lib/rhashtable.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Resizable, Scalable, Concurrent Hash Table
   4  *
   5  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
   6  * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
   7  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
   8  *
   9  * Code partially derived from nft_hash
  10  * Rewritten with rehash code from br_multicast plus single list
  11  * pointer as suggested by Josh Triplett
  12  */
  13
  14 #include <linux/atomic.h>
  15 #include <linux/kernel.h>
  16 #include <linux/init.h>
  17 #include <linux/log2.h>
  18 #include <linux/sched.h>
  19 #include <linux/rculist.h>
  20 #include <linux/slab.h>
  21 #include <linux/vmalloc.h>
  22 #include <linux/mm.h>
  23 #include <linux/jhash.h>
  24 #include <linux/random.h>
  25 #include <linux/rhashtable.h>
  26 #include <linux/err.h>
  27 #include <linux/export.h>
  28
  29 #define HASH_DEFAULT_SIZE       64UL
  30 #define HASH_MIN_SIZE           4U
  31
  32 union nested_table {
  33         union nested_table __rcu *table;
  34         struct rhash_lock_head __rcu *bucket;
  35 };
  36
  37 static u32 head_hashfn(struct rhashtable *ht,
  38                        const struct bucket_table *tbl,
  39                        const struct rhash_head *he)
  40 {
  41         return rht_head_hashfn(ht, tbl, he, ht->p);
  42 }
  43
  44 #ifdef CONFIG_PROVE_LOCKING
  45 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
  46
  47 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
  48 {
  49         return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
  50 }
  51 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
  52
  53 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
  54 {
  55         if (!debug_locks)
  56                 return 1;
  57         if (unlikely(tbl->nest))
  58                 return 1;
  59         return bit_spin_is_locked(0, (unsigned long *)&tbl->buckets[hash]);
  60 }
  61 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
  62 #else
  63 #define ASSERT_RHT_MUTEX(HT)
  64 #endif
  65
  66 static inline union nested_table *nested_table_top(
  67         const struct bucket_table *tbl)
  68 {
  69         /* The top-level bucket entry does not need RCU protection
  70          * because it's set at the same time as tbl->nest.
  71          */
  72         return (void *)rcu_dereference_protected(tbl->buckets[0], 1);
  73 }
  74
  75 static void nested_table_free(union nested_table *ntbl, unsigned int size)
  76 {
  77         const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
  78         const unsigned int len = 1 << shift;
  79         unsigned int i;
  80
  81         ntbl = rcu_dereference_protected(ntbl->table, 1);
  82         if (!ntbl)
  83                 return;
  84
  85         if (size > len) {
  86                 size >>= shift;
  87                 for (i = 0; i < len; i++)
  88                         nested_table_free(ntbl + i, size);
  89         }
  90
  91         kfree(ntbl);
  92 }
  93
  94 static void nested_bucket_table_free(const struct bucket_table *tbl)
  95 {
  96         unsigned int size = tbl->size >> tbl->nest;
  97         unsigned int len = 1 << tbl->nest;
  98         union nested_table *ntbl;
  99         unsigned int i;
 100
 101         ntbl = nested_table_top(tbl);
 102
 103         for (i = 0; i < len; i++)
 104                 nested_table_free(ntbl + i, size);
 105
 106         kfree(ntbl);
 107 }
 108
 109 static void bucket_table_free(const struct bucket_table *tbl)
 110 {
 111         if (tbl->nest)
 112                 nested_bucket_table_free(tbl);
 113
 114         kvfree(tbl);
 115 }
 116
 117 static void bucket_table_free_rcu(struct rcu_head *head)
 118 {
 119         bucket_table_free(container_of(head, struct bucket_table, rcu));
 120 }
 121
 122 static union nested_table *nested_table_alloc(struct rhashtable *ht,
 123                                               union nested_table __rcu **prev,
 124                                               bool leaf)
 125 {
 126         union nested_table *ntbl;
 127         int i;
 128
 129         ntbl = rcu_dereference(*prev);
 130         if (ntbl)
 131                 return ntbl;
 132
 133         ntbl = kzalloc(PAGE_SIZE, GFP_ATOMIC);
 134
 135         if (ntbl && leaf) {
 136                 for (i = 0; i < PAGE_SIZE / sizeof(ntbl[0]); i++)
 137                         INIT_RHT_NULLS_HEAD(ntbl[i].bucket);
 138         }
 139
 140         if (cmpxchg((union nested_table **)prev, NULL, ntbl) == NULL)
 141                 return ntbl;
 142         /* Raced with another thread. */
 143         kfree(ntbl);
 144         return rcu_dereference(*prev);
 145 }
 146
 147 static struct bucket_table *nested_bucket_table_alloc(struct rhashtable *ht,
 148                                                       size_t nbuckets,
 149                                                       gfp_t gfp)
 150 {
 151         const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
 152         struct bucket_table *tbl;
 153         size_t size;
 154
 155         if (nbuckets < (1 << (shift + 1)))
 156                 return NULL;
 157
 158         size = sizeof(*tbl) + sizeof(tbl->buckets[0]);
 159
 160         tbl = kzalloc(size, gfp);
 161         if (!tbl)
 162                 return NULL;
 163
 164         if (!nested_table_alloc(ht, (union nested_table __rcu **)tbl->buckets,
 165                                 false)) {
 166                 kfree(tbl);
 167                 return NULL;
 168         }
 169
 170         tbl->nest = (ilog2(nbuckets) - 1) % shift + 1;
 171
 172         return tbl;
 173 }
 174
 175 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
 176                                                size_t nbuckets,
 177                                                gfp_t gfp)
 178 {
 179         struct bucket_table *tbl = NULL;
 180         size_t size;
 181         int i;
 182         static struct lock_class_key __key;
 183
 184         tbl = kvzalloc(struct_size(tbl, buckets, nbuckets), gfp);
 185
 186         size = nbuckets;
 187
 188         if (tbl == NULL && (gfp & ~__GFP_NOFAIL) != GFP_KERNEL) {
 189                 tbl = nested_bucket_table_alloc(ht, nbuckets, gfp);
 190                 nbuckets = 0;
 191         }
 192
 193         if (tbl == NULL)
 194                 return NULL;
 195
 196         lockdep_init_map(&tbl->dep_map, "rhashtable_bucket", &__key, 0);
 197
 198         tbl->size = size;
 199
 200         rcu_head_init(&tbl->rcu);
 201         INIT_LIST_HEAD(&tbl->walkers);
 202
 203         tbl->hash_rnd = get_random_u32();
 204
 205         for (i = 0; i < nbuckets; i++)
 206                 INIT_RHT_NULLS_HEAD(tbl->buckets[i]);
 207
 208         return tbl;
 209 }
 210
 211 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
 212                                                   struct bucket_table *tbl)
 213 {
 214         struct bucket_table *new_tbl;
 215
 216         do {
 217                 new_tbl = tbl;
 218                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 219         } while (tbl);
 220
 221         return new_tbl;
 222 }
 223
 224 static int rhashtable_rehash_one(struct rhashtable *ht,
 225                                  struct rhash_lock_head __rcu **bkt,
 226                                  unsigned int old_hash)
 227 {
 228         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 229         struct bucket_table *new_tbl = rhashtable_last_table(ht, old_tbl);
 230         int err = -EAGAIN;
 231         struct rhash_head *head, *next, *entry;
 232         struct rhash_head __rcu **pprev = NULL;
 233         unsigned int new_hash;
 234         unsigned long flags;
 235
 236         if (new_tbl->nest)
 237                 goto out;
 238
 239         err = -ENOENT;
 240
 241         rht_for_each_from(entry, rht_ptr(bkt, old_tbl, old_hash),
 242                           old_tbl, old_hash) {
 243                 err = 0;
 244                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
 245
 246                 if (rht_is_a_nulls(next))
 247                         break;
 248
 249                 pprev = &entry->next;
 250         }
 251
 252         if (err)
 253                 goto out;
 254
 255         new_hash = head_hashfn(ht, new_tbl, entry);
 256
 257         flags = rht_lock_nested(new_tbl, &new_tbl->buckets[new_hash],
 258                                 SINGLE_DEPTH_NESTING);
 259
 260         head = rht_ptr(new_tbl->buckets + new_hash, new_tbl, new_hash);
 261
 262         RCU_INIT_POINTER(entry->next, head);
 263
 264         rht_assign_unlock(new_tbl, &new_tbl->buckets[new_hash], entry, flags);
 265
 266         if (pprev)
 267                 rcu_assign_pointer(*pprev, next);
 268         else
 269                 /* Need to preserved the bit lock. */
 270                 rht_assign_locked(bkt, next);
 271
 272 out:
 273         return err;
 274 }
 275
 276 static int rhashtable_rehash_chain(struct rhashtable *ht,
 277                                     unsigned int old_hash)
 278 {
 279         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 280         struct rhash_lock_head __rcu **bkt = rht_bucket_var(old_tbl, old_hash);
 281         unsigned long flags;
 282         int err;
 283
 284         if (!bkt)
 285                 return 0;
 286         flags = rht_lock(old_tbl, bkt);
 287
 288         while (!(err = rhashtable_rehash_one(ht, bkt, old_hash)))
 289                 ;
 290
 291         if (err == -ENOENT)
 292                 err = 0;
 293         rht_unlock(old_tbl, bkt, flags);
 294
 295         return err;
 296 }
 297
 298 static int rhashtable_rehash_attach(struct rhashtable *ht,
 299                                     struct bucket_table *old_tbl,
 300                                     struct bucket_table *new_tbl)
 301 {
 302         /* Make insertions go into the new, empty table right away. Deletions
 303          * and lookups will be attempted in both tables until we synchronize.
 304          * As cmpxchg() provides strong barriers, we do not need
 305          * rcu_assign_pointer().
 306          */
 307
 308         if (cmpxchg((struct bucket_table **)&old_tbl->future_tbl, NULL,
 309                     new_tbl) != NULL)
 310                 return -EEXIST;
 311
 312         return 0;
 313 }
 314
 315 static int rhashtable_rehash_table(struct rhashtable *ht)
 316 {
 317         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 318         struct bucket_table *new_tbl;
 319         struct rhashtable_walker *walker;
 320         unsigned int old_hash;
 321         int err;
 322
 323         new_tbl = rht_dereference(old_tbl->future_tbl, ht);
 324         if (!new_tbl)
 325                 return 0;
 326
 327         for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
 328                 err = rhashtable_rehash_chain(ht, old_hash);
 329                 if (err)
 330                         return err;
 331                 cond_resched();
 332         }
 333
 334         /* Publish the new table pointer. */
 335         rcu_assign_pointer(ht->tbl, new_tbl);
 336
 337         spin_lock(&ht->lock);
 338         list_for_each_entry(walker, &old_tbl->walkers, list)
 339                 walker->tbl = NULL;
 340
 341         /* Wait for readers. All new readers will see the new
 342          * table, and thus no references to the old table will
 343          * remain.
 344          * We do this inside the locked region so that
 345          * rhashtable_walk_stop() can use rcu_head_after_call_rcu()
 346          * to check if it should not re-link the table.
 347          */
 348         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
 349         spin_unlock(&ht->lock);
 350
 351         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
 352 }
 353
 354 static int rhashtable_rehash_alloc(struct rhashtable *ht,
 355                                    struct bucket_table *old_tbl,
 356                                    unsigned int size)
 357 {
 358         struct bucket_table *new_tbl;
 359         int err;
 360
 361         ASSERT_RHT_MUTEX(ht);
 362
 363         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
 364         if (new_tbl == NULL)
 365                 return -ENOMEM;
 366
 367         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
 368         if (err)
 369                 bucket_table_free(new_tbl);
 370
 371         return err;
 372 }
 373
 374 /**
 375  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 376  * @ht:         the hash table to shrink
 377  *
 378  * This function shrinks the hash table to fit, i.e., the smallest
 379  * size would not cause it to expand right away automatically.
 380  *
 381  * The caller must ensure that no concurrent resizing occurs by holding
 382  * ht->mutex.
 383  *
 384  * The caller must ensure that no concurrent table mutations take place.
 385  * It is however valid to have concurrent lookups if they are RCU protected.
 386  *
 387  * It is valid to have concurrent insertions and deletions protected by per
 388  * bucket locks or concurrent RCU protected lookups and traversals.
 389  */
 390 static int rhashtable_shrink(struct rhashtable *ht)
 391 {
 392         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
 393         unsigned int nelems = atomic_read(&ht->nelems);
 394         unsigned int size = 0;
 395
 396         if (nelems)
 397                 size = roundup_pow_of_two(nelems * 3 / 2);
 398         if (size < ht->p.min_size)
 399                 size = ht->p.min_size;
 400
 401         if (old_tbl->size <= size)
 402                 return 0;
 403
 404         if (rht_dereference(old_tbl->future_tbl, ht))
 405                 return -EEXIST;
 406
 407         return rhashtable_rehash_alloc(ht, old_tbl, size);
 408 }
 409
 410 static void rht_deferred_worker(struct work_struct *work)
 411 {
 412         struct rhashtable *ht;
 413         struct bucket_table *tbl;
 414         int err = 0;
 415
 416         ht = container_of(work, struct rhashtable, run_work);
 417         mutex_lock(&ht->mutex);
 418
 419         tbl = rht_dereference(ht->tbl, ht);
 420         tbl = rhashtable_last_table(ht, tbl);
 421
 422         if (rht_grow_above_75(ht, tbl))
 423                 err = rhashtable_rehash_alloc(ht, tbl, tbl->size * 2);
 424         else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
 425                 err = rhashtable_shrink(ht);
 426         else if (tbl->nest)
 427                 err = rhashtable_rehash_alloc(ht, tbl, tbl->size);
 428
 429         if (!err || err == -EEXIST) {
 430                 int nerr;
 431
 432                 nerr = rhashtable_rehash_table(ht);
 433                 err = err ?: nerr;
 434         }
 435
 436         mutex_unlock(&ht->mutex);
 437
 438         if (err)
 439                 schedule_work(&ht->run_work);
 440 }
 441
 442 static int rhashtable_insert_rehash(struct rhashtable *ht,
 443                                     struct bucket_table *tbl)
 444 {
 445         struct bucket_table *old_tbl;
 446         struct bucket_table *new_tbl;
 447         unsigned int size;
 448         int err;
 449
 450         old_tbl = rht_dereference_rcu(ht->tbl, ht);
 451
 452         size = tbl->size;
 453
 454         err = -EBUSY;
 455
 456         if (rht_grow_above_75(ht, tbl))
 457                 size *= 2;
 458         /* Do not schedule more than one rehash */
 459         else if (old_tbl != tbl)
 460                 goto fail;
 461
 462         err = -ENOMEM;
 463
 464         new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC | __GFP_NOWARN);
 465         if (new_tbl == NULL)
 466                 goto fail;
 467
 468         err = rhashtable_rehash_attach(ht, tbl, new_tbl);
 469         if (err) {
 470                 bucket_table_free(new_tbl);
 471                 if (err == -EEXIST)
 472                         err = 0;
 473         } else
 474                 schedule_work(&ht->run_work);
 475
 476         return err;
 477
 478 fail:
 479         /* Do not fail the insert if someone else did a rehash. */
 480         if (likely(rcu_access_pointer(tbl->future_tbl)))
 481                 return 0;
 482
 483         /* Schedule async rehash to retry allocation in process context. */
 484         if (err == -ENOMEM)
 485                 schedule_work(&ht->run_work);
 486
 487         return err;
 488 }
 489
 490 static void *rhashtable_lookup_one(struct rhashtable *ht,
 491                                    struct rhash_lock_head __rcu **bkt,
 492                                    struct bucket_table *tbl, unsigned int hash,
 493                                    const void *key, struct rhash_head *obj)
 494 {
 495         struct rhashtable_compare_arg arg = {
 496                 .ht = ht,
 497                 .key = key,
 498         };
 499         struct rhash_head __rcu **pprev = NULL;
 500         struct rhash_head *head;
 501         int elasticity;
 502
 503         elasticity = RHT_ELASTICITY;
 504         rht_for_each_from(head, rht_ptr(bkt, tbl, hash), tbl, hash) {
 505                 struct rhlist_head *list;
 506                 struct rhlist_head *plist;
 507
 508                 elasticity--;
 509                 if (!key ||
 510                     (ht->p.obj_cmpfn ?
 511                      ht->p.obj_cmpfn(&arg, rht_obj(ht, head)) :
 512                      rhashtable_compare(&arg, rht_obj(ht, head)))) {
 513                         pprev = &head->next;
 514                         continue;
 515                 }
 516
 517                 if (!ht->rhlist)
 518                         return rht_obj(ht, head);
 519
 520                 list = container_of(obj, struct rhlist_head, rhead);
 521                 plist = container_of(head, struct rhlist_head, rhead);
 522
 523                 RCU_INIT_POINTER(list->next, plist);
 524                 head = rht_dereference_bucket(head->next, tbl, hash);
 525                 RCU_INIT_POINTER(list->rhead.next, head);
 526                 if (pprev)
 527                         rcu_assign_pointer(*pprev, obj);
 528                 else
 529                         /* Need to preserve the bit lock */
 530                         rht_assign_locked(bkt, obj);
 531
 532                 return NULL;
 533         }
 534
 535         if (elasticity <= 0)
 536                 return ERR_PTR(-EAGAIN);
 537
 538         return ERR_PTR(-ENOENT);
 539 }
 540
 541 static struct bucket_table *rhashtable_insert_one(
 542         struct rhashtable *ht, struct rhash_lock_head __rcu **bkt,
 543         struct bucket_table *tbl, unsigned int hash, struct rhash_head *obj,
 544         void *data)
 545 {
 546         struct bucket_table *new_tbl;
 547         struct rhash_head *head;
 548
 549         if (!IS_ERR_OR_NULL(data))
 550                 return ERR_PTR(-EEXIST);
 551
 552         if (PTR_ERR(data) != -EAGAIN && PTR_ERR(data) != -ENOENT)
 553                 return ERR_CAST(data);
 554
 555         new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 556         if (new_tbl)
 557                 return new_tbl;
 558
 559         if (PTR_ERR(data) != -ENOENT)
 560                 return ERR_CAST(data);
 561
 562         if (unlikely(rht_grow_above_max(ht, tbl)))
 563                 return ERR_PTR(-E2BIG);
 564
 565         if (unlikely(rht_grow_above_100(ht, tbl)))
 566                 return ERR_PTR(-EAGAIN);
 567
 568         head = rht_ptr(bkt, tbl, hash);
 569
 570         RCU_INIT_POINTER(obj->next, head);
 571         if (ht->rhlist) {
 572                 struct rhlist_head *list;
 573
 574                 list = container_of(obj, struct rhlist_head, rhead);
 575                 RCU_INIT_POINTER(list->next, NULL);
 576         }
 577
 578         /* bkt is always the head of the list, so it holds
 579          * the lock, which we need to preserve
 580          */
 581         rht_assign_locked(bkt, obj);
 582
 583         atomic_inc(&ht->nelems);
 584         if (rht_grow_above_75(ht, tbl))
 585                 schedule_work(&ht->run_work);
 586
 587         return NULL;
 588 }
 589
 590 static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
 591                                    struct rhash_head *obj)
 592 {
 593         struct bucket_table *new_tbl;
 594         struct bucket_table *tbl;
 595         struct rhash_lock_head __rcu **bkt;
 596         unsigned long flags;
 597         unsigned int hash;
 598         void *data;
 599
 600         new_tbl = rcu_dereference(ht->tbl);
 601
 602         do {
 603                 tbl = new_tbl;
 604                 hash = rht_head_hashfn(ht, tbl, obj, ht->p);
 605                 if (rcu_access_pointer(tbl->future_tbl))
 606                         /* Failure is OK */
 607                         bkt = rht_bucket_var(tbl, hash);
 608                 else
 609                         bkt = rht_bucket_insert(ht, tbl, hash);
 610                 if (bkt == NULL) {
 611                         new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 612                         data = ERR_PTR(-EAGAIN);
 613                 } else {
 614                         flags = rht_lock(tbl, bkt);
 615                         data = rhashtable_lookup_one(ht, bkt, tbl,
 616                                                      hash, key, obj);
 617                         new_tbl = rhashtable_insert_one(ht, bkt, tbl,
 618                                                         hash, obj, data);
 619                         if (PTR_ERR(new_tbl) != -EEXIST)
 620                                 data = ERR_CAST(new_tbl);
 621
 622                         rht_unlock(tbl, bkt, flags);
 623                 }
 624         } while (!IS_ERR_OR_NULL(new_tbl));
 625
 626         if (PTR_ERR(data) == -EAGAIN)
 627                 data = ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?:
 628                                -EAGAIN);
 629
 630         return data;
 631 }
 632
 633 void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
 634                              struct rhash_head *obj)
 635 {
 636         void *data;
 637
 638         do {
 639                 rcu_read_lock();
 640                 data = rhashtable_try_insert(ht, key, obj);
 641                 rcu_read_unlock();
 642         } while (PTR_ERR(data) == -EAGAIN);
 643
 644         return data;
 645 }
 646 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
 647
 648 /**
 649  * rhashtable_walk_enter - Initialise an iterator
 650  * @ht:         Table to walk over
 651  * @iter:       Hash table Iterator
 652  *
 653  * This function prepares a hash table walk.
 654  *
 655  * Note that if you restart a walk after rhashtable_walk_stop you
 656  * may see the same object twice.  Also, you may miss objects if
 657  * there are removals in between rhashtable_walk_stop and the next
 658  * call to rhashtable_walk_start.
 659  *
 660  * For a completely stable walk you should construct your own data
 661  * structure outside the hash table.
 662  *
 663  * This function may be called from any process context, including
 664  * non-preemptable context, but cannot be called from softirq or
 665  * hardirq context.
 666  *
 667  * You must call rhashtable_walk_exit after this function returns.
 668  */
 669 void rhashtable_walk_enter(struct rhashtable *ht, struct rhashtable_iter *iter)
 670 {
 671         iter->ht = ht;
 672         iter->p = NULL;
 673         iter->slot = 0;
 674         iter->skip = 0;
 675         iter->end_of_table = 0;
 676
 677         spin_lock(&ht->lock);
 678         iter->walker.tbl =
 679                 rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
 680         list_add(&iter->walker.list, &iter->walker.tbl->walkers);
 681         spin_unlock(&ht->lock);
 682 }
 683 EXPORT_SYMBOL_GPL(rhashtable_walk_enter);
 684
 685 /**
 686  * rhashtable_walk_exit - Free an iterator
 687  * @iter:       Hash table Iterator
 688  *
 689  * This function frees resources allocated by rhashtable_walk_enter.
 690  */
 691 void rhashtable_walk_exit(struct rhashtable_iter *iter)
 692 {
 693         spin_lock(&iter->ht->lock);
 694         if (iter->walker.tbl)
 695                 list_del(&iter->walker.list);
 696         spin_unlock(&iter->ht->lock);
 697 }
 698 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
 699
 700 /**
 701  * rhashtable_walk_start_check - Start a hash table walk
 702  * @iter:       Hash table iterator
 703  *
 704  * Start a hash table walk at the current iterator position.  Note that we take
 705  * the RCU lock in all cases including when we return an error.  So you must
 706  * always call rhashtable_walk_stop to clean up.
 707  *
 708  * Returns zero if successful.
 709  *
 710  * Returns -EAGAIN if resize event occurred.  Note that the iterator
 711  * will rewind back to the beginning and you may use it immediately
 712  * by calling rhashtable_walk_next.
 713  *
 714  * rhashtable_walk_start is defined as an inline variant that returns
 715  * void. This is preferred in cases where the caller would ignore
 716  * resize events and always continue.
 717  */
 718 int rhashtable_walk_start_check(struct rhashtable_iter *iter)
 719         __acquires(RCU)
 720 {
 721         struct rhashtable *ht = iter->ht;
 722         bool rhlist = ht->rhlist;
 723
 724         rcu_read_lock();
 725
 726         spin_lock(&ht->lock);
 727         if (iter->walker.tbl)
 728                 list_del(&iter->walker.list);
 729         spin_unlock(&ht->lock);
 730
 731         if (iter->end_of_table)
 732                 return 0;
 733         if (!iter->walker.tbl) {
 734                 iter->walker.tbl = rht_dereference_rcu(ht->tbl, ht);
 735                 iter->slot = 0;
 736                 iter->skip = 0;
 737                 return -EAGAIN;
 738         }
 739
 740         if (iter->p && !rhlist) {
 741                 /*
 742                  * We need to validate that 'p' is still in the table, and
 743                  * if so, update 'skip'
 744                  */
 745                 struct rhash_head *p;
 746                 int skip = 0;
 747                 rht_for_each_rcu(p, iter->walker.tbl, iter->slot) {
 748                         skip++;
 749                         if (p == iter->p) {
 750                                 iter->skip = skip;
 751                                 goto found;
 752                         }
 753                 }
 754                 iter->p = NULL;
 755         } else if (iter->p && rhlist) {
 756                 /* Need to validate that 'list' is still in the table, and
 757                  * if so, update 'skip' and 'p'.
 758                  */
 759                 struct rhash_head *p;
 760                 struct rhlist_head *list;
 761                 int skip = 0;
 762                 rht_for_each_rcu(p, iter->walker.tbl, iter->slot) {
 763                         for (list = container_of(p, struct rhlist_head, rhead);
 764                              list;
 765                              list = rcu_dereference(list->next)) {
 766                                 skip++;
 767                                 if (list == iter->list) {
 768                                         iter->p = p;
 769                                         iter->skip = skip;
 770                                         goto found;
 771                                 }
 772                         }
 773                 }
 774                 iter->p = NULL;
 775         }
 776 found:
 777         return 0;
 778 }
 779 EXPORT_SYMBOL_GPL(rhashtable_walk_start_check);
 780
 781 /**
 782  * __rhashtable_walk_find_next - Find the next element in a table (or the first
 783  * one in case of a new walk).
 784  *
 785  * @iter:       Hash table iterator
 786  *
 787  * Returns the found object or NULL when the end of the table is reached.
 788  *
 789  * Returns -EAGAIN if resize event occurred.
 790  */
 791 static void *__rhashtable_walk_find_next(struct rhashtable_iter *iter)
 792 {
 793         struct bucket_table *tbl = iter->walker.tbl;
 794         struct rhlist_head *list = iter->list;
 795         struct rhashtable *ht = iter->ht;
 796         struct rhash_head *p = iter->p;
 797         bool rhlist = ht->rhlist;
 798
 799         if (!tbl)
 800                 return NULL;
 801
 802         for (; iter->slot < tbl->size; iter->slot++) {
 803                 int skip = iter->skip;
 804
 805                 rht_for_each_rcu(p, tbl, iter->slot) {
 806                         if (rhlist) {
 807                                 list = container_of(p, struct rhlist_head,
 808                                                     rhead);
 809                                 do {
 810                                         if (!skip)
 811                                                 goto next;
 812                                         skip--;
 813                                         list = rcu_dereference(list->next);
 814                                 } while (list);
 815
 816                                 continue;
 817                         }
 818                         if (!skip)
 819                                 break;
 820                         skip--;
 821                 }
 822
 823 next:
 824                 if (!rht_is_a_nulls(p)) {
 825                         iter->skip++;
 826                         iter->p = p;
 827                         iter->list = list;
 828                         return rht_obj(ht, rhlist ? &list->rhead : p);
 829                 }
 830
 831                 iter->skip = 0;
 832         }
 833
 834         iter->p = NULL;
 835
 836         /* Ensure we see any new tables. */
 837         smp_rmb();
 838
 839         iter->walker.tbl = rht_dereference_rcu(tbl->future_tbl, ht);
 840         if (iter->walker.tbl) {
 841                 iter->slot = 0;
 842                 iter->skip = 0;
 843                 return ERR_PTR(-EAGAIN);
 844         } else {
 845                 iter->end_of_table = true;
 846         }
 847
 848         return NULL;
 849 }
 850
 851 /**
 852  * rhashtable_walk_next - Return the next object and advance the iterator
 853  * @iter:       Hash table iterator
 854  *
 855  * Note that you must call rhashtable_walk_stop when you are finished
 856  * with the walk.
 857  *
 858  * Returns the next object or NULL when the end of the table is reached.
 859  *
 860  * Returns -EAGAIN if resize event occurred.  Note that the iterator
 861  * will rewind back to the beginning and you may continue to use it.
 862  */
 863 void *rhashtable_walk_next(struct rhashtable_iter *iter)
 864 {
 865         struct rhlist_head *list = iter->list;
 866         struct rhashtable *ht = iter->ht;
 867         struct rhash_head *p = iter->p;
 868         bool rhlist = ht->rhlist;
 869
 870         if (p) {
 871                 if (!rhlist || !(list = rcu_dereference(list->next))) {
 872                         p = rcu_dereference(p->next);
 873                         list = container_of(p, struct rhlist_head, rhead);
 874                 }
 875                 if (!rht_is_a_nulls(p)) {
 876                         iter->skip++;
 877                         iter->p = p;
 878                         iter->list = list;
 879                         return rht_obj(ht, rhlist ? &list->rhead : p);
 880                 }
 881
 882                 /* At the end of this slot, switch to next one and then find
 883                  * next entry from that point.
 884                  */
 885                 iter->skip = 0;
 886                 iter->slot++;
 887         }
 888
 889         return __rhashtable_walk_find_next(iter);
 890 }
 891 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
 892
 893 /**
 894  * rhashtable_walk_peek - Return the next object but don't advance the iterator
 895  * @iter:       Hash table iterator
 896  *
 897  * Returns the next object or NULL when the end of the table is reached.
 898  *
 899  * Returns -EAGAIN if resize event occurred.  Note that the iterator
 900  * will rewind back to the beginning and you may continue to use it.
 901  */
 902 void *rhashtable_walk_peek(struct rhashtable_iter *iter)
 903 {
 904         struct rhlist_head *list = iter->list;
 905         struct rhashtable *ht = iter->ht;
 906         struct rhash_head *p = iter->p;
 907
 908         if (p)
 909                 return rht_obj(ht, ht->rhlist ? &list->rhead : p);
 910
 911         /* No object found in current iter, find next one in the table. */
 912
 913         if (iter->skip) {
 914                 /* A nonzero skip value points to the next entry in the table
 915                  * beyond that last one that was found. Decrement skip so
 916                  * we find the current value. __rhashtable_walk_find_next
 917                  * will restore the original value of skip assuming that
 918                  * the table hasn't changed.
 919                  */
 920                 iter->skip--;
 921         }
 922
 923         return __rhashtable_walk_find_next(iter);
 924 }
 925 EXPORT_SYMBOL_GPL(rhashtable_walk_peek);
 926
 927 /**
 928  * rhashtable_walk_stop - Finish a hash table walk
 929  * @iter:       Hash table iterator
 930  *
 931  * Finish a hash table walk.  Does not reset the iterator to the start of the
 932  * hash table.
 933  */
 934 void rhashtable_walk_stop(struct rhashtable_iter *iter)
 935         __releases(RCU)
 936 {
 937         struct rhashtable *ht;
 938         struct bucket_table *tbl = iter->walker.tbl;
 939
 940         if (!tbl)
 941                 goto out;
 942
 943         ht = iter->ht;
 944
 945         spin_lock(&ht->lock);
 946         if (rcu_head_after_call_rcu(&tbl->rcu, bucket_table_free_rcu))
 947                 /* This bucket table is being freed, don't re-link it. */
 948                 iter->walker.tbl = NULL;
 949         else
 950                 list_add(&iter->walker.list, &tbl->walkers);
 951         spin_unlock(&ht->lock);
 952
 953 out:
 954         rcu_read_unlock();
 955 }
 956 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
 957
 958 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
 959 {
 960         size_t retsize;
 961
 962         if (params->nelem_hint)
 963                 retsize = max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
 964                               (unsigned long)params->min_size);
 965         else
 966                 retsize = max(HASH_DEFAULT_SIZE,
 967                               (unsigned long)params->min_size);
 968
 969         return retsize;
 970 }
 971
 972 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
 973 {
 974         return jhash2(key, length, seed);
 975 }
 976
 977 /**
 978  * rhashtable_init - initialize a new hash table
 979  * @ht:         hash table to be initialized
 980  * @params:     configuration parameters
 981  *
 982  * Initializes a new hash table based on the provided configuration
 983  * parameters. A table can be configured either with a variable or
 984  * fixed length key:
 985  *
 986  * Configuration Example 1: Fixed length keys
 987  * struct test_obj {
 988  *      int                     key;
 989  *      void *                  my_member;
 990  *      struct rhash_head       node;
 991  * };
 992  *
 993  * struct rhashtable_params params = {
 994  *      .head_offset = offsetof(struct test_obj, node),
 995  *      .key_offset = offsetof(struct test_obj, key),
 996  *      .key_len = sizeof(int),
 997  *      .hashfn = jhash,
 998  * };
 999  *
1000  * Configuration Example 2: Variable length keys
1001  * struct test_obj {
1002  *      [...]
1003  *      struct rhash_head       node;
1004  * };
1005  *
1006  * u32 my_hash_fn(const void *data, u32 len, u32 seed)
1007  * {
1008  *      struct test_obj *obj = data;
1009  *
1010  *      return [... hash ...];
1011  * }
1012  *
1013  * struct rhashtable_params params = {
1014  *      .head_offset = offsetof(struct test_obj, node),
1015  *      .hashfn = jhash,
1016  *      .obj_hashfn = my_hash_fn,
1017  * };
1018  */
1019 int rhashtable_init(struct rhashtable *ht,
1020                     const struct rhashtable_params *params)
1021 {
1022         struct bucket_table *tbl;
1023         size_t size;
1024
1025         if ((!params->key_len && !params->obj_hashfn) ||
1026             (params->obj_hashfn && !params->obj_cmpfn))
1027                 return -EINVAL;
1028
1029         memset(ht, 0, sizeof(*ht));
1030         mutex_init(&ht->mutex);
1031         spin_lock_init(&ht->lock);
1032         memcpy(&ht->p, params, sizeof(*params));
1033
1034         if (params->min_size)
1035                 ht->p.min_size = roundup_pow_of_two(params->min_size);
1036
1037         /* Cap total entries at 2^31 to avoid nelems overflow. */
1038         ht->max_elems = 1u << 31;
1039
1040         if (params->max_size) {
1041                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
1042                 if (ht->p.max_size < ht->max_elems / 2)
1043                         ht->max_elems = ht->p.max_size * 2;
1044         }
1045
1046         ht->p.min_size = max_t(u16, ht->p.min_size, HASH_MIN_SIZE);
1047
1048         size = rounded_hashtable_size(&ht->p);
1049
1050         ht->key_len = ht->p.key_len;
1051         if (!params->hashfn) {
1052                 ht->p.hashfn = jhash;
1053
1054                 if (!(ht->key_len & (sizeof(u32) - 1))) {
1055                         ht->key_len /= sizeof(u32);
1056                         ht->p.hashfn = rhashtable_jhash2;
1057                 }
1058         }
1059
1060         /*
1061          * This is api initialization and thus we need to guarantee the
1062          * initial rhashtable allocation. Upon failure, retry with the
1063          * smallest possible size with __GFP_NOFAIL semantics.
1064          */
1065         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
1066         if (unlikely(tbl == NULL)) {
1067                 size = max_t(u16, ht->p.min_size, HASH_MIN_SIZE);
1068                 tbl = bucket_table_alloc(ht, size, GFP_KERNEL | __GFP_NOFAIL);
1069         }
1070
1071         atomic_set(&ht->nelems, 0);
1072
1073         RCU_INIT_POINTER(ht->tbl, tbl);
1074
1075         INIT_WORK(&ht->run_work, rht_deferred_worker);
1076
1077         return 0;
1078 }
1079 EXPORT_SYMBOL_GPL(rhashtable_init);
1080
1081 /**
1082  * rhltable_init - initialize a new hash list table
1083  * @hlt:        hash list table to be initialized
1084  * @params:     configuration parameters
1085  *
1086  * Initializes a new hash list table.
1087  *
1088  * See documentation for rhashtable_init.
1089  */
1090 int rhltable_init(struct rhltable *hlt, const struct rhashtable_params *params)
1091 {
1092         int err;
1093
1094         err = rhashtable_init(&hlt->ht, params);
1095         hlt->ht.rhlist = true;
1096         return err;
1097 }
1098 EXPORT_SYMBOL_GPL(rhltable_init);
1099
1100 static void rhashtable_free_one(struct rhashtable *ht, struct rhash_head *obj,
1101                                 void (*free_fn)(void *ptr, void *arg),
1102                                 void *arg)
1103 {
1104         struct rhlist_head *list;
1105
1106         if (!ht->rhlist) {
1107                 free_fn(rht_obj(ht, obj), arg);
1108                 return;
1109         }
1110
1111         list = container_of(obj, struct rhlist_head, rhead);
1112         do {
1113                 obj = &list->rhead;
1114                 list = rht_dereference(list->next, ht);
1115                 free_fn(rht_obj(ht, obj), arg);
1116         } while (list);
1117 }
1118
1119 /**
1120  * rhashtable_free_and_destroy - free elements and destroy hash table
1121  * @ht:         the hash table to destroy
1122  * @free_fn:    callback to release resources of element
1123  * @arg:        pointer passed to free_fn
1124  *
1125  * Stops an eventual async resize. If defined, invokes free_fn for each
1126  * element to releasal resources. Please note that RCU protected
1127  * readers may still be accessing the elements. Releasing of resources
1128  * must occur in a compatible manner. Then frees the bucket array.
1129  *
1130  * This function will eventually sleep to wait for an async resize
1131  * to complete. The caller is responsible that no further write operations
1132  * occurs in parallel.
1133  */
1134 void rhashtable_free_and_destroy(struct rhashtable *ht,
1135                                  void (*free_fn)(void *ptr, void *arg),
1136                                  void *arg)
1137 {
1138         struct bucket_table *tbl, *next_tbl;
1139         unsigned int i;
1140
1141         cancel_work_sync(&ht->run_work);
1142
1143         mutex_lock(&ht->mutex);
1144         tbl = rht_dereference(ht->tbl, ht);
1145 restart:
1146         if (free_fn) {
1147                 for (i = 0; i < tbl->size; i++) {
1148                         struct rhash_head *pos, *next;
1149
1150                         cond_resched();
1151                         for (pos = rht_ptr_exclusive(rht_bucket(tbl, i)),
1152                              next = !rht_is_a_nulls(pos) ?
1153                                         rht_dereference(pos->next, ht) : NULL;
1154                              !rht_is_a_nulls(pos);
1155                              pos = next,
1156                              next = !rht_is_a_nulls(pos) ?
1157                                         rht_dereference(pos->next, ht) : NULL)
1158                                 rhashtable_free_one(ht, pos, free_fn, arg);
1159                 }
1160         }
1161
1162         next_tbl = rht_dereference(tbl->future_tbl, ht);
1163         bucket_table_free(tbl);
1164         if (next_tbl) {
1165                 tbl = next_tbl;
1166                 goto restart;
1167         }
1168         mutex_unlock(&ht->mutex);
1169 }
1170 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
1171
1172 void rhashtable_destroy(struct rhashtable *ht)
1173 {
1174         return rhashtable_free_and_destroy(ht, NULL, NULL);
1175 }
1176 EXPORT_SYMBOL_GPL(rhashtable_destroy);
1177
1178 struct rhash_lock_head __rcu **__rht_bucket_nested(
1179         const struct bucket_table *tbl, unsigned int hash)
1180 {
1181         const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
1182         unsigned int index = hash & ((1 << tbl->nest) - 1);
1183         unsigned int size = tbl->size >> tbl->nest;
1184         unsigned int subhash = hash;
1185         union nested_table *ntbl;
1186
1187         ntbl = nested_table_top(tbl);
1188         ntbl = rht_dereference_bucket_rcu(ntbl[index].table, tbl, hash);
1189         subhash >>= tbl->nest;
1190
1191         while (ntbl && size > (1 << shift)) {
1192                 index = subhash & ((1 << shift) - 1);
1193                 ntbl = rht_dereference_bucket_rcu(ntbl[index].table,
1194                                                   tbl, hash);
1195                 size >>= shift;
1196                 subhash >>= shift;
1197         }
1198
1199         if (!ntbl)
1200                 return NULL;
1201
1202         return &ntbl[subhash].bucket;
1203
1204 }
1205 EXPORT_SYMBOL_GPL(__rht_bucket_nested);
1206
1207 struct rhash_lock_head __rcu **rht_bucket_nested(
1208         const struct bucket_table *tbl, unsigned int hash)
1209 {
1210         static struct rhash_lock_head __rcu *rhnull;
1211
1212         if (!rhnull)
1213                 INIT_RHT_NULLS_HEAD(rhnull);
1214         return __rht_bucket_nested(tbl, hash) ?: &rhnull;
1215 }
1216 EXPORT_SYMBOL_GPL(rht_bucket_nested);
1217
1218 struct rhash_lock_head __rcu **rht_bucket_nested_insert(
1219         struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash)
1220 {
1221         const unsigned int shift = PAGE_SHIFT - ilog2(sizeof(void *));
1222         unsigned int index = hash & ((1 << tbl->nest) - 1);
1223         unsigned int size = tbl->size >> tbl->nest;
1224         union nested_table *ntbl;
1225
1226         ntbl = nested_table_top(tbl);
1227         hash >>= tbl->nest;
1228         ntbl = nested_table_alloc(ht, &ntbl[index].table,
1229                                   size <= (1 << shift));
1230
1231         while (ntbl && size > (1 << shift)) {
1232                 index = hash & ((1 << shift) - 1);
1233                 size >>= shift;
1234                 hash >>= shift;
1235                 ntbl = nested_table_alloc(ht, &ntbl[index].table,
1236                                           size <= (1 << shift));
1237         }
1238
1239         if (!ntbl)
1240                 return NULL;
1241
1242         return &ntbl[hash].bucket;
1243
1244 }
1245 EXPORT_SYMBOL_GPL(rht_bucket_nested_insert);