rhashtable: Supports for nulls marker

[deliverable/linux.git] / lib / rhashtable.c

/*
 * Resizable, Scalable, Concurrent Hash Table
 *
 * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
 * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
 *
 * Based on the following paper:
 * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
 *
 * Code partially derived from nft_hash
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/log2.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <linux/rhashtable.h>

#define HASH_DEFAULT_SIZE       64UL
#define HASH_MIN_SIZE           4UL
#define BUCKET_LOCKS_PER_CPU   128UL

/* Base bits plus 1 bit for nulls marker */
#define HASH_RESERVED_SPACE     (RHT_BASE_BITS + 1)

enum {
        RHT_LOCK_NORMAL,
        RHT_LOCK_NESTED,
        RHT_LOCK_NESTED2,
};

/* The bucket lock is selected based on the hash and protects mutations
 * on a group of hash buckets.
 *
 * IMPORTANT: When holding the bucket lock of both the old and new table
 * during expansions and shrinking, the old bucket lock must always be
 * acquired first.
 */
static spinlock_t *bucket_lock(const struct bucket_table *tbl, u32 hash)
{
        return &tbl->locks[hash & tbl->locks_mask];
}

#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
#define ASSERT_BUCKET_LOCK(TBL, HASH) \
        BUG_ON(!lockdep_rht_bucket_is_held(TBL, HASH))

#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(struct rhashtable *ht)
{
        return (debug_locks) ? lockdep_is_held(&ht->mutex) : 1;
}
EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);

int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash)
{
        spinlock_t *lock = bucket_lock(tbl, hash);

        return (debug_locks) ? lockdep_is_held(lock) : 1;
}
EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held);
#endif

static void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
{
        return (void *) he - ht->p.head_offset;
}

static u32 rht_bucket_index(const struct bucket_table *tbl, u32 hash)
{
        return hash & (tbl->size - 1);
}

static u32 obj_raw_hashfn(const struct rhashtable *ht, const void *ptr)
{
        u32 hash;

        if (unlikely(!ht->p.key_len))
                hash = ht->p.obj_hashfn(ptr, ht->p.hash_rnd);
        else
                hash = ht->p.hashfn(ptr + ht->p.key_offset, ht->p.key_len,
                                    ht->p.hash_rnd);

        return hash >> HASH_RESERVED_SPACE;
}

static u32 key_hashfn(struct rhashtable *ht, const void *key, u32 len)
{
        struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
        u32 hash;

        hash = ht->p.hashfn(key, len, ht->p.hash_rnd);
        hash >>= HASH_RESERVED_SPACE;

        return rht_bucket_index(tbl, hash);
}

static u32 head_hashfn(const struct rhashtable *ht,
                       const struct bucket_table *tbl,
                       const struct rhash_head *he)
{
        return rht_bucket_index(tbl, obj_raw_hashfn(ht, rht_obj(ht, he)));
}

static struct rhash_head __rcu **bucket_tail(struct bucket_table *tbl, u32 n)
{
        struct rhash_head __rcu **pprev;

        for (pprev = &tbl->buckets[n];
             !rht_is_a_nulls(rht_dereference_bucket(*pprev, tbl, n));
             pprev = &rht_dereference_bucket(*pprev, tbl, n)->next)
                ;

        return pprev;
}

static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl)
{
        unsigned int i, size;
#if defined(CONFIG_PROVE_LOCKING)
        unsigned int nr_pcpus = 2;
#else
        unsigned int nr_pcpus = num_possible_cpus();
#endif

        nr_pcpus = min_t(unsigned int, nr_pcpus, 32UL);
        size = roundup_pow_of_two(nr_pcpus * ht->p.locks_mul);

        /* Never allocate more than one lock per bucket */
        size = min_t(unsigned int, size, tbl->size);

        if (sizeof(spinlock_t) != 0) {
#ifdef CONFIG_NUMA
                if (size * sizeof(spinlock_t) > PAGE_SIZE)
                        tbl->locks = vmalloc(size * sizeof(spinlock_t));
                else
#endif
                tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
                                           GFP_KERNEL);
                if (!tbl->locks)
                        return -ENOMEM;
                for (i = 0; i < size; i++)
                        spin_lock_init(&tbl->locks[i]);
        }
        tbl->locks_mask = size - 1;

        return 0;
}

static void bucket_table_free(const struct bucket_table *tbl)
{
        if (tbl)
                kvfree(tbl->locks);

        kvfree(tbl);
}

static struct bucket_table *bucket_table_alloc(struct rhashtable *ht,
                                               size_t nbuckets)
{
        struct bucket_table *tbl;
        size_t size;
        int i;

        size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
        tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
        if (tbl == NULL)
                tbl = vzalloc(size);

        if (tbl == NULL)
                return NULL;

        tbl->size = nbuckets;

        if (alloc_bucket_locks(ht, tbl) < 0) {
                bucket_table_free(tbl);
                return NULL;
        }

        for (i = 0; i < nbuckets; i++)
                INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i);

        return tbl;
}

/**
 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
 * @ht:         hash table
 * @new_size:   new table size
 */
bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
{
        /* Expand table when exceeding 75% load */
        return atomic_read(&ht->nelems) > (new_size / 4 * 3);
}
EXPORT_SYMBOL_GPL(rht_grow_above_75);

/**
 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
 * @ht:         hash table
 * @new_size:   new table size
 */
bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
{
        /* Shrink table beneath 30% load */
        return atomic_read(&ht->nelems) < (new_size * 3 / 10);
}
EXPORT_SYMBOL_GPL(rht_shrink_below_30);

static void hashtable_chain_unzip(const struct rhashtable *ht,
                                  const struct bucket_table *new_tbl,
                                  struct bucket_table *old_tbl,
                                  size_t old_hash)
{
        struct rhash_head *he, *p, *next;
        spinlock_t *new_bucket_lock, *new_bucket_lock2 = NULL;
        unsigned int new_hash, new_hash2;

        ASSERT_BUCKET_LOCK(old_tbl, old_hash);

        /* Old bucket empty, no work needed. */
        p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl,
                                   old_hash);
        if (rht_is_a_nulls(p))
                return;

        new_hash = new_hash2 = head_hashfn(ht, new_tbl, p);
        new_bucket_lock = bucket_lock(new_tbl, new_hash);

        /* Advance the old bucket pointer one or more times until it
         * reaches a node that doesn't hash to the same bucket as the
         * previous node p. Call the previous node p;
         */
        rht_for_each_continue(he, p->next, old_tbl, old_hash) {
                new_hash2 = head_hashfn(ht, new_tbl, he);
                if (new_hash != new_hash2)
                        break;
                p = he;
        }
        rcu_assign_pointer(old_tbl->buckets[old_hash], p->next);

        spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);

        /* If we have encountered an entry that maps to a different bucket in
         * the new table, lock down that bucket as well as we might cut off
         * the end of the chain.
         */
        new_bucket_lock2 = bucket_lock(new_tbl, new_hash);
        if (new_bucket_lock != new_bucket_lock2)
                spin_lock_bh_nested(new_bucket_lock2, RHT_LOCK_NESTED2);

        /* Find the subsequent node which does hash to the same
         * bucket as node P, or NULL if no such node exists.
         */
        INIT_RHT_NULLS_HEAD(next, ht, old_hash);
        if (!rht_is_a_nulls(he)) {
                rht_for_each_continue(he, he->next, old_tbl, old_hash) {
                        if (head_hashfn(ht, new_tbl, he) == new_hash) {
                                next = he;
                                break;
                        }
                }
        }

        /* Set p's next pointer to that subsequent node pointer,
         * bypassing the nodes which do not hash to p's bucket
         */
        rcu_assign_pointer(p->next, next);

        if (new_bucket_lock != new_bucket_lock2)
                spin_unlock_bh(new_bucket_lock2);
        spin_unlock_bh(new_bucket_lock);
}

static void link_old_to_new(struct bucket_table *new_tbl,
                            unsigned int new_hash, struct rhash_head *entry)
{
        spinlock_t *new_bucket_lock;

        new_bucket_lock = bucket_lock(new_tbl, new_hash);

        spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED);
        rcu_assign_pointer(*bucket_tail(new_tbl, new_hash), entry);
        spin_unlock_bh(new_bucket_lock);
}

/**
 * rhashtable_expand - Expand hash table while allowing concurrent lookups
 * @ht:         the hash table to expand
 *
 * A secondary bucket array is allocated and the hash entries are migrated
 * while keeping them on both lists until the end of the RCU grace period.
 *
 * This function may only be called in a context where it is safe to call
 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 *
 * The caller must ensure that no concurrent resizing occurs by holding
 * ht->mutex.
 *
 * It is valid to have concurrent insertions and deletions protected by per
 * bucket locks or concurrent RCU protected lookups and traversals.
 */
int rhashtable_expand(struct rhashtable *ht)
{
        struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
        struct rhash_head *he;
        spinlock_t *old_bucket_lock;
        unsigned int new_hash, old_hash;
        bool complete = false;

        ASSERT_RHT_MUTEX(ht);

        if (ht->p.max_shift && ht->shift >= ht->p.max_shift)
                return 0;

        new_tbl = bucket_table_alloc(ht, old_tbl->size * 2);
        if (new_tbl == NULL)
                return -ENOMEM;

        ht->shift++;

        /* Make insertions go into the new, empty table right away. Deletions
         * and lookups will be attempted in both tables until we synchronize.
         * The synchronize_rcu() guarantees for the new table to be picked up
         * so no new additions go into the old table while we relink.
         */
        rcu_assign_pointer(ht->future_tbl, new_tbl);
        synchronize_rcu();

        /* For each new bucket, search the corresponding old bucket for the
         * first entry that hashes to the new bucket, and link the end of
         * newly formed bucket chain (containing entries added to future
         * table) to that entry. Since all the entries which will end up in
         * the new bucket appear in the same old bucket, this constructs an
         * entirely valid new hash table, but with multiple buckets
         * "zipped" together into a single imprecise chain.
         */
        for (new_hash = 0; new_hash < new_tbl->size; new_hash++) {
                old_hash = rht_bucket_index(old_tbl, new_hash);
                old_bucket_lock = bucket_lock(old_tbl, old_hash);

                spin_lock_bh(old_bucket_lock);
                rht_for_each(he, old_tbl, old_hash) {
                        if (head_hashfn(ht, new_tbl, he) == new_hash) {
                                link_old_to_new(new_tbl, new_hash, he);
                                break;
                        }
                }
                spin_unlock_bh(old_bucket_lock);
        }

        /* Publish the new table pointer. Lookups may now traverse
         * the new table, but they will not benefit from any
         * additional efficiency until later steps unzip the buckets.
         */
        rcu_assign_pointer(ht->tbl, new_tbl);

        /* Unzip interleaved hash chains */
        while (!complete && !ht->being_destroyed) {
                /* Wait for readers. All new readers will see the new
                 * table, and thus no references to the old table will
                 * remain.
                 */
                synchronize_rcu();

                /* For each bucket in the old table (each of which
                 * contains items from multiple buckets of the new
                 * table): ...
                 */
                complete = true;
                for (old_hash = 0; old_hash < old_tbl->size; old_hash++) {
                        struct rhash_head *head;

                        old_bucket_lock = bucket_lock(old_tbl, old_hash);
                        spin_lock_bh(old_bucket_lock);

                        hashtable_chain_unzip(ht, new_tbl, old_tbl, old_hash);
                        head = rht_dereference_bucket(old_tbl->buckets[old_hash],
                                                      old_tbl, old_hash);
                        if (!rht_is_a_nulls(head))
                                complete = false;

                        spin_unlock_bh(old_bucket_lock);
                }
        }

        bucket_table_free(old_tbl);
        return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_expand);

/**
 * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
 * @ht:         the hash table to shrink
 *
 * This function may only be called in a context where it is safe to call
 * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
 *
 * The caller must ensure that no concurrent resizing occurs by holding
 * ht->mutex.
 *
 * The caller must ensure that no concurrent table mutations take place.
 * It is however valid to have concurrent lookups if they are RCU protected.
 *
 * It is valid to have concurrent insertions and deletions protected by per
 * bucket locks or concurrent RCU protected lookups and traversals.
 */
int rhashtable_shrink(struct rhashtable *ht)
{
        struct bucket_table *new_tbl, *tbl = rht_dereference(ht->tbl, ht);
        spinlock_t *new_bucket_lock, *old_bucket_lock1, *old_bucket_lock2;
        unsigned int new_hash;

        ASSERT_RHT_MUTEX(ht);

        if (ht->shift <= ht->p.min_shift)
                return 0;

        new_tbl = bucket_table_alloc(ht, tbl->size / 2);
        if (new_tbl == NULL)
                return -ENOMEM;

        rcu_assign_pointer(ht->future_tbl, new_tbl);
        synchronize_rcu();

        /* Link the first entry in the old bucket to the end of the
         * bucket in the new table. As entries are concurrently being
         * added to the new table, lock down the new bucket. As we
         * always divide the size in half when shrinking, each bucket
         * in the new table maps to exactly two buckets in the old
         * table.
         *
         * As removals can occur concurrently on the old table, we need
         * to lock down both matching buckets in the old table.
         */
        for (new_hash = 0; new_hash < new_tbl->size; new_hash++) {
                old_bucket_lock1 = bucket_lock(tbl, new_hash);
                old_bucket_lock2 = bucket_lock(tbl, new_hash + new_tbl->size);
                new_bucket_lock = bucket_lock(new_tbl, new_hash);

                spin_lock_bh(old_bucket_lock1);
                spin_lock_bh_nested(old_bucket_lock2, RHT_LOCK_NESTED);
                spin_lock_bh_nested(new_bucket_lock, RHT_LOCK_NESTED2);

                rcu_assign_pointer(*bucket_tail(new_tbl, new_hash),
                                   tbl->buckets[new_hash]);
                rcu_assign_pointer(*bucket_tail(new_tbl, new_hash),
                                   tbl->buckets[new_hash + new_tbl->size]);

                spin_unlock_bh(new_bucket_lock);
                spin_unlock_bh(old_bucket_lock2);
                spin_unlock_bh(old_bucket_lock1);
        }

        /* Publish the new, valid hash table */
        rcu_assign_pointer(ht->tbl, new_tbl);
        ht->shift--;

        /* Wait for readers. No new readers will have references to the
         * old hash table.
         */
        synchronize_rcu();

        bucket_table_free(tbl);

        return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_shrink);

static void rht_deferred_worker(struct work_struct *work)
{
        struct rhashtable *ht;
        struct bucket_table *tbl;

        ht = container_of(work, struct rhashtable, run_work.work);
        mutex_lock(&ht->mutex);
        tbl = rht_dereference(ht->tbl, ht);

        if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
                rhashtable_expand(ht);
        else if (ht->p.shrink_decision && ht->p.shrink_decision(ht, tbl->size))
                rhashtable_shrink(ht);

        mutex_unlock(&ht->mutex);
}

/**
 * rhashtable_insert - insert object into hash hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 *
 * Will take a per bucket spinlock to protect against mutual mutations
 * on the same bucket. Multiple insertions may occur in parallel unless
 * they map to the same bucket lock.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if the size grows
 * beyond the watermark indicated by grow_decision() which can be passed
 * to rhashtable_init().
 */
void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj)
{
        struct bucket_table *tbl;
        struct rhash_head *head;
        spinlock_t *lock;
        unsigned hash;

        rcu_read_lock();

        tbl = rht_dereference_rcu(ht->future_tbl, ht);
        hash = head_hashfn(ht, tbl, obj);
        lock = bucket_lock(tbl, hash);

        spin_lock_bh(lock);
        head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash);
        if (rht_is_a_nulls(head))
                INIT_RHT_NULLS_HEAD(obj->next, ht, hash);
        else
                RCU_INIT_POINTER(obj->next, head);

        rcu_assign_pointer(tbl->buckets[hash], obj);
        spin_unlock_bh(lock);

        atomic_inc(&ht->nelems);

        /* Only grow the table if no resizing is currently in progress. */
        if (ht->tbl != ht->future_tbl &&
            ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
                schedule_delayed_work(&ht->run_work, 0);

        rcu_read_unlock();
}
EXPORT_SYMBOL_GPL(rhashtable_insert);

/**
 * rhashtable_remove - remove object from hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 *
 * Since the hash chain is single linked, the removal operation needs to
 * walk the bucket chain upon removal. The removal operation is thus
 * considerable slow if the hash table is not correctly sized.
 *
 * Will automatically shrink the table via rhashtable_expand() if the the
 * shrink_decision function specified at rhashtable_init() returns true.
 *
 * The caller must ensure that no concurrent table mutations occur. It is
 * however valid to have concurrent lookups if they are RCU protected.
 */
bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj)
{
        struct bucket_table *tbl;
        struct rhash_head __rcu **pprev;
        struct rhash_head *he;
        spinlock_t *lock;
        unsigned int hash;

        rcu_read_lock();
        tbl = rht_dereference_rcu(ht->tbl, ht);
        hash = head_hashfn(ht, tbl, obj);

        lock = bucket_lock(tbl, hash);
        spin_lock_bh(lock);

restart:
        pprev = &tbl->buckets[hash];
        rht_for_each(he, tbl, hash) {
                if (he != obj) {
                        pprev = &he->next;
                        continue;
                }

                rcu_assign_pointer(*pprev, obj->next);
                atomic_dec(&ht->nelems);

                spin_unlock_bh(lock);

                if (ht->tbl != ht->future_tbl &&
                    ht->p.shrink_decision &&
                    ht->p.shrink_decision(ht, tbl->size))
                        schedule_delayed_work(&ht->run_work, 0);

                rcu_read_unlock();

                return true;
        }

        if (tbl != rht_dereference_rcu(ht->tbl, ht)) {
                spin_unlock_bh(lock);

                tbl = rht_dereference_rcu(ht->tbl, ht);
                hash = head_hashfn(ht, tbl, obj);

                lock = bucket_lock(tbl, hash);
                spin_lock_bh(lock);
                goto restart;
        }

        spin_unlock_bh(lock);
        rcu_read_unlock();

        return false;
}
EXPORT_SYMBOL_GPL(rhashtable_remove);

/**
 * rhashtable_lookup - lookup key in hash table
 * @ht:         hash table
 * @key:        pointer to key
 *
 * Computes the hash value for the key and traverses the bucket chain looking
 * for a entry with an identical key. The first matching entry is returned.
 *
 * This lookup function may only be used for fixed key hash table (key_len
 * paramter set). It will BUG() if used inappropriately.
 *
 * Lookups may occur in parallel with hashtable mutations and resizing.
 */
void *rhashtable_lookup(struct rhashtable *ht, const void *key)
{
        const struct bucket_table *tbl, *old_tbl;
        struct rhash_head *he;
        u32 hash;

        BUG_ON(!ht->p.key_len);

        rcu_read_lock();
        old_tbl = rht_dereference_rcu(ht->tbl, ht);
        tbl = rht_dereference_rcu(ht->future_tbl, ht);
        hash = key_hashfn(ht, key, ht->p.key_len);
restart:
        rht_for_each_rcu(he, tbl, rht_bucket_index(tbl, hash)) {
                if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key,
                           ht->p.key_len))
                        continue;
                rcu_read_unlock();
                return rht_obj(ht, he);
        }

        if (unlikely(tbl != old_tbl)) {
                tbl = old_tbl;
                goto restart;
        }

        rcu_read_unlock();
        return NULL;
}
EXPORT_SYMBOL_GPL(rhashtable_lookup);

/**
 * rhashtable_lookup_compare - search hash table with compare function
 * @ht:         hash table
 * @key:        the pointer to the key
 * @compare:    compare function, must return true on match
 * @arg:        argument passed on to compare function
 *
 * Traverses the bucket chain behind the provided hash value and calls the
 * specified compare function for each entry.
 *
 * Lookups may occur in parallel with hashtable mutations and resizing.
 *
 * Returns the first entry on which the compare function returned true.
 */
void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key,
                                bool (*compare)(void *, void *), void *arg)
{
        const struct bucket_table *tbl, *old_tbl;
        struct rhash_head *he;
        u32 hash;

        rcu_read_lock();

        old_tbl = rht_dereference_rcu(ht->tbl, ht);
        tbl = rht_dereference_rcu(ht->future_tbl, ht);
        hash = key_hashfn(ht, key, ht->p.key_len);
restart:
        rht_for_each_rcu(he, tbl, rht_bucket_index(tbl, hash)) {
                if (!compare(rht_obj(ht, he), arg))
                        continue;
                rcu_read_unlock();
                return rht_obj(ht, he);
        }

        if (unlikely(tbl != old_tbl)) {
                tbl = old_tbl;
                goto restart;
        }
        rcu_read_unlock();

        return NULL;
}
EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);

static size_t rounded_hashtable_size(struct rhashtable_params *params)
{
        return max(roundup_pow_of_two(params->nelem_hint * 4 / 3),
                   1UL << params->min_shift);
}

/**
 * rhashtable_init - initialize a new hash table
 * @ht:         hash table to be initialized
 * @params:     configuration parameters
 *
 * Initializes a new hash table based on the provided configuration
 * parameters. A table can be configured either with a variable or
 * fixed length key:
 *
 * Configuration Example 1: Fixed length keys
 * struct test_obj {
 *      int                     key;
 *      void *                  my_member;
 *      struct rhash_head       node;
 * };
 *
 * struct rhashtable_params params = {
 *      .head_offset = offsetof(struct test_obj, node),
 *      .key_offset = offsetof(struct test_obj, key),
 *      .key_len = sizeof(int),
 *      .hashfn = jhash,
 *      .nulls_base = (1U << RHT_BASE_SHIFT),
 * };
 *
 * Configuration Example 2: Variable length keys
 * struct test_obj {
 *      [...]
 *      struct rhash_head       node;
 * };
 *
 * u32 my_hash_fn(const void *data, u32 seed)
 * {
 *      struct test_obj *obj = data;
 *
 *      return [... hash ...];
 * }
 *
 * struct rhashtable_params params = {
 *      .head_offset = offsetof(struct test_obj, node),
 *      .hashfn = jhash,
 *      .obj_hashfn = my_hash_fn,
 * };
 */
int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
{
        struct bucket_table *tbl;
        size_t size;

        size = HASH_DEFAULT_SIZE;

        if ((params->key_len && !params->hashfn) ||
            (!params->key_len && !params->obj_hashfn))
                return -EINVAL;

        if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT))
                return -EINVAL;

        params->min_shift = max_t(size_t, params->min_shift,
                                  ilog2(HASH_MIN_SIZE));

        if (params->nelem_hint)
                size = rounded_hashtable_size(params);

        memset(ht, 0, sizeof(*ht));
        mutex_init(&ht->mutex);
        memcpy(&ht->p, params, sizeof(*params));

        if (params->locks_mul)
                ht->p.locks_mul = roundup_pow_of_two(params->locks_mul);
        else
                ht->p.locks_mul = BUCKET_LOCKS_PER_CPU;

        tbl = bucket_table_alloc(ht, size);
        if (tbl == NULL)
                return -ENOMEM;

        ht->shift = ilog2(tbl->size);
        RCU_INIT_POINTER(ht->tbl, tbl);
        RCU_INIT_POINTER(ht->future_tbl, tbl);

        if (!ht->p.hash_rnd)
                get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd));

        if (ht->p.grow_decision || ht->p.shrink_decision)
                INIT_DEFERRABLE_WORK(&ht->run_work, rht_deferred_worker);

        return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_init);

/**
 * rhashtable_destroy - destroy hash table
 * @ht:         the hash table to destroy
 *
 * Frees the bucket array. This function is not rcu safe, therefore the caller
 * has to make sure that no resizing may happen by unpublishing the hashtable
 * and waiting for the quiescent cycle before releasing the bucket array.
 */
void rhashtable_destroy(struct rhashtable *ht)
{
        ht->being_destroyed = true;

        mutex_lock(&ht->mutex);

        cancel_delayed_work(&ht->run_work);
        bucket_table_free(rht_dereference(ht->tbl, ht));

        mutex_unlock(&ht->mutex);
}
EXPORT_SYMBOL_GPL(rhashtable_destroy);

/**************************************************************************
 * Self Test
 **************************************************************************/

#ifdef CONFIG_TEST_RHASHTABLE

#define TEST_HT_SIZE    8
#define TEST_ENTRIES    2048
#define TEST_PTR        ((void *) 0xdeadbeef)
#define TEST_NEXPANDS   4

struct test_obj {
        void                    *ptr;
        int                     value;
        struct rhash_head       node;
};

static int __init test_rht_lookup(struct rhashtable *ht)
{
        unsigned int i;

        for (i = 0; i < TEST_ENTRIES * 2; i++) {
                struct test_obj *obj;
                bool expected = !(i % 2);
                u32 key = i;

                obj = rhashtable_lookup(ht, &key);

                if (expected && !obj) {
                        pr_warn("Test failed: Could not find key %u\n", key);
                        return -ENOENT;
                } else if (!expected && obj) {
                        pr_warn("Test failed: Unexpected entry found for key %u\n",
                                key);
                        return -EEXIST;
                } else if (expected && obj) {
                        if (obj->ptr != TEST_PTR || obj->value != i) {
                                pr_warn("Test failed: Lookup value mismatch %p!=%p, %u!=%u\n",
                                        obj->ptr, TEST_PTR, obj->value, i);
                                return -EINVAL;
                        }
                }
        }

        return 0;
}

static void test_bucket_stats(struct rhashtable *ht, bool quiet)
{
        unsigned int cnt, rcu_cnt, i, total = 0;
        struct rhash_head *pos;
        struct test_obj *obj;
        struct bucket_table *tbl;

        tbl = rht_dereference_rcu(ht->tbl, ht);
        for (i = 0; i < tbl->size; i++) {
                rcu_cnt = cnt = 0;

                if (!quiet)
                        pr_info(" [%#4x/%zu]", i, tbl->size);

                rht_for_each_entry_rcu(obj, pos, tbl, i, node) {
                        cnt++;
                        total++;
                        if (!quiet)
                                pr_cont(" [%p],", obj);
                }

                rht_for_each_entry_rcu(obj, pos, tbl, i, node)
                        rcu_cnt++;

                if (rcu_cnt != cnt)
                        pr_warn("Test failed: Chain count mismach %d != %d",
                                cnt, rcu_cnt);

                if (!quiet)
                        pr_cont("\n  [%#x] first element: %p, chain length: %u\n",
                                i, tbl->buckets[i], cnt);
        }

        pr_info("  Traversal complete: counted=%u, nelems=%u, entries=%d\n",
                total, atomic_read(&ht->nelems), TEST_ENTRIES);

        if (total != atomic_read(&ht->nelems) || total != TEST_ENTRIES)
                pr_warn("Test failed: Total count mismatch ^^^");
}

static int __init test_rhashtable(struct rhashtable *ht)
{
        struct bucket_table *tbl;
        struct test_obj *obj;
        struct rhash_head *pos, *next;
        int err;
        unsigned int i;

        /*
         * Insertion Test:
         * Insert TEST_ENTRIES into table with all keys even numbers
         */
        pr_info("  Adding %d keys\n", TEST_ENTRIES);
        for (i = 0; i < TEST_ENTRIES; i++) {
                struct test_obj *obj;

                obj = kzalloc(sizeof(*obj), GFP_KERNEL);
                if (!obj) {
                        err = -ENOMEM;
                        goto error;
                }

                obj->ptr = TEST_PTR;
                obj->value = i * 2;

                rhashtable_insert(ht, &obj->node);
        }

        rcu_read_lock();
        test_bucket_stats(ht, true);
        test_rht_lookup(ht);
        rcu_read_unlock();

        for (i = 0; i < TEST_NEXPANDS; i++) {
                pr_info("  Table expansion iteration %u...\n", i);
                mutex_lock(&ht->mutex);
                rhashtable_expand(ht);
                mutex_unlock(&ht->mutex);

                rcu_read_lock();
                pr_info("  Verifying lookups...\n");
                test_rht_lookup(ht);
                rcu_read_unlock();
        }

        for (i = 0; i < TEST_NEXPANDS; i++) {
                pr_info("  Table shrinkage iteration %u...\n", i);
                mutex_lock(&ht->mutex);
                rhashtable_shrink(ht);
                mutex_unlock(&ht->mutex);

                rcu_read_lock();
                pr_info("  Verifying lookups...\n");
                test_rht_lookup(ht);
                rcu_read_unlock();
        }

        rcu_read_lock();
        test_bucket_stats(ht, true);
        rcu_read_unlock();

        pr_info("  Deleting %d keys\n", TEST_ENTRIES);
        for (i = 0; i < TEST_ENTRIES; i++) {
                u32 key = i * 2;

                obj = rhashtable_lookup(ht, &key);
                BUG_ON(!obj);

                rhashtable_remove(ht, &obj->node);
                kfree(obj);
        }

        return 0;

error:
        tbl = rht_dereference_rcu(ht->tbl, ht);
        for (i = 0; i < tbl->size; i++)
                rht_for_each_entry_safe(obj, pos, next, tbl, i, node)
                        kfree(obj);

        return err;
}

static int __init test_rht_init(void)
{
        struct rhashtable ht;
        struct rhashtable_params params = {
                .nelem_hint = TEST_HT_SIZE,
                .head_offset = offsetof(struct test_obj, node),
                .key_offset = offsetof(struct test_obj, value),
                .key_len = sizeof(int),
                .hashfn = jhash,
                .nulls_base = (3U << RHT_BASE_SHIFT),
                .grow_decision = rht_grow_above_75,
                .shrink_decision = rht_shrink_below_30,
        };
        int err;

        pr_info("Running resizable hashtable tests...\n");

        err = rhashtable_init(&ht, &params);
        if (err < 0) {
                pr_warn("Test failed: Unable to initialize hashtable: %d\n",
                        err);
                return err;
        }

        err = test_rhashtable(&ht);

        rhashtable_destroy(&ht);

        return err;
}

subsys_initcall(test_rht_init);

#endif /* CONFIG_TEST_RHASHTABLE */