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    32UL
  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, 64UL);
  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                 tbl->locks = NULL;
  81 #ifdef CONFIG_NUMA
  82                 if (size * sizeof(spinlock_t) > PAGE_SIZE &&
  83                     gfp == GFP_KERNEL)
  84                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
  85 #endif
  86                 if (gfp != GFP_KERNEL)
  87                         gfp |= __GFP_NOWARN | __GFP_NORETRY;
  88
  89                 if (!tbl->locks)
  90                         tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
  91                                                    gfp);
  92                 if (!tbl->locks)
  93                         return -ENOMEM;
  94                 for (i = 0; i < size; i++)
  95                         spin_lock_init(&tbl->locks[i]);
  96         }
  97         tbl->locks_mask = size - 1;
  98
  99         return 0;
 100 }
 101
 102 static void bucket_table_free(const struct bucket_table *tbl)
 103 {
 104         if (tbl)
 105                 kvfree(tbl->locks);
 106
 107         kvfree(tbl);
 108 }
 109
 110 static void bucket_table_free_rcu(struct rcu_head *head)
 111 {
 112         bucket_table_free(container_of(head, struct bucket_table, rcu));
 113 }
 114
 115 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 116                                                size_t nbuckets,
 117                                                gfp_t gfp)
 118 {
 119         struct bucket_table *tbl = NULL;
 120         size_t size;
 121         int i;
 122
 123         size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
 124         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
 125             gfp != GFP_KERNEL)
 126                 tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
 127         if (tbl == NULL && gfp == GFP_KERNEL)
 128                 tbl = vzalloc(size);
 129         if (tbl == NULL)
 130                 return NULL;
 131
 132         tbl->size = nbuckets;
 133
 134         if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
 135                 bucket_table_free(tbl);
 136                 return NULL;
 137         }
 138
 139         INIT_LIST_HEAD(&tbl->walkers);
 140
 141         get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
 142
 143         for (i = 0; i < nbuckets; i++)
 144                 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
 145
 146         return tbl;
 147 }
 148
 149 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
 150                                                   struct bucket_table *tbl)
 151 {
 152         struct bucket_table *new_tbl;
 153
 154         do {
 155                 new_tbl = tbl;
 156                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 157         } while (tbl);
 158
 159         return new_tbl;
 160 }
 161
 162 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
 163 {
 164         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 165         struct bucket_table *new_tbl = rhashtable_last_table(ht,
 166                 rht_dereference_rcu(old_tbl->future_tbl, ht));
 167         struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
 168         int err = -ENOENT;
 169         struct rhash_head *head, *next, *entry;
 170         spinlock_t *new_bucket_lock;
 171         unsigned int new_hash;
 172
 173         rht_for_each(entry, old_tbl, old_hash) {
 174                 err = 0;
 175                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
 176
 177                 if (rht_is_a_nulls(next))
 178                         break;
 179
 180                 pprev = &entry->next;
 181         }
 182
 183         if (err)
 184                 goto out;
 185
 186         new_hash = head_hashfn(ht, new_tbl, entry);
 187
 188         new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
 189
 190         spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
 191         head = rht_dereference_bucket(new_tbl->buckets[new_hash],
 192                                       new_tbl, new_hash);
 193
 194         RCU_INIT_POINTER(entry->next, head);
 195
 196         rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
 197         spin_unlock(new_bucket_lock);
 198
 199         rcu_assign_pointer(*pprev, next);
 200
 201 out:
 202         return err;
 203 }
 204
 205 static void rhashtable_rehash_chain(struct rhashtable *ht,
 206                                     unsigned int old_hash)
 207 {
 208         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 209         spinlock_t *old_bucket_lock;
 210
 211         old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
 212
 213         spin_lock_bh(old_bucket_lock);
 214         while (!rhashtable_rehash_one(ht, old_hash))
 215                 ;
 216         old_tbl->rehash++;
 217         spin_unlock_bh(old_bucket_lock);
 218 }
 219
 220 static int rhashtable_rehash_attach(struct rhashtable *ht,
 221                                     struct bucket_table *old_tbl,
 222                                     struct bucket_table *new_tbl)
 223 {
 224         /* Protect future_tbl using the first bucket lock. */
 225         spin_lock_bh(old_tbl->locks);
 226
 227         /* Did somebody beat us to it? */
 228         if (rcu_access_pointer(old_tbl->future_tbl)) {
 229                 spin_unlock_bh(old_tbl->locks);
 230                 return -EEXIST;
 231         }
 232
 233         /* Make insertions go into the new, empty table right away. Deletions
 234          * and lookups will be attempted in both tables until we synchronize.
 235          */
 236         rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
 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                 cond_resched();
 257         }
 258
 259         /* Publish the new table pointer. */
 260         rcu_assign_pointer(ht->tbl, new_tbl);
 261
 262         spin_lock(&ht->lock);
 263         list_for_each_entry(walker, &old_tbl->walkers, list)
 264                 walker->tbl = NULL;
 265         spin_unlock(&ht->lock);
 266
 267         /* Wait for readers. All new readers will see the new
 268          * table, and thus no references to the old table will
 269          * remain.
 270          */
 271         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
 272
 273         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 274 }
 275
 276 /**
 277  * rhashtable_expand - Expand hash table while allowing concurrent lookups
 278  * @ht:         the hash table to expand
 279  *
 280  * A secondary bucket array is allocated and the hash entries are migrated.
 281  *
 282  * This function may only be called in a context where it is safe to call
 283  * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 284  *
 285  * The caller must ensure that no concurrent resizing occurs by holding
 286  * ht->mutex.
 287  *
 288  * It is valid to have concurrent insertions and deletions protected by per
 289  * bucket locks or concurrent RCU protected lookups and traversals.
 290  */
 291 static int rhashtable_expand(struct rhashtable *ht)
 292 {
 293         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 294         int err;
 295
 296         ASSERT_RHT_MUTEX(ht);
 297
 298         old_tbl = rhashtable_last_table(ht, old_tbl);
 299
 300         new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
 301         if (new_tbl == NULL)
 302                 return -ENOMEM;
 303
 304         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 305         if (err)
 306                 bucket_table_free(new_tbl);
 307
 308         return err;
 309 }
 310
 311 /**
 312  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 313  * @ht:         the hash table to shrink
 314  *
 315  * This function shrinks the hash table to fit, i.e., the smallest
 316  * size would not cause it to expand right away automatically.
 317  *
 318  * The caller must ensure that no concurrent resizing occurs by holding
 319  * ht->mutex.
 320  *
 321  * The caller must ensure that no concurrent table mutations take place.
 322  * It is however valid to have concurrent lookups if they are RCU protected.
 323  *
 324  * It is valid to have concurrent insertions and deletions protected by per
 325  * bucket locks or concurrent RCU protected lookups and traversals.
 326  */
 327 static int rhashtable_shrink(struct rhashtable *ht)
 328 {
 329         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
 330         unsigned int nelems = atomic_read(&ht->nelems);
 331         unsigned int size = 0;
 332         int err;
 333
 334         ASSERT_RHT_MUTEX(ht);
 335
 336         if (nelems)
 337                 size = roundup_pow_of_two(nelems * 3 / 2);
 338         if (size < ht->p.min_size)
 339                 size = ht->p.min_size;
 340
 341         if (old_tbl->size <= size)
 342                 return 0;
 343
 344         if (rht_dereference(old_tbl->future_tbl, ht))
 345                 return -EEXIST;
 346
 347         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 348         if (new_tbl == NULL)
 349                 return -ENOMEM;
 350
 351         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 352         if (err)
 353                 bucket_table_free(new_tbl);
 354
 355         return err;
 356 }
 357
 358 static void rht_deferred_worker(struct work_struct *work)
 359 {
 360         struct rhashtable *ht;
 361         struct bucket_table *tbl;
 362         int err = 0;
 363
 364         ht = container_of(work, struct rhashtable, run_work);
 365         mutex_lock(&ht->mutex);
 366
 367         tbl = rht_dereference(ht->tbl, ht);
 368         tbl = rhashtable_last_table(ht, tbl);
 369
 370         if (rht_grow_above_75(ht, tbl))
 371                 rhashtable_expand(ht);
 372         else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
 373                 rhashtable_shrink(ht);
 374
 375         err = rhashtable_rehash_table(ht);
 376
 377         mutex_unlock(&ht->mutex);
 378
 379         if (err)
 380                 schedule_work(&ht->run_work);
 381 }
 382
 383 static int rhashtable_insert_rehash(struct rhashtable *ht,
 384                                     struct bucket_table *tbl)
 385 {
 386         struct bucket_table *old_tbl;
 387         struct bucket_table *new_tbl;
 388         unsigned int size;
 389         int err;
 390
 391         old_tbl = rht_dereference_rcu(ht->tbl, ht);
 392
 393         size = tbl->size;
 394
 395         err = -EBUSY;
 396
 397         if (rht_grow_above_75(ht, tbl))
 398                 size *= 2;
 399         /* Do not schedule more than one rehash */
 400         else if (old_tbl != tbl)
 401                 goto fail;
 402
 403         err = -ENOMEM;
 404
 405         new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
 406         if (new_tbl == NULL)
 407                 goto fail;
 408
 409         err = rhashtable_rehash_attach(ht, tbl, new_tbl);
 410         if (err) {
 411                 bucket_table_free(new_tbl);
 412                 if (err == -EEXIST)
 413                         err = 0;
 414         } else
 415                 schedule_work(&ht->run_work);
 416
 417         return err;
 418
 419 fail:
 420         /* Do not fail the insert if someone else did a rehash. */
 421         if (likely(rcu_dereference_raw(tbl->future_tbl)))
 422                 return 0;
 423
 424         /* Schedule async rehash to retry allocation in process context. */
 425         if (err == -ENOMEM)
 426                 schedule_work(&ht->run_work);
 427
 428         return err;
 429 }
 430
 431 static void *rhashtable_lookup_one(struct rhashtable *ht,
 432                                    struct bucket_table *tbl, unsigned int hash,
 433                                    const void *key, struct rhash_head *obj)
 434 {
 435         struct rhashtable_compare_arg arg = {
 436                 .ht = ht,
 437                 .key = key,
 438         };
 439         struct rhash_head __rcu **pprev;
 440         struct rhash_head *head;
 441         int elasticity;
 442
 443         elasticity = ht->elasticity;
 444         pprev = &tbl->buckets[hash];
 445         rht_for_each(head, tbl, hash) {
 446                 struct rhlist_head *list;
 447                 struct rhlist_head *plist;
 448
 449                 elasticity--;
 450                 if (!key ||
 451                     (ht->p.obj_cmpfn ?
 452                      ht->p.obj_cmpfn(&arg, rht_obj(ht, head)) :
 453                      rhashtable_compare(&arg, rht_obj(ht, head)))) {
 454                         pprev = &head->next;
 455                         continue;
 456                 }
 457
 458                 if (!ht->rhlist)
 459                         return rht_obj(ht, head);
 460
 461                 list = container_of(obj, struct rhlist_head, rhead);
 462                 plist = container_of(head, struct rhlist_head, rhead);
 463
 464                 RCU_INIT_POINTER(list->next, plist);
 465                 head = rht_dereference_bucket(head->next, tbl, hash);
 466                 RCU_INIT_POINTER(list->rhead.next, head);
 467                 rcu_assign_pointer(*pprev, obj);
 468
 469                 return NULL;
 470         }
 471
 472         if (elasticity <= 0)
 473                 return ERR_PTR(-EAGAIN);
 474
 475         return ERR_PTR(-ENOENT);
 476 }
 477
 478 static struct bucket_table *rhashtable_insert_one(struct rhashtable *ht,
 479                                                   struct bucket_table *tbl,
 480                                                   unsigned int hash,
 481                                                   struct rhash_head *obj,
 482                                                   void *data)
 483 {
 484         struct bucket_table *new_tbl;
 485         struct rhash_head *head;
 486
 487         if (!IS_ERR_OR_NULL(data))
 488                 return ERR_PTR(-EEXIST);
 489
 490         if (PTR_ERR(data) != -EAGAIN && PTR_ERR(data) != -ENOENT)
 491                 return ERR_CAST(data);
 492
 493         new_tbl = rcu_dereference(tbl->future_tbl);
 494         if (new_tbl)
 495                 return new_tbl;
 496
 497         if (PTR_ERR(data) != -ENOENT)
 498                 return ERR_CAST(data);
 499
 500         if (unlikely(rht_grow_above_max(ht, tbl)))
 501                 return ERR_PTR(-E2BIG);
 502
 503         if (unlikely(rht_grow_above_100(ht, tbl)))
 504                 return ERR_PTR(-EAGAIN);
 505
 506         head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
 507
 508         RCU_INIT_POINTER(obj->next, head);
 509         if (ht->rhlist) {
 510                 struct rhlist_head *list;
 511
 512                 list = container_of(obj, struct rhlist_head, rhead);
 513                 RCU_INIT_POINTER(list->next, NULL);
 514         }
 515
 516         rcu_assign_pointer(tbl->buckets[hash], obj);
 517
 518         atomic_inc(&ht->nelems);
 519         if (rht_grow_above_75(ht, tbl))
 520                 schedule_work(&ht->run_work);
 521
 522         return NULL;
 523 }
 524
 525 static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
 526                                    struct rhash_head *obj)
 527 {
 528         struct bucket_table *new_tbl;
 529         struct bucket_table *tbl;
 530         unsigned int hash;
 531         spinlock_t *lock;
 532         void *data;
 533
 534         tbl = rcu_dereference(ht->tbl);
 535
 536         /* All insertions must grab the oldest table containing
 537          * the hashed bucket that is yet to be rehashed.
 538          */
 539         for (;;) {
 540                 hash = rht_head_hashfn(ht, tbl, obj, ht->p);
 541                 lock = rht_bucket_lock(tbl, hash);
 542                 spin_lock_bh(lock);
 543
 544                 if (tbl->rehash <= hash)
 545                         break;
 546
 547                 spin_unlock_bh(lock);
 548                 tbl = rcu_dereference(tbl->future_tbl);
 549         }
 550
 551         data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
 552         new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
 553         if (PTR_ERR(new_tbl) != -EEXIST)
 554                 data = ERR_CAST(new_tbl);
 555
 556         while (!IS_ERR_OR_NULL(new_tbl)) {
 557                 tbl = new_tbl;
 558                 hash = rht_head_hashfn(ht, tbl, obj, ht->p);
 559                 spin_lock_nested(rht_bucket_lock(tbl, hash),
 560                                  SINGLE_DEPTH_NESTING);
 561
 562                 data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
 563                 new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
 564                 if (PTR_ERR(new_tbl) != -EEXIST)
 565                         data = ERR_CAST(new_tbl);
 566
 567                 spin_unlock(rht_bucket_lock(tbl, hash));
 568         }
 569
 570         spin_unlock_bh(lock);
 571
 572         if (PTR_ERR(data) == -EAGAIN)
 573                 data = ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?:
 574                                -EAGAIN);
 575
 576         return data;
 577 }
 578
 579 void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 580                              struct rhash_head *obj)
 581 {
 582         void *data;
 583
 584         do {
 585                 rcu_read_lock();
 586                 data = rhashtable_try_insert(ht, key, obj);
 587                 rcu_read_unlock();
 588         } while (PTR_ERR(data) == -EAGAIN);
 589
 590         return data;
 591 }
 592 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
 593
 594 /**
 595  * rhashtable_walk_enter - Initialise an iterator
 596  * @ht:         Table to walk over
 597  * @iter:       Hash table Iterator
 598  *
 599  * This function prepares a hash table walk.
 600  *
 601  * Note that if you restart a walk after rhashtable_walk_stop you
 602  * may see the same object twice.  Also, you may miss objects if
 603  * there are removals in between rhashtable_walk_stop and the next
 604  * call to rhashtable_walk_start.
 605  *
 606  * For a completely stable walk you should construct your own data
 607  * structure outside the hash table.
 608  *
 609  * This function may sleep so you must not call it from interrupt
 610  * context or with spin locks held.
 611  *
 612  * You must call rhashtable_walk_exit after this function returns.
 613  */
 614 void rhashtable_walk_enter(struct rhashtable *ht, struct rhashtable_iter *iter)
 615 {
 616         iter->ht = ht;
 617         iter->p = NULL;
 618         iter->slot = 0;
 619         iter->skip = 0;
 620
 621         spin_lock(&ht->lock);
 622         iter->walker.tbl =
 623                 rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
 624         list_add(&iter->walker.list, &iter->walker.tbl->walkers);
 625         spin_unlock(&ht->lock);
 626 }
 627 EXPORT_SYMBOL_GPL(rhashtable_walk_enter);
 628
 629 /**
 630  * rhashtable_walk_exit - Free an iterator
 631  * @iter:       Hash table Iterator
 632  *
 633  * This function frees resources allocated by rhashtable_walk_init.
 634  */
 635 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 636 {
 637         spin_lock(&iter->ht->lock);
 638         if (iter->walker.tbl)
 639                 list_del(&iter->walker.list);
 640         spin_unlock(&iter->ht->lock);
 641 }
 642 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
 643
 644 /**
 645  * rhashtable_walk_start - Start a hash table walk
 646  * @iter:       Hash table iterator
 647  *
 648  * Start a hash table walk.  Note that we take the RCU lock in all
 649  * cases including when we return an error.  So you must always call
 650  * rhashtable_walk_stop to clean up.
 651  *
 652  * Returns zero if successful.
 653  *
 654  * Returns -EAGAIN if resize event occured.  Note that the iterator
 655  * will rewind back to the beginning and you may use it immediately
 656  * by calling rhashtable_walk_next.
 657  */
 658 int rhashtable_walk_start(struct rhashtable_iter *iter)
 659         __acquires(RCU)
 660 {
 661         struct rhashtable *ht = iter->ht;
 662
 663         rcu_read_lock();
 664
 665         spin_lock(&ht->lock);
 666         if (iter->walker.tbl)
 667                 list_del(&iter->walker.list);
 668         spin_unlock(&ht->lock);
 669
 670         if (!iter->walker.tbl) {
 671                 iter->walker.tbl = rht_dereference_rcu(ht->tbl, ht);
 672                 return -EAGAIN;
 673         }
 674
 675         return 0;
 676 }
 677 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
 678
 679 /**
 680  * rhashtable_walk_next - Return the next object and advance the iterator
 681  * @iter:       Hash table iterator
 682  *
 683  * Note that you must call rhashtable_walk_stop when you are finished
 684  * with the walk.
 685  *
 686  * Returns the next object or NULL when the end of the table is reached.
 687  *
 688  * Returns -EAGAIN if resize event occured.  Note that the iterator
 689  * will rewind back to the beginning and you may continue to use it.
 690  */
 691 void *rhashtable_walk_next(struct rhashtable_iter *iter)
 692 {
 693         struct bucket_table *tbl = iter->walker.tbl;
 694         struct rhlist_head *list = iter->list;
 695         struct rhashtable *ht = iter->ht;
 696         struct rhash_head *p = iter->p;
 697         bool rhlist = ht->rhlist;
 698
 699         if (p) {
 700                 if (!rhlist || !(list = rcu_dereference(list->next))) {
 701                         p = rcu_dereference(p->next);
 702                         list = container_of(p, struct rhlist_head, rhead);
 703                 }
 704                 goto next;
 705         }
 706
 707         for (; iter->slot < tbl->size; iter->slot++) {
 708                 int skip = iter->skip;
 709
 710                 rht_for_each_rcu(p, tbl, iter->slot) {
 711                         if (rhlist) {
 712                                 list = container_of(p, struct rhlist_head,
 713                                                     rhead);
 714                                 do {
 715                                         if (!skip)
 716                                                 goto next;
 717                                         skip--;
 718                                         list = rcu_dereference(list->next);
 719                                 } while (list);
 720
 721                                 continue;
 722                         }
 723                         if (!skip)
 724                                 break;
 725                         skip--;
 726                 }
 727
 728 next:
 729                 if (!rht_is_a_nulls(p)) {
 730                         iter->skip++;
 731                         iter->p = p;
 732                         iter->list = list;
 733                         return rht_obj(ht, rhlist ? &list->rhead : p);
 734                 }
 735
 736                 iter->skip = 0;
 737         }
 738
 739         iter->p = NULL;
 740
 741         /* Ensure we see any new tables. */
 742         smp_rmb();
 743
 744         iter->walker.tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 745         if (iter->walker.tbl) {
 746                 iter->slot = 0;
 747                 iter->skip = 0;
 748                 return ERR_PTR(-EAGAIN);
 749         }
 750
 751         return NULL;
 752 }
 753 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 754
 755 /**
 756  * rhashtable_walk_stop - Finish a hash table walk
 757  * @iter:       Hash table iterator
 758  *
 759  * Finish a hash table walk.
 760  */
 761 void rhashtable_walk_stop(struct rhashtable_iter *iter)
 762         __releases(RCU)
 763 {
 764         struct rhashtable *ht;
 765         struct bucket_table *tbl = iter->walker.tbl;
 766
 767         if (!tbl)
 768                 goto out;
 769
 770         ht = iter->ht;
 771
 772         spin_lock(&ht->lock);
 773         if (tbl->rehash < tbl->size)
 774                 list_add(&iter->walker.list, &tbl->walkers);
 775         else
 776                 iter->walker.tbl = NULL;
 777         spin_unlock(&ht->lock);
 778
 779         iter->p = NULL;
 780
 781 out:
 782         rcu_read_unlock();
 783 }
 784 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
 785
 786 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 787 {
 788         size_t retsize;
 789
 790         if (params->nelem_hint)
 791                 retsize = max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
 792                               (unsigned long)params->min_size);
 793         else
 794                 retsize = max(HASH_DEFAULT_SIZE,
 795                               (unsigned long)params->min_size);
 796
 797         return retsize;
 798 }
 799
 800 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
 801 {
 802         return jhash2(key, length, seed);
 803 }
 804
 805 /**
 806  * rhashtable_init - initialize a new hash table
 807  * @ht:         hash table to be initialized
 808  * @params:     configuration parameters
 809  *
 810  * Initializes a new hash table based on the provided configuration
 811  * parameters. A table can be configured either with a variable or
 812  * fixed length key:
 813  *
 814  * Configuration Example 1: Fixed length keys
 815  * struct test_obj {
 816  *      int                     key;
 817  *      void *                  my_member;
 818  *      struct rhash_head       node;
 819  * };
 820  *
 821  * struct rhashtable_params params = {
 822  *      .head_offset = offsetof(struct test_obj, node),
 823  *      .key_offset = offsetof(struct test_obj, key),
 824  *      .key_len = sizeof(int),
 825  *      .hashfn = jhash,
 826  *      .nulls_base = (1U << RHT_BASE_SHIFT),
 827  * };
 828  *
 829  * Configuration Example 2: Variable length keys
 830  * struct test_obj {
 831  *      [...]
 832  *      struct rhash_head       node;
 833  * };
 834  *
 835  * u32 my_hash_fn(const void *data, u32 len, u32 seed)
 836  * {
 837  *      struct test_obj *obj = data;
 838  *
 839  *      return [... hash ...];
 840  * }
 841  *
 842  * struct rhashtable_params params = {
 843  *      .head_offset = offsetof(struct test_obj, node),
 844  *      .hashfn = jhash,
 845  *      .obj_hashfn = my_hash_fn,
 846  * };
 847  */
 848 int rhashtable_init(struct rhashtable *ht,
 849                     const struct rhashtable_params *params)
 850 {
 851         struct bucket_table *tbl;
 852         size_t size;
 853
 854         if ((!params->key_len && !params->obj_hashfn) ||
 855             (params->obj_hashfn && !params->obj_cmpfn))
 856                 return -EINVAL;
 857
 858         if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
 859                 return -EINVAL;
 860
 861         memset(ht, 0, sizeof(*ht));
 862         mutex_init(&ht->mutex);
 863         spin_lock_init(&ht->lock);
 864         memcpy(&ht->p, params, sizeof(*params));
 865
 866         if (params->min_size)
 867                 ht->p.min_size = roundup_pow_of_two(params->min_size);
 868
 869         if (params->max_size)
 870                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
 871
 872         if (params->insecure_max_entries)
 873                 ht->p.insecure_max_entries =
 874                         rounddown_pow_of_two(params->insecure_max_entries);
 875         else
 876                 ht->p.insecure_max_entries = ht->p.max_size * 2;
 877
 878         ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
 879
 880         size = rounded_hashtable_size(&ht->p);
 881
 882         /* The maximum (not average) chain length grows with the
 883          * size of the hash table, at a rate of (log N)/(log log N).
 884          * The value of 16 is selected so that even if the hash
 885          * table grew to 2^32 you would not expect the maximum
 886          * chain length to exceed it unless we are under attack
 887          * (or extremely unlucky).
 888          *
 889          * As this limit is only to detect attacks, we don't need
 890          * to set it to a lower value as you'd need the chain
 891          * length to vastly exceed 16 to have any real effect
 892          * on the system.
 893          */
 894         if (!params->insecure_elasticity)
 895                 ht->elasticity = 16;
 896
 897         if (params->locks_mul)
 898                 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
 899         else
 900                 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
 901
 902         ht->key_len = ht->p.key_len;
 903         if (!params->hashfn) {
 904                 ht->p.hashfn = jhash;
 905
 906                 if (!(ht->key_len & (sizeof(u32) - 1))) {
 907                         ht->key_len /= sizeof(u32);
 908                         ht->p.hashfn = rhashtable_jhash2;
 909                 }
 910         }
 911
 912         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 913         if (tbl == NULL)
 914                 return -ENOMEM;
 915
 916         atomic_set(&ht->nelems, 0);
 917
 918         RCU_INIT_POINTER(ht->tbl, tbl);
 919
 920         INIT_WORK(&ht->run_work, rht_deferred_worker);
 921
 922         return 0;
 923 }
 924 EXPORT_SYMBOL_GPL(rhashtable_init);
 925
 926 /**
 927  * rhltable_init - initialize a new hash list table
 928  * @hlt:        hash list table to be initialized
 929  * @params:     configuration parameters
 930  *
 931  * Initializes a new hash list table.
 932  *
 933  * See documentation for rhashtable_init.
 934  */
 935 int rhltable_init(struct rhltable *hlt, const struct rhashtable_params *params)
 936 {
 937         int err;
 938
 939         /* No rhlist NULLs marking for now. */
 940         if (params->nulls_base)
 941                 return -EINVAL;
 942
 943         err = rhashtable_init(&hlt->ht, params);
 944         hlt->ht.rhlist = true;
 945         return err;
 946 }
 947 EXPORT_SYMBOL_GPL(rhltable_init);
 948
 949 static void rhashtable_free_one(struct rhashtable *ht, struct rhash_head *obj,
 950                                 void (*free_fn)(void *ptr, void *arg),
 951                                 void *arg)
 952 {
 953         struct rhlist_head *list;
 954
 955         if (!ht->rhlist) {
 956                 free_fn(rht_obj(ht, obj), arg);
 957                 return;
 958         }
 959
 960         list = container_of(obj, struct rhlist_head, rhead);
 961         do {
 962                 obj = &list->rhead;
 963                 list = rht_dereference(list->next, ht);
 964                 free_fn(rht_obj(ht, obj), arg);
 965         } while (list);
 966 }
 967
 968 /**
 969  * rhashtable_free_and_destroy - free elements and destroy hash table
 970  * @ht:         the hash table to destroy
 971  * @free_fn:    callback to release resources of element
 972  * @arg:        pointer passed to free_fn
 973  *
 974  * Stops an eventual async resize. If defined, invokes free_fn for each
 975  * element to releasal resources. Please note that RCU protected
 976  * readers may still be accessing the elements. Releasing of resources
 977  * must occur in a compatible manner. Then frees the bucket array.
 978  *
 979  * This function will eventually sleep to wait for an async resize
 980  * to complete. The caller is responsible that no further write operations
 981  * occurs in parallel.
 982  */
 983 void rhashtable_free_and_destroy(struct rhashtable *ht,
 984                                  void (*free_fn)(void *ptr, void *arg),
 985                                  void *arg)
 986 {
 987         const struct bucket_table *tbl;
 988         unsigned int i;
 989
 990         cancel_work_sync(&ht->run_work);
 991
 992         mutex_lock(&ht->mutex);
 993         tbl = rht_dereference(ht->tbl, ht);
 994         if (free_fn) {
 995                 for (i = 0; i < tbl->size; i++) {
 996                         struct rhash_head *pos, *next;
 997
 998                         cond_resched();
 999                         for (pos = rht_dereference(tbl->buckets[i], ht),
1000                              next = !rht_is_a_nulls(pos) ?
1001                                         rht_dereference(pos->next, ht) : NULL;
1002                              !rht_is_a_nulls(pos);
1003                              pos = next,
1004                              next = !rht_is_a_nulls(pos) ?
1005                                         rht_dereference(pos->next, ht) : NULL)
1006                                 rhashtable_free_one(ht, pos, free_fn, arg);
1007                 }
1008         }
1009
1010         bucket_table_free(tbl);
1011         mutex_unlock(&ht->mutex);
1012 }
1013 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
1014
1015 void rhashtable_destroy(struct rhashtable *ht)
1016 {
1017         return rhashtable_free_and_destroy(ht, NULL, NULL);
1018 }
1019 EXPORT_SYMBOL_GPL(rhashtable_destroy);