/* * Resizable, Scalable, Concurrent Hash Table * * Copyright (c) 2015 Herbert Xu <herbert@gondor.apana.org.au> * Copyright (c) 2014-2015 Thomas Graf <tgraf@suug.ch> * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net> * * Code partially derived from nft_hash * Rewritten with rehash code from br_multicast plus single list * pointer as suggested by Josh Triplett * * 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/atomic.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/log2.h> #include <linux/sched.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> #include <linux/err.h> #include <linux/export.h> #define HASH_DEFAULT_SIZE 64UL #define HASH_MIN_SIZE 4U #define BUCKET_LOCKS_PER_CPU 128UL static u32 head_hashfn(struct rhashtable *ht, const struct bucket_table *tbl, const struct rhash_head *he) { return rht_head_hashfn(ht, tbl, he, ht->p); } #ifdef CONFIG_PROVE_LOCKING #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT)) 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 = rht_bucket_lock(tbl, hash); return (debug_locks) ? lockdep_is_held(lock) : 1; } EXPORT_SYMBOL_GPL(lockdep_rht_bucket_is_held); #else #define ASSERT_RHT_MUTEX(HT) #endif static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl, gfp_t gfp) { 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 0.5 locks per bucket */ size = min_t(unsigned int, size, tbl->size >> 1); if (sizeof(spinlock_t) != 0) { #ifdef CONFIG_NUMA if (size * sizeof(spinlock_t) > PAGE_SIZE && gfp == GFP_KERNEL) tbl->locks = vmalloc(size * sizeof(spinlock_t)); else #endif tbl->locks = kmalloc_array(size, sizeof(spinlock_t), gfp); 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 void bucket_table_free_rcu(struct rcu_head *head) { bucket_table_free(container_of(head, struct bucket_table, rcu)); } static struct bucket_table *bucket_table_alloc(struct rhashtable *ht, size_t nbuckets, gfp_t gfp) { struct bucket_table *tbl = NULL; size_t size; int i; size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]); if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER) || gfp != GFP_KERNEL) tbl = kzalloc(size, gfp | __GFP_NOWARN | __GFP_NORETRY); if (tbl == NULL && gfp == GFP_KERNEL) tbl = vzalloc(size); if (tbl == NULL) return NULL; tbl->size = nbuckets; if (alloc_bucket_locks(ht, tbl, gfp) < 0) { bucket_table_free(tbl); return NULL; } INIT_LIST_HEAD(&tbl->walkers); get_random_bytes(&tbl->hash_rnd, sizeof(tbl->hash_rnd)); for (i = 0; i < nbuckets; i++) INIT_RHT_NULLS_HEAD(tbl->buckets[i], ht, i); return tbl; } static struct bucket_table *rhashtable_last_table(struct rhashtable *ht, struct bucket_table *tbl) { struct bucket_table *new_tbl; do { new_tbl = tbl; tbl = rht_dereference_rcu(tbl->future_tbl, ht); } while (tbl); return new_tbl; } static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash) { struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht); struct bucket_table *new_tbl = rhashtable_last_table(ht, rht_dereference_rcu(old_tbl->future_tbl, ht)); struct rhash_head __rcu **pprev = &old_tbl->buckets[old_hash]; int err = -ENOENT; struct rhash_head *head, *next, *entry; spinlock_t *new_bucket_lock; unsigned int new_hash; rht_for_each(entry, old_tbl, old_hash) { err = 0; next = rht_dereference_bucket(entry->next, old_tbl, old_hash); if (rht_is_a_nulls(next)) break; pprev = &entry->next; } if (err) goto out; new_hash = head_hashfn(ht, new_tbl, entry); new_bucket_lock = rht_bucket_lock(new_tbl, new_hash); spin_lock_nested(new_bucket_lock, SINGLE_DEPTH_NESTING); head = rht_dereference_bucket(new_tbl->buckets[new_hash], new_tbl, new_hash); RCU_INIT_POINTER(entry->next, head); rcu_assign_pointer(new_tbl->buckets[new_hash], entry); spin_unlock(new_bucket_lock); rcu_assign_pointer(*pprev, next); out: return err; } static void rhashtable_rehash_chain(struct rhashtable *ht, unsigned int old_hash) { struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht); spinlock_t *old_bucket_lock; old_bucket_lock = rht_bucket_lock(old_tbl, old_hash); spin_lock_bh(old_bucket_lock); while (!rhashtable_rehash_one(ht, old_hash)) ; old_tbl->rehash++; spin_unlock_bh(old_bucket_lock); } static int rhashtable_rehash_attach(struct rhashtable *ht, struct bucket_table *old_tbl, struct bucket_table *new_tbl) { /* Protect future_tbl using the first bucket lock. */ spin_lock_bh(old_tbl->locks); /* Did somebody beat us to it? */ if (rcu_access_pointer(old_tbl->future_tbl)) { spin_unlock_bh(old_tbl->locks); return -EEXIST; } /* Make insertions go into the new, empty table right away. Deletions * and lookups will be attempted in both tables until we synchronize. */ rcu_assign_pointer(old_tbl->future_tbl, new_tbl); spin_unlock_bh(old_tbl->locks); return 0; } static int rhashtable_rehash_table(struct rhashtable *ht) { struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht); struct bucket_table *new_tbl; struct rhashtable_walker *walker; unsigned int old_hash; new_tbl = rht_dereference(old_tbl->future_tbl, ht); if (!new_tbl) return 0; for (old_hash = 0; old_hash < old_tbl->size; old_hash++) rhashtable_rehash_chain(ht, old_hash); /* Publish the new table pointer. */ rcu_assign_pointer(ht->tbl, new_tbl); spin_lock(&ht->lock); list_for_each_entry(walker, &old_tbl->walkers, list) walker->tbl = NULL; spin_unlock(&ht->lock); /* Wait for readers. All new readers will see the new * table, and thus no references to the old table will * remain. */ call_rcu(&old_tbl->rcu, bucket_table_free_rcu); return rht_dereference(new_tbl->future_tbl, ht) ? -EAGAIN : 0; } /** * 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. * * 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. */ static int rhashtable_expand(struct rhashtable *ht) { struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht); int err; ASSERT_RHT_MUTEX(ht); old_tbl = rhashtable_last_table(ht, old_tbl); new_tbl = bucket_table_alloc(ht, old_tbl->size * 2, GFP_KERNEL); if (new_tbl == NULL) return -ENOMEM; err = rhashtable_rehash_attach(ht, old_tbl, new_tbl); if (err) bucket_table_free(new_tbl); return err; } /** * rhashtable_shrink - Shrink hash table while allowing concurrent lookups * @ht: the hash table to shrink * * This function shrinks the hash table to fit, i.e., the smallest * size would not cause it to expand right away automatically. * * 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. */ static int rhashtable_shrink(struct rhashtable *ht) { struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht); unsigned int size; int err; ASSERT_RHT_MUTEX(ht); size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2); if (size < ht->p.min_size) size = ht->p.min_size; if (old_tbl->size <= size) return 0; if (rht_dereference(old_tbl->future_tbl, ht)) return -EEXIST; new_tbl = bucket_table_alloc(ht, size, GFP_KERNEL); if (new_tbl == NULL) return -ENOMEM; err = rhashtable_rehash_attach(ht, old_tbl, new_tbl); if (err) bucket_table_free(new_tbl); return err; } static void rht_deferred_worker(struct work_struct *work) { struct rhashtable *ht; struct bucket_table *tbl; int err = 0; ht = container_of(work, struct rhashtable, run_work); mutex_lock(&ht->mutex); tbl = rht_dereference(ht->tbl, ht); tbl = rhashtable_last_table(ht, tbl); if (rht_grow_above_75(ht, tbl)) rhashtable_expand(ht); else if (ht->p.automatic_shrinking && rht_shrink_below_30(ht, tbl)) rhashtable_shrink(ht); err = rhashtable_rehash_table(ht); mutex_unlock(&ht->mutex); if (err) schedule_work(&ht->run_work); } static bool rhashtable_check_elasticity(struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash) { unsigned int elasticity = ht->elasticity; struct rhash_head *head; rht_for_each(head, tbl, hash) if (!--elasticity) return true; return false; } int rhashtable_insert_rehash(struct rhashtable *ht, struct bucket_table *tbl) { struct bucket_table *old_tbl; struct bucket_table *new_tbl; unsigned int size; int err; old_tbl = rht_dereference_rcu(ht->tbl, ht); size = tbl->size; err = -EBUSY; if (rht_grow_above_75(ht, tbl)) size *= 2; /* Do not schedule more than one rehash */ else if (old_tbl != tbl) goto fail; err = -ENOMEM; new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC); if (new_tbl == NULL) goto fail; err = rhashtable_rehash_attach(ht, tbl, new_tbl); if (err) { bucket_table_free(new_tbl); if (err == -EEXIST) err = 0; } else schedule_work(&ht->run_work); return err; fail: /* Do not fail the insert if someone else did a rehash. */ if (likely(rcu_dereference_raw(tbl->future_tbl))) return 0; /* Schedule async rehash to retry allocation in process context. */ if (err == -ENOMEM) schedule_work(&ht->run_work); return err; } EXPORT_SYMBOL_GPL(rhashtable_insert_rehash); struct bucket_table *rhashtable_insert_slow(struct rhashtable *ht, const void *key, struct rhash_head *obj, struct bucket_table *tbl) { struct rhash_head *head; unsigned int hash; int err; tbl = rhashtable_last_table(ht, tbl); hash = head_hashfn(ht, tbl, obj); spin_lock_nested(rht_bucket_lock(tbl, hash), SINGLE_DEPTH_NESTING); err = -EEXIST; if (key && rhashtable_lookup_fast(ht, key, ht->p)) goto exit; err = -E2BIG; if (unlikely(rht_grow_above_max(ht, tbl))) goto exit; err = -EAGAIN; if (rhashtable_check_elasticity(ht, tbl, hash) || rht_grow_above_100(ht, tbl)) goto exit; err = 0; head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash); RCU_INIT_POINTER(obj->next, head); rcu_assign_pointer(tbl->buckets[hash], obj); atomic_inc(&ht->nelems); exit: spin_unlock(rht_bucket_lock(tbl, hash)); if (err == 0) return NULL; else if (err == -EAGAIN) return tbl; else return ERR_PTR(err); } EXPORT_SYMBOL_GPL(rhashtable_insert_slow); /** * rhashtable_walk_init - Initialise an iterator * @ht: Table to walk over * @iter: Hash table Iterator * * This function prepares a hash table walk. * * Note that if you restart a walk after rhashtable_walk_stop you * may see the same object twice. Also, you may miss objects if * there are removals in between rhashtable_walk_stop and the next * call to rhashtable_walk_start. * * For a completely stable walk you should construct your own data * structure outside the hash table. * * This function may sleep so you must not call it from interrupt * context or with spin locks held. * * You must call rhashtable_walk_exit if this function returns * successfully. */ int rhashtable_walk_init(struct rhashtable *ht, struct rhashtable_iter *iter) { iter->ht = ht; iter->p = NULL; iter->slot = 0; iter->skip = 0; iter->walker = kmalloc(sizeof(*iter->walker), GFP_KERNEL); if (!iter->walker) return -ENOMEM; spin_lock(&ht->lock); iter->walker->tbl = rcu_dereference_protected(ht->tbl, lockdep_is_held(&ht->lock)); list_add(&iter->walker->list, &iter->walker->tbl->walkers); spin_unlock(&ht->lock); return 0; } EXPORT_SYMBOL_GPL(rhashtable_walk_init); /** * rhashtable_walk_exit - Free an iterator * @iter: Hash table Iterator * * This function frees resources allocated by rhashtable_walk_init. */ void rhashtable_walk_exit(struct rhashtable_iter *iter) { spin_lock(&iter->ht->lock); if (iter->walker->tbl) list_del(&iter->walker->list); spin_unlock(&iter->ht->lock); kfree(iter->walker); } EXPORT_SYMBOL_GPL(rhashtable_walk_exit); /** * rhashtable_walk_start - Start a hash table walk * @iter: Hash table iterator * * Start a hash table walk. Note that we take the RCU lock in all * cases including when we return an error. So you must always call * rhashtable_walk_stop to clean up. * * Returns zero if successful. * * Returns -EAGAIN if resize event occured. Note that the iterator * will rewind back to the beginning and you may use it immediately * by calling rhashtable_walk_next. */ int rhashtable_walk_start(struct rhashtable_iter *iter) __acquires(RCU) { struct rhashtable *ht = iter->ht; rcu_read_lock(); spin_lock(&ht->lock); if (iter->walker->tbl) list_del(&iter->walker->list); spin_unlock(&ht->lock); if (!iter->walker->tbl) { iter->walker->tbl = rht_dereference_rcu(ht->tbl, ht); return -EAGAIN; } return 0; } EXPORT_SYMBOL_GPL(rhashtable_walk_start); /** * rhashtable_walk_next - Return the next object and advance the iterator * @iter: Hash table iterator * * Note that you must call rhashtable_walk_stop when you are finished * with the walk. * * Returns the next object or NULL when the end of the table is reached. * * Returns -EAGAIN if resize event occured. Note that the iterator * will rewind back to the beginning and you may continue to use it. */ void *rhashtable_walk_next(struct rhashtable_iter *iter) { struct bucket_table *tbl = iter->walker->tbl; struct rhashtable *ht = iter->ht; struct rhash_head *p = iter->p; if (p) { p = rht_dereference_bucket_rcu(p->next, tbl, iter->slot); goto next; } for (; iter->slot < tbl->size; iter->slot++) { int skip = iter->skip; rht_for_each_rcu(p, tbl, iter->slot) { if (!skip) break; skip--; } next: if (!rht_is_a_nulls(p)) { iter->skip++; iter->p = p; return rht_obj(ht, p); } iter->skip = 0; } iter->p = NULL; /* Ensure we see any new tables. */ smp_rmb(); iter->walker->tbl = rht_dereference_rcu(tbl->future_tbl, ht); if (iter->walker->tbl) { iter->slot = 0; iter->skip = 0; return ERR_PTR(-EAGAIN); } return NULL; } EXPORT_SYMBOL_GPL(rhashtable_walk_next); /** * rhashtable_walk_stop - Finish a hash table walk * @iter: Hash table iterator * * Finish a hash table walk. */ void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases(RCU) { struct rhashtable *ht; struct bucket_table *tbl = iter->walker->tbl; if (!tbl) goto out; ht = iter->ht; spin_lock(&ht->lock); if (tbl->rehash < tbl->size) list_add(&iter->walker->list, &tbl->walkers); else iter->walker->tbl = NULL; spin_unlock(&ht->lock); iter->p = NULL; out: rcu_read_unlock(); } EXPORT_SYMBOL_GPL(rhashtable_walk_stop); static size_t rounded_hashtable_size(const struct rhashtable_params *params) { return max(roundup_pow_of_two(params->nelem_hint * 4 / 3), (unsigned long)params->min_size); } static u32 rhashtable_jhash2(const void *key, u32 length, u32 seed) { return jhash2(key, length, seed); } /** * 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 len, 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, const struct rhashtable_params *params) { struct bucket_table *tbl; size_t size; size = HASH_DEFAULT_SIZE; if ((!params->key_len && !params->obj_hashfn) || (params->obj_hashfn && !params->obj_cmpfn)) return -EINVAL; if (params->nulls_base && params->nulls_base < (1U << RHT_BASE_SHIFT)) return -EINVAL; memset(ht, 0, sizeof(*ht)); mutex_init(&ht->mutex); spin_lock_init(&ht->lock); memcpy(&ht->p, params, sizeof(*params)); if (params->min_size) ht->p.min_size = roundup_pow_of_two(params->min_size); if (params->max_size) ht->p.max_size = rounddown_pow_of_two(params->max_size); if (params->insecure_max_entries) ht->p.insecure_max_entries = rounddown_pow_of_two(params->insecure_max_entries); else ht->p.insecure_max_entries = ht->p.max_size * 2; ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE); if (params->nelem_hint) size = rounded_hashtable_size(&ht->p); /* The maximum (not average) chain length grows with the * size of the hash table, at a rate of (log N)/(log log N). * The value of 16 is selected so that even if the hash * table grew to 2^32 you would not expect the maximum * chain length to exceed it unless we are under attack * (or extremely unlucky). * * As this limit is only to detect attacks, we don't need * to set it to a lower value as you'd need the chain * length to vastly exceed 16 to have any real effect * on the system. */ if (!params->insecure_elasticity) ht->elasticity = 16; if (params->locks_mul) ht->p.locks_mul = roundup_pow_of_two(params->locks_mul); else ht->p.locks_mul = BUCKET_LOCKS_PER_CPU; ht->key_len = ht->p.key_len; if (!params->hashfn) { ht->p.hashfn = jhash; if (!(ht->key_len & (sizeof(u32) - 1))) { ht->key_len /= sizeof(u32); ht->p.hashfn = rhashtable_jhash2; } } tbl = bucket_table_alloc(ht, size, GFP_KERNEL); if (tbl == NULL) return -ENOMEM; atomic_set(&ht->nelems, 0); RCU_INIT_POINTER(ht->tbl, tbl); INIT_WORK(&ht->run_work, rht_deferred_worker); return 0; } EXPORT_SYMBOL_GPL(rhashtable_init); /** * rhashtable_free_and_destroy - free elements and destroy hash table * @ht: the hash table to destroy * @free_fn: callback to release resources of element * @arg: pointer passed to free_fn * * Stops an eventual async resize. If defined, invokes free_fn for each * element to releasal resources. Please note that RCU protected * readers may still be accessing the elements. Releasing of resources * must occur in a compatible manner. Then frees the bucket array. * * This function will eventually sleep to wait for an async resize * to complete. The caller is responsible that no further write operations * occurs in parallel. */ void rhashtable_free_and_destroy(struct rhashtable *ht, void (*free_fn)(void *ptr, void *arg), void *arg) { const struct bucket_table *tbl; unsigned int i; cancel_work_sync(&ht->run_work); mutex_lock(&ht->mutex); tbl = rht_dereference(ht->tbl, ht); if (free_fn) { for (i = 0; i < tbl->size; i++) { struct rhash_head *pos, *next; for (pos = rht_dereference(tbl->buckets[i], ht), next = !rht_is_a_nulls(pos) ? rht_dereference(pos->next, ht) : NULL; !rht_is_a_nulls(pos); pos = next, next = !rht_is_a_nulls(pos) ? rht_dereference(pos->next, ht) : NULL) free_fn(rht_obj(ht, pos), arg); } } bucket_table_free(tbl); mutex_unlock(&ht->mutex); } EXPORT_SYMBOL_GPL(rhashtable_free_and_destroy); void rhashtable_destroy(struct rhashtable *ht) { return rhashtable_free_and_destroy(ht, NULL, NULL); } EXPORT_SYMBOL_GPL(rhashtable_destroy);