blob: 090641db4c0d25648951a8078ba1945c8ebc1487 [file] [log] [blame]
/*
* 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/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);
}
/* 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);
}
}
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);
}
/* 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);