/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Resizable, Scalable, Concurrent Hash Table
 *
 * Copyright (c) 2015-2016 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.
 */

#ifndef _LINUX_RHASHTABLE_H
#define _LINUX_RHASHTABLE_H

#include <linux/err.h>
#include <linux/errno.h>
#include <linux/jhash.h>
#include <linux/list_nulls.h>
#include <linux/workqueue.h>
#include <linux/rculist.h>
#include <linux/bit_spinlock.h>

#include <linux/rhashtable-types.h>
/*
 * Objects in an rhashtable have an embedded struct rhash_head
 * which is linked into as hash chain from the hash table - or one
 * of two or more hash tables when the rhashtable is being resized.
 * The end of the chain is marked with a special nulls marks which has
 * the least significant bit set but otherwise stores the address of
 * the hash bucket.  This allows us to be sure we've found the end
 * of the right list.
 * The value stored in the hash bucket has BIT(0) used as a lock bit.
 * This bit must be atomically set before any changes are made to
 * the chain.  To avoid dereferencing this pointer without clearing
 * the bit first, we use an opaque 'struct rhash_lock_head *' for the
 * pointer stored in the bucket.  This struct needs to be defined so
 * that rcu_dereference() works on it, but it has no content so a
 * cast is needed for it to be useful.  This ensures it isn't
 * used by mistake with clearing the lock bit first.
 */
struct rhash_lock_head {};

/* Maximum chain length before rehash
 *
 * 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.
 */
#define RHT_ELASTICITY  16u

/**
 * struct bucket_table - Table of hash buckets
 * @size: Number of hash buckets
 * @nest: Number of bits of first-level nested table.
 * @rehash: Current bucket being rehashed
 * @hash_rnd: Random seed to fold into hash
 * @walkers: List of active walkers
 * @rcu: RCU structure for freeing the table
 * @future_tbl: Table under construction during rehashing
 * @ntbl: Nested table used when out of memory.
 * @buckets: size * hash buckets
 */
struct bucket_table {
        unsigned int            size;
        unsigned int            nest;
        u32                     hash_rnd;
        struct list_head        walkers;
        struct rcu_head         rcu;

        struct bucket_table __rcu *future_tbl;

        struct lockdep_map      dep_map;

        struct rhash_lock_head __rcu *buckets[] ____cacheline_aligned_in_smp;
};

/*
 * NULLS_MARKER() expects a hash value with the low
 * bits mostly likely to be significant, and it discards
 * the msb.
 * We give it an address, in which the bottom bit is
 * always 0, and the msb might be significant.
 * So we shift the address down one bit to align with
 * expectations and avoid losing a significant bit.
 *
 * We never store the NULLS_MARKER in the hash table
 * itself as we need the lsb for locking.
 * Instead we store a NULL
 */
#define RHT_NULLS_MARKER(ptr)   \
        ((void *)NULLS_MARKER(((unsigned long) (ptr)) >> 1))
#define INIT_RHT_NULLS_HEAD(ptr)        \
        ((ptr) = NULL)

static inline bool rht_is_a_nulls(const struct rhash_head *ptr)
{
        return ((unsigned long) ptr & 1);
}

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

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

static __always_inline unsigned int rht_key_get_hash(struct rhashtable *ht,
        const void *key, const struct rhashtable_params params,
        unsigned int hash_rnd)
{
        unsigned int hash;

        /* params must be equal to ht->p if it isn't constant. */
        if (!__builtin_constant_p(params.key_len))
                hash = ht->p.hashfn(key, ht->key_len, hash_rnd);
        else if (params.key_len) {
                unsigned int key_len = params.key_len;

                if (params.hashfn)
                        hash = params.hashfn(key, key_len, hash_rnd);
                else if (key_len & (sizeof(u32) - 1))
                        hash = jhash(key, key_len, hash_rnd);
                else
                        hash = jhash2(key, key_len / sizeof(u32), hash_rnd);
        } else {
                unsigned int key_len = ht->p.key_len;

                if (params.hashfn)
                        hash = params.hashfn(key, key_len, hash_rnd);
                else
                        hash = jhash(key, key_len, hash_rnd);
        }

        return hash;
}

static __always_inline unsigned int rht_key_hashfn(
        struct rhashtable *ht, const struct bucket_table *tbl,
        const void *key, const struct rhashtable_params params)
{
        unsigned int hash = rht_key_get_hash(ht, key, params, tbl->hash_rnd);

        return rht_bucket_index(tbl, hash);
}

static __always_inline unsigned int rht_head_hashfn(
        struct rhashtable *ht, const struct bucket_table *tbl,
        const struct rhash_head *he, const struct rhashtable_params params)
{
        const char *ptr = rht_obj(ht, he);

        return likely(params.obj_hashfn) ?
               rht_bucket_index(tbl, params.obj_hashfn(ptr, params.key_len ?:
                                                            ht->p.key_len,
                                                       tbl->hash_rnd)) :
               rht_key_hashfn(ht, tbl, ptr + params.key_offset, params);
}

/**
 * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
 * @ht:         hash table
 * @tbl:        current table
 */
static inline bool rht_grow_above_75(const struct rhashtable *ht,
                                     const struct bucket_table *tbl)
{
        /* Expand table when exceeding 75% load */
        return atomic_read(&ht->nelems) > (tbl->size / 4 * 3) &&
               (!ht->p.max_size || tbl->size < ht->p.max_size);
}

/**
 * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
 * @ht:         hash table
 * @tbl:        current table
 */
static inline bool rht_shrink_below_30(const struct rhashtable *ht,
                                       const struct bucket_table *tbl)
{
        /* Shrink table beneath 30% load */
        return atomic_read(&ht->nelems) < (tbl->size * 3 / 10) &&
               tbl->size > ht->p.min_size;
}

/**
 * rht_grow_above_100 - returns true if nelems > table-size
 * @ht:         hash table
 * @tbl:        current table
 */
static inline bool rht_grow_above_100(const struct rhashtable *ht,
                                      const struct bucket_table *tbl)
{
        return atomic_read(&ht->nelems) > tbl->size &&
                (!ht->p.max_size || tbl->size < ht->p.max_size);
}

/**
 * rht_grow_above_max - returns true if table is above maximum
 * @ht:         hash table
 * @tbl:        current table
 */
static inline bool rht_grow_above_max(const struct rhashtable *ht,
                                      const struct bucket_table *tbl)
{
        return atomic_read(&ht->nelems) >= ht->max_elems;
}

#ifdef CONFIG_PROVE_LOCKING
int lockdep_rht_mutex_is_held(struct rhashtable *ht);
int lockdep_rht_bucket_is_held(const struct bucket_table *tbl, u32 hash);
#else
static inline int lockdep_rht_mutex_is_held(struct rhashtable *ht)
{
        return 1;
}

static inline int lockdep_rht_bucket_is_held(const struct bucket_table *tbl,
                                             u32 hash)
{
        return 1;
}
#endif /* CONFIG_PROVE_LOCKING */

void *rhashtable_insert_slow(struct rhashtable *ht, const void *key,
                             struct rhash_head *obj);

void rhashtable_walk_enter(struct rhashtable *ht,
                           struct rhashtable_iter *iter);
void rhashtable_walk_exit(struct rhashtable_iter *iter);
int rhashtable_walk_start_check(struct rhashtable_iter *iter) __acquires_shared(RCU);

static inline void rhashtable_walk_start(struct rhashtable_iter *iter)
        __acquires_shared(RCU)
{
        (void)rhashtable_walk_start_check(iter);
}

void *rhashtable_walk_next(struct rhashtable_iter *iter);
void *rhashtable_walk_peek(struct rhashtable_iter *iter);
void rhashtable_walk_stop(struct rhashtable_iter *iter) __releases_shared(RCU);

void rhashtable_free_and_destroy(struct rhashtable *ht,
                                 void (*free_fn)(void *ptr, void *arg),
                                 void *arg);
void rhashtable_destroy(struct rhashtable *ht);

struct rhash_lock_head __rcu **rht_bucket_nested(
        const struct bucket_table *tbl, unsigned int hash);
struct rhash_lock_head __rcu **__rht_bucket_nested(
        const struct bucket_table *tbl, unsigned int hash);
struct rhash_lock_head __rcu **rht_bucket_nested_insert(
        struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash);

#define rht_dereference(p, ht) \
        rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))

#define rht_dereference_rcu(p, ht) \
        rcu_dereference_all_check(p, lockdep_rht_mutex_is_held(ht))

#define rht_dereference_bucket(p, tbl, hash) \
        rcu_dereference_protected(p, lockdep_rht_bucket_is_held(tbl, hash))

#define rht_dereference_bucket_rcu(p, tbl, hash) \
        rcu_dereference_all_check(p, lockdep_rht_bucket_is_held(tbl, hash))

#define rht_entry(tpos, pos, member) \
        ({ tpos = container_of(pos, typeof(*tpos), member); 1; })

static inline struct rhash_lock_head __rcu *const *rht_bucket(
        const struct bucket_table *tbl, unsigned int hash)
{
        return unlikely(tbl->nest) ? rht_bucket_nested(tbl, hash) :
                                     &tbl->buckets[hash];
}

static inline struct rhash_lock_head __rcu **rht_bucket_var(
        struct bucket_table *tbl, unsigned int hash)
{
        return unlikely(tbl->nest) ? __rht_bucket_nested(tbl, hash) :
                                     &tbl->buckets[hash];
}

static inline struct rhash_lock_head __rcu **rht_bucket_insert(
        struct rhashtable *ht, struct bucket_table *tbl, unsigned int hash)
{
        return unlikely(tbl->nest) ? rht_bucket_nested_insert(ht, tbl, hash) :
                                     &tbl->buckets[hash];
}

/*
 * We lock a bucket by setting BIT(0) in the pointer - this is always
 * zero in real pointers.  The NULLS mark is never stored in the bucket,
 * rather we store NULL if the bucket is empty.
 * bit_spin_locks do not handle contention well, but the whole point
 * of the hashtable design is to achieve minimum per-bucket contention.
 * A nested hash table might not have a bucket pointer.  In that case
 * we cannot get a lock.  For remove and replace the bucket cannot be
 * interesting and doesn't need locking.
 * For insert we allocate the bucket if this is the last bucket_table,
 * and then take the lock.
 * Sometimes we unlock a bucket by writing a new pointer there.  In that
 * case we don't need to unlock, but we do need to reset state such as
 * local_bh. For that we have rht_assign_unlock().  As rcu_assign_pointer()
 * provides the same release semantics that bit_spin_unlock() provides,
 * this is safe.
 * When we write to a bucket without unlocking, we use rht_assign_locked().
 */

static inline unsigned long rht_lock(struct bucket_table *tbl,
                                     struct rhash_lock_head __rcu **bkt)
        __acquires(__bitlock(0, bkt))
{
        unsigned long flags;

        local_irq_save(flags);
        bit_spin_lock(0, (unsigned long *)bkt);
        lock_map_acquire(&tbl->dep_map);
        return flags;
}

static inline unsigned long rht_lock_nested(struct bucket_table *tbl,
                                        struct rhash_lock_head __rcu **bucket,
                                        unsigned int subclass)
        __acquires(__bitlock(0, bucket))
{
        unsigned long flags;

        local_irq_save(flags);
        bit_spin_lock(0, (unsigned long *)bucket);
        lock_acquire_exclusive(&tbl->dep_map, subclass, 0, NULL, _THIS_IP_);
        return flags;
}

static inline void rht_unlock(struct bucket_table *tbl,
                              struct rhash_lock_head __rcu **bkt,
                              unsigned long flags)
        __releases(__bitlock(0, bkt))
{
        lock_map_release(&tbl->dep_map);
        bit_spin_unlock(0, (unsigned long *)bkt);
        local_irq_restore(flags);
}

enum rht_lookup_freq {
        RHT_LOOKUP_NORMAL,
        RHT_LOOKUP_LIKELY,
};

static __always_inline struct rhash_head *__rht_ptr(
        struct rhash_lock_head *p, struct rhash_lock_head __rcu *const *bkt,
        const enum rht_lookup_freq freq)
{
        unsigned long p_val = (unsigned long)p & ~BIT(0);

        BUILD_BUG_ON(!__builtin_constant_p(freq));

        if (freq == RHT_LOOKUP_LIKELY)
                return (struct rhash_head *)
                        (likely(p_val) ? p_val : (unsigned long)RHT_NULLS_MARKER(bkt));
        else
                return (struct rhash_head *)
                        (p_val ?: (unsigned long)RHT_NULLS_MARKER(bkt));
}

/*
 * Where 'bkt' is a bucket and might be locked:
 *   rht_ptr_rcu() dereferences that pointer and clears the lock bit.
 *   rht_ptr() dereferences in a context where the bucket is locked.
 *   rht_ptr_exclusive() dereferences in a context where exclusive
 *            access is guaranteed, such as when destroying the table.
 */
static __always_inline struct rhash_head *__rht_ptr_rcu(
        struct rhash_lock_head __rcu *const *bkt,
        const enum rht_lookup_freq freq)
{
        return __rht_ptr(rcu_dereference_all(*bkt), bkt, freq);
}

static inline struct rhash_head *rht_ptr_rcu(
        struct rhash_lock_head __rcu *const *bkt)
{
        return __rht_ptr_rcu(bkt, RHT_LOOKUP_NORMAL);
}

static inline struct rhash_head *rht_ptr(
        struct rhash_lock_head __rcu *const *bkt,
        struct bucket_table *tbl,
        unsigned int hash)
{
        return __rht_ptr(rht_dereference_bucket(*bkt, tbl, hash), bkt,
                         RHT_LOOKUP_NORMAL);
}

static inline struct rhash_head *rht_ptr_exclusive(
        struct rhash_lock_head __rcu *const *bkt)
{
        return __rht_ptr(rcu_dereference_protected(*bkt, 1), bkt,
                         RHT_LOOKUP_NORMAL);
}

static inline void rht_assign_locked(struct rhash_lock_head __rcu **bkt,
                                     struct rhash_head *obj)
{
        if (rht_is_a_nulls(obj))
                obj = NULL;
        rcu_assign_pointer(*bkt, (void *)((unsigned long)obj | BIT(0)));
}

static inline void rht_assign_unlock(struct bucket_table *tbl,
                                     struct rhash_lock_head __rcu **bkt,
                                     struct rhash_head *obj,
                                     unsigned long flags)
        __releases(__bitlock(0, bkt))
{
        if (rht_is_a_nulls(obj))
                obj = NULL;
        lock_map_release(&tbl->dep_map);
        rcu_assign_pointer(*bkt, (void *)obj);
        preempt_enable();
        __release(__bitlock(0, bkt));
        local_irq_restore(flags);
}

/**
 * rht_for_each_from - iterate over hash chain from given head
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @head:       the &struct rhash_head to start from
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 */
#define rht_for_each_from(pos, head, tbl, hash) \
        for (pos = head;                        \
             !rht_is_a_nulls(pos);              \
             pos = rht_dereference_bucket((pos)->next, tbl, hash))

/**
 * rht_for_each - iterate over hash chain
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 */
#define rht_for_each(pos, tbl, hash) \
        rht_for_each_from(pos, rht_ptr(rht_bucket(tbl, hash), tbl, hash),  \
                          tbl, hash)

/**
 * rht_for_each_entry_from - iterate over hash chain from given head
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @head:       the &struct rhash_head to start from
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 * @member:     name of the &struct rhash_head within the hashable struct.
 */
#define rht_for_each_entry_from(tpos, pos, head, tbl, hash, member)     \
        for (pos = head;                                                \
             (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);    \
             pos = rht_dereference_bucket((pos)->next, tbl, hash))

/**
 * rht_for_each_entry - iterate over hash chain of given type
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 * @member:     name of the &struct rhash_head within the hashable struct.
 */
#define rht_for_each_entry(tpos, pos, tbl, hash, member)                \
        rht_for_each_entry_from(tpos, pos,                              \
                                rht_ptr(rht_bucket(tbl, hash), tbl, hash), \
                                tbl, hash, member)

/**
 * rht_for_each_entry_safe - safely iterate over hash chain of given type
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @next:       the &struct rhash_head to use as next in loop cursor.
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 * @member:     name of the &struct rhash_head within the hashable struct.
 *
 * This hash chain list-traversal primitive allows for the looped code to
 * remove the loop cursor from the list.
 */
#define rht_for_each_entry_safe(tpos, pos, next, tbl, hash, member)           \
        for (pos = rht_ptr(rht_bucket(tbl, hash), tbl, hash),                 \
             next = !rht_is_a_nulls(pos) ?                                    \
                       rht_dereference_bucket(pos->next, tbl, hash) : NULL;   \
             (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);          \
             pos = next,                                                      \
             next = !rht_is_a_nulls(pos) ?                                    \
                       rht_dereference_bucket(pos->next, tbl, hash) : NULL)

/**
 * rht_for_each_rcu_from - iterate over rcu hash chain from given head
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @head:       the &struct rhash_head to start from
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_rcu_from(pos, head, tbl, hash)                     \
        for (({barrier(); }),                                           \
             pos = head;                                                \
             !rht_is_a_nulls(pos);                                      \
             pos = rcu_dereference_all(pos->next))

/**
 * rht_for_each_rcu - iterate over rcu hash chain
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_rcu(pos, tbl, hash)                        \
        for (({barrier(); }),                                   \
             pos = rht_ptr_rcu(rht_bucket(tbl, hash));          \
             !rht_is_a_nulls(pos);                              \
             pos = rcu_dereference_all(pos->next))

/**
 * rht_for_each_entry_rcu_from - iterated over rcu hash chain from given head
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @head:       the &struct rhash_head to start from
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 * @member:     name of the &struct rhash_head within the hashable struct.
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_entry_rcu_from(tpos, pos, head, tbl, hash, member) \
        for (({barrier(); }),                                               \
             pos = head;                                                    \
             (!rht_is_a_nulls(pos)) && rht_entry(tpos, pos, member);        \
             pos = rht_dereference_bucket_rcu(pos->next, tbl, hash))

/**
 * rht_for_each_entry_rcu - iterate over rcu hash chain of given type
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rhash_head to use as a loop cursor.
 * @tbl:        the &struct bucket_table
 * @hash:       the hash value / bucket index
 * @member:     name of the &struct rhash_head within the hashable struct.
 *
 * This hash chain list-traversal primitive may safely run concurrently with
 * the _rcu mutation primitives such as rhashtable_insert() as long as the
 * traversal is guarded by rcu_read_lock().
 */
#define rht_for_each_entry_rcu(tpos, pos, tbl, hash, member)               \
        rht_for_each_entry_rcu_from(tpos, pos,                             \
                                    rht_ptr_rcu(rht_bucket(tbl, hash)),    \
                                    tbl, hash, member)

/**
 * rhl_for_each_rcu - iterate over rcu hash table list
 * @pos:        the &struct rlist_head to use as a loop cursor.
 * @list:       the head of the list
 *
 * This hash chain list-traversal primitive should be used on the
 * list returned by rhltable_lookup.
 */
#define rhl_for_each_rcu(pos, list)                                     \
        for (pos = list; pos; pos = rcu_dereference_all(pos->next))

/**
 * rhl_for_each_entry_rcu - iterate over rcu hash table list of given type
 * @tpos:       the type * to use as a loop cursor.
 * @pos:        the &struct rlist_head to use as a loop cursor.
 * @list:       the head of the list
 * @member:     name of the &struct rlist_head within the hashable struct.
 *
 * This hash chain list-traversal primitive should be used on the
 * list returned by rhltable_lookup.
 */
#define rhl_for_each_entry_rcu(tpos, pos, list, member)                 \
        for (pos = list; pos && rht_entry(tpos, pos, member);           \
             pos = rcu_dereference_all(pos->next))

static inline int rhashtable_compare(struct rhashtable_compare_arg *arg,
                                     const void *obj)
{
        struct rhashtable *ht = arg->ht;
        const char *ptr = obj;

        return memcmp(ptr + ht->p.key_offset, arg->key, ht->p.key_len);
}

/* Internal function, do not use. */
static __always_inline struct rhash_head *__rhashtable_lookup(
        struct rhashtable *ht, const void *key,
        const struct rhashtable_params params,
        const enum rht_lookup_freq freq)
        __must_hold_shared(RCU)
{
        struct rhashtable_compare_arg arg = {
                .ht = ht,
                .key = key,
        };
        struct rhash_lock_head __rcu *const *bkt;
        struct bucket_table *tbl;
        struct rhash_head *he;
        unsigned int hash;

        BUILD_BUG_ON(!__builtin_constant_p(freq));
        tbl = rht_dereference_rcu(ht->tbl, ht);
restart:
        hash = rht_key_hashfn(ht, tbl, key, params);
        bkt = rht_bucket(tbl, hash);
        do {
                rht_for_each_rcu_from(he, __rht_ptr_rcu(bkt, freq), tbl, hash) {
                        if (params.obj_cmpfn ?
                            params.obj_cmpfn(&arg, rht_obj(ht, he)) :
                            rhashtable_compare(&arg, rht_obj(ht, he)))
                                continue;
                        return he;
                }
                /* An object might have been moved to a different hash chain,
                 * while we walk along it - better check and retry.
                 */
        } while (he != RHT_NULLS_MARKER(bkt));

        /* Ensure we see any new tables. */
        smp_rmb();

        tbl = rht_dereference_rcu(tbl->future_tbl, ht);
        if (unlikely(tbl))
                goto restart;

        return NULL;
}

/**
 * rhashtable_lookup - search hash table
 * @ht:         hash table
 * @key:        the pointer to the key
 * @params:     hash table parameters
 *
 * Computes the hash value for the key and traverses the bucket chain looking
 * for an entry with an identical key. The first matching entry is returned.
 *
 * This must only be called under the RCU read lock.
 *
 * Returns the first entry on which the compare function returned true.
 */
static __always_inline void *rhashtable_lookup(
        struct rhashtable *ht, const void *key,
        const struct rhashtable_params params)
        __must_hold_shared(RCU)
{
        struct rhash_head *he = __rhashtable_lookup(ht, key, params,
                                                    RHT_LOOKUP_NORMAL);

        return he ? rht_obj(ht, he) : NULL;
}

static __always_inline void *rhashtable_lookup_likely(
        struct rhashtable *ht, const void *key,
        const struct rhashtable_params params)
        __must_hold_shared(RCU)
{
        struct rhash_head *he = __rhashtable_lookup(ht, key, params,
                                                    RHT_LOOKUP_LIKELY);

        return likely(he) ? rht_obj(ht, he) : NULL;
}

/**
 * rhashtable_lookup_fast - search hash table, without RCU read lock
 * @ht:         hash table
 * @key:        the pointer to the key
 * @params:     hash table parameters
 *
 * Computes the hash value for the key and traverses the bucket chain looking
 * for an entry with an identical key. The first matching entry is returned.
 *
 * Only use this function when you have other mechanisms guaranteeing
 * that the object won't go away after the RCU read lock is released.
 *
 * Returns the first entry on which the compare function returned true.
 */
static __always_inline void *rhashtable_lookup_fast(
        struct rhashtable *ht, const void *key,
        const struct rhashtable_params params)
{
        void *obj;

        rcu_read_lock();
        obj = rhashtable_lookup(ht, key, params);
        rcu_read_unlock();

        return obj;
}

/**
 * rhltable_lookup - search hash list table
 * @hlt:        hash table
 * @key:        the pointer to the key
 * @params:     hash table parameters
 *
 * Computes the hash value for the key and traverses the bucket chain looking
 * for an entry with an identical key.  All matching entries are returned
 * in a list.
 *
 * This must only be called under the RCU read lock.
 *
 * Returns the list of entries that match the given key.
 */
static __always_inline struct rhlist_head *rhltable_lookup(
        struct rhltable *hlt, const void *key,
        const struct rhashtable_params params)
        __must_hold_shared(RCU)
{
        struct rhash_head *he = __rhashtable_lookup(&hlt->ht, key, params,
                                                    RHT_LOOKUP_NORMAL);

        return he ? container_of(he, struct rhlist_head, rhead) : NULL;
}

static __always_inline struct rhlist_head *rhltable_lookup_likely(
        struct rhltable *hlt, const void *key,
        const struct rhashtable_params params)
        __must_hold_shared(RCU)
{
        struct rhash_head *he = __rhashtable_lookup(&hlt->ht, key, params,
                                                    RHT_LOOKUP_LIKELY);

        return likely(he) ? container_of(he, struct rhlist_head, rhead) : NULL;
}

/* Internal function, please use rhashtable_insert_fast() instead. This
 * function returns the existing element already in hashes if there is a clash,
 * otherwise it returns an error via ERR_PTR().
 */
static __always_inline void *__rhashtable_insert_fast(
        struct rhashtable *ht, const void *key, struct rhash_head *obj,
        const struct rhashtable_params params, bool rhlist)
{
        struct rhashtable_compare_arg arg = {
                .ht = ht,
                .key = key,
        };
        struct rhash_lock_head __rcu **bkt;
        struct rhash_head __rcu **pprev;
        struct bucket_table *tbl;
        struct rhash_head *head;
        unsigned long flags;
        unsigned int hash;
        int elasticity;
        void *data;

        rcu_read_lock();

        tbl = rht_dereference_rcu(ht->tbl, ht);
        hash = rht_head_hashfn(ht, tbl, obj, params);
        elasticity = RHT_ELASTICITY;
        bkt = rht_bucket_insert(ht, tbl, hash);
        data = ERR_PTR(-ENOMEM);
        if (!bkt)
                goto out;
        pprev = NULL;
        flags = rht_lock(tbl, bkt);

        if (unlikely(rcu_access_pointer(tbl->future_tbl))) {
slow_path:
                rht_unlock(tbl, bkt, flags);
                rcu_read_unlock();
                return rhashtable_insert_slow(ht, key, obj);
        }

        rht_for_each_from(head, rht_ptr(bkt, tbl, hash), tbl, hash) {
                struct rhlist_head *plist;
                struct rhlist_head *list;

                elasticity--;
                if (!key ||
                    (params.obj_cmpfn ?
                     params.obj_cmpfn(&arg, rht_obj(ht, head)) :
                     rhashtable_compare(&arg, rht_obj(ht, head)))) {
                        pprev = &head->next;
                        continue;
                }

                data = rht_obj(ht, head);

                if (!rhlist)
                        goto out_unlock;


                list = container_of(obj, struct rhlist_head, rhead);
                plist = container_of(head, struct rhlist_head, rhead);

                RCU_INIT_POINTER(list->next, plist);
                head = rht_dereference_bucket(head->next, tbl, hash);
                RCU_INIT_POINTER(list->rhead.next, head);
                if (pprev) {
                        rcu_assign_pointer(*pprev, obj);
                        rht_unlock(tbl, bkt, flags);
                } else
                        rht_assign_unlock(tbl, bkt, obj, flags);
                data = NULL;
                goto out;
        }

        if (elasticity <= 0)
                goto slow_path;

        data = ERR_PTR(-E2BIG);
        if (unlikely(rht_grow_above_max(ht, tbl)))
                goto out_unlock;

        if (unlikely(rht_grow_above_100(ht, tbl)))
                goto slow_path;

        /* Inserting at head of list makes unlocking free. */
        head = rht_ptr(bkt, tbl, hash);

        RCU_INIT_POINTER(obj->next, head);
        if (rhlist) {
                struct rhlist_head *list;

                list = container_of(obj, struct rhlist_head, rhead);
                RCU_INIT_POINTER(list->next, NULL);
        }

        atomic_inc(&ht->nelems);
        rht_assign_unlock(tbl, bkt, obj, flags);

        if (rht_grow_above_75(ht, tbl))
                schedule_work(&ht->run_work);

        data = NULL;
out:
        rcu_read_unlock();

        return data;

out_unlock:
        rht_unlock(tbl, bkt, flags);
        goto out;
}

/**
 * rhashtable_insert_fast - insert object into hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * Will take the per bucket bitlock to protect against mutual mutations
 * on the same bucket. Multiple insertions may occur in parallel unless
 * they map to the same bucket.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if residency in the
 * table grows beyond 70%.
 */
static __always_inline int rhashtable_insert_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        void *ret;

        ret = __rhashtable_insert_fast(ht, NULL, obj, params, false);
        if (IS_ERR(ret))
                return PTR_ERR(ret);

        return ret == NULL ? 0 : -EEXIST;
}

/**
 * rhltable_insert_key - insert object into hash list table
 * @hlt:        hash list table
 * @key:        the pointer to the key
 * @list:       pointer to hash list head inside object
 * @params:     hash table parameters
 *
 * Will take the per bucket bitlock to protect against mutual mutations
 * on the same bucket. Multiple insertions may occur in parallel unless
 * they map to the same bucket.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if residency in the
 * table grows beyond 70%.
 */
static __always_inline int rhltable_insert_key(
        struct rhltable *hlt, const void *key, struct rhlist_head *list,
        const struct rhashtable_params params)
{
        return PTR_ERR(__rhashtable_insert_fast(&hlt->ht, key, &list->rhead,
                                                params, true));
}

/**
 * rhltable_insert - insert object into hash list table
 * @hlt:        hash list table
 * @list:       pointer to hash list head inside object
 * @params:     hash table parameters
 *
 * Will take the per bucket bitlock to protect against mutual mutations
 * on the same bucket. Multiple insertions may occur in parallel unless
 * they map to the same bucket.
 *
 * It is safe to call this function from atomic context.
 *
 * Will trigger an automatic deferred table resizing if residency in the
 * table grows beyond 70%.
 */
static __always_inline int rhltable_insert(
        struct rhltable *hlt, struct rhlist_head *list,
        const struct rhashtable_params params)
{
        const char *key = rht_obj(&hlt->ht, &list->rhead);

        key += params.key_offset;

        return rhltable_insert_key(hlt, key, list, params);
}

/**
 * rhashtable_lookup_insert_fast - lookup and insert object into hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * 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 residency in the
 * table grows beyond 70%.
 */
static __always_inline int rhashtable_lookup_insert_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        const char *key = rht_obj(ht, obj);
        void *ret;

        BUG_ON(ht->p.obj_hashfn);

        ret = __rhashtable_insert_fast(ht, key + ht->p.key_offset, obj, params,
                                       false);
        if (IS_ERR(ret))
                return PTR_ERR(ret);

        return ret == NULL ? 0 : -EEXIST;
}

/**
 * rhashtable_lookup_get_insert_fast - lookup and insert object into hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * Just like rhashtable_lookup_insert_fast(), but this function returns the
 * object if it exists, NULL if it did not and the insertion was successful,
 * and an ERR_PTR otherwise.
 */
static __always_inline void *rhashtable_lookup_get_insert_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        const char *key = rht_obj(ht, obj);

        BUG_ON(ht->p.obj_hashfn);

        return __rhashtable_insert_fast(ht, key + ht->p.key_offset, obj, params,
                                        false);
}

/**
 * rhashtable_lookup_insert_key - search and insert object to hash table
 *                                with explicit key
 * @ht:         hash table
 * @key:        key
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * Lookups may occur in parallel with hashtable mutations and resizing.
 *
 * Will trigger an automatic deferred table resizing if residency in the
 * table grows beyond 70%.
 *
 * Returns zero on success.
 */
static __always_inline int rhashtable_lookup_insert_key(
        struct rhashtable *ht, const void *key, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        void *ret;

        BUG_ON(!ht->p.obj_hashfn || !key);

        ret = __rhashtable_insert_fast(ht, key, obj, params, false);
        if (IS_ERR(ret))
                return PTR_ERR(ret);

        return ret == NULL ? 0 : -EEXIST;
}

/**
 * rhashtable_lookup_get_insert_key - lookup and insert object into hash table
 * @ht:         hash table
 * @key:        key
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * Just like rhashtable_lookup_insert_key(), but this function returns the
 * object if it exists, NULL if it does not and the insertion was successful,
 * and an ERR_PTR otherwise.
 */
static __always_inline void *rhashtable_lookup_get_insert_key(
        struct rhashtable *ht, const void *key, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        BUG_ON(!ht->p.obj_hashfn || !key);

        return __rhashtable_insert_fast(ht, key, obj, params, false);
}

/* Internal function, please use rhashtable_remove_fast() instead */
static __always_inline int __rhashtable_remove_fast_one(
        struct rhashtable *ht, struct bucket_table *tbl,
        struct rhash_head *obj, const struct rhashtable_params params,
        bool rhlist)
{
        struct rhash_lock_head __rcu **bkt;
        struct rhash_head __rcu **pprev;
        struct rhash_head *he;
        unsigned long flags;
        unsigned int hash;
        int err = -ENOENT;

        hash = rht_head_hashfn(ht, tbl, obj, params);
        bkt = rht_bucket_var(tbl, hash);
        if (!bkt)
                return -ENOENT;
        pprev = NULL;
        flags = rht_lock(tbl, bkt);

        rht_for_each_from(he, rht_ptr(bkt, tbl, hash), tbl, hash) {
                struct rhlist_head *list;

                list = container_of(he, struct rhlist_head, rhead);

                if (he != obj) {
                        struct rhlist_head __rcu **lpprev;

                        pprev = &he->next;

                        if (!rhlist)
                                continue;

                        do {
                                lpprev = &list->next;
                                list = rht_dereference_bucket(list->next,
                                                              tbl, hash);
                        } while (list && obj != &list->rhead);

                        if (!list)
                                continue;

                        list = rht_dereference_bucket(list->next, tbl, hash);
                        RCU_INIT_POINTER(*lpprev, list);
                        err = 0;
                        break;
                }

                obj = rht_dereference_bucket(obj->next, tbl, hash);
                err = 1;

                if (rhlist) {
                        list = rht_dereference_bucket(list->next, tbl, hash);
                        if (list) {
                                RCU_INIT_POINTER(list->rhead.next, obj);
                                obj = &list->rhead;
                                err = 0;
                        }
                }

                if (pprev) {
                        rcu_assign_pointer(*pprev, obj);
                        rht_unlock(tbl, bkt, flags);
                } else {
                        rht_assign_unlock(tbl, bkt, obj, flags);
                }
                goto unlocked;
        }

        rht_unlock(tbl, bkt, flags);
unlocked:
        if (err > 0) {
                atomic_dec(&ht->nelems);
                if (unlikely(ht->p.automatic_shrinking &&
                             rht_shrink_below_30(ht, tbl)))
                        schedule_work(&ht->run_work);
                err = 0;
        }

        return err;
}

/* Internal function, please use rhashtable_remove_fast() instead */
static __always_inline int __rhashtable_remove_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params, bool rhlist)
{
        struct bucket_table *tbl;
        int err;

        rcu_read_lock();

        tbl = rht_dereference_rcu(ht->tbl, ht);

        /* Because we have already taken (and released) the bucket
         * lock in old_tbl, if we find that future_tbl is not yet
         * visible then that guarantees the entry to still be in
         * the old tbl if it exists.
         */
        while ((err = __rhashtable_remove_fast_one(ht, tbl, obj, params,
                                                   rhlist)) &&
               (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
                ;

        rcu_read_unlock();

        return err;
}

/**
 * rhashtable_remove_fast - remove object from hash table
 * @ht:         hash table
 * @obj:        pointer to hash head inside object
 * @params:     hash table parameters
 *
 * 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 if permitted when residency drops
 * below 30%.
 *
 * Returns zero on success, -ENOENT if the entry could not be found.
 */
static __always_inline int rhashtable_remove_fast(
        struct rhashtable *ht, struct rhash_head *obj,
        const struct rhashtable_params params)
{
        return __rhashtable_remove_fast(ht, obj, params, false);
}

/**
 * rhltable_remove - remove object from hash list table
 * @hlt:        hash list table
 * @list:       pointer to hash list head inside object
 * @params:     hash table parameters
 *
 * Since the hash chain is single linked, the removal operation needs to
 * walk the bucket chain upon removal. The removal operation is thus
 * considerably slower if the hash table is not correctly sized.
 *
 * Will automatically shrink the table if permitted when residency drops
 * below 30%
 *
 * Returns zero on success, -ENOENT if the entry could not be found.
 */
static __always_inline int rhltable_remove(
        struct rhltable *hlt, struct rhlist_head *list,
        const struct rhashtable_params params)
{
        return __rhashtable_remove_fast(&hlt->ht, &list->rhead, params, true);
}

/* Internal function, please use rhashtable_replace_fast() instead */
static __always_inline int __rhashtable_replace_fast(
        struct rhashtable *ht, struct bucket_table *tbl,
        struct rhash_head *obj_old, struct rhash_head *obj_new,
        const struct rhashtable_params params)
{
        struct rhash_lock_head __rcu **bkt;
        struct rhash_head __rcu **pprev;
        struct rhash_head *he;
        unsigned long flags;
        unsigned int hash;
        int err = -ENOENT;

        /* Minimally, the old and new objects must have same hash
         * (which should mean identifiers are the same).
         */
        hash = rht_head_hashfn(ht, tbl, obj_old, params);
        if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
                return -EINVAL;

        bkt = rht_bucket_var(tbl, hash);
        if (!bkt)
                return -ENOENT;

        pprev = NULL;
        flags = rht_lock(tbl, bkt);

        rht_for_each_from(he, rht_ptr(bkt, tbl, hash), tbl, hash) {
                if (he != obj_old) {
                        pprev = &he->next;
                        continue;
                }

                rcu_assign_pointer(obj_new->next, obj_old->next);
                if (pprev) {
                        rcu_assign_pointer(*pprev, obj_new);
                        rht_unlock(tbl, bkt, flags);
                } else {
                        rht_assign_unlock(tbl, bkt, obj_new, flags);
                }
                err = 0;
                goto unlocked;
        }

        rht_unlock(tbl, bkt, flags);

unlocked:
        return err;
}

/**
 * rhashtable_replace_fast - replace an object in hash table
 * @ht:         hash table
 * @obj_old:    pointer to hash head inside object being replaced
 * @obj_new:    pointer to hash head inside object which is new
 * @params:     hash table parameters
 *
 * Replacing an object doesn't affect the number of elements in the hash table
 * or bucket, so we don't need to worry about shrinking or expanding the
 * table here.
 *
 * Returns zero on success, -ENOENT if the entry could not be found,
 * -EINVAL if hash is not the same for the old and new objects.
 */
static __always_inline int rhashtable_replace_fast(
        struct rhashtable *ht, struct rhash_head *obj_old,
        struct rhash_head *obj_new,
        const struct rhashtable_params params)
{
        struct bucket_table *tbl;
        int err;

        rcu_read_lock();

        tbl = rht_dereference_rcu(ht->tbl, ht);

        /* Because we have already taken (and released) the bucket
         * lock in old_tbl, if we find that future_tbl is not yet
         * visible then that guarantees the entry to still be in
         * the old tbl if it exists.
         */
        while ((err = __rhashtable_replace_fast(ht, tbl, obj_old,
                                                obj_new, params)) &&
               (tbl = rht_dereference_rcu(tbl->future_tbl, ht)))
                ;

        rcu_read_unlock();

        return err;
}

/**
 * rhltable_walk_enter - Initialise an iterator
 * @hlt:        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 be called from any process context, including
 * non-preemptable context, but cannot be called from softirq or
 * hardirq context.
 *
 * You must call rhashtable_walk_exit after this function returns.
 */
static inline void rhltable_walk_enter(struct rhltable *hlt,
                                       struct rhashtable_iter *iter)
{
        rhashtable_walk_enter(&hlt->ht, iter);
}

/**
 * rhltable_free_and_destroy - free elements and destroy hash list table
 * @hlt:        the hash list table to destroy
 * @free_fn:    callback to release resources of element
 * @arg:        pointer passed to free_fn
 *
 * See documentation for rhashtable_free_and_destroy.
 */
static inline void rhltable_free_and_destroy(struct rhltable *hlt,
                                             void (*free_fn)(void *ptr,
                                                             void *arg),
                                             void *arg)
{
        rhashtable_free_and_destroy(&hlt->ht, free_fn, arg);
}

static inline void rhltable_destroy(struct rhltable *hlt)
{
        rhltable_free_and_destroy(hlt, NULL, NULL);
}

#endif /* _LINUX_RHASHTABLE_H */