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