Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/lib/rhashtable.c

  1 /*
  2  * Resizable, Scalable, Concurrent Hash Table
  3  *
  4  * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au>
  5  * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch>
  6  * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
  7  *
  8  * Code partially derived from nft_hash
  9  * Rewritten with rehash code from br_multicast plus single list
 10  * pointer as suggested by Josh Triplett
 11  *
 12  * This program is free software; you can redistribute it and/or modify
 13  * it under the terms of the GNU General Public License version 2 as
 14  * published by the Free Software Foundation.
 15  */
 16 
 17 #include <linux/atomic.h>
 18 #include <linux/kernel.h>
 19 #include <linux/init.h>
 20 #include <linux/log2.h>
 21 #include <linux/sched.h>
 22 #include <linux/slab.h>
 23 #include <linux/vmalloc.h>
 24 #include <linux/mm.h>
 25 #include <linux/jhash.h>
 26 #include <linux/random.h>
 27 #include <linux/rhashtable.h>
 28 #include <linux/err.h>
 29 #include <linux/export.h>
 30 
 31 #define HASH_DEFAULT_SIZE       64UL
 32 #define HASH_MIN_SIZE           4U
 33 #define BUCKET_LOCKS_PER_CPU    32UL
 34 
 35 static u32 head_hashfn(struct rhashtable *ht,
 36                        const struct bucket_table *tbl,
 37                        const struct rhash_head *he)
 38 {
 39         return rht_head_hashfn(ht, tbl, he, ht->p);
 40 }
 41 
 42 #ifdef CONFIG_PROVE_LOCKING
 43 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
 44 
 45 int lockdep_rht_mutex_is_held(struct rhashtable *ht)
 46 {
 47         return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
 48 }
 49 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
 50 
 51 int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
 52 {
 53         spinlock_t *lock = rht_bucket_lock(tbl, hash);
 54 
 55         return (debug_locks) ? lockdep_is_held(lock) : 1;
 56 }
 57 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
 58 #else
 59 #define ASSERT_RHT_MUTEX(HT)
 60 #endif
 61 
 62 
 63 static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
 64                               gfp_t gfp)
 65 {
 66         unsigned int i, size;
 67 #if defined(CONFIG_PROVE_LOCKING)
 68         unsigned int nr_pcpus = 2;
 69 #else
 70         unsigned int nr_pcpus = num_possible_cpus();
 71 #endif
 72 
 73         nr_pcpus = min_t(unsigned int, nr_pcpus, 64UL);
 74         size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);
 75 
 76         /* Never allocate more than 0.5 locks per bucket */
 77         size = min_t(unsigned int, size, tbl->size >> 1);
 78 
 79         if (sizeof(spinlock_t) != 0) {
 80                 tbl->locks = NULL;
 81 #ifdef CONFIG_NUMA
 82                 if (size * sizeof(spinlock_t) > PAGE_SIZE &&
 83                     gfp == GFP_KERNEL)
 84                         tbl->locks = vmalloc(size * sizeof(spinlock_t));
 85 #endif
 86                 if (gfp != GFP_KERNEL)
 87                         gfp |= __GFP_NOWARN | __GFP_NORETRY;
 88 
 89                 if (!tbl->locks)
 90                         tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
 91                                                    gfp);
 92                 if (!tbl->locks)
 93                         return -ENOMEM;
 94                 for (i = 0; i < size; i++)
 95                         spin_lock_init(&tbl->locks[i]);
 96         }
 97         tbl->locks_mask = size - 1;
 98 
 99         return 0;
100 }
101 
102 static void bucket_table_free(const struct bucket_table *tbl)
103 {
104         if (tbl)
105                 kvfree(tbl->locks);
106 
107         kvfree(tbl);
108 }
109 
110 static void bucket_table_free_rcu(struct rcu_head *head)
111 {
112         bucket_table_free(container_of(head, struct bucket_table, rcu));
113 }
114 
115 static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
116                                                size_t nbuckets,
117                                                gfp_t gfp)
118 {
119         struct bucket_table *tbl = NULL;
120         size_t size;
121         int i;
122 
123         size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
124         if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) ||
125             gfp != GFP_KERNEL)
126                 tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY);
127         if (tbl == NULL && gfp == GFP_KERNEL)
128                 tbl = vzalloc(size);
129         if (tbl == NULL)
130                 return NULL;
131 
132         tbl->size = nbuckets;
133 
134         if (alloc_bucket_locks(ht, tbl, gfp) < 0) {
135                 bucket_table_free(tbl);
136                 return NULL;
137         }
138 
139         INIT_LIST_HEAD(&tbl->walkers);
140 
141         get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd));
142 
143         for (i = 0; i < nbuckets; i++)
144                 INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);
145 
146         return tbl;
147 }
148 
149 static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
150                                                   struct bucket_table *tbl)
151 {
152         struct bucket_table *new_tbl;
153 
154         do {
155                 new_tbl = tbl;
156                 tbl = rht_dereference_rcu(tbl->future_tbl, ht);
157         } while (tbl);
158 
159         return new_tbl;
160 }
161 
162 static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
163 {
164         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
165         struct bucket_table *new_tbl = rhashtable_last_table(ht,
166                 rht_dereference_rcu(old_tbl->future_tbl, ht));
167         struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash];
168         int err = -ENOENT;
169         struct rhash_head *head, *next, *entry;
170         spinlock_t *new_bucket_lock;
171         unsigned int new_hash;
172 
173         rht_for_each(entry, old_tbl, old_hash) {
174                 err = 0;
175                 next = rht_dereference_bucket(entry->next, old_tbl, old_hash);
176 
177                 if (rht_is_a_nulls(next))
178                         break;
179 
180                 pprev = &entry->next;
181         }
182 
183         if (err)
184                 goto out;
185 
186         new_hash = head_hashfn(ht, new_tbl, entry);
187 
188         new_bucket_lock = rht_bucket_lock(new_tbl, new_hash);
189 
190         spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING);
191         head = rht_dereference_bucket(new_tbl->buckets[new_hash],
192                                       new_tbl, new_hash);
193 
194         RCU_INIT_POINTER(entry->next, head);
195 
196         rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
197         spin_unlock(new_bucket_lock);
198 
199         rcu_assign_pointer(*pprev, next);
200 
201 out:
202         return err;
203 }
204 
205 static void rhashtable_rehash_chain(struct rhashtable *ht,
206                                     unsigned int old_hash)
207 {
208         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
209         spinlock_t *old_bucket_lock;
210 
211         old_bucket_lock = rht_bucket_lock(old_tbl, old_hash);
212 
213         spin_lock_bh(old_bucket_lock);
214         while (!rhashtable_rehash_one(ht, old_hash))
215                 ;
216         old_tbl->rehash++;
217         spin_unlock_bh(old_bucket_lock);
218 }
219 
220 static int rhashtable_rehash_attach(struct rhashtable *ht,
221                                     struct bucket_table *old_tbl,
222                                     struct bucket_table *new_tbl)
223 {
224         /* Protect future_tbl using the first bucket lock. */
225         spin_lock_bh(old_tbl->locks);
226 
227         /* Did somebody beat us to it? */
228         if (rcu_access_pointer(old_tbl->future_tbl)) {
229                 spin_unlock_bh(old_tbl->locks);
230                 return -EEXIST;
231         }
232 
233         /* Make insertions go into the new, empty table right away. Deletions
234          * and lookups will be attempted in both tables until we synchronize.
235          */
236         rcu_assign_pointer(old_tbl->future_tbl, new_tbl);
237 
238         spin_unlock_bh(old_tbl->locks);
239 
240         return 0;
241 }
242 
243 static int rhashtable_rehash_table(struct rhashtable *ht)
244 {
245         struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
246         struct bucket_table *new_tbl;
247         struct rhashtable_walker *walker;
248         unsigned int old_hash;
249 
250         new_tbl = rht_dereference(old_tbl->future_tbl, ht);
251         if (!new_tbl)
252                 return 0;
253 
254         for (old_hash = 0; old_hash < old_tbl->size; old_hash++)
255                 rhashtable_rehash_chain(ht, old_hash);
256 
257         /* Publish the new table pointer. */
258         rcu_assign_pointer(ht->tbl, new_tbl);
259 
260         spin_lock(&ht->lock);
261         list_for_each_entry(walker, &old_tbl->walkers, list)
262                 walker->tbl = NULL;
263         spin_unlock(&ht->lock);
264 
265         /* Wait for readers. All new readers will see the new
266          * table, and thus no references to the old table will
267          * remain.
268          */
269         call_rcu(&old_tbl->rcu, bucket_table_free_rcu);
270 
271         return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0;
272 }
273 
274 /**
275  * rhashtable_expand - Expand hash table while allowing concurrent lookups
276  * @ht:         the hash table to expand
277  *
278  * A secondary bucket array is allocated and the hash entries are migrated.
279  *
280  * This function may only be called in a context where it is safe to call
281  * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
282  *
283  * The caller must ensure that no concurrent resizing occurs by holding
284  * ht->mutex.
285  *
286  * It is valid to have concurrent insertions and deletions protected by per
287  * bucket locks or concurrent RCU protected lookups and traversals.
288  */
289 static int rhashtable_expand(struct rhashtable *ht)
290 {
291         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
292         int err;
293 
294         ASSERT_RHT_MUTEX(ht);
295 
296         old_tbl = rhashtable_last_table(ht, old_tbl);
297 
298         new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL);
299         if (new_tbl == NULL)
300                 return -ENOMEM;
301 
302         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
303         if (err)
304                 bucket_table_free(new_tbl);
305 
306         return err;
307 }
308 
309 /**
310  * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
311  * @ht:         the hash table to shrink
312  *
313  * This function shrinks the hash table to fit, i.e., the smallest
314  * size would not cause it to expand right away automatically.
315  *
316  * The caller must ensure that no concurrent resizing occurs by holding
317  * ht->mutex.
318  *
319  * The caller must ensure that no concurrent table mutations take place.
320  * It is however valid to have concurrent lookups if they are RCU protected.
321  *
322  * It is valid to have concurrent insertions and deletions protected by per
323  * bucket locks or concurrent RCU protected lookups and traversals.
324  */
325 static int rhashtable_shrink(struct rhashtable *ht)
326 {
327         struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
328         unsigned int nelems = atomic_read(&ht->nelems);
329         unsigned int size = 0;
330         int err;
331 
332         ASSERT_RHT_MUTEX(ht);
333 
334         if (nelems)
335                 size = roundup_pow_of_two(nelems * 3 / 2);
336         if (size < ht->p.min_size)
337                 size = ht->p.min_size;
338 
339         if (old_tbl->size <= size)
340                 return 0;
341 
342         if (rht_dereference(old_tbl->future_tbl, ht))
343                 return -EEXIST;
344 
345         new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
346         if (new_tbl == NULL)
347                 return -ENOMEM;
348 
349         err = rhashtable_rehash_attach(ht, old_tbl, new_tbl);
350         if (err)
351                 bucket_table_free(new_tbl);
352 
353         return err;
354 }
355 
356 static void rht_deferred_worker(struct work_struct *work)
357 {
358         struct rhashtable *ht;
359         struct bucket_table *tbl;
360         int err = 0;
361 
362         ht = container_of(work, struct rhashtable, run_work);
363         mutex_lock(&ht->mutex);
364 
365         tbl = rht_dereference(ht->tbl, ht);
366         tbl = rhashtable_last_table(ht, tbl);
367 
368         if (rht_grow_above_75(ht, tbl))
369                 rhashtable_expand(ht);
370         else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl))
371                 rhashtable_shrink(ht);
372 
373         err = rhashtable_rehash_table(ht);
374 
375         mutex_unlock(&ht->mutex);
376 
377         if (err)
378                 schedule_work(&ht->run_work);
379 }
380 
381 static int rhashtable_insert_rehash(struct rhashtable *ht,
382                                     struct bucket_table *tbl)
383 {
384         struct bucket_table *old_tbl;
385         struct bucket_table *new_tbl;
386         unsigned int size;
387         int err;
388 
389         old_tbl = rht_dereference_rcu(ht->tbl, ht);
390 
391         size = tbl->size;
392 
393         err = -EBUSY;
394 
395         if (rht_grow_above_75(ht, tbl))
396                 size *= 2;
397         /* Do not schedule more than one rehash */
398         else if (old_tbl != tbl)
399                 goto fail;
400 
401         err = -ENOMEM;
402 
403         new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);
404         if (new_tbl == NULL)
405                 goto fail;
406 
407         err = rhashtable_rehash_attach(ht, tbl, new_tbl);
408         if (err) {
409                 bucket_table_free(new_tbl);
410                 if (err == -EEXIST)
411                         err = 0;
412         } else
413                 schedule_work(&ht->run_work);
414 
415         return err;
416 
417 fail:
418         /* Do not fail the insert if someone else did a rehash. */
419         if (likely(rcu_dereference_raw(tbl->future_tbl)))
420                 return 0;
421 
422         /* Schedule async rehash to retry allocation in process context. */
423         if (err == -ENOMEM)
424                 schedule_work(&ht->run_work);
425 
426         return err;
427 }
428 
429 static void *rhashtable_lookup_one(struct rhashtable *ht,
430                                    struct bucket_table *tbl, unsigned int hash,
431                                    const void *key, struct rhash_head *obj)
432 {
433         struct rhashtable_compare_arg arg = {
434                 .ht = ht,
435                 .key = key,
436         };
437         struct rhash_head __rcu **pprev;
438         struct rhash_head *head;
439         int elasticity;
440 
441         elasticity = ht->elasticity;
442         pprev = &tbl->buckets[hash];
443         rht_for_each(head, tbl, hash) {
444                 struct rhlist_head *list;
445                 struct rhlist_head *plist;
446 
447                 elasticity--;
448                 if (!key ||
449                     (ht->p.obj_cmpfn ?
450                      ht->p.obj_cmpfn(&arg, rht_obj(ht, head)) :
451                      rhashtable_compare(&arg, rht_obj(ht, head))))
452                         continue;
453 
454                 if (!ht->rhlist)
455                         return rht_obj(ht, head);
456 
457                 list = container_of(obj, struct rhlist_head, rhead);
458                 plist = container_of(head, struct rhlist_head, rhead);
459 
460                 RCU_INIT_POINTER(list->next, plist);
461                 head = rht_dereference_bucket(head->next, tbl, hash);
462                 RCU_INIT_POINTER(list->rhead.next, head);
463                 rcu_assign_pointer(*pprev, obj);
464 
465                 return NULL;
466         }
467 
468         if (elasticity <= 0)
469                 return ERR_PTR(-EAGAIN);
470 
471         return ERR_PTR(-ENOENT);
472 }
473 
474 static struct bucket_table *rhashtable_insert_one(struct rhashtable *ht,
475                                                   struct bucket_table *tbl,
476                                                   unsigned int hash,
477                                                   struct rhash_head *obj,
478                                                   void *data)
479 {
480         struct bucket_table *new_tbl;
481         struct rhash_head *head;
482 
483         if (!IS_ERR_OR_NULL(data))
484                 return ERR_PTR(-EEXIST);
485 
486         if (PTR_ERR(data) != -EAGAIN && PTR_ERR(data) != -ENOENT)
487                 return ERR_CAST(data);
488 
489         new_tbl = rcu_dereference(tbl->future_tbl);
490         if (new_tbl)
491                 return new_tbl;
492 
493         if (PTR_ERR(data) != -ENOENT)
494                 return ERR_CAST(data);
495 
496         if (unlikely(rht_grow_above_max(ht, tbl)))
497                 return ERR_PTR(-E2BIG);
498 
499         if (unlikely(rht_grow_above_100(ht, tbl)))
500                 return ERR_PTR(-EAGAIN);
501 
502         head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
503 
504         RCU_INIT_POINTER(obj->next, head);
505         if (ht->rhlist) {
506                 struct rhlist_head *list;
507 
508                 list = container_of(obj, struct rhlist_head, rhead);
509                 RCU_INIT_POINTER(list->next, NULL);
510         }
511 
512         rcu_assign_pointer(tbl->buckets[hash], obj);
513 
514         atomic_inc(&ht->nelems);
515         if (rht_grow_above_75(ht, tbl))
516                 schedule_work(&ht->run_work);
517 
518         return NULL;
519 }
520 
521 static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
522                                    struct rhash_head *obj)
523 {
524         struct bucket_table *new_tbl;
525         struct bucket_table *tbl;
526         unsigned int hash;
527         spinlock_t *lock;
528         void *data;
529 
530         tbl = rcu_dereference(ht->tbl);
531 
532         /* All insertions must grab the oldest table containing
533          * the hashed bucket that is yet to be rehashed.
534          */
535         for (;;) {
536                 hash = rht_head_hashfn(ht, tbl, obj, ht->p);
537                 lock = rht_bucket_lock(tbl, hash);
538                 spin_lock_bh(lock);
539 
540                 if (tbl->rehash <= hash)
541                         break;
542 
543                 spin_unlock_bh(lock);
544                 tbl = rcu_dereference(tbl->future_tbl);
545         }
546 
547         data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
548         new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
549         if (PTR_ERR(new_tbl) != -EEXIST)
550                 data = ERR_CAST(new_tbl);
551 
552         while (!IS_ERR_OR_NULL(new_tbl)) {
553                 tbl = new_tbl;
554                 hash = rht_head_hashfn(ht, tbl, obj, ht->p);
555                 spin_lock_nested(rht_bucket_lock(tbl, hash),
556                                  SINGLE_DEPTH_NESTING);
557 
558                 data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
559                 new_tbl = rhashtable_insert_one(ht, tbl, hash, obj, data);
560                 if (PTR_ERR(new_tbl) != -EEXIST)
561                         data = ERR_CAST(new_tbl);
562 
563                 spin_unlock(rht_bucket_lock(tbl, hash));
564         }
565 
566         spin_unlock_bh(lock);
567 
568         if (PTR_ERR(data) == -EAGAIN)
569                 data = ERR_PTR(rhashtable_insert_rehash(ht, tbl) ?:
570                                -EAGAIN);
571 
572         return data;
573 }
574 
575 void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
576                              struct rhash_head *obj)
577 {
578         void *data;
579 
580         do {
581                 rcu_read_lock();
582                 data = rhashtable_try_insert(ht, key, obj);
583                 rcu_read_unlock();
584         } while (PTR_ERR(data) == -EAGAIN);
585 
586         return data;
587 }
588 EXPORT_SYMBOL_GPL(rhashtable_insert_slow);
589 
590 /**
591  * rhashtable_walk_enter - Initialise an iterator
592  * @ht:         Table to walk over
593  * @iter:       Hash table Iterator
594  *
595  * This function prepares a hash table walk.
596  *
597  * Note that if you restart a walk after rhashtable_walk_stop you
598  * may see the same object twice.  Also, you may miss objects if
599  * there are removals in between rhashtable_walk_stop and the next
600  * call to rhashtable_walk_start.
601  *
602  * For a completely stable walk you should construct your own data
603  * structure outside the hash table.
604  *
605  * This function may sleep so you must not call it from interrupt
606  * context or with spin locks held.
607  *
608  * You must call rhashtable_walk_exit after this function returns.
609  */
610 void rhashtable_walk_enter(struct rhashtable *ht, struct rhashtable_iter *iter)
611 {
612         iter->ht = ht;
613         iter->p = NULL;
614         iter->slot = 0;
615         iter->skip = 0;
616 
617         spin_lock(&ht->lock);
618         iter->walker.tbl =
619                 rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock));
620         list_add(&iter->walker.list, &iter->walker.tbl->walkers);
621         spin_unlock(&ht->lock);
622 }
623 EXPORT_SYMBOL_GPL(rhashtable_walk_enter);
624 
625 /**
626  * rhashtable_walk_exit - Free an iterator
627  * @iter:       Hash table Iterator
628  *
629  * This function frees resources allocated by rhashtable_walk_init.
630  */
631 void rhashtable_walk_exit(struct rhashtable_iter *iter)
632 {
633         spin_lock(&iter->ht->lock);
634         if (iter->walker.tbl)
635                 list_del(&iter->walker.list);
636         spin_unlock(&iter->ht->lock);
637 }
638 EXPORT_SYMBOL_GPL(rhashtable_walk_exit);
639 
640 /**
641  * rhashtable_walk_start - Start a hash table walk
642  * @iter:       Hash table iterator
643  *
644  * Start a hash table walk.  Note that we take the RCU lock in all
645  * cases including when we return an error.  So you must always call
646  * rhashtable_walk_stop to clean up.
647  *
648  * Returns zero if successful.
649  *
650  * Returns -EAGAIN if resize event occured.  Note that the iterator
651  * will rewind back to the beginning and you may use it immediately
652  * by calling rhashtable_walk_next.
653  */
654 int rhashtable_walk_start(struct rhashtable_iter *iter)
655         __acquires(RCU)
656 {
657         struct rhashtable *ht = iter->ht;
658 
659         rcu_read_lock();
660 
661         spin_lock(&ht->lock);
662         if (iter->walker.tbl)
663                 list_del(&iter->walker.list);
664         spin_unlock(&ht->lock);
665 
666         if (!iter->walker.tbl) {
667                 iter->walker.tbl = rht_dereference_rcu(ht->tbl, ht);
668                 return -EAGAIN;
669         }
670 
671         return 0;
672 }
673 EXPORT_SYMBOL_GPL(rhashtable_walk_start);
674 
675 /**
676  * rhashtable_walk_next - Return the next object and advance the iterator
677  * @iter:       Hash table iterator
678  *
679  * Note that you must call rhashtable_walk_stop when you are finished
680  * with the walk.
681  *
682  * Returns the next object or NULL when the end of the table is reached.
683  *
684  * Returns -EAGAIN if resize event occured.  Note that the iterator
685  * will rewind back to the beginning and you may continue to use it.
686  */
687 void *rhashtable_walk_next(struct rhashtable_iter *iter)
688 {
689         struct bucket_table *tbl = iter->walker.tbl;
690         struct rhlist_head *list = iter->list;
691         struct rhashtable *ht = iter->ht;
692         struct rhash_head *p = iter->p;
693         bool rhlist = ht->rhlist;
694 
695         if (p) {
696                 if (!rhlist || !(list = rcu_dereference(list->next))) {
697                         p = rcu_dereference(p->next);
698                         list = container_of(p, struct rhlist_head, rhead);
699                 }
700                 goto next;
701         }
702 
703         for (; iter->slot < tbl->size; iter->slot++) {
704                 int skip = iter->skip;
705 
706                 rht_for_each_rcu(p, tbl, iter->slot) {
707                         if (rhlist) {
708                                 list = container_of(p, struct rhlist_head,
709                                                     rhead);
710                                 do {
711                                         if (!skip)
712                                                 goto next;
713                                         skip--;
714                                         list = rcu_dereference(list->next);
715                                 } while (list);
716 
717                                 continue;
718                         }
719                         if (!skip)
720                                 break;
721                         skip--;
722                 }
723 
724 next:
725                 if (!rht_is_a_nulls(p)) {
726                         iter->skip++;
727                         iter->p = p;
728                         iter->list = list;
729                         return rht_obj(ht, rhlist ? &list->rhead : p);
730                 }
731 
732                 iter->skip = 0;
733         }
734 
735         iter->p = NULL;
736 
737         /* Ensure we see any new tables. */
738         smp_rmb();
739 
740         iter->walker.tbl = rht_dereference_rcu(tbl->future_tbl, ht);
741         if (iter->walker.tbl) {
742                 iter->slot = 0;
743                 iter->skip = 0;
744                 return ERR_PTR(-EAGAIN);
745         }
746 
747         return NULL;
748 }
749 EXPORT_SYMBOL_GPL(rhashtable_walk_next);
750 
751 /**
752  * rhashtable_walk_stop - Finish a hash table walk
753  * @iter:       Hash table iterator
754  *
755  * Finish a hash table walk.
756  */
757 void rhashtable_walk_stop(struct rhashtable_iter *iter)
758         __releases(RCU)
759 {
760         struct rhashtable *ht;
761         struct bucket_table *tbl = iter->walker.tbl;
762 
763         if (!tbl)
764                 goto out;
765 
766         ht = iter->ht;
767 
768         spin_lock(&ht->lock);
769         if (tbl->rehash < tbl->size)
770                 list_add(&iter->walker.list, &tbl->walkers);
771         else
772                 iter->walker.tbl = NULL;
773         spin_unlock(&ht->lock);
774 
775         iter->p = NULL;
776 
777 out:
778         rcu_read_unlock();
779 }
780 EXPORT_SYMBOL_GPL(rhashtable_walk_stop);
781 
782 static size_t rounded_hashtable_size(const struct rhashtable_params *params)
783 {
784         return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
785                    (unsigned long)params->min_size);
786 }
787 
788 static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed)
789 {
790         return jhash2(key, length, seed);
791 }
792 
793 /**
794  * rhashtable_init - initialize a new hash table
795  * @ht:         hash table to be initialized
796  * @params:     configuration parameters
797  *
798  * Initializes a new hash table based on the provided configuration
799  * parameters. A table can be configured either with a variable or
800  * fixed length key:
801  *
802  * Configuration Example 1: Fixed length keys
803  * struct test_obj {
804  *      int                     key;
805  *      void *                  my_member;
806  *      struct rhash_head       node;
807  * };
808  *
809  * struct rhashtable_params params = {
810  *      .head_offset = offsetof(struct test_obj, node),
811  *      .key_offset = offsetof(struct test_obj, key),
812  *      .key_len = sizeof(int),
813  *      .hashfn = jhash,
814  *      .nulls_base = (1U << RHT_BASE_SHIFT),
815  * };
816  *
817  * Configuration Example 2: Variable length keys
818  * struct test_obj {
819  *      [...]
820  *      struct rhash_head       node;
821  * };
822  *
823  * u32 my_hash_fn(const void *data, u32 len, u32 seed)
824  * {
825  *      struct test_obj *obj = data;
826  *
827  *      return [... hash ...];
828  * }
829  *
830  * struct rhashtable_params params = {
831  *      .head_offset = offsetof(struct test_obj, node),
832  *      .hashfn = jhash,
833  *      .obj_hashfn = my_hash_fn,
834  * };
835  */
836 int rhashtable_init(struct rhashtable *ht,
837                     const struct rhashtable_params *params)
838 {
839         struct bucket_table *tbl;
840         size_t size;
841 
842         size = HASH_DEFAULT_SIZE;
843 
844         if ((!params->key_len && !params->obj_hashfn) ||
845             (params->obj_hashfn && !params->obj_cmpfn))
846                 return -EINVAL;
847 
848         if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
849                 return -EINVAL;
850 
851         memset(ht, 0, sizeof(*ht));
852         mutex_init(&ht->mutex);
853         spin_lock_init(&ht->lock);
854         memcpy(&ht->p, params, sizeof(*params));
855 
856         if (params->min_size)
857                 ht->p.min_size = roundup_pow_of_two(params->min_size);
858 
859         if (params->max_size)
860                 ht->p.max_size = rounddown_pow_of_two(params->max_size);
861 
862         if (params->insecure_max_entries)
863                 ht->p.insecure_max_entries =
864                         rounddown_pow_of_two(params->insecure_max_entries);
865         else
866                 ht->p.insecure_max_entries = ht->p.max_size * 2;
867 
868         ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
869 
870         if (params->nelem_hint)
871                 size = rounded_hashtable_size(&ht->p);
872 
873         /* The maximum (not average) chain length grows with the
874          * size of the hash table, at a rate of (log N)/(log log N).
875          * The value of 16 is selected so that even if the hash
876          * table grew to 2^32 you would not expect the maximum
877          * chain length to exceed it unless we are under attack
878          * (or extremely unlucky).
879          *
880          * As this limit is only to detect attacks, we don't need
881          * to set it to a lower value as you'd need the chain
882          * length to vastly exceed 16 to have any real effect
883          * on the system.
884          */
885         if (!params->insecure_elasticity)
886                 ht->elasticity = 16;
887 
888         if (params->locks_mul)
889                 ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
890         else
891                 ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;
892 
893         ht->key_len = ht->p.key_len;
894         if (!params->hashfn) {
895                 ht->p.hashfn = jhash;
896 
897                 if (!(ht->key_len & (sizeof(u32) - 1))) {
898                         ht->key_len /= sizeof(u32);
899                         ht->p.hashfn = rhashtable_jhash2;
900                 }
901         }
902 
903         tbl = bucket_table_alloc(ht, size, GFP_KERNEL);
904         if (tbl == NULL)
905                 return -ENOMEM;
906 
907         atomic_set(&ht->nelems, 0);
908 
909         RCU_INIT_POINTER(ht->tbl, tbl);
910 
911         INIT_WORK(&ht->run_work, rht_deferred_worker);
912 
913         return 0;
914 }
915 EXPORT_SYMBOL_GPL(rhashtable_init);
916 
917 /**
918  * rhltable_init - initialize a new hash list table
919  * @hlt:        hash list table to be initialized
920  * @params:     configuration parameters
921  *
922  * Initializes a new hash list table.
923  *
924  * See documentation for rhashtable_init.
925  */
926 int rhltable_init(struct rhltable *hlt, const struct rhashtable_params *params)
927 {
928         int err;
929 
930         /* No rhlist NULLs marking for now. */
931         if (params->nulls_base)
932                 return -EINVAL;
933 
934         err = rhashtable_init(&hlt->ht, params);
935         hlt->ht.rhlist = true;
936         return err;
937 }
938 EXPORT_SYMBOL_GPL(rhltable_init);
939 
940 static void rhashtable_free_one(struct rhashtable *ht, struct rhash_head *obj,
941                                 void (*free_fn)(void *ptr, void *arg),
942                                 void *arg)
943 {
944         struct rhlist_head *list;
945 
946         if (!ht->rhlist) {
947                 free_fn(rht_obj(ht, obj), arg);
948                 return;
949         }
950 
951         list = container_of(obj, struct rhlist_head, rhead);
952         do {
953                 obj = &list->rhead;
954                 list = rht_dereference(list->next, ht);
955                 free_fn(rht_obj(ht, obj), arg);
956         } while (list);
957 }
958 
959 /**
960  * rhashtable_free_and_destroy - free elements and destroy hash table
961  * @ht:         the hash table to destroy
962  * @free_fn:    callback to release resources of element
963  * @arg:        pointer passed to free_fn
964  *
965  * Stops an eventual async resize. If defined, invokes free_fn for each
966  * element to releasal resources. Please note that RCU protected
967  * readers may still be accessing the elements. Releasing of resources
968  * must occur in a compatible manner. Then frees the bucket array.
969  *
970  * This function will eventually sleep to wait for an async resize
971  * to complete. The caller is responsible that no further write operations
972  * occurs in parallel.
973  */
974 void rhashtable_free_and_destroy(struct rhashtable *ht,
975                                  void (*free_fn)(void *ptr, void *arg),
976                                  void *arg)
977 {
978         const struct bucket_table *tbl;
979         unsigned int i;
980 
981         cancel_work_sync(&ht->run_work);
982 
983         mutex_lock(&ht->mutex);
984         tbl = rht_dereference(ht->tbl, ht);
985         if (free_fn) {
986                 for (i = 0; i < tbl->size; i++) {
987                         struct rhash_head *pos, *next;
988 
989                         for (pos = rht_dereference(tbl->buckets[i], ht),
990                              next = !rht_is_a_nulls(pos) ?
991                                         rht_dereference(pos->next, ht) : NULL;
992                              !rht_is_a_nulls(pos);
993                              pos = next,
994                              next = !rht_is_a_nulls(pos) ?
995                                         rht_dereference(pos->next, ht) : NULL)
996                                 rhashtable_free_one(ht, pos, free_fn, arg);
997                 }
998         }
999 
1000         bucket_table_free(tbl);
1001         mutex_unlock(&ht->mutex);
1002 }
1003 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy);
1004 
1005 void rhashtable_destroy(struct rhashtable *ht)
1006 {
1007         return rhashtable_free_and_destroy(ht, NULL, NULL);
1008 }
1009 EXPORT_SYMBOL_GPL(rhashtable_destroy);
1010 

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us