Merge branch 'concurrent_hash_tables'

Thomas Graf says:

====================
Lockless netlink_lookup() with new concurrent hash table

Netlink sockets are maintained in a hash table to allow efficient lookup
via the port ID for unicast messages. However, lookups currently require
a read lock to be taken. This series adds a new generic, resizable,
scalable, concurrent hash table based on the paper referenced in the first
patch. It then makes use of the new data type to implement lockless
netlink_lookup().

Patch 3/3 to convert nft_hash is included for reference but should be
merged via the netfilter tree. Inclusion in this series is to provide
context for the suggested API.

Against net-next since the initial user of the new hash table is in net/

Changes:
v4-v5:
 - use GFP_KERNEL to alloc Netlink buckets as suggested by Nikolay
   Aleksandrov
 - free nft hash element on removal as spotted by Nikolay Aleksandrov
   and Patrick McHardy
v3-v4:
 - fixed wrong shift assignment placement as spotted by Nikolay Aleksandrov
 - reverted default size of nft_hash to 4 as requested by Patrick McHardy,
   default size for other hash tables remains at 64 if no hint is given
 - fixed copyright as requested by Patrick McHardy
v2-v3:
 - fixed typo in nft_hash_destroy() when passing rhashtable handle
v1-v2:
 - fixed traversal off-by-one as spotted by Tobias Klauser
 - removed unlikely() from BUG_ON() as spotted by Josh Triplett
 - new 3rd patch to convert nft_hash to rhashtable
 - make rhashtable_insert() return void
 - nl_sk_hash_lock must be a mutex
 - fixed wrong name of rht_shrink_below_30()
 - exported symbols rht_grow_above_75() and rht_shrink_below_30()
 - allow table freeing with RCU callback
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 806 insertions, 1 deletions

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7a638aa3545b..f11a2e8f6157 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1550,6 +1550,14 @@ config TEST_STRING_HELPERS
 config TEST_KSTRTOX
         tristate "Test kstrto*() family of functions at runtime"
 
+config TEST_RHASHTABLE
+        bool "Perform selftest on resizable hash table"
+        default n
+        help
+          Enable this option to test the rhashtable functions at boot.
+
+          If unsure, say N.
+
 endmenu # runtime tests
 
 config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index ba967a19edba..fd248e4c05ad 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
          bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
          gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
          bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
-         percpu-refcount.o percpu_ida.o hash.o
+         percpu-refcount.o percpu_ida.o hash.o rhashtable.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
new file mode 100644
index 000000000000..e6940cf16628
--- /dev/null
+++ b/lib/rhashtable.c
@@ -0,0 +1,797 @@
+/*
+ * Resizable, Scalable, Concurrent Hash Table
+ *
+ * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
+ *
+ * Based on the following paper:
+ * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
+ *
+ * Code partially derived from nft_hash
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/log2.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/hash.h>
+#include <linux/random.h>
+#include <linux/rhashtable.h>
+#include <linux/log2.h>
+
+#define HASH_DEFAULT_SIZE       64UL
+#define HASH_MIN_SIZE           4UL
+
+#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
+
+#ifdef CONFIG_PROVE_LOCKING
+int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
+{
+        return ht->p.mutex_is_held();
+}
+EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
+#endif
+
+/**
+ * rht_obj - cast hash head to outer object
+ * @ht:         hash table
+ * @he:         hashed node
+ */
+void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
+{
+        return (void *) he - ht->p.head_offset;
+}
+EXPORT_SYMBOL_GPL(rht_obj);
+
+static u32 __hashfn(const struct rhashtable *ht, const void *key,
+                      u32 len, u32 hsize)
+{
+        u32 h;
+
+        h = ht->p.hashfn(key, len, ht->p.hash_rnd);
+
+        return h & (hsize - 1);
+}
+
+/**
+ * rhashtable_hashfn - compute hash for key of given length
+ * @ht:         hash table to compuate for
+ * @key:        pointer to key
+ * @len:        length of key
+ *
+ * Computes the hash value using the hash function provided in the 'hashfn'
+ * of struct rhashtable_params. The returned value is guaranteed to be
+ * smaller than the number of buckets in the hash table.
+ */
+u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len)
+{
+        struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+        return __hashfn(ht, key, len, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_hashfn);
+
+static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize)
+{
+        if (unlikely(!ht->p.key_len)) {
+                u32 h;
+
+                h = ht->p.obj_hashfn(ptr, ht->p.hash_rnd);
+
+                return h & (hsize - 1);
+        }
+
+        return __hashfn(ht, ptr + ht->p.key_offset, ht->p.key_len, hsize);
+}
+
+/**
+ * rhashtable_obj_hashfn - compute hash for hashed object
+ * @ht:         hash table to compuate for
+ * @ptr:        pointer to hashed object
+ *
+ * Computes the hash value using the hash function `hashfn` respectively
+ * 'obj_hashfn' depending on whether the hash table is set up to work with
+ * a fixed length key. The returned value is guaranteed to be smaller than
+ * the number of buckets in the hash table.
+ */
+u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr)
+{
+        struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+        return obj_hashfn(ht, ptr, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_obj_hashfn);
+
+static u32 head_hashfn(const struct rhashtable *ht,
+                       const struct rhash_head *he, u32 hsize)
+{
+        return obj_hashfn(ht, rht_obj(ht, he), hsize);
+}
+
+static struct bucket_table *bucket_table_alloc(size_t nbuckets, gfp_t flags)
+{
+        struct bucket_table *tbl;
+        size_t size;
+
+        size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
+        tbl = kzalloc(size, flags);
+        if (tbl == NULL)
+                tbl = vzalloc(size);
+
+        if (tbl == NULL)
+                return NULL;
+
+        tbl->size = nbuckets;
+
+        return tbl;
+}
+
+static void bucket_table_free(const struct bucket_table *tbl)
+{
+        kvfree(tbl);
+}
+
+/**
+ * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
+ * @ht:         hash table
+ * @new_size:   new table size
+ */
+bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
+{
+        /* Expand table when exceeding 75% load */
+        return ht->nelems > (new_size / 4 * 3);
+}
+EXPORT_SYMBOL_GPL(rht_grow_above_75);
+
+/**
+ * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
+ * @ht:         hash table
+ * @new_size:   new table size
+ */
+bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
+{
+        /* Shrink table beneath 30% load */
+        return ht->nelems < (new_size * 3 / 10);
+}
+EXPORT_SYMBOL_GPL(rht_shrink_below_30);
+
+static void hashtable_chain_unzip(const struct rhashtable *ht,
+                                  const struct bucket_table *new_tbl,
+                                  struct bucket_table *old_tbl, size_t n)
+{
+        struct rhash_head *he, *p, *next;
+        unsigned int h;
+
+        /* Old bucket empty, no work needed. */
+        p = rht_dereference(old_tbl->buckets[n], ht);
+        if (!p)
+                return;
+
+        /* Advance the old bucket pointer one or more times until it
+         * reaches a node that doesn't hash to the same bucket as the
+         * previous node p. Call the previous node p;
+         */
+        h = head_hashfn(ht, p, new_tbl->size);
+        rht_for_each(he, p->next, ht) {
+                if (head_hashfn(ht, he, new_tbl->size) != h)
+                        break;
+                p = he;
+        }
+        RCU_INIT_POINTER(old_tbl->buckets[n], p->next);
+
+        /* Find the subsequent node which does hash to the same
+         * bucket as node P, or NULL if no such node exists.
+         */
+        next = NULL;
+        if (he) {
+                rht_for_each(he, he->next, ht) {
+                        if (head_hashfn(ht, he, new_tbl->size) == h) {
+                                next = he;
+                                break;
+                        }
+                }
+        }
+
+        /* Set p's next pointer to that subsequent node pointer,
+         * bypassing the nodes which do not hash to p's bucket
+         */
+        RCU_INIT_POINTER(p->next, next);
+}
+
+/**
+ * rhashtable_expand - Expand hash table while allowing concurrent lookups
+ * @ht:         the hash table to expand
+ * @flags:      allocation flags
+ *
+ * A secondary bucket array is allocated and the hash entries are migrated
+ * while keeping them on both lists until the end of the RCU grace period.
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_expand(struct rhashtable *ht, gfp_t flags)
+{
+        struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
+        struct rhash_head *he;
+        unsigned int i, h;
+        bool complete;
+
+        ASSERT_RHT_MUTEX(ht);
+
+        if (ht->p.max_shift && ht->shift >= ht->p.max_shift)
+                return 0;
+
+        new_tbl = bucket_table_alloc(old_tbl->size * 2, flags);
+        if (new_tbl == NULL)
+                return -ENOMEM;
+
+        ht->shift++;
+
+        /* For each new bucket, search the corresponding old bucket
+         * for the first entry that hashes to the new bucket, and
+         * link the new bucket to that entry. Since all the entries
+         * which will end up in the new bucket appear in the same
+         * old bucket, this constructs an entirely valid new hash
+         * table, but with multiple buckets "zipped" together into a
+         * single imprecise chain.
+         */
+        for (i = 0; i < new_tbl->size; i++) {
+                h = i & (old_tbl->size - 1);
+                rht_for_each(he, old_tbl->buckets[h], ht) {
+                        if (head_hashfn(ht, he, new_tbl->size) == i) {
+                                RCU_INIT_POINTER(new_tbl->buckets[i], he);
+                                break;
+                        }
+                }
+        }
+
+        /* Publish the new table pointer. Lookups may now traverse
+         * the new table, but they will not benefit from any
+         * additional efficiency until later steps unzip the buckets.
+         */
+        rcu_assign_pointer(ht->tbl, new_tbl);
+
+        /* Unzip interleaved hash chains */
+        do {
+                /* Wait for readers. All new readers will see the new
+                 * table, and thus no references to the old table will
+                 * remain.
+                 */
+                synchronize_rcu();
+
+                /* For each bucket in the old table (each of which
+                 * contains items from multiple buckets of the new
+                 * table): ...
+                 */
+                complete = true;
+                for (i = 0; i < old_tbl->size; i++) {
+                        hashtable_chain_unzip(ht, new_tbl, old_tbl, i);
+                        if (old_tbl->buckets[i] != NULL)
+                                complete = false;
+                }
+        } while (!complete);
+
+        bucket_table_free(old_tbl);
+        return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_expand);
+
+/**
+ * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
+ * @ht:         the hash table to shrink
+ * @flags:      allocation flags
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_shrink(struct rhashtable *ht, gfp_t flags)
+{
+        struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht);
+        struct rhash_head __rcu **pprev;
+        unsigned int i;
+
+        ASSERT_RHT_MUTEX(ht);
+
+        if (tbl->size <= HASH_MIN_SIZE)
+                return 0;
+
+        ntbl = bucket_table_alloc(tbl->size / 2, flags);
+        if (ntbl == NULL)
+                return -ENOMEM;
+
+        ht->shift--;
+
+        /* Link each bucket in the new table to the first bucket
+         * in the old table that contains entries which will hash
+         * to the new bucket.
+         */
+        for (i = 0; i < ntbl->size; i++) {
+                ntbl->buckets[i] = tbl->buckets[i];
+
+                /* Link each bucket in the new table to the first bucket
+                 * in the old table that contains entries which will hash
+                 * to the new bucket.
+                 */
+                for (pprev = &ntbl->buckets[i]; *pprev != NULL;
+                     pprev = &rht_dereference(*pprev, ht)->next)
+                        ;
+                RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]);
+        }
+
+        /* Publish the new, valid hash table */
+        rcu_assign_pointer(ht->tbl, ntbl);
+
+        /* Wait for readers. No new readers will have references to the
+         * old hash table.
+         */
+        synchronize_rcu();
+
+        bucket_table_free(tbl);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_shrink);
+
+/**
+ * rhashtable_insert - insert object into hash hash table
+ * @ht:         hash table
+ * @obj:        pointer to hash head inside object
+ * @flags:      allocation flags (table expansion)
+ *
+ * Will automatically grow the table via rhashtable_expand() if the the
+ * grow_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
+                       gfp_t flags)
+{
+        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+        u32 hash;
+
+        ASSERT_RHT_MUTEX(ht);
+
+        hash = head_hashfn(ht, obj, tbl->size);
+        RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
+        rcu_assign_pointer(tbl->buckets[hash], obj);
+        ht->nelems++;
+
+        if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
+                rhashtable_expand(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_insert);
+
+/**
+ * rhashtable_remove_pprev - remove object from hash table given previous element
+ * @ht:         hash table
+ * @obj:        pointer to hash head inside object
+ * @pprev:      pointer to previous element
+ * @flags:      allocation flags (table expansion)
+ *
+ * Identical to rhashtable_remove() but caller is alreayd aware of the element
+ * in front of the element to be deleted. This is in particular useful for
+ * deletion when combined with walking or lookup.
+ */
+void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
+                             struct rhash_head **pprev, gfp_t flags)
+{
+        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+        ASSERT_RHT_MUTEX(ht);
+
+        RCU_INIT_POINTER(*pprev, obj->next);
+        ht->nelems--;
+
+        if (ht->p.shrink_decision &&
+            ht->p.shrink_decision(ht, tbl->size))
+                rhashtable_shrink(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove_pprev);
+
+/**
+ * rhashtable_remove - remove object from hash table
+ * @ht:         hash table
+ * @obj:        pointer to hash head inside object
+ * @flags:      allocation flags (table expansion)
+ *
+ * Since the hash chain is single linked, the removal operation needs to
+ * walk the bucket chain upon removal. The removal operation is thus
+ * considerable slow if the hash table is not correctly sized.
+ *
+ * Will automatically shrink the table via rhashtable_expand() if the the
+ * shrink_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj,
+                       gfp_t flags)
+{
+        struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+        struct rhash_head __rcu **pprev;
+        struct rhash_head *he;
+        u32 h;
+
+        ASSERT_RHT_MUTEX(ht);
+
+        h = head_hashfn(ht, obj, tbl->size);
+
+        pprev = &tbl->buckets[h];
+        rht_for_each(he, tbl->buckets[h], ht) {
+                if (he != obj) {
+                        pprev = &he->next;
+                        continue;
+                }
+
+                rhashtable_remove_pprev(ht, he, pprev, flags);
+                return true;
+        }
+
+        return false;
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove);
+
+/**
+ * rhashtable_lookup - lookup key in hash table
+ * @ht:         hash table
+ * @key:        pointer to key
+ *
+ * Computes the hash value for the key and traverses the bucket chain looking
+ * for a entry with an identical key. The first matching entry is returned.
+ *
+ * This lookup function may only be used for fixed key hash table (key_len
+ * paramter set). It will BUG() if used inappropriately.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ */
+void *rhashtable_lookup(const struct rhashtable *ht, const void *key)
+{
+        const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+        struct rhash_head *he;
+        u32 h;
+
+        BUG_ON(!ht->p.key_len);
+
+        h = __hashfn(ht, key, ht->p.key_len, tbl->size);
+        rht_for_each_rcu(he, tbl->buckets[h], ht) {
+                if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key,
+                           ht->p.key_len))
+                        continue;
+                return (void *) he - ht->p.head_offset;
+        }
+
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup);
+
+/**
+ * rhashtable_lookup_compare - search hash table with compare function
+ * @ht:         hash table
+ * @hash:       hash value of desired entry
+ * @compare:    compare function, must return true on match
+ * @arg:        argument passed on to compare function
+ *
+ * Traverses the bucket chain behind the provided hash value and calls the
+ * specified compare function for each entry.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ *
+ * Returns the first entry on which the compare function returned true.
+ */
+void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+                                bool (*compare)(void *, void *), void *arg)
+{
+        const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+        struct rhash_head *he;
+
+        if (unlikely(hash >= tbl->size))
+                return NULL;
+
+        rht_for_each_rcu(he, tbl->buckets[hash], ht) {
+                if (!compare(rht_obj(ht, he), arg))
+                        continue;
+                return (void *) he - ht->p.head_offset;
+        }
+
+        return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
+
+static size_t rounded_hashtable_size(unsigned int nelem)
+{
+        return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE);
+}
+
+/**
+ * rhashtable_init - initialize a new hash table
+ * @ht:         hash table to be initialized
+ * @params:     configuration parameters
+ *
+ * Initializes a new hash table based on the provided configuration
+ * parameters. A table can be configured either with a variable or
+ * fixed length key:
+ *
+ * Configuration Example 1: Fixed length keys
+ * struct test_obj {
+ *      int                     key;
+ *      void *                  my_member;
+ *      struct rhash_head       node;
+ * };
+ *
+ * struct rhashtable_params params = {
+ *      .head_offset = offsetof(struct test_obj, node),
+ *      .key_offset = offsetof(struct test_obj, key),
+ *      .key_len = sizeof(int),
+ *      .hashfn = arch_fast_hash,
+ *      .mutex_is_held = &my_mutex_is_held,
+ * };
+ *
+ * Configuration Example 2: Variable length keys
+ * struct test_obj {
+ *      [...]
+ *      struct rhash_head       node;
+ * };
+ *
+ * u32 my_hash_fn(const void *data, u32 seed)
+ * {
+ *      struct test_obj *obj = data;
+ *
+ *      return [... hash ...];
+ * }
+ *
+ * struct rhashtable_params params = {
+ *      .head_offset = offsetof(struct test_obj, node),
+ *      .hashfn = arch_fast_hash,
+ *      .obj_hashfn = my_hash_fn,
+ *      .mutex_is_held = &my_mutex_is_held,
+ * };
+ */
+int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
+{
+        struct bucket_table *tbl;
+        size_t size;
+
+        size = HASH_DEFAULT_SIZE;
+
+        if ((params->key_len && !params->hashfn) ||
+            (!params->key_len && !params->obj_hashfn))
+                return -EINVAL;
+
+        if (params->nelem_hint)
+                size = rounded_hashtable_size(params->nelem_hint);
+
+        tbl = bucket_table_alloc(size, GFP_KERNEL);
+        if (tbl == NULL)
+                return -ENOMEM;
+
+        memset(ht, 0, sizeof(*ht));
+        ht->shift = ilog2(tbl->size);
+        memcpy(&ht->p, params, sizeof(*params));
+        RCU_INIT_POINTER(ht->tbl, tbl);
+
+        if (!ht->p.hash_rnd)
+                get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd));
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_init);
+
+/**
+ * rhashtable_destroy - destroy hash table
+ * @ht:         the hash table to destroy
+ *
+ * Frees the bucket array.
+ */
+void rhashtable_destroy(const struct rhashtable *ht)
+{
+        const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+        bucket_table_free(tbl);
+}
+EXPORT_SYMBOL_GPL(rhashtable_destroy);
+
+/**************************************************************************
+ * Self Test
+ **************************************************************************/
+
+#ifdef CONFIG_TEST_RHASHTABLE
+
+#define TEST_HT_SIZE    8
+#define TEST_ENTRIES    2048
+#define TEST_PTR        ((void *) 0xdeadbeef)
+#define TEST_NEXPANDS   4
+
+static int test_mutex_is_held(void)
+{
+        return 1;
+}
+
+struct test_obj {
+        void                    *ptr;
+        int                     value;
+        struct rhash_head       node;
+};
+
+static int __init test_rht_lookup(struct rhashtable *ht)
+{
+        unsigned int i;
+
+        for (i = 0; i < TEST_ENTRIES * 2; i++) {
+                struct test_obj *obj;
+                bool expected = !(i % 2);
+                u32 key = i;
+
+                obj = rhashtable_lookup(ht, &key);
+
+                if (expected && !obj) {
+                        pr_warn("Test failed: Could not find key %u\n", key);
+                        return -ENOENT;
+                } else if (!expected && obj) {
+                        pr_warn("Test failed: Unexpected entry found for key %u\n",
+                                key);
+                        return -EEXIST;
+                } else if (expected && obj) {
+                        if (obj->ptr != TEST_PTR || obj->value != i) {
+                                pr_warn("Test failed: Lookup value mismatch %p!=%p, %u!=%u\n",
+                                        obj->ptr, TEST_PTR, obj->value, i);
+                                return -EINVAL;
+                        }
+                }
+        }
+
+        return 0;
+}
+
+static void test_bucket_stats(struct rhashtable *ht,
+                                     struct bucket_table *tbl,
+                                     bool quiet)
+{
+        unsigned int cnt, i, total = 0;
+        struct test_obj *obj;
+
+        for (i = 0; i < tbl->size; i++) {
+                cnt = 0;
+
+                if (!quiet)
+                        pr_info(" [%#4x/%zu]", i, tbl->size);
+
+                rht_for_each_entry_rcu(obj, tbl->buckets[i], node) {
+                        cnt++;
+                        total++;
+                        if (!quiet)
+                                pr_cont(" [%p],", obj);
+                }
+
+                if (!quiet)
+                        pr_cont("\n  [%#x] first element: %p, chain length: %u\n",
+                                i, tbl->buckets[i], cnt);
+        }
+
+        pr_info("  Traversal complete: counted=%u, nelems=%zu, entries=%d\n",
+                total, ht->nelems, TEST_ENTRIES);
+}
+
+static int __init test_rhashtable(struct rhashtable *ht)
+{
+        struct bucket_table *tbl;
+        struct test_obj *obj, *next;
+        int err;
+        unsigned int i;
+
+        /*
+         * Insertion Test:
+         * Insert TEST_ENTRIES into table with all keys even numbers
+         */
+        pr_info("  Adding %d keys\n", TEST_ENTRIES);
+        for (i = 0; i < TEST_ENTRIES; i++) {
+                struct test_obj *obj;
+
+                obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+                if (!obj) {
+                        err = -ENOMEM;
+                        goto error;
+                }
+
+                obj->ptr = TEST_PTR;
+                obj->value = i * 2;
+
+                rhashtable_insert(ht, &obj->node, GFP_KERNEL);
+        }
+
+        rcu_read_lock();
+        tbl = rht_dereference_rcu(ht->tbl, ht);
+        test_bucket_stats(ht, tbl, true);
+        test_rht_lookup(ht);
+        rcu_read_unlock();
+
+        for (i = 0; i < TEST_NEXPANDS; i++) {
+                pr_info("  Table expansion iteration %u...\n", i);
+                rhashtable_expand(ht, GFP_KERNEL);
+
+                rcu_read_lock();
+                pr_info("  Verifying lookups...\n");
+                test_rht_lookup(ht);
+                rcu_read_unlock();
+        }
+
+        for (i = 0; i < TEST_NEXPANDS; i++) {
+                pr_info("  Table shrinkage iteration %u...\n", i);
+                rhashtable_shrink(ht, GFP_KERNEL);
+
+                rcu_read_lock();
+                pr_info("  Verifying lookups...\n");
+                test_rht_lookup(ht);
+                rcu_read_unlock();
+        }
+
+        pr_info("  Deleting %d keys\n", TEST_ENTRIES);
+        for (i = 0; i < TEST_ENTRIES; i++) {
+                u32 key = i * 2;
+
+                obj = rhashtable_lookup(ht, &key);
+                BUG_ON(!obj);
+
+                rhashtable_remove(ht, &obj->node, GFP_KERNEL);
+                kfree(obj);
+        }
+
+        return 0;
+
+error:
+        tbl = rht_dereference_rcu(ht->tbl, ht);
+        for (i = 0; i < tbl->size; i++)
+                rht_for_each_entry_safe(obj, next, tbl->buckets[i], ht, node)
+                        kfree(obj);
+
+        return err;
+}
+
+static int __init test_rht_init(void)
+{
+        struct rhashtable ht;
+        struct rhashtable_params params = {
+                .nelem_hint = TEST_HT_SIZE,
+                .head_offset = offsetof(struct test_obj, node),
+                .key_offset = offsetof(struct test_obj, value),
+                .key_len = sizeof(int),
+                .hashfn = arch_fast_hash,
+                .mutex_is_held = &test_mutex_is_held,
+                .grow_decision = rht_grow_above_75,
+                .shrink_decision = rht_shrink_below_30,
+        };
+        int err;
+
+        pr_info("Running resizable hashtable tests...\n");
+
+        err = rhashtable_init(&ht, &params);
+        if (err < 0) {
+                pr_warn("Test failed: Unable to initialize hashtable: %d\n",
+                        err);
+                return err;
+        }
+
+        err = test_rhashtable(&ht);
+
+        rhashtable_destroy(&ht);
+
+        return err;
+}
+
+subsys_initcall(test_rht_init);
+
+#endif /* CONFIG_TEST_RHASHTABLE */