2 * Resizable, Scalable, Concurrent Hash Table
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>
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
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.
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>
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>
31 #define HASH_DEFAULT_SIZE 64UL
32 #define HASH_MIN_SIZE 4U
33 #define BUCKET_LOCKS_PER_CPU 128UL
35 static u32
head_hashfn(struct rhashtable
*ht
,
36 const struct bucket_table
*tbl
,
37 const struct rhash_head
*he
)
39 return rht_head_hashfn(ht
, tbl
, he
, ht
->p
);
42 #ifdef CONFIG_PROVE_LOCKING
43 #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
45 int lockdep_rht_mutex_is_held(struct rhashtable
*ht
)
47 return (debug_locks
) ? lockdep_is_held(&ht
->mutex
) : 1;
49 EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held
);
51 int lockdep_rht_bucket_is_held(const struct bucket_table
*tbl
, u32 hash
)
53 spinlock_t
*lock
= rht_bucket_lock(tbl
, hash
);
55 return (debug_locks
) ? lockdep_is_held(lock
) : 1;
57 EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held
);
59 #define ASSERT_RHT_MUTEX(HT)
63 static int alloc_bucket_locks(struct rhashtable
*ht
, struct bucket_table
*tbl
,
67 #if defined(CONFIG_PROVE_LOCKING)
68 unsigned int nr_pcpus
= 2;
70 unsigned int nr_pcpus
= num_possible_cpus();
73 nr_pcpus
= min_t(unsigned int, nr_pcpus
, 32UL);
74 size
= roundup_pow_of_two(nr_pcpus
* ht
->p
.locks_mul
);
76 /* Never allocate more than 0.5 locks per bucket */
77 size
= min_t(unsigned int, size
, tbl
->size
>> 1);
79 if (sizeof(spinlock_t
) != 0) {
81 if (size
* sizeof(spinlock_t
) > PAGE_SIZE
&&
83 tbl
->locks
= vmalloc(size
* sizeof(spinlock_t
));
86 tbl
->locks
= kmalloc_array(size
, sizeof(spinlock_t
),
90 for (i
= 0; i
< size
; i
++)
91 spin_lock_init(&tbl
->locks
[i
]);
93 tbl
->locks_mask
= size
- 1;
98 static void bucket_table_free(const struct bucket_table
*tbl
)
106 static void bucket_table_free_rcu(struct rcu_head
*head
)
108 bucket_table_free(container_of(head
, struct bucket_table
, rcu
));
111 static struct bucket_table
*bucket_table_alloc(struct rhashtable
*ht
,
115 struct bucket_table
*tbl
= NULL
;
119 size
= sizeof(*tbl
) + nbuckets
* sizeof(tbl
->buckets
[0]);
120 if (size
<= (PAGE_SIZE
<< PAGE_ALLOC_COSTLY_ORDER
) ||
122 tbl
= kzalloc(size
, gfp
| __GFP_NOWARN
| __GFP_NORETRY
);
123 if (tbl
== NULL
&& gfp
== GFP_KERNEL
)
128 tbl
->size
= nbuckets
;
130 if (alloc_bucket_locks(ht
, tbl
, gfp
) < 0) {
131 bucket_table_free(tbl
);
135 INIT_LIST_HEAD(&tbl
->walkers
);
137 get_random_bytes(&tbl
->hash_rnd
, sizeof(tbl
->hash_rnd
));
139 for (i
= 0; i
< nbuckets
; i
++)
140 INIT_RHT_NULLS_HEAD(tbl
->buckets
[i
], ht
, i
);
145 static struct bucket_table
*rhashtable_last_table(struct rhashtable
*ht
,
146 struct bucket_table
*tbl
)
148 struct bucket_table
*new_tbl
;
152 tbl
= rht_dereference_rcu(tbl
->future_tbl
, ht
);
158 static int rhashtable_rehash_one(struct rhashtable
*ht
, unsigned int old_hash
)
160 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
161 struct bucket_table
*new_tbl
= rhashtable_last_table(ht
,
162 rht_dereference_rcu(old_tbl
->future_tbl
, ht
));
163 struct rhash_head __rcu
**pprev
= &old_tbl
->buckets
[old_hash
];
165 struct rhash_head
*head
, *next
, *entry
;
166 spinlock_t
*new_bucket_lock
;
167 unsigned int new_hash
;
169 rht_for_each(entry
, old_tbl
, old_hash
) {
171 next
= rht_dereference_bucket(entry
->next
, old_tbl
, old_hash
);
173 if (rht_is_a_nulls(next
))
176 pprev
= &entry
->next
;
182 new_hash
= head_hashfn(ht
, new_tbl
, entry
);
184 new_bucket_lock
= rht_bucket_lock(new_tbl
, new_hash
);
186 spin_lock_nested(new_bucket_lock
, SINGLE_DEPTH_NESTING
);
187 head
= rht_dereference_bucket(new_tbl
->buckets
[new_hash
],
190 RCU_INIT_POINTER(entry
->next
, head
);
192 rcu_assign_pointer(new_tbl
->buckets
[new_hash
], entry
);
193 spin_unlock(new_bucket_lock
);
195 rcu_assign_pointer(*pprev
, next
);
201 static void rhashtable_rehash_chain(struct rhashtable
*ht
,
202 unsigned int old_hash
)
204 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
205 spinlock_t
*old_bucket_lock
;
207 old_bucket_lock
= rht_bucket_lock(old_tbl
, old_hash
);
209 spin_lock_bh(old_bucket_lock
);
210 while (!rhashtable_rehash_one(ht
, old_hash
))
213 spin_unlock_bh(old_bucket_lock
);
216 static int rhashtable_rehash_attach(struct rhashtable
*ht
,
217 struct bucket_table
*old_tbl
,
218 struct bucket_table
*new_tbl
)
220 /* Protect future_tbl using the first bucket lock. */
221 spin_lock_bh(old_tbl
->locks
);
223 /* Did somebody beat us to it? */
224 if (rcu_access_pointer(old_tbl
->future_tbl
)) {
225 spin_unlock_bh(old_tbl
->locks
);
229 /* Make insertions go into the new, empty table right away. Deletions
230 * and lookups will be attempted in both tables until we synchronize.
232 rcu_assign_pointer(old_tbl
->future_tbl
, new_tbl
);
234 /* Ensure the new table is visible to readers. */
237 spin_unlock_bh(old_tbl
->locks
);
242 static int rhashtable_rehash_table(struct rhashtable
*ht
)
244 struct bucket_table
*old_tbl
= rht_dereference(ht
->tbl
, ht
);
245 struct bucket_table
*new_tbl
;
246 struct rhashtable_walker
*walker
;
247 unsigned int old_hash
;
249 new_tbl
= rht_dereference(old_tbl
->future_tbl
, ht
);
253 for (old_hash
= 0; old_hash
< old_tbl
->size
; old_hash
++)
254 rhashtable_rehash_chain(ht
, old_hash
);
256 /* Publish the new table pointer. */
257 rcu_assign_pointer(ht
->tbl
, new_tbl
);
259 spin_lock(&ht
->lock
);
260 list_for_each_entry(walker
, &old_tbl
->walkers
, list
)
262 spin_unlock(&ht
->lock
);
264 /* Wait for readers. All new readers will see the new
265 * table, and thus no references to the old table will
268 call_rcu(&old_tbl
->rcu
, bucket_table_free_rcu
);
270 return rht_dereference(new_tbl
->future_tbl
, ht
) ? -EAGAIN
: 0;
274 * rhashtable_expand - Expand hash table while allowing concurrent lookups
275 * @ht: the hash table to expand
277 * A secondary bucket array is allocated and the hash entries are migrated.
279 * This function may only be called in a context where it is safe to call
280 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
282 * The caller must ensure that no concurrent resizing occurs by holding
285 * It is valid to have concurrent insertions and deletions protected by per
286 * bucket locks or concurrent RCU protected lookups and traversals.
288 static int rhashtable_expand(struct rhashtable
*ht
)
290 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
293 ASSERT_RHT_MUTEX(ht
);
295 old_tbl
= rhashtable_last_table(ht
, old_tbl
);
297 new_tbl
= bucket_table_alloc(ht
, old_tbl
->size
* 2, GFP_KERNEL
);
301 err
= rhashtable_rehash_attach(ht
, old_tbl
, new_tbl
);
303 bucket_table_free(new_tbl
);
309 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
310 * @ht: the hash table to shrink
312 * This function shrinks the hash table to fit, i.e., the smallest
313 * size would not cause it to expand right away automatically.
315 * The caller must ensure that no concurrent resizing occurs by holding
318 * The caller must ensure that no concurrent table mutations take place.
319 * It is however valid to have concurrent lookups if they are RCU protected.
321 * It is valid to have concurrent insertions and deletions protected by per
322 * bucket locks or concurrent RCU protected lookups and traversals.
324 static int rhashtable_shrink(struct rhashtable
*ht
)
326 struct bucket_table
*new_tbl
, *old_tbl
= rht_dereference(ht
->tbl
, ht
);
330 ASSERT_RHT_MUTEX(ht
);
332 size
= roundup_pow_of_two(atomic_read(&ht
->nelems
) * 3 / 2);
333 if (size
< ht
->p
.min_size
)
334 size
= ht
->p
.min_size
;
336 if (old_tbl
->size
<= size
)
339 if (rht_dereference(old_tbl
->future_tbl
, ht
))
342 new_tbl
= bucket_table_alloc(ht
, size
, GFP_KERNEL
);
346 err
= rhashtable_rehash_attach(ht
, old_tbl
, new_tbl
);
348 bucket_table_free(new_tbl
);
353 static void rht_deferred_worker(struct work_struct
*work
)
355 struct rhashtable
*ht
;
356 struct bucket_table
*tbl
;
359 ht
= container_of(work
, struct rhashtable
, run_work
);
360 mutex_lock(&ht
->mutex
);
362 tbl
= rht_dereference(ht
->tbl
, ht
);
363 tbl
= rhashtable_last_table(ht
, tbl
);
365 if (rht_grow_above_75(ht
, tbl
))
366 rhashtable_expand(ht
);
367 else if (ht
->p
.automatic_shrinking
&& rht_shrink_below_30(ht
, tbl
))
368 rhashtable_shrink(ht
);
370 err
= rhashtable_rehash_table(ht
);
372 mutex_unlock(&ht
->mutex
);
375 schedule_work(&ht
->run_work
);
378 static bool rhashtable_check_elasticity(struct rhashtable
*ht
,
379 struct bucket_table
*tbl
,
382 unsigned int elasticity
= ht
->elasticity
;
383 struct rhash_head
*head
;
385 rht_for_each(head
, tbl
, hash
)
392 int rhashtable_insert_rehash(struct rhashtable
*ht
,
393 struct bucket_table
*tbl
)
395 struct bucket_table
*old_tbl
;
396 struct bucket_table
*new_tbl
;
400 old_tbl
= rht_dereference_rcu(ht
->tbl
, ht
);
406 if (rht_grow_above_75(ht
, tbl
))
408 /* Do not schedule more than one rehash */
409 else if (old_tbl
!= tbl
)
414 new_tbl
= bucket_table_alloc(ht
, size
, GFP_ATOMIC
);
418 err
= rhashtable_rehash_attach(ht
, tbl
, new_tbl
);
420 bucket_table_free(new_tbl
);
424 schedule_work(&ht
->run_work
);
429 /* Do not fail the insert if someone else did a rehash. */
430 if (likely(rcu_dereference_raw(tbl
->future_tbl
)))
433 /* Schedule async rehash to retry allocation in process context. */
435 schedule_work(&ht
->run_work
);
439 EXPORT_SYMBOL_GPL(rhashtable_insert_rehash
);
441 struct bucket_table
*rhashtable_insert_slow(struct rhashtable
*ht
,
443 struct rhash_head
*obj
,
444 struct bucket_table
*tbl
)
446 struct rhash_head
*head
;
450 tbl
= rhashtable_last_table(ht
, tbl
);
451 hash
= head_hashfn(ht
, tbl
, obj
);
452 spin_lock_nested(rht_bucket_lock(tbl
, hash
), SINGLE_DEPTH_NESTING
);
455 if (key
&& rhashtable_lookup_fast(ht
, key
, ht
->p
))
459 if (unlikely(rht_grow_above_max(ht
, tbl
)))
463 if (rhashtable_check_elasticity(ht
, tbl
, hash
) ||
464 rht_grow_above_100(ht
, tbl
))
469 head
= rht_dereference_bucket(tbl
->buckets
[hash
], tbl
, hash
);
471 RCU_INIT_POINTER(obj
->next
, head
);
473 rcu_assign_pointer(tbl
->buckets
[hash
], obj
);
475 atomic_inc(&ht
->nelems
);
478 spin_unlock(rht_bucket_lock(tbl
, hash
));
482 else if (err
== -EAGAIN
)
487 EXPORT_SYMBOL_GPL(rhashtable_insert_slow
);
490 * rhashtable_walk_init - Initialise an iterator
491 * @ht: Table to walk over
492 * @iter: Hash table Iterator
494 * This function prepares a hash table walk.
496 * Note that if you restart a walk after rhashtable_walk_stop you
497 * may see the same object twice. Also, you may miss objects if
498 * there are removals in between rhashtable_walk_stop and the next
499 * call to rhashtable_walk_start.
501 * For a completely stable walk you should construct your own data
502 * structure outside the hash table.
504 * This function may sleep so you must not call it from interrupt
505 * context or with spin locks held.
507 * You must call rhashtable_walk_exit if this function returns
510 int rhashtable_walk_init(struct rhashtable
*ht
, struct rhashtable_iter
*iter
)
517 iter
->walker
= kmalloc(sizeof(*iter
->walker
), GFP_KERNEL
);
521 mutex_lock(&ht
->mutex
);
522 iter
->walker
->tbl
= rht_dereference(ht
->tbl
, ht
);
523 list_add(&iter
->walker
->list
, &iter
->walker
->tbl
->walkers
);
524 mutex_unlock(&ht
->mutex
);
528 EXPORT_SYMBOL_GPL(rhashtable_walk_init
);
531 * rhashtable_walk_exit - Free an iterator
532 * @iter: Hash table Iterator
534 * This function frees resources allocated by rhashtable_walk_init.
536 void rhashtable_walk_exit(struct rhashtable_iter
*iter
)
538 mutex_lock(&iter
->ht
->mutex
);
539 if (iter
->walker
->tbl
)
540 list_del(&iter
->walker
->list
);
541 mutex_unlock(&iter
->ht
->mutex
);
544 EXPORT_SYMBOL_GPL(rhashtable_walk_exit
);
547 * rhashtable_walk_start - Start a hash table walk
548 * @iter: Hash table iterator
550 * Start a hash table walk. Note that we take the RCU lock in all
551 * cases including when we return an error. So you must always call
552 * rhashtable_walk_stop to clean up.
554 * Returns zero if successful.
556 * Returns -EAGAIN if resize event occured. Note that the iterator
557 * will rewind back to the beginning and you may use it immediately
558 * by calling rhashtable_walk_next.
560 int rhashtable_walk_start(struct rhashtable_iter
*iter
)
563 struct rhashtable
*ht
= iter
->ht
;
565 mutex_lock(&ht
->mutex
);
567 if (iter
->walker
->tbl
)
568 list_del(&iter
->walker
->list
);
572 mutex_unlock(&ht
->mutex
);
574 if (!iter
->walker
->tbl
) {
575 iter
->walker
->tbl
= rht_dereference_rcu(ht
->tbl
, ht
);
581 EXPORT_SYMBOL_GPL(rhashtable_walk_start
);
584 * rhashtable_walk_next - Return the next object and advance the iterator
585 * @iter: Hash table iterator
587 * Note that you must call rhashtable_walk_stop when you are finished
590 * Returns the next object or NULL when the end of the table is reached.
592 * Returns -EAGAIN if resize event occured. Note that the iterator
593 * will rewind back to the beginning and you may continue to use it.
595 void *rhashtable_walk_next(struct rhashtable_iter
*iter
)
597 struct bucket_table
*tbl
= iter
->walker
->tbl
;
598 struct rhashtable
*ht
= iter
->ht
;
599 struct rhash_head
*p
= iter
->p
;
602 p
= rht_dereference_bucket_rcu(p
->next
, tbl
, iter
->slot
);
606 for (; iter
->slot
< tbl
->size
; iter
->slot
++) {
607 int skip
= iter
->skip
;
609 rht_for_each_rcu(p
, tbl
, iter
->slot
) {
616 if (!rht_is_a_nulls(p
)) {
619 return rht_obj(ht
, p
);
627 /* Ensure we see any new tables. */
630 iter
->walker
->tbl
= rht_dereference_rcu(tbl
->future_tbl
, ht
);
631 if (iter
->walker
->tbl
) {
634 return ERR_PTR(-EAGAIN
);
639 EXPORT_SYMBOL_GPL(rhashtable_walk_next
);
642 * rhashtable_walk_stop - Finish a hash table walk
643 * @iter: Hash table iterator
645 * Finish a hash table walk.
647 void rhashtable_walk_stop(struct rhashtable_iter
*iter
)
650 struct rhashtable
*ht
;
651 struct bucket_table
*tbl
= iter
->walker
->tbl
;
658 spin_lock(&ht
->lock
);
659 if (tbl
->rehash
< tbl
->size
)
660 list_add(&iter
->walker
->list
, &tbl
->walkers
);
662 iter
->walker
->tbl
= NULL
;
663 spin_unlock(&ht
->lock
);
670 EXPORT_SYMBOL_GPL(rhashtable_walk_stop
);
672 static size_t rounded_hashtable_size(const struct rhashtable_params
*params
)
674 return max(roundup_pow_of_two(params
->nelem_hint
* 4 / 3),
675 (unsigned long)params
->min_size
);
678 static u32
rhashtable_jhash2(const void *key
, u32 length
, u32 seed
)
680 return jhash2(key
, length
, seed
);
684 * rhashtable_init - initialize a new hash table
685 * @ht: hash table to be initialized
686 * @params: configuration parameters
688 * Initializes a new hash table based on the provided configuration
689 * parameters. A table can be configured either with a variable or
692 * Configuration Example 1: Fixed length keys
696 * struct rhash_head node;
699 * struct rhashtable_params params = {
700 * .head_offset = offsetof(struct test_obj, node),
701 * .key_offset = offsetof(struct test_obj, key),
702 * .key_len = sizeof(int),
704 * .nulls_base = (1U << RHT_BASE_SHIFT),
707 * Configuration Example 2: Variable length keys
710 * struct rhash_head node;
713 * u32 my_hash_fn(const void *data, u32 len, u32 seed)
715 * struct test_obj *obj = data;
717 * return [... hash ...];
720 * struct rhashtable_params params = {
721 * .head_offset = offsetof(struct test_obj, node),
723 * .obj_hashfn = my_hash_fn,
726 int rhashtable_init(struct rhashtable
*ht
,
727 const struct rhashtable_params
*params
)
729 struct bucket_table
*tbl
;
732 size
= HASH_DEFAULT_SIZE
;
734 if ((!params
->key_len
&& !params
->obj_hashfn
) ||
735 (params
->obj_hashfn
&& !params
->obj_cmpfn
))
738 if (params
->nulls_base
&& params
->nulls_base
< (1U << RHT_BASE_SHIFT
))
741 if (params
->nelem_hint
)
742 size
= rounded_hashtable_size(params
);
744 memset(ht
, 0, sizeof(*ht
));
745 mutex_init(&ht
->mutex
);
746 spin_lock_init(&ht
->lock
);
747 memcpy(&ht
->p
, params
, sizeof(*params
));
749 if (params
->min_size
)
750 ht
->p
.min_size
= roundup_pow_of_two(params
->min_size
);
752 if (params
->max_size
)
753 ht
->p
.max_size
= rounddown_pow_of_two(params
->max_size
);
755 if (params
->insecure_max_entries
)
756 ht
->p
.insecure_max_entries
=
757 rounddown_pow_of_two(params
->insecure_max_entries
);
759 ht
->p
.insecure_max_entries
= ht
->p
.max_size
* 2;
761 ht
->p
.min_size
= max(ht
->p
.min_size
, HASH_MIN_SIZE
);
763 /* The maximum (not average) chain length grows with the
764 * size of the hash table, at a rate of (log N)/(log log N).
765 * The value of 16 is selected so that even if the hash
766 * table grew to 2^32 you would not expect the maximum
767 * chain length to exceed it unless we are under attack
768 * (or extremely unlucky).
770 * As this limit is only to detect attacks, we don't need
771 * to set it to a lower value as you'd need the chain
772 * length to vastly exceed 16 to have any real effect
775 if (!params
->insecure_elasticity
)
778 if (params
->locks_mul
)
779 ht
->p
.locks_mul
= roundup_pow_of_two(params
->locks_mul
);
781 ht
->p
.locks_mul
= BUCKET_LOCKS_PER_CPU
;
783 ht
->key_len
= ht
->p
.key_len
;
784 if (!params
->hashfn
) {
785 ht
->p
.hashfn
= jhash
;
787 if (!(ht
->key_len
& (sizeof(u32
) - 1))) {
788 ht
->key_len
/= sizeof(u32
);
789 ht
->p
.hashfn
= rhashtable_jhash2
;
793 tbl
= bucket_table_alloc(ht
, size
, GFP_KERNEL
);
797 atomic_set(&ht
->nelems
, 0);
799 RCU_INIT_POINTER(ht
->tbl
, tbl
);
801 INIT_WORK(&ht
->run_work
, rht_deferred_worker
);
805 EXPORT_SYMBOL_GPL(rhashtable_init
);
808 * rhashtable_free_and_destroy - free elements and destroy hash table
809 * @ht: the hash table to destroy
810 * @free_fn: callback to release resources of element
811 * @arg: pointer passed to free_fn
813 * Stops an eventual async resize. If defined, invokes free_fn for each
814 * element to releasal resources. Please note that RCU protected
815 * readers may still be accessing the elements. Releasing of resources
816 * must occur in a compatible manner. Then frees the bucket array.
818 * This function will eventually sleep to wait for an async resize
819 * to complete. The caller is responsible that no further write operations
820 * occurs in parallel.
822 void rhashtable_free_and_destroy(struct rhashtable
*ht
,
823 void (*free_fn
)(void *ptr
, void *arg
),
826 const struct bucket_table
*tbl
;
829 cancel_work_sync(&ht
->run_work
);
831 mutex_lock(&ht
->mutex
);
832 tbl
= rht_dereference(ht
->tbl
, ht
);
834 for (i
= 0; i
< tbl
->size
; i
++) {
835 struct rhash_head
*pos
, *next
;
837 for (pos
= rht_dereference(tbl
->buckets
[i
], ht
),
838 next
= !rht_is_a_nulls(pos
) ?
839 rht_dereference(pos
->next
, ht
) : NULL
;
840 !rht_is_a_nulls(pos
);
842 next
= !rht_is_a_nulls(pos
) ?
843 rht_dereference(pos
->next
, ht
) : NULL
)
844 free_fn(rht_obj(ht
, pos
), arg
);
848 bucket_table_free(tbl
);
849 mutex_unlock(&ht
->mutex
);
851 EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy
);
853 void rhashtable_destroy(struct rhashtable
*ht
)
855 return rhashtable_free_and_destroy(ht
, NULL
, NULL
);
857 EXPORT_SYMBOL_GPL(rhashtable_destroy
);