  67 #else
  68         unsigned int nr_pcpus = num_possible_cpus();
  69 #endif
  70
  71         nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
  72         size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
  73
  74         /* Never allocate more than 0.5 locks per bucket */
  75         size = min_t(unsigned int, size, tbl->size >> 1);
  76
  77         if (sizeof(spinlock_t) != 0) {
  78 #ifdef CONFIG_NUMA
  79                 if (size * sizeof(spinlock_t) > PAGE_SIZE &&
  80                     gfp == GFP_KERNEL)
  81                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
  82                 else
  83 #endif
  84                 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
  85                                            gfp);
  86                 if (!tbl->locks)
  87                         return -ENOMEM;
  88                 for (i = 0; i < size; i++)
  89                         spin_lock_init(&tbl->locks[i]);
  90         }
  91         tbl->locks_mask = size - 1;
  92
  93         return 0;
  94 }
  95
  96 static void bucket_table_free(const struct bucket_table *tbl)
  97 {
  98         if (tbl)
  99                 kvfree(tbl->locks);
 100
 101         kvfree(tbl);
 102 }
 103
 104 static void bucket_table_free_rcu(struct rcu_head *head)
 105 {
 106         bucket_table_free(container_of(head, struct bucket_table, rcu));
 107 }
 108
 109 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 110                                                size_t nbuckets,
 111                                                gfp_t gfp)
 112 {
 113         struct bucket_table *tbl = NULL;
 114         size_t size;
 115         int i;
 116
 117         size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
 118         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
 119             gfp != GFP_KERNEL)
 120                 tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
 121         if (tbl == NULL && gfp == GFP_KERNEL)
 122                 tbl = vzalloc(size);
 123         if (tbl == NULL)
 124                 return NULL;
 125
 126         tbl->size = nbuckets;
 127
 128         if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
 129                 bucket_table_free(tbl);
 130                 return NULL;
 131         }
 132
 133         INIT_LIST_HEAD(&tbl->walkers);
 134
 135         get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
 136
 137         for (i = 0; i < nbuckets; i++)
 138                 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
 139
 140         return tbl;
 141 }
 142
 143 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
 144                                                   struct bucket_table *tbl)
 145 {
 146         struct bucket_table *new_tbl;
 147
 148         do {
 149                 new_tbl = tbl;
 150                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 151         } while (tbl);
 152
 153         return new_tbl;
 154 }
 155
 156 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned old_hash)
 157 {
 158         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 159         struct bucket_table *new_tbl = rhashtable_last_table(ht,
 160                 rht_dereference_rcu(old_tbl->future_tbl, ht));
 161         struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
 162         int err = -ENOENT;
 163         struct rhash_head *head, *next, *entry;
 164         spinlock_t *new_bucket_lock;
 165         unsigned new_hash;
 166
 167         rht_for_each(entry, old_tbl, old_hash) {
 168                 err = 0;
 169                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
 170
 171                 if (rht_is_a_nulls(next))
 172                         break;
 173
 174                 pprev = &entry->next;
 175         }
 176
 177         if (err)
 178                 goto out;
 179
 180         new_hash = head_hashfn(ht, new_tbl, entry);
 181
 182         new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
 183
 184         spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
 185         head = rht_dereference_bucket(new_tbl->buckets[new_hash],
 186                                       new_tbl, new_hash);
 187
 188         if (rht_is_a_nulls(head))
 189                 INIT_RHT_NULLS_HEAD(entry->next, ht, new_hash);
 190         else
 191                 RCU_INIT_POINTER(entry->next, head);
 192
 193         rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
 194         spin_unlock(new_bucket_lock);
 195
 196         rcu_assign_pointer(*pprev, next);
 197
 198 out:
 199         return err;
 200 }
 201
 202 static void rhashtable_rehash_chain(struct rhashtable *ht, unsigned old_hash)
 203 {
 204         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 205         spinlock_t *old_bucket_lock;
 206
 207         old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
 208
 209         spin_lock_bh(old_bucket_lock);
 210         while (!rhashtable_rehash_one(ht, old_hash))
 211                 ;
 212         old_tbl->rehash++;
 213         spin_unlock_bh(old_bucket_lock);
 214 }
 215
 216 static int rhashtable_rehash_attach(struct rhashtable *ht,
 217                                     struct bucket_table *old_tbl,
 218                                     struct bucket_table *new_tbl)
 219 {
 220         /* Protect future_tbl using the first bucket lock. */
 221         spin_lock_bh(old_tbl->locks);
 222
 223         /* Did somebody beat us to it? */
 224         if (rcu_access_pointer(old_tbl->future_tbl)) {
 225                 spin_unlock_bh(old_tbl->locks);
 226                 return -EEXIST;
 227         }
 228
 229         /* Make insertions go into the new, empty table right away. Deletions
 230          * and lookups will be attempted in both tables until we synchronize.
 231          */
 232         rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
 233
 234         /* Ensure the new table is visible to readers. */
 235         smp_wmb();
 236
 237         spin_unlock_bh(old_tbl->locks);
 238
 239         return 0;
 240 }
 241
 242 static int rhashtable_rehash_table(struct rhashtable *ht)
 243 {
 244         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 245         struct bucket_table *new_tbl;
 246         struct rhashtable_walker *walker;
 247         unsigned old_hash;
 248
 249         new_tbl = rht_dereference(old_tbl->future_tbl, ht);
 250         if (!new_tbl)
 251                 return 0;
 252
 253         for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
 254                 rhashtable_rehash_chain(ht, old_hash);
 255
 256         /* Publish the new table pointer. */
 257         rcu_assign_pointer(ht->tbl, new_tbl);
 258
 259         list_for_each_entry(walker, &old_tbl->walkers, list)
 260                 walker->tbl = NULL;
 261
 262         /* Wait for readers. All new readers will see the new
 263          * table, and thus no references to the old table will
 264          * remain.
 265          */
 266         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
 267
 268         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 269 }
 270
 271 /**
 272  * rhashtable_expand - Expand hash table while allowing concurrent lookups
 273  * @ht:         the hash table to expand
 274  *
 275  * A secondary bucket array is allocated and the hash entries are migrated.
 276  *
 277  * This function may only be called in a context where it is safe to call
 278  * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 279  *
 280  * The caller must ensure that no concurrent resizing occurs by holding
 281  * ht->mutex.
 282  *
 283  * It is valid to have concurrent insertions and deletions protected by per
 284  * bucket locks or concurrent RCU protected lookups and traversals.
 285  */
 286 static int rhashtable_expand(struct rhashtable *ht)
 287 {
 288         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 289         int err;
 290
 291         ASSERT_RHT_MUTEX(ht);
 292
 293         old_tbl = rhashtable_last_table(ht, old_tbl);
 294
 295         new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
 296         if (new_tbl == NULL)
 297                 return -ENOMEM;
 298
 299         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 300         if (err)
 301                 bucket_table_free(new_tbl);
 302
 303         return err;
 304 }
 305
 306 /**
 307  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 308  * @ht:         the hash table to shrink
 309  *
 310  * This function shrinks the hash table to fit, i.e., the smallest
 311  * size would not cause it to expand right away automatically.
 312  *
 313  * The caller must ensure that no concurrent resizing occurs by holding
 314  * ht->mutex.
 315  *
 316  * The caller must ensure that no concurrent table mutations take place.
 317  * It is however valid to have concurrent lookups if they are RCU protected.
 318  *
 319  * It is valid to have concurrent insertions and deletions protected by per
 320  * bucket locks or concurrent RCU protected lookups and traversals.
 321  */
 322 static int rhashtable_shrink(struct rhashtable *ht)
 323 {
 324         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 325         unsigned size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2);
 326         int err;
 327
 328         ASSERT_RHT_MUTEX(ht);
 329
 330         if (size < ht->p.min_size)
 331                 size = ht->p.min_size;
 332
 333         if (old_tbl->size <= size)
 334                 return 0;
 335
 336         if (rht_dereference(old_tbl->future_tbl, ht))
 337                 return -EEXIST;
 338
 339         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 340         if (new_tbl == NULL)
 341                 return -ENOMEM;
 342
 343         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 344         if (err)
 345                 bucket_table_free(new_tbl);
 346
 347         return err;
 348 }
 349
 350 static void rht_deferred_worker(struct work_struct *work)
 351 {
 352         struct rhashtable *ht;
 353         struct bucket_table *tbl;
 354         int err = 0;
 355
 356         ht = container_of(work, struct rhashtable, run_work);
 357         mutex_lock(&ht->mutex);
 358         if (ht->being_destroyed)
 359                 goto unlock;
 360
 361         tbl = rht_dereference(ht->tbl, ht);
 362         tbl = rhashtable_last_table(ht, tbl);
 363
 364         if (rht_grow_above_75(ht, tbl))
 365                 rhashtable_expand(ht);
 366         else if (rht_shrink_below_30(ht, tbl))
 367                 rhashtable_shrink(ht);
 368
 369         err = rhashtable_rehash_table(ht);
 370
 371 unlock:
 372         mutex_unlock(&ht->mutex);
 373
 374         if (err)
 375                 schedule_work(&ht->run_work);
 376 }
 377
 378 int rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 379                            struct rhash_head *obj,
 380                            struct bucket_table *tbl)
 381 {
 382         struct rhash_head *head;
 383         unsigned hash;
 384         int err = -EEXIST;
 385
 386         tbl = rhashtable_last_table(ht, tbl);
 387         hash = head_hashfn(ht, tbl, obj);
 388         spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
 389
 390         if (key && rhashtable_lookup_fast(ht, key, ht->p))
 391                 goto exit;
 392
 393         err = 0;
 394
 395         head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
 396
 397         RCU_INIT_POINTER(obj->next, head);
 398
 399         rcu_assign_pointer(tbl->buckets[hash], obj);
 400
 401         atomic_inc(&ht->nelems);
 402
 403 exit:
 404         spin_unlock(rht_bucket_lock(tbl, hash));
 405
 406         return err;
 407 }
 408 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
 409
 410 /**
 411  * rhashtable_walk_init - Initialise an iterator
 412  * @ht:         Table to walk over
 413  * @iter:       Hash table Iterator
 414  *
 415  * This function prepares a hash table walk.
 416  *
 417  * Note that if you restart a walk after rhashtable_walk_stop you
 418  * may see the same object twice.  Also, you may miss objects if
 419  * there are removals in between rhashtable_walk_stop and the next
 420  * call to rhashtable_walk_start.
 421  *
 422  * For a completely stable walk you should construct your own data
 423  * structure outside the hash table.
 424  *
 425  * This function may sleep so you must not call it from interrupt
 426  * context or with spin locks held.
 427  *
 428  * You must call rhashtable_walk_exit if this function returns
 429  * successfully.
 430  */
 431 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
 432 {
 433         iter->ht = ht;
 434         iter->p = NULL;
 435         iter->slot = 0;
 436         iter->skip = 0;
 437
 438         iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
 439         if (!iter->walker)
 440                 return -ENOMEM;
 441
 442         mutex_lock(&ht->mutex);
 443         iter->walker->tbl = rht_dereference(ht->tbl, ht);
 444         list_add(&iter->walker->list, &iter->walker->tbl->walkers);
 445         mutex_unlock(&ht->mutex);
 446
 447         return 0;
 448 }
 449 EXPORT_SYMBOL_GPL(rhashtable_walk_init);
 450
 451 /**
 452  * rhashtable_walk_exit - Free an iterator
 453  * @iter:       Hash table Iterator
 454  *
 455  * This function frees resources allocated by rhashtable_walk_init.
 456  */
 457 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 458 {
 459         mutex_lock(&iter->ht->mutex);
 460         if (iter->walker->tbl)
 461                 list_del(&iter->walker->list);
 462         mutex_unlock(&iter->ht->mutex);
 463         kfree(iter->walker);
 464 }
 465 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
 466
 467 /**
 468  * rhashtable_walk_start - Start a hash table walk
 469  * @iter:       Hash table iterator
 470  *
 471  * Start a hash table walk.  Note that we take the RCU lock in all
 472  * cases including when we return an error.  So you must always call
 473  * rhashtable_walk_stop to clean up.
 474  *
 475  * Returns zero if successful.
 476  *
 477  * Returns -EAGAIN if resize event occured.  Note that the iterator
 478  * will rewind back to the beginning and you may use it immediately
 479  * by calling rhashtable_walk_next.
 480  */
 481 int rhashtable_walk_start(struct rhashtable_iter *iter)
 482         __acquires(RCU)
 483 {
 484         struct rhashtable *ht = iter->ht;
 485
 486         mutex_lock(&ht->mutex);
 487
 488         if (iter->walker->tbl)
 489                 list_del(&iter->walker->list);
 490
 491         rcu_read_lock();
 492
 493         mutex_unlock(&ht->mutex);
 494
 495         if (!iter->walker->tbl) {
 496                 iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
 497                 return -EAGAIN;
 498         }
 499
 500         return 0;
 501 }
 502 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
 503
 504 /**
 505  * rhashtable_walk_next - Return the next object and advance the iterator
 506  * @iter:       Hash table iterator
 507  *
 508  * Note that you must call rhashtable_walk_stop when you are finished
 509  * with the walk.
 510  *
 511  * Returns the next object or NULL when the end of the table is reached.
 512  *
 513  * Returns -EAGAIN if resize event occured.  Note that the iterator
 514  * will rewind back to the beginning and you may continue to use it.
 515  */
 516 void *rhashtable_walk_next(struct rhashtable_iter *iter)
 517 {
 518         struct bucket_table *tbl = iter->walker->tbl;
 519         struct rhashtable *ht = iter->ht;
 520         struct rhash_head *p = iter->p;
 521         void *obj = NULL;
 522
 523         if (p) {
 524                 p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
 525                 goto next;
 526         }
 527
 528         for (; iter->slot < tbl->size; iter->slot++) {
 529                 int skip = iter->skip;
 530
 531                 rht_for_each_rcu(p, tbl, iter->slot) {
 532                         if (!skip)
 533                                 break;
 534                         skip--;
 535                 }
 536
 537 next:
 538                 if (!rht_is_a_nulls(p)) {
 539                         iter->skip++;
 540                         iter->p = p;
 541                         obj = rht_obj(ht, p);
 542                         goto out;
 543                 }
 544
 545                 iter->skip = 0;
 546         }
 547
 548         /* Ensure we see any new tables. */
 549         smp_rmb();
 550
 551         iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 552         if (iter->walker->tbl) {
 553                 iter->slot = 0;
 554                 iter->skip = 0;
 555                 return ERR_PTR(-EAGAIN);
 556         }
 557
 558         iter->p = NULL;
 559
 560 out:
 561
 562         return obj;
 563 }
 564 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 565
 566 /**
 567  * rhashtable_walk_stop - Finish a hash table walk
 568  * @iter:       Hash table iterator
 569  *
 570  * Finish a hash table walk.
 571  */
 572 void rhashtable_walk_stop(struct rhashtable_iter *iter)
 573         __releases(RCU)
 574 {
 575         struct rhashtable *ht;
 576         struct bucket_table *tbl = iter->walker->tbl;
 577
 578         if (!tbl)
 579                 goto out;
 580
 581         ht = iter->ht;
 582
 583         mutex_lock(&ht->mutex);
 584         if (tbl->rehash < tbl->size)
 585                 list_add(&iter->walker->list, &tbl->walkers);
 586         else
 587                 iter->walker->tbl = NULL;
 588         mutex_unlock(&ht->mutex);
 589
 590         iter->p = NULL;
 591
 592 out:
 593         rcu_read_unlock();
 594 }
 595 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
 596
 597 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 598 {
 599         return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
 600                    (unsigned long)params->min_size);
 601 }
 602
 603 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
 604 {
 605         return jhash2(key, length, seed);
 606 }
 607
 608 /**
 609  * rhashtable_init - initialize a new hash table
 610  * @ht:         hash table to be initialized
 611  * @params:     configuration parameters
 612  *
 613  * Initializes a new hash table based on the provided configuration
 614  * parameters. A table can be configured either with a variable or
 615  * fixed length key:
 616  *
 617  * Configuration Example 1: Fixed length keys
 618  * struct test_obj {
 619  *      int                     key;
 620  *      void *                  my_member;
 621  *      struct rhash_head       node;
 622  * };
 623  *
 624  * struct rhashtable_params params = {
 625  *      .head_offset = offsetof(struct test_obj, node),
 626  *      .key_offset = offsetof(struct test_obj, key),
 627  *      .key_len = sizeof(int),
 628  *      .hashfn = jhash,
 629  *      .nulls_base = (1U << RHT_BASE_SHIFT),
 630  * };
 631  *
 632  * Configuration Example 2: Variable length keys
 633  * struct test_obj {
 634  *      [...]
 635  *      struct rhash_head       node;
 636  * };
 637  *
 638  * u32 my_hash_fn(const void *data, u32 seed)
 639  * {
 640  *      struct test_obj *obj = data;
 641  *
 642  *      return [... hash ...];
 643  * }
 644  *
 645  * struct rhashtable_params params = {
 646  *      .head_offset = offsetof(struct test_obj, node),
 647  *      .hashfn = jhash,
 648  *      .obj_hashfn = my_hash_fn,
 649  * };
 650  */
 651 int rhashtable_init(struct rhashtable *ht,
 652                     const struct rhashtable_params *params)
 653 {
 654         struct bucket_table *tbl;
 655         size_t size;
 656
 657         size = HASH_DEFAULT_SIZE;
 658
 659         if ((!params->key_len && !params->obj_hashfn) ||
 660             (params->obj_hashfn && !params->obj_cmpfn))
 661                 return -EINVAL;
 662
 663         if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
 664                 return -EINVAL;
 665
 666         if (params->nelem_hint)
 667                 size = rounded_hashtable_size(params);
 668
 669         memset(ht, 0, sizeof(*ht));
 670         mutex_init(&ht->mutex);
 671         memcpy(&ht->p, params, sizeof(*params));
 672
 673         if (params->min_size)
 674                 ht->p.min_size = roundup_pow_of_two(params->min_size);
 675
 676         if (params->max_size)
 677                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
 678
 679         ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
 680
 681         if (params->locks_mul)
 682                 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
 683         else
 684                 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
 685
 686         ht->key_len = ht->p.key_len;
 687         if (!params->hashfn) {
 688                 ht->p.hashfn = jhash;
 689
 690                 if (!(ht->key_len & (sizeof(u32) - 1))) {
 691                         ht->key_len /= sizeof(u32);
 692                         ht->p.hashfn = rhashtable_jhash2;
 693                 }
 694         }
 695
 696         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 697         if (tbl == NULL)
 698                 return -ENOMEM;
 699
 700         atomic_set(&ht->nelems, 0);
 701
 702         RCU_INIT_POINTER(ht->tbl, tbl);
 703
 704         INIT_WORK(&ht->run_work, rht_deferred_worker);
 705
 706         return 0;
 707 }
 708 EXPORT_SYMBOL_GPL(rhashtable_init);
 709
 710 /**
 711  * rhashtable_destroy - destroy hash table
 712  * @ht:         the hash table to destroy
 713  *
 714  * Frees the bucket array. This function is not rcu safe, therefore the caller
 715  * has to make sure that no resizing may happen by unpublishing the hashtable
 716  * and waiting for the quiescent cycle before releasing the bucket array.
 717  */
 718 void rhashtable_destroy(struct rhashtable *ht)
 719 {
 720         ht->being_destroyed = true;
 721
 722         cancel_work_sync(&ht->run_work);
 723
 724         mutex_lock(&ht->mutex);
 725         bucket_table_free(rht_dereference(ht->tbl, ht));
 726         mutex_unlock(&ht->mutex);
 727 }
 728 EXPORT_SYMBOL_GPL(rhashtable_destroy);