Fixed according to comments from Jesse.
v1-v2:
        - uses genl_mutex to protect flow-hash-table.
        - adds REHASH cmd to dp_datapath_genl_ops so that we can
          rehash flow-table holding genl_mutex.

--8<--------------------------cut here-------------------------->8--

Following patch introduces a timer based event to rehash flow-hash
table. It makes finding collisions difficult to for an attacker.

Suggested-by: Herbert Xu <herb...@gondor.apana.org.au>
Signed-off-by: Pravin B Shelar <pshe...@nicira.com>
---
 datapath/datapath.c                             |   84 +++++++++-
 datapath/flow.c                                 |   80 ++++++---
 datapath/flow.h                                 |    6 +-
 datapath/linux/Modules.mk                       |    3 +-
 datapath/linux/compat/include/linux/workqueue.h |   76 ++++++---
 datapath/linux/compat/workqueue.c               |  217 +++++++++++++++++++++++
 include/linux/openvswitch.h                     |    3 +-
 7 files changed, 416 insertions(+), 53 deletions(-)
 create mode 100644 datapath/linux/compat/workqueue.c

diff --git a/datapath/datapath.c b/datapath/datapath.c
index c86c20b..50fd00e 100644
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -63,6 +63,11 @@
 #error Kernels before 2.6.18 or after 3.2 are not supported by this version of 
Open vSwitch.
 #endif
 
+#define REHASH_FLOW_INTERVAL (10 * 60 * HZ)
+
+static void rehash_flow_table(struct work_struct *work);
+static DECLARE_DELAYED_WORK(rehash_flow_wq, rehash_flow_table);
+
 int (*ovs_dp_ioctl_hook)(struct net_device *dev, struct ifreq *rq, int cmd);
 EXPORT_SYMBOL(ovs_dp_ioctl_hook);
 
@@ -1559,6 +1564,31 @@ static int ovs_dp_cmd_dump(struct sk_buff *skb, struct 
netlink_callback *cb)
        return skb->len;
 }
 
+static void __rehash_flow_table(void)
+{
+       struct datapath *dp;
+
+       list_for_each_entry(dp, &dps, list_node) {
+               struct flow_table *old_table = genl_dereference(dp->table);
+               struct flow_table *new_table;
+
+               new_table = ovs_flow_tbl_rehash(old_table);
+
+               if (!IS_ERR(new_table)) {
+                       rcu_assign_pointer(dp->table, new_table);
+                       ovs_flow_tbl_deferred_destroy(old_table);
+               }
+       }
+}
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,35)
+static int ovs_dp_cmd_rehash(struct sk_buff *skb, struct genl_info *info)
+{
+       __rehash_flow_table();
+       return 0;
+}
+#endif
+
 static struct genl_ops dp_datapath_genl_ops[] = {
        { .cmd = OVS_DP_CMD_NEW,
          .flags = GENL_ADMIN_PERM, /* Requires CAP_NET_ADMIN privilege. */
@@ -1581,6 +1611,13 @@ static struct genl_ops dp_datapath_genl_ops[] = {
          .policy = datapath_policy,
          .doit = ovs_dp_cmd_set,
        },
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,35)
+       { .cmd = OVS_DP_CMD_REHASH,
+         .flags = 0,
+         .policy = datapath_policy,
+         .doit = ovs_dp_cmd_rehash,
+       },
+#endif
 };
 
 static const struct nla_policy vport_policy[OVS_VPORT_ATTR_MAX + 1] = {
@@ -2039,6 +2076,40 @@ error:
        return err;
 }
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,35)
+static void rehash_flow_table(struct work_struct *work)
+{
+       struct nlmsghdr *nlh;
+       struct ovs_header *hdr;
+       struct sk_buff *skb;
+
+       skb = genlmsg_new(NLMSG_DEFAULT_SIZE, GFP_ATOMIC);
+       if (!skb)
+               goto out;
+
+       hdr = genlmsg_put(skb, 0, 0, &dp_datapath_genl_family,
+                         0, OVS_DP_CMD_REHASH);
+       if (!hdr) {
+               kfree_skb(skb);
+               return;
+       }
+
+       nlh = nlmsg_hdr(skb);
+       nlh->nlmsg_flags |= NLM_F_REQUEST;
+       genlmsg_unicast(&init_net, skb, 0);
+out:
+       schedule_delayed_work(&rehash_flow_wq, REHASH_FLOW_INTERVAL);
+}
+#else
+static void rehash_flow_table(struct work_struct *work)
+{
+       genl_lock();
+       __rehash_flow_table();
+       genl_unlock();
+       schedule_delayed_work(&rehash_flow_wq, REHASH_FLOW_INTERVAL);
+}
+#endif
+
 static int __init dp_init(void)
 {
        struct sk_buff *dummy_skb;
@@ -2049,10 +2120,14 @@ static int __init dp_init(void)
        pr_info("Open vSwitch switching datapath %s, built "__DATE__" 
"__TIME__"\n",
                VERSION BUILDNR);
 
-       err = ovs_tnl_init();
+       err = ovs_workqueues_init();
        if (err)
                goto error;
 
+       err = ovs_tnl_init();
+       if (err)
+               goto error_wq;
+
        err = ovs_flow_init();
        if (err)
                goto error_tnl_exit;
@@ -2069,8 +2144,9 @@ static int __init dp_init(void)
        if (err < 0)
                goto error_unreg_notifier;
 
-       return 0;
+       schedule_delayed_work(&rehash_flow_wq, REHASH_FLOW_INTERVAL);
 
+       return 0;
 error_unreg_notifier:
        unregister_netdevice_notifier(&ovs_dp_device_notifier);
 error_vport_exit:
@@ -2079,6 +2155,8 @@ error_flow_exit:
        ovs_flow_exit();
 error_tnl_exit:
        ovs_tnl_exit();
+error_wq:
+       ovs_workqueues_exit();
 error:
        return err;
 }
@@ -2086,6 +2164,8 @@ error:
 static void dp_cleanup(void)
 {
        rcu_barrier();
+       cancel_delayed_work_sync(&rehash_flow_wq);
+       ovs_workqueues_exit();
        dp_unregister_genl(ARRAY_SIZE(dp_genl_families));
        unregister_netdevice_notifier(&ovs_dp_device_notifier);
        ovs_vport_exit();
diff --git a/datapath/flow.c b/datapath/flow.c
index 78dea3a..bb9533a 100644
--- a/datapath/flow.c
+++ b/datapath/flow.c
@@ -47,7 +47,6 @@
 #include "vlan.h"
 
 static struct kmem_cache *flow_cache;
-static unsigned int hash_seed __read_mostly;
 
 static int check_header(struct sk_buff *skb, int len)
 {
@@ -238,6 +237,7 @@ struct sw_flow *ovs_flow_alloc(void)
 
 static struct hlist_head *find_bucket(struct flow_table *table, u32 hash)
 {
+       hash = jhash_1word(hash, table->hash_seed);
        return flex_array_get(table->buckets,
                                (hash & (table->n_buckets - 1)));
 }
@@ -285,6 +285,9 @@ struct flow_table *ovs_flow_tbl_alloc(int new_size)
        }
        table->n_buckets = new_size;
        table->count = 0;
+       table->node_ver = 0;
+       table->keep_flows = false;
+       get_random_bytes(&table->hash_seed, sizeof(u32));
 
        return table;
 }
@@ -302,17 +305,22 @@ void ovs_flow_tbl_destroy(struct flow_table *table)
        if (!table)
                return;
 
+       if (table->keep_flows)
+               goto skip_flows;
+
        for (i = 0; i < table->n_buckets; i++) {
                struct sw_flow *flow;
                struct hlist_head *head = flex_array_get(table->buckets, i);
                struct hlist_node *node, *n;
+               int ver = table->node_ver;
 
-               hlist_for_each_entry_safe(flow, node, n, head, hash_node) {
-                       hlist_del_init_rcu(&flow->hash_node);
+               hlist_for_each_entry_safe(flow, node, n, head, hash_node[ver]) {
+                       hlist_del_rcu(&flow->hash_node[ver]);
                        flow_free(flow);
                }
        }
 
+skip_flows:
        free_buckets(table->buckets);
        kfree(table);
 }
@@ -337,12 +345,14 @@ struct sw_flow *ovs_flow_tbl_next(struct flow_table 
*table, u32 *bucket, u32 *la
        struct sw_flow *flow;
        struct hlist_head *head;
        struct hlist_node *n;
+       int ver;
        int i;
 
+       ver = table->node_ver;
        while (*bucket < table->n_buckets) {
                i = 0;
                head = flex_array_get(table->buckets, *bucket);
-               hlist_for_each_entry_rcu(flow, n, head, hash_node) {
+               hlist_for_each_entry_rcu(flow, n, head, hash_node[ver]) {
                        if (i < *last) {
                                i++;
                                continue;
@@ -357,32 +367,52 @@ struct sw_flow *ovs_flow_tbl_next(struct flow_table 
*table, u32 *bucket, u32 *la
        return NULL;
 }
 
-struct flow_table *ovs_flow_tbl_expand(struct flow_table *table)
+static void flow_table_copy_flows(struct flow_table *old, struct flow_table 
*new)
 {
-       struct flow_table *new_table;
-       int n_buckets = table->n_buckets * 2;
+       int old_ver;
        int i;
 
-       new_table = ovs_flow_tbl_alloc(n_buckets);
-       if (!new_table)
-               return ERR_PTR(-ENOMEM);
+       old_ver = old->node_ver;
+       new->node_ver = !old_ver;
 
-       for (i = 0; i < table->n_buckets; i++) {
+       /* Insert in new table. */
+       for (i = 0; i < old->n_buckets; i++) {
                struct sw_flow *flow;
                struct hlist_head *head;
-               struct hlist_node *n, *pos;
+               struct hlist_node *n;
 
-               head = flex_array_get(table->buckets, i);
+               head = flex_array_get(old->buckets, i);
 
-               hlist_for_each_entry_safe(flow, n, pos, head, hash_node) {
-                       hlist_del_init_rcu(&flow->hash_node);
-                       ovs_flow_tbl_insert(new_table, flow);
-               }
+               hlist_for_each_entry(flow, n, head, hash_node[old_ver])
+                       ovs_flow_tbl_insert(new, flow);
        }
+       old->keep_flows = true;
+}
+
+static struct flow_table *__flow_tbl_rehash(struct flow_table *table,
+                                           int n_buckets)
+{
+       struct flow_table *new_table;
+
+       new_table = ovs_flow_tbl_alloc(n_buckets);
+       if (!new_table)
+               return ERR_PTR(-ENOMEM);
+
+       flow_table_copy_flows(table, new_table);
 
        return new_table;
 }
 
+struct flow_table *ovs_flow_tbl_rehash(struct flow_table *table)
+{
+       return __flow_tbl_rehash(table, table->n_buckets);
+}
+
+struct flow_table *ovs_flow_tbl_expand(struct flow_table *table)
+{
+       return __flow_tbl_rehash(table, table->n_buckets * 2);
+}
+
 /* RCU callback used by ovs_flow_deferred_free. */
 static void rcu_free_flow_callback(struct rcu_head *rcu)
 {
@@ -761,7 +791,7 @@ out:
 
 u32 ovs_flow_hash(const struct sw_flow_key *key, int key_len)
 {
-       return jhash2((u32 *)key, DIV_ROUND_UP(key_len, sizeof(u32)), 
hash_seed);
+       return jhash2((u32 *)key, DIV_ROUND_UP(key_len, sizeof(u32)), 0);
 }
 
 struct sw_flow *ovs_flow_tbl_lookup(struct flow_table *table,
@@ -775,7 +805,7 @@ struct sw_flow *ovs_flow_tbl_lookup(struct flow_table 
*table,
        hash = ovs_flow_hash(key, key_len);
 
        head = find_bucket(table, hash);
-       hlist_for_each_entry_rcu(flow, n, head, hash_node) {
+       hlist_for_each_entry_rcu(flow, n, head, hash_node[table->node_ver]) {
 
                if (flow->hash == hash &&
                    !memcmp(&flow->key, key, key_len)) {
@@ -790,17 +820,15 @@ void ovs_flow_tbl_insert(struct flow_table *table, struct 
sw_flow *flow)
        struct hlist_head *head;
 
        head = find_bucket(table, flow->hash);
-       hlist_add_head_rcu(&flow->hash_node, head);
+       hlist_add_head_rcu(&flow->hash_node[table->node_ver], head);
        table->count++;
 }
 
 void ovs_flow_tbl_remove(struct flow_table *table, struct sw_flow *flow)
 {
-       if (!hlist_unhashed(&flow->hash_node)) {
-               hlist_del_init_rcu(&flow->hash_node);
-               table->count--;
-               BUG_ON(table->count < 0);
-       }
+       hlist_del_rcu(&flow->hash_node[table->node_ver]);
+       table->count--;
+       BUG_ON(table->count < 0);
 }
 
 /* The size of the argument for each %OVS_KEY_ATTR_* Netlink attribute.  */
@@ -1345,8 +1373,6 @@ int ovs_flow_init(void)
        if (flow_cache == NULL)
                return -ENOMEM;
 
-       get_random_bytes(&hash_seed, sizeof(hash_seed));
-
        return 0;
 }
 
diff --git a/datapath/flow.h b/datapath/flow.h
index 36e738d..1a91d68 100644
--- a/datapath/flow.h
+++ b/datapath/flow.h
@@ -96,7 +96,7 @@ struct sw_flow_key {
 
 struct sw_flow {
        struct rcu_head rcu;
-       struct hlist_node  hash_node;
+       struct hlist_node  hash_node[2];
        u32 hash;
 
        struct sw_flow_key key;
@@ -174,6 +174,9 @@ struct flow_table {
        struct flex_array *buckets;
        unsigned int count, n_buckets;
        struct rcu_head rcu;
+       int node_ver;
+       u32 hash_seed;
+       bool keep_flows;
 };
 
 static inline int ovs_flow_tbl_count(struct flow_table *table)
@@ -192,6 +195,7 @@ void ovs_flow_tbl_destroy(struct flow_table *table);
 void ovs_flow_tbl_deferred_destroy(struct flow_table *table);
 struct flow_table *ovs_flow_tbl_alloc(int new_size);
 struct flow_table *ovs_flow_tbl_expand(struct flow_table *table);
+struct flow_table *ovs_flow_tbl_rehash(struct flow_table *table);
 void ovs_flow_tbl_insert(struct flow_table *table, struct sw_flow *flow);
 void ovs_flow_tbl_remove(struct flow_table *table, struct sw_flow *flow);
 u32 ovs_flow_hash(const struct sw_flow_key *key, int key_len);
diff --git a/datapath/linux/Modules.mk b/datapath/linux/Modules.mk
index fdd952e..b3d8078 100644
--- a/datapath/linux/Modules.mk
+++ b/datapath/linux/Modules.mk
@@ -9,7 +9,8 @@ openvswitch_sources += \
        linux/compat/netdevice.c \
        linux/compat/reciprocal_div.c \
        linux/compat/skbuff-openvswitch.c \
-       linux/compat/time.c
+       linux/compat/time.c     \
+       linux/compat/workqueue.c
 openvswitch_headers += \
        linux/compat/include/linux/compiler.h \
        linux/compat/include/linux/compiler-gcc.h \
diff --git a/datapath/linux/compat/include/linux/workqueue.h 
b/datapath/linux/compat/include/linux/workqueue.h
index 01c6345..2754f60 100644
--- a/datapath/linux/compat/include/linux/workqueue.h
+++ b/datapath/linux/compat/include/linux/workqueue.h
@@ -1,41 +1,75 @@
 #ifndef __LINUX_WORKQUEUE_WRAPPER_H
 #define __LINUX_WORKQUEUE_WRAPPER_H 1
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,23)
 #include_next <linux/workqueue.h>
+static inline int __init ovs_workqueues_init(void) { return 0; }
+static inline void  ovs_workqueues_exit(void) {}
+
+#else
+#include <linux/timer.h>
+
+int __init ovs_workqueues_init(void);
+void ovs_workqueues_exit(void);
 
-#include <linux/version.h>
-#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23)
 
 /* Older kernels have an implementation of work queues with some very bad
  * characteristics when trying to cancel work (potential deadlocks, use after
- * free, etc.  Here we directly use timers instead for delayed work.  It's not
- * optimal but it is better than the alternative.  Note that work queues
- * normally run in process context but this will cause them to operate in
- * softirq context.
+ * free, etc.  Therefore we implement simple ovs specific work queue using
+ * single worker thread. work-queue API are kept similar for compatibility.
  */
 
-#include <linux/timer.h>
+struct workqueue_struct;
 
-#undef DECLARE_DELAYED_WORK
-#define DECLARE_DELAYED_WORK(n, f) \
-       struct timer_list n = TIMER_INITIALIZER((void (*)(unsigned long))f, 0, 
0)
+struct work_struct;
+typedef void (*work_func_t)(struct work_struct *work);
 
-#define schedule_delayed_work rpl_schedule_delayed_work
-static inline int schedule_delayed_work(struct timer_list *timer, unsigned 
long delay)
-{
-       if (timer_pending(timer))
-               return 0;
+#define work_data_bits(work) ((unsigned long *)(&(work)->data))
+
+struct work_struct {
+#define WORK_STRUCT_PENDING 0           /* T if work item pending execution */
+       atomic_long_t data;
+       struct list_head entry;
+       work_func_t func;
+};
+
+#define WORK_DATA_INIT()        ATOMIC_LONG_INIT(0)
+
+#define work_clear_pending(work)                               \
+       clear_bit(WORK_STRUCT_PENDING, work_data_bits(work))
 
-       mod_timer(timer, jiffies + delay);
-       return 1;
+struct delayed_work {
+       struct work_struct work;
+       struct timer_list timer;
+};
+
+#define __WORK_INITIALIZER(n, f) {                             \
+       .data = WORK_DATA_INIT(),                               \
+       .entry  = { &(n).entry, &(n).entry },                   \
+       .func = (f),                                            \
 }
 
-#define cancel_delayed_work_sync rpl_cancel_delayed_work_sync
-static inline int cancel_delayed_work_sync(struct timer_list *timer)
-{
-       return del_timer_sync(timer);
+#define __DELAYED_WORK_INITIALIZER(n, f) {                     \
+       .work = __WORK_INITIALIZER((n).work, (f)),              \
+       .timer = TIMER_INITIALIZER(NULL, 0, 0),                 \
 }
 
+#define DECLARE_DELAYED_WORK(n, f)                             \
+       struct delayed_work n = __DELAYED_WORK_INITIALIZER(n, f)
+
+#define schedule_delayed_work rpl_schedule_delayed_work
+int schedule_delayed_work(struct delayed_work *dwork, unsigned long delay);
+
+#define cancel_delayed_work_sync rpl_cancel_delayed_work_sync
+int cancel_delayed_work_sync(struct delayed_work *dwork);
+
+#define INIT_WORK(_work, _func)                                        \
+       do {                                                    \
+               (_work)->data = (atomic_long_t) WORK_DATA_INIT();               
\
+               INIT_LIST_HEAD(&(_work)->entry);                \
+               (_work)->func = (_func);                        \
+       } while (0)
+
 #endif /* kernel version < 2.6.23 */
 
 #endif
diff --git a/datapath/linux/compat/workqueue.c 
b/datapath/linux/compat/workqueue.c
new file mode 100644
index 0000000..f74a08f
--- /dev/null
+++ b/datapath/linux/compat/workqueue.c
@@ -0,0 +1,217 @@
+/*
+ * Derived from the kernel/workqueue.c
+ *
+ * This is the generic async execution mechanism.  Work items as are
+ * executed in process context.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/signal.h>
+#include <linux/completion.h>
+#include <linux/workqueue.h>
+#include <linux/slab.h>
+#include <linux/cpu.h>
+#include <linux/notifier.h>
+#include <linux/kthread.h>
+#include <linux/hardirq.h>
+#include <linux/mempolicy.h>
+#include <linux/kallsyms.h>
+#include <linux/debug_locks.h>
+#include <linux/lockdep.h>
+#include <linux/idr.h>
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23)
+
+static spinlock_t wq_lock;
+static struct list_head workq;
+static wait_queue_head_t more_work;
+static struct task_struct *workq_thread;
+static struct work_struct *current_work;
+
+static void queue_work(struct work_struct *work)
+{
+       unsigned long flags;
+
+       spin_lock_irqsave(&wq_lock, flags);
+       list_add_tail(&work->entry, &workq);
+       wake_up(&more_work);
+       spin_unlock_irqrestore(&wq_lock, flags);
+}
+
+static void _delayed_work_timer_fn(unsigned long __data)
+{
+       struct delayed_work *dwork = (struct delayed_work *)__data;
+       queue_work(&dwork->work);
+}
+
+static void __queue_delayed_work(struct delayed_work *dwork,
+               unsigned long delay)
+{
+       struct timer_list *timer = &dwork->timer;
+       struct work_struct *work = &dwork->work;
+
+       BUG_ON(timer_pending(timer));
+       BUG_ON(!list_empty(&work->entry));
+
+       timer->expires = jiffies + delay;
+       timer->data = (unsigned long)dwork;
+       timer->function = _delayed_work_timer_fn;
+
+       add_timer(timer);
+}
+
+int schedule_delayed_work(struct delayed_work *dwork, unsigned long delay)
+{
+       if (test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(&dwork->work)))
+               return 0;
+
+       if (delay == 0)
+               queue_work(&dwork->work);
+       else
+               __queue_delayed_work(dwork, delay);
+
+       return 1;
+}
+
+struct wq_barrier {
+       struct work_struct      work;
+       struct completion       done;
+};
+
+static void wq_barrier_func(struct work_struct *work)
+{
+       struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
+       complete(&barr->done);
+}
+
+static void workqueue_barrier(struct work_struct *work)
+{
+       bool need_barrier;
+       struct wq_barrier barr;
+
+       spin_lock_irq(&wq_lock);
+       if (current_work != work)
+               need_barrier = false;
+       else {
+               INIT_WORK(&barr.work, wq_barrier_func);
+               init_completion(&barr.done);
+               list_add(&work->entry, &workq);
+               wake_up(&more_work);
+               need_barrier = true;
+       }
+       spin_unlock_irq(&wq_lock);
+
+       if (need_barrier)
+               wait_for_completion(&barr.done);
+}
+
+static int try_to_grab_pending(struct work_struct *work)
+{
+       int ret;
+
+       BUG_ON(in_interrupt());
+
+       if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work)))
+               return 0;
+
+       spin_lock_irq(&wq_lock);
+       if (!list_empty(&work->entry)) {
+               list_del_init(&work->entry);
+               ret = 0;
+       } else
+               /* Already executed, retry. */
+               ret = -1;
+       spin_unlock_irq(&wq_lock);
+
+       return ret;
+}
+
+static int __cancel_work_timer(struct work_struct *work,
+                              struct timer_list *timer)
+{
+       int ret;
+
+       for (;;) {
+               ret = (timer && likely(del_timer(timer)));
+               if (ret) /* Was active timer, return true. */
+                       break;
+
+               /* Inactive timer case */
+               ret = try_to_grab_pending(work);
+               if (!ret)
+                       break;
+       }
+       workqueue_barrier(work);
+       work_clear_pending(work);
+       return ret;
+}
+
+int cancel_delayed_work_sync(struct delayed_work *dwork)
+{
+       return __cancel_work_timer(&dwork->work, &dwork->timer);
+}
+
+static void run_workqueue(void)
+{
+       spin_lock_irq(&wq_lock);
+       while (!list_empty(&workq)) {
+               struct work_struct *work = list_entry(workq.next,
+                               struct work_struct, entry);
+
+               work_func_t f = work->func;
+               list_del_init(workq.next);
+               current_work = work;
+               spin_unlock_irq(&wq_lock);
+
+               work_clear_pending(work);
+               f(work);
+
+               BUG_ON(in_interrupt());
+               spin_lock_irq(&wq_lock);
+               current_work = NULL;
+       }
+       spin_unlock_irq(&wq_lock);
+}
+
+static int worker_thread(void *dummy)
+{
+       DEFINE_WAIT(wait);
+
+       for (;;) {
+               prepare_to_wait(&more_work, &wait, TASK_INTERRUPTIBLE);
+               if (!kthread_should_stop() && list_empty(&workq))
+                       schedule();
+               finish_wait(&more_work, &wait);
+
+               if (kthread_should_stop())
+                       break;
+
+               run_workqueue();
+       }
+
+       return 0;
+}
+
+int __init ovs_workqueues_init(void)
+{
+       spin_lock_init(&wq_lock);
+       INIT_LIST_HEAD(&workq);
+       init_waitqueue_head(&more_work);
+
+       workq_thread = kthread_create(worker_thread, NULL, "ovs_workq");
+       if (IS_ERR(workq_thread))
+               return PTR_ERR(workq_thread);
+
+       wake_up_process(workq_thread);
+       return 0;
+}
+
+void  ovs_workqueues_exit(void)
+{
+       BUG_ON(!list_empty(&workq));
+       kthread_stop(workq_thread);
+}
+#endif
diff --git a/include/linux/openvswitch.h b/include/linux/openvswitch.h
index 0578b5f..21f1060 100644
--- a/include/linux/openvswitch.h
+++ b/include/linux/openvswitch.h
@@ -66,7 +66,8 @@ enum ovs_datapath_cmd {
        OVS_DP_CMD_NEW,
        OVS_DP_CMD_DEL,
        OVS_DP_CMD_GET,
-       OVS_DP_CMD_SET
+       OVS_DP_CMD_SET,
+       OVS_DP_CMD_REHASH,
 };
 
 /**
-- 
1.7.1

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