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>

1 files changed, 37 insertions, 86 deletions

diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 800ae854247..219e165aea1 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: