Linux 3.17-rc2

[linux/fpc-iii.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/hash.h>
#include <linux/random.h>
#include <linux/rhashtable.h>
#include <linux/log2.h>

#define HASH_DEFAULT_SIZE       64UL
#define HASH_MIN_SIZE           4UL

#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))

#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
{
        return ht->p.mutex_is_held();
}
EXPORT_SYMBOL_GPL(lockdep_rht_mutex_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 __hashfn(const struct rhashtable *ht, const void *key,
                      u32 len, u32 hsize)
{
        u32 h;

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

        return h & (hsize - 1);
}

/**
 * rhashtable_hashfn - compute hash for key of given length
 * @ht:         hash table to compuate for
 * @key:        pointer to key
 * @len:        length of key
 *
 * Computes the hash value using the hash function provided in the 'hashfn'
 * of struct rhashtable_params. The returned value is guaranteed to be
 * smaller than the number of buckets in the hash table.
 */
u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len)
{
        struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);

        return __hashfn(ht, key, len, tbl->size);
}
EXPORT_SYMBOL_GPL(rhashtable_hashfn);

static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize)
{
        if (unlikely(!ht->p.key_len)) {
                u32 h;

                h = ht->p.obj_hashfn(ptr, ht->p.hash_rnd);

                return h & (hsize - 1);
        }

        return __hashfn(ht, ptr + ht->p.key_offset, ht->p.key_len, hsize);
}

/**
 * rhashtable_obj_hashfn - compute hash for hashed object
 * @ht:         hash table to compuate for
 * @ptr:        pointer to hashed object
 *
 * Computes the hash value using the hash function `hashfn` respectively
 * 'obj_hashfn' depending on whether the hash table is set up to work with
 * a fixed length key. The returned value is guaranteed to be smaller than
 * the number of buckets in the hash table.
 */
u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr)
{
        struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);

        return obj_hashfn(ht, ptr, tbl->size);
}
EXPORT_SYMBOL_GPL(rhashtable_obj_hashfn);

static u32 head_hashfn(const struct rhashtable *ht,
                       const struct rhash_head *he, u32 hsize)
{
        return obj_hashfn(ht, rht_obj(ht, he), hsize);
}

static struct bucket_table *bucket_table_alloc(size_t nbuckets, gfp_t flags)
{
        struct bucket_table *tbl;
        size_t size;

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

        if (tbl == NULL)
                return NULL;

        tbl->size = nbuckets;

        return tbl;
}

static void bucket_table_free(const struct bucket_table *tbl)
{
        kvfree(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 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 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 n)
{
        struct rhash_head *he, *p, *next;
        unsigned int h;

        /* Old bucket empty, no work needed. */
        p = rht_dereference(old_tbl->buckets[n], ht);
        if (!p)
                return;

        /* 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;
         */
        h = head_hashfn(ht, p, new_tbl->size);
        rht_for_each(he, p->next, ht) {
                if (head_hashfn(ht, he, new_tbl->size) != h)
                        break;
                p = he;
        }
        RCU_INIT_POINTER(old_tbl->buckets[n], p->next);

        /* Find the subsequent node which does hash to the same
         * bucket as node P, or NULL if no such node exists.
         */
        next = NULL;
        if (he) {
                rht_for_each(he, he->next, ht) {
                        if (head_hashfn(ht, he, new_tbl->size) == h) {
                                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_INIT_POINTER(p->next, next);
}

/**
 * rhashtable_expand - Expand hash table while allowing concurrent lookups
 * @ht:         the hash table to expand
 * @flags:      allocation flags
 *
 * 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 table mutations take place.
 * It is however valid to have concurrent lookups if they are RCU protected.
 */
int rhashtable_expand(struct rhashtable *ht, gfp_t flags)
{
        struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
        struct rhash_head *he;
        unsigned int i, h;
        bool complete;

        ASSERT_RHT_MUTEX(ht);

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

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

        ht->shift++;

        /* For each new bucket, search the corresponding old bucket
         * for the first entry that hashes to the new bucket, and
         * link the new bucket 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 (i = 0; i < new_tbl->size; i++) {
                h = i & (old_tbl->size - 1);
                rht_for_each(he, old_tbl->buckets[h], ht) {
                        if (head_hashfn(ht, he, new_tbl->size) == i) {
                                RCU_INIT_POINTER(new_tbl->buckets[i], he);
                                break;
                        }
                }
        }

        /* 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 */
        do {
                /* 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 (i = 0; i < old_tbl->size; i++) {
                        hashtable_chain_unzip(ht, new_tbl, old_tbl, i);
                        if (old_tbl->buckets[i] != NULL)
                                complete = false;
                }
        } while (!complete);

        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
 * @flags:      allocation flags
 *
 * 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 table mutations take place.
 * It is however valid to have concurrent lookups if they are RCU protected.
 */
int rhashtable_shrink(struct rhashtable *ht, gfp_t flags)
{
        struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht);
        struct rhash_head __rcu **pprev;
        unsigned int i;

        ASSERT_RHT_MUTEX(ht);

        if (tbl->size <= HASH_MIN_SIZE)
                return 0;

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

        ht->shift--;

        /* Link each bucket in the new table to the first bucket
         * in the old table that contains entries which will hash
         * to the new bucket.
         */
        for (i = 0; i < ntbl->size; i++) {
                ntbl->buckets[i] = tbl->buckets[i];

                /* Link each bucket in the new table to the first bucket
                 * in the old table that contains entries which will hash
                 * to the new bucket.
                 */
                for (pprev = &ntbl->buckets[i]; *pprev != NULL;
                     pprev = &rht_dereference(*pprev, ht)->next)
                        ;
                RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]);
        }

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

        /* 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);

/**
 * rhashtable_insert - insert object into hash hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @flags:      allocation flags (table expansion)
 *
 * Will automatically grow the table via rhashtable_expand() if the the
 * grow_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.
 */
void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
                       gfp_t flags)
{
        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
        u32 hash;

        ASSERT_RHT_MUTEX(ht);

        hash = head_hashfn(ht, obj, tbl->size);
        RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
        rcu_assign_pointer(tbl->buckets[hash], obj);
        ht->nelems++;

        if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
                rhashtable_expand(ht, flags);
}
EXPORT_SYMBOL_GPL(rhashtable_insert);

/**
 * rhashtable_remove_pprev - remove object from hash table given previous element
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @pprev:      pointer to previous element
 * @flags:      allocation flags (table expansion)
 *
 * Identical to rhashtable_remove() but caller is alreayd aware of the element
 * in front of the element to be deleted. This is in particular useful for
 * deletion when combined with walking or lookup.
 */
void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
                             struct rhash_head __rcu **pprev, gfp_t flags)
{
        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);

        ASSERT_RHT_MUTEX(ht);

        RCU_INIT_POINTER(*pprev, obj->next);
        ht->nelems--;

        if (ht->p.shrink_decision &&
            ht->p.shrink_decision(ht, tbl->size))
                rhashtable_shrink(ht, flags);
}
EXPORT_SYMBOL_GPL(rhashtable_remove_pprev);

/**
 * rhashtable_remove - remove object from hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @flags:      allocation flags (table expansion)
 *
 * 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,
                       gfp_t flags)
{
        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
        struct rhash_head __rcu **pprev;
        struct rhash_head *he;
        u32 h;

        ASSERT_RHT_MUTEX(ht);

        h = head_hashfn(ht, obj, tbl->size);

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

                rhashtable_remove_pprev(ht, he, pprev, flags);
                return true;
        }

        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 hash mutations as long as the lookup is
 * guarded by rcu_read_lock(). The caller must take care of this.
 */
void *rhashtable_lookup(const struct rhashtable *ht, const void *key)
{
        const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
        struct rhash_head *he;
        u32 h;

        BUG_ON(!ht->p.key_len);

        h = __hashfn(ht, key, ht->p.key_len, tbl->size);
        rht_for_each_rcu(he, tbl->buckets[h], ht) {
                if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key,
                           ht->p.key_len))
                        continue;
                return (void *) he - ht->p.head_offset;
        }

        return NULL;
}
EXPORT_SYMBOL_GPL(rhashtable_lookup);

/**
 * rhashtable_lookup_compare - search hash table with compare function
 * @ht:         hash table
 * @hash:       hash value of desired entry
 * @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 hash mutations as long as the lookup is
 * guarded by rcu_read_lock(). The caller must take care of this.
 *
 * Returns the first entry on which the compare function returned true.
 */
void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
                                bool (*compare)(void *, void *), void *arg)
{
        const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
        struct rhash_head *he;

        if (unlikely(hash >= tbl->size))
                return NULL;

        rht_for_each_rcu(he, tbl->buckets[hash], ht) {
                if (!compare(rht_obj(ht, he), arg))
                        continue;
                return (void *) he - ht->p.head_offset;
        }

        return NULL;
}
EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);

static size_t rounded_hashtable_size(unsigned int nelem)
{
        return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE);
}

/**
 * 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 = arch_fast_hash,
 *      .mutex_is_held = &my_mutex_is_held,
 * };
 *
 * 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 = arch_fast_hash,
 *      .obj_hashfn = my_hash_fn,
 *      .mutex_is_held = &my_mutex_is_held,
 * };
 */
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->nelem_hint)
                size = rounded_hashtable_size(params->nelem_hint);

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

        memset(ht, 0, sizeof(*ht));
        ht->shift = ilog2(tbl->size);
        memcpy(&ht->p, params, sizeof(*params));
        RCU_INIT_POINTER(ht->tbl, tbl);

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

        return 0;
}
EXPORT_SYMBOL_GPL(rhashtable_init);

/**
 * rhashtable_destroy - destroy hash table
 * @ht:         the hash table to destroy
 *
 * Frees the bucket array.
 */
void rhashtable_destroy(const struct rhashtable *ht)
{
        const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);

        bucket_table_free(tbl);
}
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

static int test_mutex_is_held(void)
{
        return 1;
}

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,
                                     struct bucket_table *tbl,
                                     bool quiet)
{
        unsigned int cnt, i, total = 0;
        struct test_obj *obj;

        for (i = 0; i < tbl->size; i++) {
                cnt = 0;

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

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

                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=%zu, entries=%d\n",
                total, ht->nelems, TEST_ENTRIES);
}

static int __init test_rhashtable(struct rhashtable *ht)
{
        struct bucket_table *tbl;
        struct test_obj *obj, *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, GFP_KERNEL);
        }

        rcu_read_lock();
        tbl = rht_dereference_rcu(ht->tbl, ht);
        test_bucket_stats(ht, tbl, true);
        test_rht_lookup(ht);
        rcu_read_unlock();

        for (i = 0; i < TEST_NEXPANDS; i++) {
                pr_info("  Table expansion iteration %u...\n", i);
                rhashtable_expand(ht, GFP_KERNEL);

                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);
                rhashtable_shrink(ht, GFP_KERNEL);

                rcu_read_lock();
                pr_info("  Verifying lookups...\n");
                test_rht_lookup(ht);
                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, GFP_KERNEL);
                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, next, tbl->buckets[i], ht, 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 = arch_fast_hash,
                .mutex_is_held = &test_mutex_is_held,
                .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 */