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