/* * Resizable, Scalable, Concurrent Hash Table * * Copyright (c) 2014-2015 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/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> #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, }; /* The bucket lock is selected based on the hash and protects mutations * on a group of hash buckets. * * A maximum of tbl->size/2 bucket locks is allocated. This ensures that * a single lock always covers both buckets which may both contains * entries which link to the same bucket of the old table during resizing. * This allows to simplify the locking as locking the bucket in both * tables during resize always guarantee protection. * * 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]; } 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) { return ht->p.hashfn(key, len, ht->p.hash_rnd) >> HASH_RESERVED_SPACE; } 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))); } #ifdef CONFIG_PROVE_LOCKING static void debug_dump_buckets(const struct rhashtable *ht, const struct bucket_table *tbl) { struct rhash_head *he; unsigned int i, hash; for (i = 0; i < tbl->size; i++) { pr_warn(" [Bucket %d] ", i); rht_for_each_rcu(he, tbl, i) { hash = head_hashfn(ht, tbl, he); pr_cont("[hash = %#x, lock = %p] ", hash, bucket_lock(tbl, hash)); } pr_cont("\n"); } } static void debug_dump_table(struct rhashtable *ht, const struct bucket_table *tbl, unsigned int hash) { struct bucket_table *old_tbl, *future_tbl; pr_emerg("BUG: lock for hash %#x in table %p not held\n", hash, tbl); rcu_read_lock(); future_tbl = rht_dereference_rcu(ht->future_tbl, ht); old_tbl = rht_dereference_rcu(ht->tbl, ht); if (future_tbl != old_tbl) { pr_warn("Future table %p (size: %zd)\n", future_tbl, future_tbl->size); debug_dump_buckets(ht, future_tbl); } pr_warn("Table %p (size: %zd)\n", old_tbl, old_tbl->size); debug_dump_buckets(ht, old_tbl); rcu_read_unlock(); } #define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT)) #define ASSERT_BUCKET_LOCK(HT, TBL, HASH) \ do { \ if (unlikely(!lockdep_rht_bucket_is_held(TBL, HASH))) { \ debug_dump_table(HT, TBL, HASH); \ BUG(); \ } \ } while (0) 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); #else #define ASSERT_RHT_MUTEX(HT) #define ASSERT_BUCKET_LOCK(HT, TBL, HASH) #endif 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 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) 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 = NULL; size_t size; int i; size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]); if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) tbl = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY); 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 */ static 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) && (!ht->p.max_shift || atomic_read(&ht->shift) < ht->p.max_shift); } /** * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size * @ht: hash table * @new_size: new table size */ static 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) && (atomic_read(&ht->shift) > ht->p.min_shift); } static void lock_buckets(struct bucket_table *new_tbl, struct bucket_table *old_tbl, unsigned int hash) __acquires(old_bucket_lock) { spin_lock_bh(bucket_lock(old_tbl, hash)); if (new_tbl != old_tbl) spin_lock_bh_nested(bucket_lock(new_tbl, hash), RHT_LOCK_NESTED); } static void unlock_buckets(struct bucket_table *new_tbl, struct bucket_table *old_tbl, unsigned int hash) __releases(old_bucket_lock) { if (new_tbl != old_tbl) spin_unlock_bh(bucket_lock(new_tbl, hash)); spin_unlock_bh(bucket_lock(old_tbl, hash)); } /** * Unlink entries on bucket which hash to different bucket. * * Returns true if no more work needs to be performed on the bucket. */ static bool hashtable_chain_unzip(struct rhashtable *ht, const struct bucket_table *new_tbl, struct bucket_table *old_tbl, size_t old_hash) { struct rhash_head *he, *p, *next; unsigned int new_hash, new_hash2; ASSERT_BUCKET_LOCK(ht, 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 false; new_hash = head_hashfn(ht, new_tbl, p); ASSERT_BUCKET_LOCK(ht, 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); ASSERT_BUCKET_LOCK(ht, new_tbl, new_hash2); if (new_hash != new_hash2) break; p = he; } rcu_assign_pointer(old_tbl->buckets[old_hash], p->next); /* 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); p = rht_dereference_bucket(old_tbl->buckets[old_hash], old_tbl, old_hash); return !rht_is_a_nulls(p); } static void link_old_to_new(struct rhashtable *ht, struct bucket_table *new_tbl, unsigned int new_hash, struct rhash_head *entry) { ASSERT_BUCKET_LOCK(ht, new_tbl, new_hash); rcu_assign_pointer(*bucket_tail(new_tbl, new_hash), entry); } /** * 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; unsigned int new_hash, old_hash; bool complete = false; ASSERT_RHT_MUTEX(ht); new_tbl = bucket_table_alloc(ht, old_tbl->size * 2); if (new_tbl == NULL) return -ENOMEM; atomic_inc(&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); lock_buckets(new_tbl, old_tbl, new_hash); rht_for_each(he, old_tbl, old_hash) { if (head_hashfn(ht, new_tbl, he) == new_hash) { link_old_to_new(ht, new_tbl, new_hash, he); break; } } unlock_buckets(new_tbl, old_tbl, new_hash); cond_resched(); } /* 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++) { lock_buckets(new_tbl, old_tbl, old_hash); if (hashtable_chain_unzip(ht, new_tbl, old_tbl, old_hash)) complete = false; unlock_buckets(new_tbl, old_tbl, old_hash); cond_resched(); } } rcu_assign_pointer(ht->tbl, new_tbl); synchronize_rcu(); 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); unsigned int new_hash; ASSERT_RHT_MUTEX(ht); 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. */ for (new_hash = 0; new_hash < new_tbl->size; new_hash++) { lock_buckets(new_tbl, tbl, new_hash); rcu_assign_pointer(*bucket_tail(new_tbl, new_hash), tbl->buckets[new_hash]); ASSERT_BUCKET_LOCK(ht, tbl, new_hash + new_tbl->size); rcu_assign_pointer(*bucket_tail(new_tbl, new_hash), tbl->buckets[new_hash + new_tbl->size]); unlock_buckets(new_tbl, tbl, new_hash); cond_resched(); } /* Publish the new, valid hash table */ rcu_assign_pointer(ht->tbl, new_tbl); atomic_dec(&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; struct rhashtable_walker *walker; ht = container_of(work, struct rhashtable, run_work); mutex_lock(&ht->mutex); if (ht->being_destroyed) goto unlock; tbl = rht_dereference(ht->tbl, ht); list_for_each_entry(walker, &ht->walkers, list) walker->resize = true; if (rht_grow_above_75(ht, tbl->size)) rhashtable_expand(ht); else if (rht_shrink_below_30(ht, tbl->size)) rhashtable_shrink(ht); unlock: mutex_unlock(&ht->mutex); } static void __rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj, struct bucket_table *tbl, const struct bucket_table *old_tbl, u32 hash) { bool no_resize_running = tbl == old_tbl; struct rhash_head *head; hash = rht_bucket_index(tbl, hash); head = rht_dereference_bucket(tbl->buckets[hash], tbl, hash); ASSERT_BUCKET_LOCK(ht, 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); atomic_inc(&ht->nelems); if (no_resize_running && rht_grow_above_75(ht, tbl->size)) schedule_work(&ht->run_work); } /** * rhashtable_insert - insert object into 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, *old_tbl; unsigned hash; rcu_read_lock(); tbl = rht_dereference_rcu(ht->future_tbl, ht); old_tbl = rht_dereference_rcu(ht->tbl, ht); hash = obj_raw_hashfn(ht, rht_obj(ht, obj)); lock_buckets(tbl, old_tbl, hash); __rhashtable_insert(ht, obj, tbl, old_tbl, hash); unlock_buckets(tbl, old_tbl, hash); 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 * 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, *new_tbl, *old_tbl; struct rhash_head __rcu **pprev; struct rhash_head *he, *he2; unsigned int hash, new_hash; bool ret = false; rcu_read_lock(); old_tbl = rht_dereference_rcu(ht->tbl, ht); tbl = new_tbl = rht_dereference_rcu(ht->future_tbl, ht); new_hash = obj_raw_hashfn(ht, rht_obj(ht, obj)); lock_buckets(new_tbl, old_tbl, new_hash); restart: hash = rht_bucket_index(tbl, new_hash); pprev = &tbl->buckets[hash]; rht_for_each(he, tbl, hash) { if (he != obj) { pprev = &he->next; continue; } ASSERT_BUCKET_LOCK(ht, tbl, hash); if (old_tbl->size > new_tbl->size && tbl == old_tbl && !rht_is_a_nulls(obj->next) && head_hashfn(ht, tbl, obj->next) != hash) { rcu_assign_pointer(*pprev, (struct rhash_head *) rht_marker(ht, hash)); } else if (unlikely(old_tbl->size < new_tbl->size && tbl == new_tbl)) { rht_for_each_continue(he2, obj->next, tbl, hash) { if (head_hashfn(ht, tbl, he2) == hash) { rcu_assign_pointer(*pprev, he2); goto found; } } rcu_assign_pointer(*pprev, (struct rhash_head *) rht_marker(ht, hash)); } else { rcu_assign_pointer(*pprev, obj->next); } found: ret = true; break; } /* The entry may be linked in either 'tbl', 'future_tbl', or both. * 'future_tbl' only exists for a short period of time during * resizing. Thus traversing both is fine and the added cost is * very rare. */ if (tbl != old_tbl) { tbl = old_tbl; goto restart; } unlock_buckets(new_tbl, old_tbl, new_hash); if (ret) { bool no_resize_running = new_tbl == old_tbl; atomic_dec(&ht->nelems); if (no_resize_running && rht_shrink_below_30(ht, new_tbl->size)) schedule_work(&ht->run_work); } rcu_read_unlock(); return ret; } EXPORT_SYMBOL_GPL(rhashtable_remove); struct rhashtable_compare_arg { struct rhashtable *ht; const void *key; }; static bool rhashtable_compare(void *ptr, void *arg) { struct rhashtable_compare_arg *x = arg; struct rhashtable *ht = x->ht; return !memcmp(ptr + ht->p.key_offset, x->key, ht->p.key_len); } /** * 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 * parameter 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) { struct rhashtable_compare_arg arg = { .ht = ht, .key = key, }; BUG_ON(!ht->p.key_len); return rhashtable_lookup_compare(ht, key, &rhashtable_compare, &arg); } 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); /** * rhashtable_lookup_insert - lookup and insert object into hash table * @ht: hash table * @obj: pointer to hash head inside object * * Locks down the bucket chain in both the old and new table if a resize * is in progress to ensure that writers can't remove from the old table * and can't insert to the new table during the atomic operation of search * and insertion. Searches for duplicates in both the old and new table if * a resize is in progress. * * This lookup function may only be used for fixed key hash table (key_len * parameter set). It will BUG() if used inappropriately. * * 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(). */ bool rhashtable_lookup_insert(struct rhashtable *ht, struct rhash_head *obj) { struct rhashtable_compare_arg arg = { .ht = ht, .key = rht_obj(ht, obj) + ht->p.key_offset, }; BUG_ON(!ht->p.key_len); return rhashtable_lookup_compare_insert(ht, obj, &rhashtable_compare, &arg); } EXPORT_SYMBOL_GPL(rhashtable_lookup_insert); /** * rhashtable_lookup_compare_insert - search and insert object to hash table * with compare function * @ht: hash table * @obj: pointer to hash head inside object * @compare: compare function, must return true on match * @arg: argument passed on to compare function * * Locks down the bucket chain in both the old and new table if a resize * is in progress to ensure that writers can't remove from the old table * and can't insert to the new table during the atomic operation of search * and insertion. Searches for duplicates in both the old and new table if * a resize is in progress. * * Lookups may occur in parallel with hashtable mutations and resizing. * * 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(). */ bool rhashtable_lookup_compare_insert(struct rhashtable *ht, struct rhash_head *obj, bool (*compare)(void *, void *), void *arg) { struct bucket_table *new_tbl, *old_tbl; u32 new_hash; bool success = true; BUG_ON(!ht->p.key_len); rcu_read_lock(); old_tbl = rht_dereference_rcu(ht->tbl, ht); new_tbl = rht_dereference_rcu(ht->future_tbl, ht); new_hash = obj_raw_hashfn(ht, rht_obj(ht, obj)); lock_buckets(new_tbl, old_tbl, new_hash); if (rhashtable_lookup_compare(ht, rht_obj(ht, obj) + ht->p.key_offset, compare, arg)) { success = false; goto exit; } __rhashtable_insert(ht, obj, new_tbl, old_tbl, new_hash); exit: unlock_buckets(new_tbl, old_tbl, new_hash); rcu_read_unlock(); return success; } EXPORT_SYMBOL_GPL(rhashtable_lookup_compare_insert); /** * 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; INIT_LIST_HEAD(&iter->walker->list); iter->walker->resize = false; mutex_lock(&ht->mutex); list_add(&iter->walker->list, &ht->walkers); mutex_unlock(&ht->mutex); 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) { mutex_lock(&iter->ht->mutex); list_del(&iter->walker->list); mutex_unlock(&iter->ht->mutex); 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) { rcu_read_lock(); if (iter->walker->resize) { iter->slot = 0; iter->skip = 0; iter->walker->resize = false; 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) { const struct bucket_table *tbl; struct rhashtable *ht = iter->ht; struct rhash_head *p = iter->p; void *obj = NULL; tbl = rht_dereference_rcu(ht->tbl, ht); 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; obj = rht_obj(ht, p); goto out; } iter->skip = 0; } iter->p = NULL; out: if (iter->walker->resize) { iter->p = NULL; iter->slot = 0; iter->skip = 0; iter->walker->resize = false; return ERR_PTR(-EAGAIN); } return obj; } 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) { rcu_read_unlock(); iter->p = NULL; } EXPORT_SYMBOL_GPL(rhashtable_walk_stop); 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)); INIT_LIST_HEAD(&ht->walkers); 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; atomic_set(&ht->nelems, 0); atomic_set(&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)); INIT_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; cancel_work_sync(&ht->run_work); mutex_lock(&ht->mutex); bucket_table_free(rht_dereference(ht->tbl, ht)); mutex_unlock(&ht->mutex); } EXPORT_SYMBOL_GPL(rhashtable_destroy);