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/atomic.h>
  18 #include <linux/kernel.h>
  19 #include <linux/init.h>
  20 #include <linux/log2.h>
  21 #include <linux/sched.h>
  22 #include <linux/slab.h>
  23 #include <linux/vmalloc.h>
  24 #include <linux/mm.h>
  25 #include <linux/jhash.h>
  26 #include <linux/random.h>
  27 #include <linux/rhashtable.h>
  28 #include <linux/err.h>
  29 #include <linux/export.h>
  30
  31 #define HASH_DEFAULT_SIZE       64UL
  32 #define HASH_MIN_SIZE           4U
  33 #define BUCKET_LOCKS_PER_CPU   128UL
  34
  35 static u32 head_hashfn(struct rhashtable *ht,
  36                        const struct bucket_table *tbl,
  37                        const struct rhash_head *he)
  38 {
  39         return rht_head_hashfn(ht, tbl, he, ht->p);
  40 }
  41
  42 #ifdef CONFIG_PROVE_LOCKING
  43 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
  44
  45 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
  46 {
  47         return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
  48 }
  49 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
  50
  51 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
  52 {
  53         spinlock_t *lock = rht_bucket_lock(tbl, hash);
  54
  55         return (debug_locks) ? lockdep_is_held(lock) : 1;
  56 }
  57 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
  58 #else
  59 #define ASSERT_RHT_MUTEX(HT)
  60 #endif
  61
  62
  63 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
  64                               gfp_t gfp)
  65 {
  66         unsigned int i, size;
  67 #if defined(CONFIG_PROVE_LOCKING)
  68         unsigned int nr_pcpus = 2;
  69 #else
  70         unsigned int nr_pcpus = num_possible_cpus();
  71 #endif
  72
  73         nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
  74         size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
  75
  76         /* Never allocate more than 0.5 locks per bucket */
  77         size = min_t(unsigned int, size, tbl->size >> 1);
  78
  79         if (sizeof(spinlock_t) != 0) {
  80 #ifdef CONFIG_NUMA
  81                 if (size * sizeof(spinlock_t) > PAGE_SIZE &&
  82                     gfp == GFP_KERNEL)
  83                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
  84                 else
  85 #endif
  86                 tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
  87                                            gfp);
  88                 if (!tbl->locks)
  89                         return -ENOMEM;
  90                 for (i = 0; i < size; i++)
  91                         spin_lock_init(&tbl->locks[i]);
  92         }
  93         tbl->locks_mask = size - 1;
  94
  95         return 0;
  96 }
  97
  98 static void bucket_table_free(const struct bucket_table *tbl)
  99 {
 100         if (tbl)
 101                 kvfree(tbl->locks);
 102
 103         kvfree(tbl);
 104 }
 105
 106 static void bucket_table_free_rcu(struct rcu_head *head)
 107 {
 108         bucket_table_free(container_of(head, struct bucket_table, rcu));
 109 }
 110
 111 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 112                                                size_t nbuckets,
 113                                                gfp_t gfp)
 114 {
 115         struct bucket_table *tbl = NULL;
 116         size_t size;
 117         int i;
 118
 119         size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
 120         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
 121             gfp != GFP_KERNEL)
 122                 tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
 123         if (tbl == NULL)
 124                 tbl = __vmalloc(size, gfp | __GFP_HIGHMEM | __GFP_ZERO,
 125                                 PAGE_KERNEL);
 126         if (tbl == NULL)
 127                 return NULL;
 128
 129         tbl->size = nbuckets;
 130
 131         if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
 132                 bucket_table_free(tbl);
 133                 return NULL;
 134         }
 135
 136         INIT_LIST_HEAD(&tbl->walkers);
 137
 138         get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
 139
 140         for (i = 0; i < nbuckets; i++)
 141                 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
 142
 143         return tbl;
 144 }
 145
 146 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
 147                                                   struct bucket_table *tbl)
 148 {
 149         struct bucket_table *new_tbl;
 150
 151         do {
 152                 new_tbl = tbl;
 153                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 154         } while (tbl);
 155
 156         return new_tbl;
 157 }
 158
 159 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
 160 {
 161         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 162         struct bucket_table *new_tbl = rhashtable_last_table(ht,
 163                 rht_dereference_rcu(old_tbl->future_tbl, ht));
 164         struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
 165         int err = -ENOENT;
 166         struct rhash_head *head, *next, *entry;
 167         spinlock_t *new_bucket_lock;
 168         unsigned int new_hash;
 169
 170         rht_for_each(entry, old_tbl, old_hash) {
 171                 err = 0;
 172                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
 173
 174                 if (rht_is_a_nulls(next))
 175                         break;
 176
 177                 pprev = &entry->next;
 178         }
 179
 180         if (err)
 181                 goto out;
 182
 183         new_hash = head_hashfn(ht, new_tbl, entry);
 184
 185         new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
 186
 187         spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
 188         head = rht_dereference_bucket(new_tbl->buckets[new_hash],
 189                                       new_tbl, new_hash);
 190
 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,
 203                                     unsigned int old_hash)
 204 {
 205         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 206         spinlock_t *old_bucket_lock;
 207
 208         old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
 209
 210         spin_lock_bh(old_bucket_lock);
 211         while (!rhashtable_rehash_one(ht, old_hash))
 212                 ;
 213         old_tbl->rehash++;
 214         spin_unlock_bh(old_bucket_lock);
 215 }
 216
 217 static int rhashtable_rehash_attach(struct rhashtable *ht,
 218                                     struct bucket_table *old_tbl,
 219                                     struct bucket_table *new_tbl)
 220 {
 221         /* Protect future_tbl using the first bucket lock. */
 222         spin_lock_bh(old_tbl->locks);
 223
 224         /* Did somebody beat us to it? */
 225         if (rcu_access_pointer(old_tbl->future_tbl)) {
 226                 spin_unlock_bh(old_tbl->locks);
 227                 return -EEXIST;
 228         }
 229
 230         /* Make insertions go into the new, empty table right away. Deletions
 231          * and lookups will be attempted in both tables until we synchronize.
 232          */
 233         rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
 234
 235         /* Ensure the new table is visible to readers. */
 236         smp_wmb();
 237
 238         spin_unlock_bh(old_tbl->locks);
 239
 240         return 0;
 241 }
 242
 243 static int rhashtable_rehash_table(struct rhashtable *ht)
 244 {
 245         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 246         struct bucket_table *new_tbl;
 247         struct rhashtable_walker *walker;
 248         unsigned int old_hash;
 249
 250         new_tbl = rht_dereference(old_tbl->future_tbl, ht);
 251         if (!new_tbl)
 252                 return 0;
 253
 254         for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
 255                 rhashtable_rehash_chain(ht, old_hash);
 256
 257         /* Publish the new table pointer. */
 258         rcu_assign_pointer(ht->tbl, new_tbl);
 259
 260         spin_lock(&ht->lock);
 261         list_for_each_entry(walker, &old_tbl->walkers, list)
 262                 walker->tbl = NULL;
 263         spin_unlock(&ht->lock);
 264
 265         /* Wait for readers. All new readers will see the new
 266          * table, and thus no references to the old table will
 267          * remain.
 268          */
 269         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
 270
 271         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 272 }
 273
 274 /**
 275  * rhashtable_expand - Expand hash table while allowing concurrent lookups
 276  * @ht:         the hash table to expand
 277  *
 278  * A secondary bucket array is allocated and the hash entries are migrated.
 279  *
 280  * This function may only be called in a context where it is safe to call
 281  * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 282  *
 283  * The caller must ensure that no concurrent resizing occurs by holding
 284  * ht->mutex.
 285  *
 286  * It is valid to have concurrent insertions and deletions protected by per
 287  * bucket locks or concurrent RCU protected lookups and traversals.
 288  */
 289 static int rhashtable_expand(struct rhashtable *ht)
 290 {
 291         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 292         int err;
 293
 294         ASSERT_RHT_MUTEX(ht);
 295
 296         old_tbl = rhashtable_last_table(ht, old_tbl);
 297
 298         new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
 299         if (new_tbl == NULL)
 300                 return -ENOMEM;
 301
 302         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 303         if (err)
 304                 bucket_table_free(new_tbl);
 305
 306         return err;
 307 }
 308
 309 /**
 310  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 311  * @ht:         the hash table to shrink
 312  *
 313  * This function shrinks the hash table to fit, i.e., the smallest
 314  * size would not cause it to expand right away automatically.
 315  *
 316  * The caller must ensure that no concurrent resizing occurs by holding
 317  * ht->mutex.
 318  *
 319  * The caller must ensure that no concurrent table mutations take place.
 320  * It is however valid to have concurrent lookups if they are RCU protected.
 321  *
 322  * It is valid to have concurrent insertions and deletions protected by per
 323  * bucket locks or concurrent RCU protected lookups and traversals.
 324  */
 325 static int rhashtable_shrink(struct rhashtable *ht)
 326 {
 327         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 328         unsigned int size;
 329         int err;
 330
 331         ASSERT_RHT_MUTEX(ht);
 332
 333         size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2);
 334         if (size < ht->p.min_size)
 335                 size = ht->p.min_size;
 336
 337         if (old_tbl->size <= size)
 338                 return 0;
 339
 340         if (rht_dereference(old_tbl->future_tbl, ht))
 341                 return -EEXIST;
 342
 343         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 344         if (new_tbl == NULL)
 345                 return -ENOMEM;
 346
 347         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 348         if (err)
 349                 bucket_table_free(new_tbl);
 350
 351         return err;
 352 }
 353
 354 static void rht_deferred_worker(struct work_struct *work)
 355 {
 356         struct rhashtable *ht;
 357         struct bucket_table *tbl;
 358         int err = 0;
 359
 360         ht = container_of(work, struct rhashtable, run_work);
 361         mutex_lock(&ht->mutex);
 362
 363         tbl = rht_dereference(ht->tbl, ht);
 364         tbl = rhashtable_last_table(ht, tbl);
 365
 366         if (rht_grow_above_75(ht, tbl))
 367                 rhashtable_expand(ht);
 368         else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
 369                 rhashtable_shrink(ht);
 370
 371         err = rhashtable_rehash_table(ht);
 372
 373         mutex_unlock(&ht->mutex);
 374
 375         if (err)
 376                 schedule_work(&ht->run_work);
 377 }
 378
 379 static bool rhashtable_check_elasticity(struct rhashtable *ht,
 380                                         struct bucket_table *tbl,
 381                                         unsigned int hash)
 382 {
 383         unsigned int elasticity = ht->elasticity;
 384         struct rhash_head *head;
 385
 386         rht_for_each(head, tbl, hash)
 387                 if (!--elasticity)
 388                         return true;
 389
 390         return false;
 391 }
 392
 393 int rhashtable_insert_rehash(struct rhashtable *ht,
 394                              struct bucket_table *tbl)
 395 {
 396         struct bucket_table *old_tbl;
 397         struct bucket_table *new_tbl;
 398         unsigned int size;
 399         int err;
 400
 401         old_tbl = rht_dereference_rcu(ht->tbl, ht);
 402
 403         size = tbl->size;
 404
 405         err = -EBUSY;
 406
 407         if (rht_grow_above_75(ht, tbl))
 408                 size *= 2;
 409         /* Do not schedule more than one rehash */
 410         else if (old_tbl != tbl)
 411                 goto fail;
 412
 413         err = -ENOMEM;
 414
 415         new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
 416         if (new_tbl == NULL)
 417                 goto fail;
 418
 419         err = rhashtable_rehash_attach(ht, tbl, new_tbl);
 420         if (err) {
 421                 bucket_table_free(new_tbl);
 422                 if (err == -EEXIST)
 423                         err = 0;
 424         } else
 425                 schedule_work(&ht->run_work);
 426
 427         return err;
 428
 429 fail:
 430         /* Do not fail the insert if someone else did a rehash. */
 431         if (likely(rcu_dereference_raw(tbl->future_tbl)))
 432                 return 0;
 433
 434         /* Schedule async rehash to retry allocation in process context. */
 435         if (err == -ENOMEM)
 436                 schedule_work(&ht->run_work);
 437
 438         return err;
 439 }
 440 EXPORT_SYMBOL_GPL(rhashtable_insert_rehash);
 441
 442 struct bucket_table *rhashtable_insert_slow(struct rhashtable *ht,
 443                                             const void *key,
 444                                             struct rhash_head *obj,
 445                                             struct bucket_table *tbl)
 446 {
 447         struct rhash_head *head;
 448         unsigned int hash;
 449         int err;
 450
 451         tbl = rhashtable_last_table(ht, tbl);
 452         hash = head_hashfn(ht, tbl, obj);
 453         spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING);
 454
 455         err = -EEXIST;
 456         if (key && rhashtable_lookup_fast(ht, key, ht->p))
 457                 goto exit;
 458
 459         err = -E2BIG;
 460         if (unlikely(rht_grow_above_max(ht, tbl)))
 461                 goto exit;
 462
 463         err = -EAGAIN;
 464         if (rhashtable_check_elasticity(ht, tbl, hash) ||
 465             rht_grow_above_100(ht, tbl))
 466                 goto exit;
 467
 468         err = 0;
 469
 470         head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
 471
 472         RCU_INIT_POINTER(obj->next, head);
 473
 474         rcu_assign_pointer(tbl->buckets[hash], obj);
 475
 476         atomic_inc(&ht->nelems);
 477
 478 exit:
 479         spin_unlock(rht_bucket_lock(tbl, hash));
 480
 481         if (err == 0)
 482                 return NULL;
 483         else if (err == -EAGAIN)
 484                 return tbl;
 485         else
 486                 return ERR_PTR(err);
 487 }
 488 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
 489
 490 /**
 491  * rhashtable_walk_init - Initialise an iterator
 492  * @ht:         Table to walk over
 493  * @iter:       Hash table Iterator
 494  *
 495  * This function prepares a hash table walk.
 496  *
 497  * Note that if you restart a walk after rhashtable_walk_stop you
 498  * may see the same object twice.  Also, you may miss objects if
 499  * there are removals in between rhashtable_walk_stop and the next
 500  * call to rhashtable_walk_start.
 501  *
 502  * For a completely stable walk you should construct your own data
 503  * structure outside the hash table.
 504  *
 505  * This function may sleep so you must not call it from interrupt
 506  * context or with spin locks held.
 507  *
 508  * You must call rhashtable_walk_exit if this function returns
 509  * successfully.
 510  */
 511 int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter)
 512 {
 513         iter->ht = ht;
 514         iter->p = NULL;
 515         iter->slot = 0;
 516         iter->skip = 0;
 517
 518         iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL);
 519         if (!iter->walker)
 520                 return -ENOMEM;
 521
 522         mutex_lock(&ht->mutex);
 523         iter->walker->tbl = rht_dereference(ht->tbl, ht);
 524         list_add(&iter->walker->list, &iter->walker->tbl->walkers);
 525         mutex_unlock(&ht->mutex);
 526
 527         return 0;
 528 }
 529 EXPORT_SYMBOL_GPL(rhashtable_walk_init);
 530
 531 /**
 532  * rhashtable_walk_exit - Free an iterator
 533  * @iter:       Hash table Iterator
 534  *
 535  * This function frees resources allocated by rhashtable_walk_init.
 536  */
 537 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 538 {
 539         mutex_lock(&iter->ht->mutex);
 540         if (iter->walker->tbl)
 541                 list_del(&iter->walker->list);
 542         mutex_unlock(&iter->ht->mutex);
 543         kfree(iter->walker);
 544 }
 545 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
 546
 547 /**
 548  * rhashtable_walk_start - Start a hash table walk
 549  * @iter:       Hash table iterator
 550  *
 551  * Start a hash table walk.  Note that we take the RCU lock in all
 552  * cases including when we return an error.  So you must always call
 553  * rhashtable_walk_stop to clean up.
 554  *
 555  * Returns zero if successful.
 556  *
 557  * Returns -EAGAIN if resize event occured.  Note that the iterator
 558  * will rewind back to the beginning and you may use it immediately
 559  * by calling rhashtable_walk_next.
 560  */
 561 int rhashtable_walk_start(struct rhashtable_iter *iter)
 562         __acquires(RCU)
 563 {
 564         struct rhashtable *ht = iter->ht;
 565
 566         mutex_lock(&ht->mutex);
 567
 568         if (iter->walker->tbl)
 569                 list_del(&iter->walker->list);
 570
 571         rcu_read_lock();
 572
 573         mutex_unlock(&ht->mutex);
 574
 575         if (!iter->walker->tbl) {
 576                 iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht);
 577                 return -EAGAIN;
 578         }
 579
 580         return 0;
 581 }
 582 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
 583
 584 /**
 585  * rhashtable_walk_next - Return the next object and advance the iterator
 586  * @iter:       Hash table iterator
 587  *
 588  * Note that you must call rhashtable_walk_stop when you are finished
 589  * with the walk.
 590  *
 591  * Returns the next object or NULL when the end of the table is reached.
 592  *
 593  * Returns -EAGAIN if resize event occured.  Note that the iterator
 594  * will rewind back to the beginning and you may continue to use it.
 595  */
 596 void *rhashtable_walk_next(struct rhashtable_iter *iter)
 597 {
 598         struct bucket_table *tbl = iter->walker->tbl;
 599         struct rhashtable *ht = iter->ht;
 600         struct rhash_head *p = iter->p;
 601
 602         if (p) {
 603                 p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot);
 604                 goto next;
 605         }
 606
 607         for (; iter->slot < tbl->size; iter->slot++) {
 608                 int skip = iter->skip;
 609
 610                 rht_for_each_rcu(p, tbl, iter->slot) {
 611                         if (!skip)
 612                                 break;
 613                         skip--;
 614                 }
 615
 616 next:
 617                 if (!rht_is_a_nulls(p)) {
 618                         iter->skip++;
 619                         iter->p = p;
 620                         return rht_obj(ht, p);
 621                 }
 622
 623                 iter->skip = 0;
 624         }
 625
 626         iter->p = NULL;
 627
 628         /* Ensure we see any new tables. */
 629         smp_rmb();
 630
 631         iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 632         if (iter->walker->tbl) {
 633                 iter->slot = 0;
 634                 iter->skip = 0;
 635                 return ERR_PTR(-EAGAIN);
 636         }
 637
 638         return NULL;
 639 }
 640 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 641
 642 /**
 643  * rhashtable_walk_stop - Finish a hash table walk
 644  * @iter:       Hash table iterator
 645  *
 646  * Finish a hash table walk.
 647  */
 648 void rhashtable_walk_stop(struct rhashtable_iter *iter)
 649         __releases(RCU)
 650 {
 651         struct rhashtable *ht;
 652         struct bucket_table *tbl = iter->walker->tbl;
 653
 654         if (!tbl)
 655                 goto out;
 656
 657         ht = iter->ht;
 658
 659         spin_lock(&ht->lock);
 660         if (tbl->rehash < tbl->size)
 661                 list_add(&iter->walker->list, &tbl->walkers);
 662         else
 663                 iter->walker->tbl = NULL;
 664         spin_unlock(&ht->lock);
 665
 666         iter->p = NULL;
 667
 668 out:
 669         rcu_read_unlock();
 670 }
 671 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
 672
 673 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 674 {
 675         return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
 676                    (unsigned long)params->min_size);
 677 }
 678
 679 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
 680 {
 681         return jhash2(key, length, seed);
 682 }
 683
 684 /**
 685  * rhashtable_init - initialize a new hash table
 686  * @ht:         hash table to be initialized
 687  * @params:     configuration parameters
 688  *
 689  * Initializes a new hash table based on the provided configuration
 690  * parameters. A table can be configured either with a variable or
 691  * fixed length key:
 692  *
 693  * Configuration Example 1: Fixed length keys
 694  * struct test_obj {
 695  *      int                     key;
 696  *      void *                  my_member;
 697  *      struct rhash_head       node;
 698  * };
 699  *
 700  * struct rhashtable_params params = {
 701  *      .head_offset = offsetof(struct test_obj, node),
 702  *      .key_offset = offsetof(struct test_obj, key),
 703  *      .key_len = sizeof(int),
 704  *      .hashfn = jhash,
 705  *      .nulls_base = (1U << RHT_BASE_SHIFT),
 706  * };
 707  *
 708  * Configuration Example 2: Variable length keys
 709  * struct test_obj {
 710  *      [...]
 711  *      struct rhash_head       node;
 712  * };
 713  *
 714  * u32 my_hash_fn(const void *data, u32 len, u32 seed)
 715  * {
 716  *      struct test_obj *obj = data;
 717  *
 718  *      return [... hash ...];
 719  * }
 720  *
 721  * struct rhashtable_params params = {
 722  *      .head_offset = offsetof(struct test_obj, node),
 723  *      .hashfn = jhash,
 724  *      .obj_hashfn = my_hash_fn,
 725  * };
 726  */
 727 int rhashtable_init(struct rhashtable *ht,
 728                     const struct rhashtable_params *params)
 729 {
 730         struct bucket_table *tbl;
 731         size_t size;
 732
 733         size = HASH_DEFAULT_SIZE;
 734
 735         if ((!params->key_len && !params->obj_hashfn) ||
 736             (params->obj_hashfn && !params->obj_cmpfn))
 737                 return -EINVAL;
 738
 739         if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
 740                 return -EINVAL;
 741
 742         if (params->nelem_hint)
 743                 size = rounded_hashtable_size(params);
 744
 745         memset(ht, 0, sizeof(*ht));
 746         mutex_init(&ht->mutex);
 747         spin_lock_init(&ht->lock);
 748         memcpy(&ht->p, params, sizeof(*params));
 749
 750         if (params->min_size)
 751                 ht->p.min_size = roundup_pow_of_two(params->min_size);
 752
 753         if (params->max_size)
 754                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
 755
 756         if (params->insecure_max_entries)
 757                 ht->p.insecure_max_entries =
 758                         rounddown_pow_of_two(params->insecure_max_entries);
 759         else
 760                 ht->p.insecure_max_entries = ht->p.max_size * 2;
 761
 762         ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
 763
 764         /* The maximum (not average) chain length grows with the
 765          * size of the hash table, at a rate of (log N)/(log log N).
 766          * The value of 16 is selected so that even if the hash
 767          * table grew to 2^32 you would not expect the maximum
 768          * chain length to exceed it unless we are under attack
 769          * (or extremely unlucky).
 770          *
 771          * As this limit is only to detect attacks, we don't need
 772          * to set it to a lower value as you'd need the chain
 773          * length to vastly exceed 16 to have any real effect
 774          * on the system.
 775          */
 776         if (!params->insecure_elasticity)
 777                 ht->elasticity = 16;
 778
 779         if (params->locks_mul)
 780                 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
 781         else
 782                 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
 783
 784         ht->key_len = ht->p.key_len;
 785         if (!params->hashfn) {
 786                 ht->p.hashfn = jhash;
 787
 788                 if (!(ht->key_len & (sizeof(u32) - 1))) {
 789                         ht->key_len /= sizeof(u32);
 790                         ht->p.hashfn = rhashtable_jhash2;
 791                 }
 792         }
 793
 794         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 795         if (tbl == NULL)
 796                 return -ENOMEM;
 797
 798         atomic_set(&ht->nelems, 0);
 799
 800         RCU_INIT_POINTER(ht->tbl, tbl);
 801
 802         INIT_WORK(&ht->run_work, rht_deferred_worker);
 803
 804         return 0;
 805 }
 806 EXPORT_SYMBOL_GPL(rhashtable_init);
 807
 808 /**
 809  * rhashtable_free_and_destroy - free elements and destroy hash table
 810  * @ht:         the hash table to destroy
 811  * @free_fn:    callback to release resources of element
 812  * @arg:        pointer passed to free_fn
 813  *
 814  * Stops an eventual async resize. If defined, invokes free_fn for each
 815  * element to releasal resources. Please note that RCU protected
 816  * readers may still be accessing the elements. Releasing of resources
 817  * must occur in a compatible manner. Then frees the bucket array.
 818  *
 819  * This function will eventually sleep to wait for an async resize
 820  * to complete. The caller is responsible that no further write operations
 821  * occurs in parallel.
 822  */
 823 void rhashtable_free_and_destroy(struct rhashtable *ht,
 824                                  void (*free_fn)(void *ptr, void *arg),
 825                                  void *arg)
 826 {
 827         const struct bucket_table *tbl;
 828         unsigned int i;
 829
 830         cancel_work_sync(&ht->run_work);
 831
 832         mutex_lock(&ht->mutex);
 833         tbl = rht_dereference(ht->tbl, ht);
 834         if (free_fn) {
 835                 for (i = 0; i < tbl->size; i++) {
 836                         struct rhash_head *pos, *next;
 837
 838                         for (pos = rht_dereference(tbl->buckets[i], ht),
 839                              next = !rht_is_a_nulls(pos) ?
 840                                         rht_dereference(pos->next, ht) : NULL;
 841                              !rht_is_a_nulls(pos);
 842                              pos = next,
 843                              next = !rht_is_a_nulls(pos) ?
 844                                         rht_dereference(pos->next, ht) : NULL)
 845                                 free_fn(rht_obj(ht, pos), arg);
 846                 }
 847         }
 848
 849         bucket_table_free(tbl);
 850         mutex_unlock(&ht->mutex);
 851 }
 852 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
 853
 854 void rhashtable_destroy(struct rhashtable *ht)
 855 {
 856         return rhashtable_free_and_destroy(ht, NULL, NULL);
 857 }
 858 EXPORT_SYMBOL_GPL(rhashtable_destroy);