netfilter: revised locking for x_tables

The x_tables are organized with a table structure and a per-cpu copies
of the counters and rules. On older kernels there was a reader/writer 
lock per table which was a performance bottleneck. In 2.6.30-rc, this
was converted to use RCU and the counters/rules which solved the performance
problems for do_table but made replacing rules much slower because of
the necessary RCU grace period.

This version uses a per-cpu set of spinlocks and counters to allow to
table processing to proceed without the cache thrashing of a global
reader lock and keeps the same performance for table updates.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 204 insertions, 296 deletions

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 7b1a652066c0..1b2e43502ef7 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -354,9 +354,6 @@ struct xt_table
         /* What hooks you will enter on */
         unsigned int valid_hooks;
 
-        /* Lock for the curtain */
-        struct mutex lock;
-
         /* Man behind the curtain... */
         struct xt_table_info *private;
 
@@ -434,8 +431,74 @@ extern void xt_proto_fini(struct net *net, u_int8_t af);
 
 extern struct xt_table_info *xt_alloc_table_info(unsigned int size);
 extern void xt_free_table_info(struct xt_table_info *info);
-extern void xt_table_entry_swap_rcu(struct xt_table_info *old,
-                                    struct xt_table_info *new);
+
+/*
+ * Per-CPU spinlock associated with per-cpu table entries, and
+ * with a counter for the "reading" side that allows a recursive
+ * reader to avoid taking the lock and deadlocking.
+ *
+ * "reading" is used by ip/arp/ip6 tables rule processing which runs per-cpu.
+ * It needs to ensure that the rules are not being changed while the packet
+ * is being processed. In some cases, the read lock will be acquired
+ * twice on the same CPU; this is okay because of the count.
+ *
+ * "writing" is used when reading counters.
+ *  During replace any readers that are using the old tables have to complete
+ *  before freeing the old table. This is handled by the write locking
+ *  necessary for reading the counters.
+ */
+struct xt_info_lock {
+        spinlock_t lock;
+        unsigned char readers;
+};
+DECLARE_PER_CPU(struct xt_info_lock, xt_info_locks);
+
+/*
+ * Note: we need to ensure that preemption is disabled before acquiring
+ * the per-cpu-variable, so we do it as a two step process rather than
+ * using "spin_lock_bh()".
+ *
+ * We _also_ need to disable bottom half processing before updating our
+ * nesting count, to make sure that the only kind of re-entrancy is this
+ * code being called by itself: since the count+lock is not an atomic
+ * operation, we can allow no races.
+ *
+ * _Only_ that special combination of being per-cpu and never getting
+ * re-entered asynchronously means that the count is safe.
+ */
+static inline void xt_info_rdlock_bh(void)
+{
+        struct xt_info_lock *lock;
+
+        local_bh_disable();
+        lock = &__get_cpu_var(xt_info_locks);
+        if (!lock->readers++)
+                spin_lock(&lock->lock);
+}
+
+static inline void xt_info_rdunlock_bh(void)
+{
+        struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);
+
+        if (!--lock->readers)
+                spin_unlock(&lock->lock);
+        local_bh_enable();
+}
+
+/*
+ * The "writer" side needs to get exclusive access to the lock,
+ * regardless of readers.  This must be called with bottom half
+ * processing (and thus also preemption) disabled.
+ */
+static inline void xt_info_wrlock(unsigned int cpu)
+{
+        spin_lock(&per_cpu(xt_info_locks, cpu).lock);
+}
+
+static inline void xt_info_wrunlock(unsigned int cpu)
+{
+        spin_unlock(&per_cpu(xt_info_locks, cpu).lock);
+}
 
 /*
  * This helper is performance critical and must be inlined
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 5ba533d234db..831fe1879dc0 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -253,9 +253,9 @@ unsigned int arpt_do_table(struct sk_buff *skb,
         indev = in ? in->name : nulldevname;
         outdev = out ? out->name : nulldevname;
 
-        rcu_read_lock_bh();
-        private = rcu_dereference(table->private);
-        table_base = rcu_dereference(private->entries[smp_processor_id()]);
+        xt_info_rdlock_bh();
+        private = table->private;
+        table_base = private->entries[smp_processor_id()];
 
         e = get_entry(table_base, private->hook_entry[hook]);
         back = get_entry(table_base, private->underflow[hook]);
@@ -273,6 +273,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
 
                         hdr_len = sizeof(*arp) + (2 * sizeof(struct in_addr)) +
                                 (2 * skb->dev->addr_len);
+
                         ADD_COUNTER(e->counters, hdr_len, 1);
 
                         t = arpt_get_target(e);
@@ -328,8 +329,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
                         e = (void *)e + e->next_offset;
                 }
         } while (!hotdrop);
-
-        rcu_read_unlock_bh();
+        xt_info_rdunlock_bh();
 
         if (hotdrop)
                 return NF_DROP;
@@ -711,9 +711,12 @@ static void get_counters(const struct xt_table_info *t,
         /* Instead of clearing (by a previous call to memset())
          * the counters and using adds, we set the counters
          * with data used by 'current' CPU
-         * We dont care about preemption here.
+         *
+         * Bottom half has to be disabled to prevent deadlock
+         * if new softirq were to run and call ipt_do_table
          */
-        curcpu = raw_smp_processor_id();
+        local_bh_disable();
+        curcpu = smp_processor_id();
 
         i = 0;
         ARPT_ENTRY_ITERATE(t->entries[curcpu],
@@ -726,73 +729,22 @@ static void get_counters(const struct xt_table_info *t,
                 if (cpu == curcpu)
                         continue;
                 i = 0;
+                xt_info_wrlock(cpu);
                 ARPT_ENTRY_ITERATE(t->entries[cpu],
                                    t->size,
                                    add_entry_to_counter,
                                    counters,
                                    &i);
+                xt_info_wrunlock(cpu);
         }
-}
-
-
-/* We're lazy, and add to the first CPU; overflow works its fey magic
- * and everything is OK. */
-static int
-add_counter_to_entry(struct arpt_entry *e,
-                     const struct xt_counters addme[],
-                     unsigned int *i)
-{
-        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
-
-        (*i)++;
-        return 0;
-}
-
-/* Take values from counters and add them back onto the current cpu */
-static void put_counters(struct xt_table_info *t,
-                         const struct xt_counters counters[])
-{
-        unsigned int i, cpu;
-
-        local_bh_disable();
-        cpu = smp_processor_id();
-        i = 0;
-        ARPT_ENTRY_ITERATE(t->entries[cpu],
-                          t->size,
-                          add_counter_to_entry,
-                          counters,
-                          &i);
         local_bh_enable();
 }
 
-static inline int
-zero_entry_counter(struct arpt_entry *e, void *arg)
-{
-        e->counters.bcnt = 0;
-        e->counters.pcnt = 0;
-        return 0;
-}
-
-static void
-clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
-{
-        unsigned int cpu;
-        const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
-
-        memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
-        for_each_possible_cpu(cpu) {
-                memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
-                ARPT_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
-                                  zero_entry_counter, NULL);
-        }
-}
-
 static struct xt_counters *alloc_counters(struct xt_table *table)
 {
         unsigned int countersize;
         struct xt_counters *counters;
         struct xt_table_info *private = table->private;
-        struct xt_table_info *info;
 
         /* We need atomic snapshot of counters: rest doesn't change
          * (other than comefrom, which userspace doesn't care
@@ -802,30 +754,11 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
         counters = vmalloc_node(countersize, numa_node_id());
 
         if (counters == NULL)
-                goto nomem;
-
-        info = xt_alloc_table_info(private->size);
-        if (!info)
-                goto free_counters;
-
-        clone_counters(info, private);
-
-        mutex_lock(&table->lock);
-        xt_table_entry_swap_rcu(private, info);
-        synchronize_net();      /* Wait until smoke has cleared */
+                return ERR_PTR(-ENOMEM);
 
-        get_counters(info, counters);
-        put_counters(private, counters);
-        mutex_unlock(&table->lock);
-
-        xt_free_table_info(info);
+        get_counters(private, counters);
 
         return counters;
-
- free_counters:
-        vfree(counters);
- nomem:
-        return ERR_PTR(-ENOMEM);
 }
 
 static int copy_entries_to_user(unsigned int total_size,
@@ -1094,8 +1027,9 @@ static int __do_replace(struct net *net, const char *name,
             (newinfo->number <= oldinfo->initial_entries))
                 module_put(t->me);
 
-        /* Get the old counters. */
+        /* Get the old counters, and synchronize with replace */
         get_counters(oldinfo, counters);
+
         /* Decrease module usage counts and free resource */
         loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
         ARPT_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
@@ -1165,10 +1099,23 @@ static int do_replace(struct net *net, void __user *user, unsigned int len)
         return ret;
 }
 
+/* We're lazy, and add to the first CPU; overflow works its fey magic
+ * and everything is OK. */
+static int
+add_counter_to_entry(struct arpt_entry *e,
+                     const struct xt_counters addme[],
+                     unsigned int *i)
+{
+        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
+
+        (*i)++;
+        return 0;
+}
+
 static int do_add_counters(struct net *net, void __user *user, unsigned int len,
                            int compat)
 {
-        unsigned int i;
+        unsigned int i, curcpu;
         struct xt_counters_info tmp;
         struct xt_counters *paddc;
         unsigned int num_counters;
@@ -1224,26 +1171,26 @@ static int do_add_counters(struct net *net, void __user *user, unsigned int len,
                 goto free;
         }
 
-        mutex_lock(&t->lock);
+        local_bh_disable();
         private = t->private;
         if (private->number != num_counters) {
                 ret = -EINVAL;
                 goto unlock_up_free;
         }
 
-        preempt_disable();
         i = 0;
         /* Choose the copy that is on our node */
-        loc_cpu_entry = private->entries[smp_processor_id()];
+        curcpu = smp_processor_id();
+        loc_cpu_entry = private->entries[curcpu];
+        xt_info_wrlock(curcpu);
         ARPT_ENTRY_ITERATE(loc_cpu_entry,
                            private->size,
                            add_counter_to_entry,
                            paddc,
                            &i);
-        preempt_enable();
+        xt_info_wrunlock(curcpu);
  unlock_up_free:
-        mutex_unlock(&t->lock);
-
+        local_bh_enable();
         xt_table_unlock(t);
         module_put(t->me);
  free:
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 810c0b62c7d4..2ec8d7290c40 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -338,10 +338,9 @@ ipt_do_table(struct sk_buff *skb,
         tgpar.hooknum = hook;
 
         IP_NF_ASSERT(table->valid_hooks & (1 << hook));
-
-        rcu_read_lock_bh();
-        private = rcu_dereference(table->private);
-        table_base = rcu_dereference(private->entries[smp_processor_id()]);
+        xt_info_rdlock_bh();
+        private = table->private;
+        table_base = private->entries[smp_processor_id()];
 
         e = get_entry(table_base, private->hook_entry[hook]);
 
@@ -436,8 +435,7 @@ ipt_do_table(struct sk_buff *skb,
                         e = (void *)e + e->next_offset;
                 }
         } while (!hotdrop);
-
-        rcu_read_unlock_bh();
+        xt_info_rdunlock_bh();
 
 #ifdef DEBUG_ALLOW_ALL
         return NF_ACCEPT;
@@ -896,10 +894,13 @@ get_counters(const struct xt_table_info *t,
 
         /* Instead of clearing (by a previous call to memset())
          * the counters and using adds, we set the counters
-         * with data used by 'current' CPU
-         * We dont care about preemption here.
+         * with data used by 'current' CPU.
+         *
+         * Bottom half has to be disabled to prevent deadlock
+         * if new softirq were to run and call ipt_do_table
          */
-        curcpu = raw_smp_processor_id();
+        local_bh_disable();
+        curcpu = smp_processor_id();
 
         i = 0;
         IPT_ENTRY_ITERATE(t->entries[curcpu],
@@ -912,74 +913,22 @@ get_counters(const struct xt_table_info *t,
                 if (cpu == curcpu)
                         continue;
                 i = 0;
+                xt_info_wrlock(cpu);
                 IPT_ENTRY_ITERATE(t->entries[cpu],
                                   t->size,
                                   add_entry_to_counter,
                                   counters,
                                   &i);
+                xt_info_wrunlock(cpu);
         }
-
-}
-
-/* We're lazy, and add to the first CPU; overflow works its fey magic
- * and everything is OK. */
-static int
-add_counter_to_entry(struct ipt_entry *e,
-                     const struct xt_counters addme[],
-                     unsigned int *i)
-{
-        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
-
-        (*i)++;
-        return 0;
-}
-
-/* Take values from counters and add them back onto the current cpu */
-static void put_counters(struct xt_table_info *t,
-                         const struct xt_counters counters[])
-{
-        unsigned int i, cpu;
-
-        local_bh_disable();
-        cpu = smp_processor_id();
-        i = 0;
-        IPT_ENTRY_ITERATE(t->entries[cpu],
-                          t->size,
-                          add_counter_to_entry,
-                          counters,
-                          &i);
         local_bh_enable();
 }
 
-
-static inline int
-zero_entry_counter(struct ipt_entry *e, void *arg)
-{
-        e->counters.bcnt = 0;
-        e->counters.pcnt = 0;
-        return 0;
-}
-
-static void
-clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
-{
-        unsigned int cpu;
-        const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
-
-        memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
-        for_each_possible_cpu(cpu) {
-                memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
-                IPT_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
-                                  zero_entry_counter, NULL);
-        }
-}
-
 static struct xt_counters * alloc_counters(struct xt_table *table)
 {
         unsigned int countersize;
         struct xt_counters *counters;
         struct xt_table_info *private = table->private;
-        struct xt_table_info *info;
 
         /* We need atomic snapshot of counters: rest doesn't change
            (other than comefrom, which userspace doesn't care
@@ -988,30 +937,11 @@ static struct xt_counters * alloc_counters(struct xt_table *table)
         counters = vmalloc_node(countersize, numa_node_id());
 
         if (counters == NULL)
-                goto nomem;
+                return ERR_PTR(-ENOMEM);
 
-        info = xt_alloc_table_info(private->size);
-        if (!info)
-                goto free_counters;
-
-        clone_counters(info, private);
-
-        mutex_lock(&table->lock);
-        xt_table_entry_swap_rcu(private, info);
-        synchronize_net();      /* Wait until smoke has cleared */
-
-        get_counters(info, counters);
-        put_counters(private, counters);
-        mutex_unlock(&table->lock);
-
-        xt_free_table_info(info);
+        get_counters(private, counters);
 
         return counters;
-
- free_counters:
-        vfree(counters);
- nomem:
-        return ERR_PTR(-ENOMEM);
 }
 
 static int
@@ -1306,8 +1236,9 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
             (newinfo->number <= oldinfo->initial_entries))
                 module_put(t->me);
 
-        /* Get the old counters. */
+        /* Get the old counters, and synchronize with replace */
         get_counters(oldinfo, counters);
+
         /* Decrease module usage counts and free resource */
         loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
         IPT_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
@@ -1377,11 +1308,23 @@ do_replace(struct net *net, void __user *user, unsigned int len)
         return ret;
 }
 
+/* We're lazy, and add to the first CPU; overflow works its fey magic
+ * and everything is OK. */
+static int
+add_counter_to_entry(struct ipt_entry *e,
+                     const struct xt_counters addme[],
+                     unsigned int *i)
+{
+        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
+
+        (*i)++;
+        return 0;
+}
 
 static int
 do_add_counters(struct net *net, void __user *user, unsigned int len, int compat)
 {
-        unsigned int i;
+        unsigned int i, curcpu;
         struct xt_counters_info tmp;
         struct xt_counters *paddc;
         unsigned int num_counters;
@@ -1437,25 +1380,26 @@ do_add_counters(struct net *net, void __user *user, unsigned int len, int compat
                 goto free;
         }
 
-        mutex_lock(&t->lock);
+        local_bh_disable();
         private = t->private;
         if (private->number != num_counters) {
                 ret = -EINVAL;
                 goto unlock_up_free;
         }
 
-        preempt_disable();
         i = 0;
         /* Choose the copy that is on our node */
-        loc_cpu_entry = private->entries[raw_smp_processor_id()];
+        curcpu = smp_processor_id();
+        loc_cpu_entry = private->entries[curcpu];
+        xt_info_wrlock(curcpu);
         IPT_ENTRY_ITERATE(loc_cpu_entry,
                           private->size,
                           add_counter_to_entry,
                           paddc,
                           &i);
-        preempt_enable();
+        xt_info_wrunlock(curcpu);
  unlock_up_free:
-        mutex_unlock(&t->lock);
+        local_bh_enable();
         xt_table_unlock(t);
         module_put(t->me);
  free:
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 800ae8542471..219e165aea10 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -365,9 +365,9 @@ ip6t_do_table(struct sk_buff *skb,
 
         IP_NF_ASSERT(table->valid_hooks & (1 << hook));
 
-        rcu_read_lock_bh();
-        private = rcu_dereference(table->private);
-        table_base = rcu_dereference(private->entries[smp_processor_id()]);
+        xt_info_rdlock_bh();
+        private = table->private;
+        table_base = private->entries[smp_processor_id()];
 
         e = get_entry(table_base, private->hook_entry[hook]);
 
@@ -466,7 +466,7 @@ ip6t_do_table(struct sk_buff *skb,
 #ifdef CONFIG_NETFILTER_DEBUG
         ((struct ip6t_entry *)table_base)->comefrom = NETFILTER_LINK_POISON;
 #endif
-        rcu_read_unlock_bh();
+        xt_info_rdunlock_bh();
 
 #ifdef DEBUG_ALLOW_ALL
         return NF_ACCEPT;
@@ -926,9 +926,12 @@ get_counters(const struct xt_table_info *t,
         /* Instead of clearing (by a previous call to memset())
          * the counters and using adds, we set the counters
          * with data used by 'current' CPU
-         * We dont care about preemption here.
+         *
+         * Bottom half has to be disabled to prevent deadlock
+         * if new softirq were to run and call ipt_do_table
          */
-        curcpu = raw_smp_processor_id();
+        local_bh_disable();
+        curcpu = smp_processor_id();
 
         i = 0;
         IP6T_ENTRY_ITERATE(t->entries[curcpu],
@@ -941,72 +944,22 @@ get_counters(const struct xt_table_info *t,
                 if (cpu == curcpu)
                         continue;
                 i = 0;
+                xt_info_wrlock(cpu);
                 IP6T_ENTRY_ITERATE(t->entries[cpu],
                                   t->size,
                                   add_entry_to_counter,
                                   counters,
                                   &i);
+                xt_info_wrunlock(cpu);
         }
-}
-
-/* We're lazy, and add to the first CPU; overflow works its fey magic
- * and everything is OK. */
-static int
-add_counter_to_entry(struct ip6t_entry *e,
-                     const struct xt_counters addme[],
-                     unsigned int *i)
-{
-        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
-
-        (*i)++;
-        return 0;
-}
-
-/* Take values from counters and add them back onto the current cpu */
-static void put_counters(struct xt_table_info *t,
-                         const struct xt_counters counters[])
-{
-        unsigned int i, cpu;
-
-        local_bh_disable();
-        cpu = smp_processor_id();
-        i = 0;
-        IP6T_ENTRY_ITERATE(t->entries[cpu],
-                           t->size,
-                           add_counter_to_entry,
-                           counters,
-                           &i);
         local_bh_enable();
 }
 
-static inline int
-zero_entry_counter(struct ip6t_entry *e, void *arg)
-{
-        e->counters.bcnt = 0;
-        e->counters.pcnt = 0;
-        return 0;
-}
-
-static void
-clone_counters(struct xt_table_info *newinfo, const struct xt_table_info *info)
-{
-        unsigned int cpu;
-        const void *loc_cpu_entry = info->entries[raw_smp_processor_id()];
-
-        memcpy(newinfo, info, offsetof(struct xt_table_info, entries));
-        for_each_possible_cpu(cpu) {
-                memcpy(newinfo->entries[cpu], loc_cpu_entry, info->size);
-                IP6T_ENTRY_ITERATE(newinfo->entries[cpu], newinfo->size,
-                                   zero_entry_counter, NULL);
-        }
-}
-
 static struct xt_counters *alloc_counters(struct xt_table *table)
 {
         unsigned int countersize;
         struct xt_counters *counters;
         struct xt_table_info *private = table->private;
-        struct xt_table_info *info;
 
         /* We need atomic snapshot of counters: rest doesn't change
            (other than comefrom, which userspace doesn't care
@@ -1015,30 +968,11 @@ static struct xt_counters *alloc_counters(struct xt_table *table)
         counters = vmalloc_node(countersize, numa_node_id());
 
         if (counters == NULL)
-                goto nomem;
+                return ERR_PTR(-ENOMEM);
 
-        info = xt_alloc_table_info(private->size);
-        if (!info)
-                goto free_counters;
-
-        clone_counters(info, private);
-
-        mutex_lock(&table->lock);
-        xt_table_entry_swap_rcu(private, info);
-        synchronize_net();      /* Wait until smoke has cleared */
-
-        get_counters(info, counters);
-        put_counters(private, counters);
-        mutex_unlock(&table->lock);
-
-        xt_free_table_info(info);
+        get_counters(private, counters);
 
         return counters;
-
- free_counters:
-        vfree(counters);
- nomem:
-        return ERR_PTR(-ENOMEM);
 }
 
 static int
@@ -1334,8 +1268,9 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
             (newinfo->number <= oldinfo->initial_entries))
                 module_put(t->me);
 
-        /* Get the old counters. */
+        /* Get the old counters, and synchronize with replace */
         get_counters(oldinfo, counters);
+
         /* Decrease module usage counts and free resource */
         loc_cpu_old_entry = oldinfo->entries[raw_smp_processor_id()];
         IP6T_ENTRY_ITERATE(loc_cpu_old_entry, oldinfo->size, cleanup_entry,
@@ -1405,11 +1340,24 @@ do_replace(struct net *net, void __user *user, unsigned int len)
         return ret;
 }
 
+/* We're lazy, and add to the first CPU; overflow works its fey magic
+ * and everything is OK. */
+static int
+add_counter_to_entry(struct ip6t_entry *e,
+                     const struct xt_counters addme[],
+                     unsigned int *i)
+{
+        ADD_COUNTER(e->counters, addme[*i].bcnt, addme[*i].pcnt);
+
+        (*i)++;
+        return 0;
+}
+
 static int
 do_add_counters(struct net *net, void __user *user, unsigned int len,
                 int compat)
 {
-        unsigned int i;
+        unsigned int i, curcpu;
         struct xt_counters_info tmp;
         struct xt_counters *paddc;
         unsigned int num_counters;
@@ -1465,25 +1413,28 @@ do_add_counters(struct net *net, void __user *user, unsigned int len,
                 goto free;
         }
 
-        mutex_lock(&t->lock);
+
+        local_bh_disable();
         private = t->private;
         if (private->number != num_counters) {
                 ret = -EINVAL;
                 goto unlock_up_free;
         }
 
-        preempt_disable();
         i = 0;
         /* Choose the copy that is on our node */
-        loc_cpu_entry = private->entries[raw_smp_processor_id()];
+        curcpu = smp_processor_id();
+        xt_info_wrlock(curcpu);
+        loc_cpu_entry = private->entries[curcpu];
         IP6T_ENTRY_ITERATE(loc_cpu_entry,
                           private->size,
                           add_counter_to_entry,
                           paddc,
                           &i);
-        preempt_enable();
+        xt_info_wrunlock(curcpu);
+
  unlock_up_free:
-        mutex_unlock(&t->lock);
+        local_bh_enable();
         xt_table_unlock(t);
         module_put(t->me);
  free:
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 509a95621f9f..150e5cf62f85 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -625,20 +625,6 @@ void xt_free_table_info(struct xt_table_info *info)
 }
 EXPORT_SYMBOL(xt_free_table_info);
 
-void xt_table_entry_swap_rcu(struct xt_table_info *oldinfo,
-                             struct xt_table_info *newinfo)
-{
-        unsigned int cpu;
-
-        for_each_possible_cpu(cpu) {
-                void *p = oldinfo->entries[cpu];
-                rcu_assign_pointer(oldinfo->entries[cpu], newinfo->entries[cpu]);
-                newinfo->entries[cpu] = p;
-        }
-
-}
-EXPORT_SYMBOL_GPL(xt_table_entry_swap_rcu);
-
 /* Find table by name, grabs mutex & ref.  Returns ERR_PTR() on error. */
 struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
                                     const char *name)
@@ -676,32 +662,43 @@ void xt_compat_unlock(u_int8_t af)
 EXPORT_SYMBOL_GPL(xt_compat_unlock);
 #endif
 
+DEFINE_PER_CPU(struct xt_info_lock, xt_info_locks);
+EXPORT_PER_CPU_SYMBOL_GPL(xt_info_locks);
+
+
 struct xt_table_info *
 xt_replace_table(struct xt_table *table,
               unsigned int num_counters,
               struct xt_table_info *newinfo,
               int *error)
 {
-        struct xt_table_info *oldinfo, *private;
+        struct xt_table_info *private;
 
         /* Do the substitution. */
-        mutex_lock(&table->lock);
+        local_bh_disable();
         private = table->private;
+
         /* Check inside lock: is the old number correct? */
         if (num_counters != private->number) {
                 duprintf("num_counters != table->private->number (%u/%u)\n",
                          num_counters, private->number);
-                mutex_unlock(&table->lock);
+                local_bh_enable();
                 *error = -EAGAIN;
                 return NULL;
         }
-        oldinfo = private;
-        rcu_assign_pointer(table->private, newinfo);
-        newinfo->initial_entries = oldinfo->initial_entries;
-        mutex_unlock(&table->lock);
 
-        synchronize_net();
-        return oldinfo;
+        table->private = newinfo;
+        newinfo->initial_entries = private->initial_entries;
+
+        /*
+         * Even though table entries have now been swapped, other CPU's
+         * may still be using the old entries. This is okay, because
+         * resynchronization happens because of the locking done
+         * during the get_counters() routine.
+         */
+        local_bh_enable();
+
+        return private;
 }
 EXPORT_SYMBOL_GPL(xt_replace_table);
 
@@ -734,7 +731,6 @@ struct xt_table *xt_register_table(struct net *net, struct xt_table *table,
 
         /* Simplifies replace_table code. */
         table->private = bootstrap;
-        mutex_init(&table->lock);
 
         if (!xt_replace_table(table, 0, newinfo, &ret))
                 goto unlock;
@@ -1147,7 +1143,14 @@ static struct pernet_operations xt_net_ops = {
 
 static int __init xt_init(void)
 {
-        int i, rv;
+        unsigned int i;
+        int rv;
+
+        for_each_possible_cpu(i) {
+                struct xt_info_lock *lock = &per_cpu(xt_info_locks, i);
+                spin_lock_init(&lock->lock);
+                lock->readers = 0;
+        }
 
         xt = kmalloc(sizeof(struct xt_af) * NFPROTO_NUMPROTO, GFP_KERNEL);
         if (!xt)