datapath: fix sparse warning in function tbl_mask_array_delete_mask()

[mirror_ovs.git] / datapath / flow_table.c

/*
 * Copyright (c) 2007-2013 Nicira, Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA
 */

#include "flow.h"
#include "datapath.h"
#include <linux/uaccess.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>
#include <linux/if_ether.h>
#include <linux/if_vlan.h>
#include <net/llc_pdu.h>
#include <linux/kernel.h>
#include <linux/hash.h>
#include <linux/jiffies.h>
#include <linux/llc.h>
#include <linux/module.h>
#include <linux/in.h>
#include <linux/rcupdate.h>
#include <linux/if_arp.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/sctp.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/icmp.h>
#include <linux/icmpv6.h>
#include <linux/rculist.h>
#include <net/ip.h>
#include <net/ipv6.h>
#include <net/ndisc.h>

#include "vlan.h"

#define TBL_MIN_BUCKETS         1024
#define MASK_ARRAY_SIZE_MIN     16
#define REHASH_INTERVAL         (10 * 60 * HZ)

#define MC_HASH_SHIFT           8
#define MC_HASH_ENTRIES         (1u << MC_HASH_SHIFT)
#define MC_HASH_SEGS            ((sizeof(uint32_t) * 8) / MC_HASH_SHIFT)

static struct kmem_cache *flow_cache;
struct kmem_cache *flow_stats_cache __read_mostly;

static u16 range_n_bytes(const struct sw_flow_key_range *range)
{
        return range->end - range->start;
}

void ovs_flow_mask_key(struct sw_flow_key *dst, const struct sw_flow_key *src,
                       const struct sw_flow_mask *mask)
{
        const long *m = (const long *)((const u8 *)&mask->key +
                                mask->range.start);
        const long *s = (const long *)((const u8 *)src +
                                mask->range.start);
        long *d = (long *)((u8 *)dst + mask->range.start);
        int i;

        /* The memory outside of the 'mask->range' are not set since
         * further operations on 'dst' only uses contents within
         * 'mask->range'.
         */
        for (i = 0; i < range_n_bytes(&mask->range); i += sizeof(long))
                *d++ = *s++ & *m++;
}

struct sw_flow *ovs_flow_alloc(void)
{
        struct sw_flow *flow;
        struct flow_stats *stats;
        int node;

        flow = kmem_cache_alloc(flow_cache, GFP_KERNEL);
        if (!flow)
                return ERR_PTR(-ENOMEM);

        flow->sf_acts = NULL;
        flow->mask = NULL;
        flow->stats_last_writer = NUMA_NO_NODE;

        /* Initialize the default stat node. */
        stats = kmem_cache_alloc_node(flow_stats_cache,
                                      GFP_KERNEL | __GFP_ZERO, 0);
        if (!stats)
                goto err;

        spin_lock_init(&stats->lock);

        RCU_INIT_POINTER(flow->stats[0], stats);

        for_each_node(node)
                if (node != 0)
                        RCU_INIT_POINTER(flow->stats[node], NULL);

        return flow;
err:
        kmem_cache_free(flow_cache, flow);
        return ERR_PTR(-ENOMEM);
}

int ovs_flow_tbl_count(struct flow_table *table)
{
        return table->count;
}

static struct flex_array *alloc_buckets(unsigned int n_buckets)
{
        struct flex_array *buckets;
        int i, err;

        buckets = flex_array_alloc(sizeof(struct hlist_head),
                                   n_buckets, GFP_KERNEL);
        if (!buckets)
                return NULL;

        err = flex_array_prealloc(buckets, 0, n_buckets, GFP_KERNEL);
        if (err) {
                flex_array_free(buckets);
                return NULL;
        }

        for (i = 0; i < n_buckets; i++)
                INIT_HLIST_HEAD((struct hlist_head *)
                                        flex_array_get(buckets, i));

        return buckets;
}

static void flow_free(struct sw_flow *flow)
{
        int node;

        kfree((struct sw_flow_actions __force *)flow->sf_acts);
        for_each_node(node)
                if (flow->stats[node])
                        kmem_cache_free(flow_stats_cache,
                                        (struct flow_stats __force *)flow->stats[node]);
        kmem_cache_free(flow_cache, flow);
}

static void rcu_free_flow_callback(struct rcu_head *rcu)
{
        struct sw_flow *flow = container_of(rcu, struct sw_flow, rcu);

        flow_free(flow);
}

static void rcu_free_sw_flow_mask_cb(struct rcu_head *rcu)
{
        struct sw_flow_mask *mask = container_of(rcu, struct sw_flow_mask, rcu);

        kfree(mask);
}

void ovs_flow_free(struct sw_flow *flow, bool deferred)
{
        if (!flow)
                return;

        if (deferred)
                call_rcu(&flow->rcu, rcu_free_flow_callback);
        else
                flow_free(flow);
}

static void free_buckets(struct flex_array *buckets)
{
        flex_array_free(buckets);
}


static void __table_instance_destroy(struct table_instance *ti)
{
        free_buckets(ti->buckets);
        kfree(ti);
}

static struct table_instance *table_instance_alloc(int new_size)
{
        struct table_instance *ti = kmalloc(sizeof(*ti), GFP_KERNEL);

        if (!ti)
                return NULL;

        ti->buckets = alloc_buckets(new_size);

        if (!ti->buckets) {
                kfree(ti);
                return NULL;
        }
        ti->n_buckets = new_size;
        ti->node_ver = 0;
        ti->keep_flows = false;
        get_random_bytes(&ti->hash_seed, sizeof(u32));

        return ti;
}

static void mask_array_rcu_cb(struct rcu_head *rcu)
{
        struct mask_array *ma = container_of(rcu, struct mask_array, rcu);

        kfree(ma);
}

static struct mask_array *tbl_mask_array_alloc(int size)
{
        struct mask_array *new;

        new = kzalloc(sizeof(struct mask_array) +
                      sizeof(struct sw_flow_mask *) * size, GFP_KERNEL);
        if (!new)
                return NULL;

        new->count = 0;
        new->max = size;

        return new;
}

static int tbl_mask_array_realloc(struct flow_table *tbl, int size)
{
        struct mask_array *old;
        struct mask_array *new;

        new = tbl_mask_array_alloc(size);
        if (!new)
                return -ENOMEM;

        old = ovsl_dereference(tbl->mask_array);
        if (old) {
                int i;

                for (i = 0; i < old->max; i++)
                        new->masks[i] = old->masks[i];

                new->count = old->count;
        }
        rcu_assign_pointer(tbl->mask_array, new);

        if (old)
                call_rcu(&old->rcu, mask_array_rcu_cb);

        return 0;
}

static void tbl_mask_array_delete_mask(struct mask_array *ma,
                                       const struct sw_flow_mask *mask)
{
        int i = 0;

        /* Delete a mask pointer from the valid section.
         *
         * Also move the last entry in its place, so there is no
         * whole in the valid section.
         *
         * Notice the last entry still points to the original mask.
         *
         * <Note>: there is a small race window that may cause a mask
         * to be missed in a search. Imaging a core is
         * walking through the array, passing the index of deleting mask.
         * But before reaching the last entry, it is overwritten,
         * by another core that is adding a new mask, now the last entry
         * will point to the new mask. In this case, the moved up last
         * entry can be missed by the core walking the mask array.
         *
         * In case this missed mask would have led to successful
         * lookup, Hitting the race window could cause a packet to miss
         * kernel flow cache, and be sent to the user space.
         * </Note>
         */
        for (i = 0; i < ma->count; i++)
                if (mask == ovsl_dereference(ma->masks[i])) {
                        struct sw_flow_mask *last;

                        last = ovsl_dereference(ma->masks[ma->count - 1]);
                        rcu_assign_pointer(ma->masks[i], last);
                        ma->count--;
                        break;
                }

        /* Remove the deleted mask pointers from the invalid section. */
        for (i = ma->count; i < ma->max; i++)
                if (mask == ovsl_dereference(ma->masks[i]))
                        RCU_INIT_POINTER(ma->masks[i], NULL);
}

int ovs_flow_tbl_init(struct flow_table *table)
{
        struct table_instance *ti;
        struct mask_array *ma;

        table->mask_cache = __alloc_percpu(sizeof(struct mask_cache_entry) *
                                          MC_HASH_ENTRIES, __alignof__(struct mask_cache_entry));
        if (!table->mask_cache)
                return -ENOMEM;

        ma = tbl_mask_array_alloc(MASK_ARRAY_SIZE_MIN);
        if (!ma)
                goto free_mask_cache;

        ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!ti)
                goto free_mask_array;

        rcu_assign_pointer(table->ti, ti);
        rcu_assign_pointer(table->mask_array, ma);
        table->last_rehash = jiffies;
        table->count = 0;
        return 0;

free_mask_array:
        kfree((struct mask_array __force *)table->mask_array);
free_mask_cache:
        free_percpu(table->mask_cache);
        return -ENOMEM;
}

static void flow_tbl_destroy_rcu_cb(struct rcu_head *rcu)
{
        struct table_instance *ti = container_of(rcu, struct table_instance, rcu);

        __table_instance_destroy(ti);
}

static void table_instance_destroy(struct table_instance *ti, bool deferred)
{
        int i;

        if (!ti)
                return;

        if (ti->keep_flows)
                goto skip_flows;

        for (i = 0; i < ti->n_buckets; i++) {
                struct sw_flow *flow;
                struct hlist_head *head = flex_array_get(ti->buckets, i);
                struct hlist_node *n;
                int ver = ti->node_ver;

                hlist_for_each_entry_safe(flow, n, head, hash_node[ver]) {
                        hlist_del_rcu(&flow->hash_node[ver]);
                        ovs_flow_free(flow, deferred);
                }
        }

skip_flows:
        if (deferred)
                call_rcu(&ti->rcu, flow_tbl_destroy_rcu_cb);
        else
                __table_instance_destroy(ti);
}

/* No need for locking this function is called from RCU callback or
 * error path. */
void ovs_flow_tbl_destroy(struct flow_table *table)
{
        struct table_instance *ti = (struct table_instance __force *)table->ti;

        free_percpu(table->mask_cache);
        kfree((struct mask_array __force *)table->mask_array);
        table_instance_destroy(ti, false);
}

struct sw_flow *ovs_flow_tbl_dump_next(struct table_instance *ti,
                                       u32 *bucket, u32 *last)
{
        struct sw_flow *flow;
        struct hlist_head *head;
        int ver;
        int i;

        ver = ti->node_ver;
        while (*bucket < ti->n_buckets) {
                i = 0;
                head = flex_array_get(ti->buckets, *bucket);
                hlist_for_each_entry_rcu(flow, head, hash_node[ver]) {
                        if (i < *last) {
                                i++;
                                continue;
                        }
                        *last = i + 1;
                        return flow;
                }
                (*bucket)++;
                *last = 0;
        }

        return NULL;
}

static struct hlist_head *find_bucket(struct table_instance *ti, u32 hash)
{
        hash = jhash_1word(hash, ti->hash_seed);
        return flex_array_get(ti->buckets,
                                (hash & (ti->n_buckets - 1)));
}

static void table_instance_insert(struct table_instance *ti, struct sw_flow *flow)
{
        struct hlist_head *head;

        head = find_bucket(ti, flow->hash);
        hlist_add_head_rcu(&flow->hash_node[ti->node_ver], head);
}

static void flow_table_copy_flows(struct table_instance *old,
                                  struct table_instance *new)
{
        int old_ver;
        int i;

        old_ver = old->node_ver;
        new->node_ver = !old_ver;

        /* Insert in new table. */
        for (i = 0; i < old->n_buckets; i++) {
                struct sw_flow *flow;
                struct hlist_head *head;

                head = flex_array_get(old->buckets, i);

                hlist_for_each_entry(flow, head, hash_node[old_ver])
                        table_instance_insert(new, flow);
        }

        old->keep_flows = true;
}

static struct table_instance *table_instance_rehash(struct table_instance *ti,
                                            int n_buckets)
{
        struct table_instance *new_ti;

        new_ti = table_instance_alloc(n_buckets);
        if (!new_ti)
                return NULL;

        flow_table_copy_flows(ti, new_ti);

        return new_ti;
}

int ovs_flow_tbl_flush(struct flow_table *flow_table)
{
        struct table_instance *old_ti;
        struct table_instance *new_ti;

        old_ti = ovsl_dereference(flow_table->ti);
        new_ti = table_instance_alloc(TBL_MIN_BUCKETS);
        if (!new_ti)
                return -ENOMEM;

        rcu_assign_pointer(flow_table->ti, new_ti);
        flow_table->last_rehash = jiffies;
        flow_table->count = 0;

        table_instance_destroy(old_ti, true);
        return 0;
}

static u32 flow_hash(const struct sw_flow_key *key, int key_start,
                     int key_end)
{
        const u32 *hash_key = (const u32 *)((const u8 *)key + key_start);
        int hash_u32s = (key_end - key_start) >> 2;

        /* Make sure number of hash bytes are multiple of u32. */
        BUILD_BUG_ON(sizeof(long) % sizeof(u32));

        return arch_fast_hash2(hash_key, hash_u32s, 0);
}

static int flow_key_start(const struct sw_flow_key *key)
{
        if (key->tun_key.ipv4_dst)
                return 0;
        else
                return rounddown(offsetof(struct sw_flow_key, phy),
                                          sizeof(long));
}

static bool cmp_key(const struct sw_flow_key *key1,
                    const struct sw_flow_key *key2,
                    int key_start, int key_end)
{
        const long *cp1 = (const long *)((const u8 *)key1 + key_start);
        const long *cp2 = (const long *)((const u8 *)key2 + key_start);
        long diffs = 0;
        int i;

        for (i = key_start; i < key_end;  i += sizeof(long))
                diffs |= *cp1++ ^ *cp2++;

        return diffs == 0;
}

static bool flow_cmp_masked_key(const struct sw_flow *flow,
                                const struct sw_flow_key *key,
                                int key_start, int key_end)
{
        return cmp_key(&flow->key, key, key_start, key_end);
}

bool ovs_flow_cmp_unmasked_key(const struct sw_flow *flow,
                               struct sw_flow_match *match)
{
        struct sw_flow_key *key = match->key;
        int key_start = flow_key_start(key);
        int key_end = match->range.end;

        return cmp_key(&flow->unmasked_key, key, key_start, key_end);
}

static struct sw_flow *masked_flow_lookup(struct table_instance *ti,
                                          const struct sw_flow_key *unmasked,
                                          struct sw_flow_mask *mask,
                                          u32 *n_mask_hit)
{
        struct sw_flow *flow;
        struct hlist_head *head;
        int key_start = mask->range.start;
        int key_end = mask->range.end;
        u32 hash;
        struct sw_flow_key masked_key;

        ovs_flow_mask_key(&masked_key, unmasked, mask);
        hash = flow_hash(&masked_key, key_start, key_end);
        head = find_bucket(ti, hash);
        (*n_mask_hit)++;
        hlist_for_each_entry_rcu(flow, head, hash_node[ti->node_ver]) {
                if (flow->mask == mask && flow->hash == hash &&
                    flow_cmp_masked_key(flow, &masked_key,
                                          key_start, key_end))
                        return flow;
        }
        return NULL;
}

static struct sw_flow *flow_lookup(struct flow_table *tbl,
                                   struct table_instance *ti,
                                   struct mask_array *ma,
                                   const struct sw_flow_key *key,
                                   u32 *n_mask_hit,
                                   u32 *index)
{
        struct sw_flow *flow;
        int i;

        for (i = 0; i < ma->count; i++) {
                struct sw_flow_mask *mask;

                mask = rcu_dereference_ovsl(ma->masks[i]);
                if (mask) {
                        flow = masked_flow_lookup(ti, key, mask, n_mask_hit);
                        if (flow) { /* Found */
                                *index = i;
                                return flow;
                        }
                }
        }

        return NULL;
}

/* If the the cache index is outside of the valid region, update the index
 * in case cache entry was moved up. */
static void fixup_cache_entry_index(struct mask_cache_entry *e,
                                    const struct mask_array *ma,
                                    const struct sw_flow_mask *cache)
{
        int i;

        for (i = 0; i < ma->count; i++)
                if (cache == ovsl_dereference(ma->masks[i])) {
                        e->mask_index = i;
                        return;
                }
}

/*
 * mask_cache maps flow to probable mask. This cache is not tightly
 * coupled cache, It means updates to  mask list can result in inconsistent
 * cache entry in mask cache.
 * This is per cpu cache and is divided in MC_HASH_SEGS segments.
 * In case of a hash collision the entry is hashed in next segment.
 * */
struct sw_flow *ovs_flow_tbl_lookup_stats(struct flow_table *tbl,
                                          const struct sw_flow_key *key,
                                          u32 skb_hash,
                                          u32 *n_mask_hit)
{
        struct mask_array *ma = rcu_dereference_ovsl(tbl->mask_array);
        struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
        struct mask_cache_entry *entries, *ce;
        struct sw_flow *flow;
        u32 hash = skb_hash;
        int seg;

        *n_mask_hit = 0;
        if (unlikely(!skb_hash)) {
                u32 __always_unused mask_index;

                return flow_lookup(tbl, ti, ma, key, n_mask_hit, &mask_index);
        }

        ce = NULL;
        entries = this_cpu_ptr(tbl->mask_cache);

        /* Find the cache entry 'ce' to operate on. */
        for (seg = 0; seg < MC_HASH_SEGS; seg++) {
                int index = hash & (MC_HASH_ENTRIES - 1);
                struct mask_cache_entry *e;

                e = &entries[index];
                if (e->skb_hash == skb_hash) {
                        struct sw_flow_mask *cache;
                        int i = e->mask_index;

                        if (likely(i < ma->count)) {
                                cache = rcu_dereference_ovsl(ma->masks[i]);
                                flow = masked_flow_lookup(ti, key, cache,
                                                          n_mask_hit);
                        } else if (i < ma->max) {
                                flow = NULL;
                                cache = rcu_dereference_ovsl(ma->masks[i]);
                                if (cache) {
                                        fixup_cache_entry_index(e, ma, cache);
                                        flow = masked_flow_lookup(ti, key,
                                                        cache, n_mask_hit);
                                }
                        } else {
                                flow = NULL;
                        }

                        if (flow)  /* Cache hit. */
                                return flow;

                        /* Cache miss. This is the best cache
                         * replacement candidate.  */
                        e->skb_hash = 0;
                        ce = e;
                        break;
                }

                if (!ce || e->skb_hash < ce->skb_hash)
                        ce = e;  /* A better replacement cache candidate. */

                hash >>= MC_HASH_SHIFT;
        }

        /* Cache miss, do full lookup. */
        flow = flow_lookup(tbl, ti, ma, key, n_mask_hit, &ce->mask_index);
        if (flow)
                ce->skb_hash = skb_hash;

        return flow;
}

struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *tbl,
                                    const struct sw_flow_key *key)
{
        struct table_instance *ti = rcu_dereference_ovsl(tbl->ti);
        struct mask_array *ma = rcu_dereference_ovsl(tbl->mask_array);
        u32 __always_unused n_mask_hit;
        u32 __always_unused index;

        n_mask_hit = 0;
        return flow_lookup(tbl, ti, ma, key, &n_mask_hit, &index);
}

int ovs_flow_tbl_num_masks(const struct flow_table *table)
{
        struct mask_array *ma;

        ma = rcu_dereference_ovsl(table->mask_array);
        return ma->count;
}

static struct table_instance *table_instance_expand(struct table_instance *ti)
{
        return table_instance_rehash(ti, ti->n_buckets * 2);
}

/* Remove 'mask' from the mask list, if it is not needed any more. */
static void flow_mask_remove(struct flow_table *tbl, struct sw_flow_mask *mask)
{
        if (mask) {
                /* ovs-lock is required to protect mask-refcount and
                 * mask list.
                 */
                ASSERT_OVSL();
                BUG_ON(!mask->ref_count);
                mask->ref_count--;

                if (!mask->ref_count) {
                        struct mask_array *ma;

                        ma = ovsl_dereference(tbl->mask_array);
                        /* Shrink the mask array if necessary. */
                        if (ma->max > MASK_ARRAY_SIZE_MIN * 2
                                && ma->count <= ma->max / 4) {

                                tbl_mask_array_realloc(tbl, ma->max / 2);
                                ma = ovsl_dereference(tbl->mask_array);
                        }

                        tbl_mask_array_delete_mask(ma, mask);
                        call_rcu(&mask->rcu, rcu_free_sw_flow_mask_cb);
                }
        }
}

/* Must be called with OVS mutex held. */
void ovs_flow_tbl_remove(struct flow_table *table, struct sw_flow *flow)
{
        struct table_instance *ti = ovsl_dereference(table->ti);

        BUG_ON(table->count == 0);
        hlist_del_rcu(&flow->hash_node[ti->node_ver]);
        table->count--;

        /* RCU delete the mask. 'flow->mask' is not NULLed, as it should be
         * accessible as long as the RCU read lock is held. */
        flow_mask_remove(table, flow->mask);
}

static struct sw_flow_mask *mask_alloc(void)
{
        struct sw_flow_mask *mask;

        mask = kmalloc(sizeof(*mask), GFP_KERNEL);
        if (mask)
                mask->ref_count = 1;

        return mask;
}

static bool mask_equal(const struct sw_flow_mask *a,
                       const struct sw_flow_mask *b)
{
        const u8 *a_ = (const u8 *)&a->key + a->range.start;
        const u8 *b_ = (const u8 *)&b->key + b->range.start;

        return  (a->range.end == b->range.end)
                && (a->range.start == b->range.start)
                && (memcmp(a_, b_, range_n_bytes(&a->range)) == 0);
}

static struct sw_flow_mask *flow_mask_find(const struct flow_table *tbl,
                                           const struct sw_flow_mask *mask)
{
        struct mask_array *ma;
        int i;

        ma = ovsl_dereference(tbl->mask_array);
        for (i = 0; i < ma->count; i++) {
                struct sw_flow_mask *t;

                t = ovsl_dereference(ma->masks[i]);
                if (t && mask_equal(mask, t))
                        return t;
        }

        return NULL;
}

/* Add 'mask' into the mask list, if it is not already there. */
static int flow_mask_insert(struct flow_table *tbl, struct sw_flow *flow,
                            struct sw_flow_mask *new)
{
        struct sw_flow_mask *mask;

        mask = flow_mask_find(tbl, new);
        if (!mask) {
                struct mask_array *ma;

                /* Allocate a new mask if none exsits. */
                mask = mask_alloc();
                if (!mask)
                        return -ENOMEM;

                mask->key = new->key;
                mask->range = new->range;

                /* Add mask to mask-list. */
                ma = ovsl_dereference(tbl->mask_array);
                if (ma->count >= ma->max) {
                        int err;

                        err = tbl_mask_array_realloc(tbl, ma->max +
                                                        MASK_ARRAY_SIZE_MIN);
                        if (err) {
                                kfree(mask);
                                return err;
                        }
                        ma = ovsl_dereference(tbl->mask_array);
                }

                rcu_assign_pointer(ma->masks[ma->count], mask);
                ma->count++;
        } else {
                BUG_ON(!mask->ref_count);
                mask->ref_count++;
        }

        flow->mask = mask;
        return 0;
}

/* Must be called with OVS mutex held. */
int ovs_flow_tbl_insert(struct flow_table *table, struct sw_flow *flow,
                        struct sw_flow_mask *mask)
{
        struct table_instance *new_ti = NULL;
        struct table_instance *ti;
        int err;

        err = flow_mask_insert(table, flow, mask);
        if (err)
                return err;

        flow->hash = flow_hash(&flow->key, flow->mask->range.start,
                        flow->mask->range.end);
        ti = ovsl_dereference(table->ti);
        table_instance_insert(ti, flow);
        table->count++;

        /* Expand table, if necessary, to make room. */
        if (table->count > ti->n_buckets)
                new_ti = table_instance_expand(ti);
        else if (time_after(jiffies, table->last_rehash + REHASH_INTERVAL))
                new_ti = table_instance_rehash(ti, ti->n_buckets);

        if (new_ti) {
                rcu_assign_pointer(table->ti, new_ti);
                table_instance_destroy(ti, true);
                table->last_rehash = jiffies;
        }
        return 0;
}

/* Initializes the flow module.
 * Returns zero if successful or a negative error code. */
int ovs_flow_init(void)
{
        BUILD_BUG_ON(__alignof__(struct sw_flow_key) % __alignof__(long));
        BUILD_BUG_ON(sizeof(struct sw_flow_key) % sizeof(long));

        flow_cache = kmem_cache_create("sw_flow", sizeof(struct sw_flow)
                                       + (num_possible_nodes()
                                          * sizeof(struct flow_stats *)),
                                       0, 0, NULL);
        if (flow_cache == NULL)
                return -ENOMEM;

        flow_stats_cache
                = kmem_cache_create("sw_flow_stats", sizeof(struct flow_stats),
                                    0, SLAB_HWCACHE_ALIGN, NULL);
        if (flow_stats_cache == NULL) {
                kmem_cache_destroy(flow_cache);
                flow_cache = NULL;
                return -ENOMEM;
        }

        return 0;
}

/* Uninitializes the flow module. */
void ovs_flow_exit(void)
{
        kmem_cache_destroy(flow_stats_cache);
        kmem_cache_destroy(flow_cache);
}