netfilter: CLUSTERIP: RCU conversion

- clusterip_lock becomes a spinlock
- lockless lookups
- kfree() deferred after RCU grace period
- rcu_barrier_bh() inserted in clusterip_tg_exit()

v2)
- As Patrick pointed out, we use atomic_inc_not_zero() in
clusterip_config_find_get().
- list_add_rcu() and list_del_rcu() variants are used.
- atomic_dec_and_lock() used in clusterip_config_entry_put()

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 29 insertions, 19 deletions

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index f91c94b9a790..64d0875f5192 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -53,12 +53,13 @@ struct clusterip_config {
 #endif
         enum clusterip_hashmode hash_mode;      /* which hashing mode */
         u_int32_t hash_initval;                 /* hash initialization */
+        struct rcu_head rcu;
 };
 
 static LIST_HEAD(clusterip_configs);
 
 /* clusterip_lock protects the clusterip_configs list */
-static DEFINE_RWLOCK(clusterip_lock);
+static DEFINE_SPINLOCK(clusterip_lock);
 
 #ifdef CONFIG_PROC_FS
 static const struct file_operations clusterip_proc_fops;
@@ -71,11 +72,17 @@ clusterip_config_get(struct clusterip_config *c)
         atomic_inc(&c->refcount);
 }
 
+
+static void clusterip_config_rcu_free(struct rcu_head *head)
+{
+        kfree(container_of(head, struct clusterip_config, rcu));
+}
+
 static inline void
 clusterip_config_put(struct clusterip_config *c)
 {
         if (atomic_dec_and_test(&c->refcount))
-                kfree(c);
+                call_rcu_bh(&c->rcu, clusterip_config_rcu_free);
 }
 
 /* decrease the count of entries using/referencing this config.  If last
@@ -84,10 +91,11 @@ clusterip_config_put(struct clusterip_config *c)
 static inline void
 clusterip_config_entry_put(struct clusterip_config *c)
 {
-        write_lock_bh(&clusterip_lock);
-        if (atomic_dec_and_test(&c->entries)) {
-                list_del(&c->list);
-                write_unlock_bh(&clusterip_lock);
+        local_bh_disable();
+        if (atomic_dec_and_lock(&c->entries, &clusterip_lock)) {
+                list_del_rcu(&c->list);
+                spin_unlock(&clusterip_lock);
+                local_bh_enable();
 
                 dev_mc_del(c->dev, c->clustermac);
                 dev_put(c->dev);
@@ -100,7 +108,7 @@ clusterip_config_entry_put(struct clusterip_config *c)
 #endif
                 return;
         }
-        write_unlock_bh(&clusterip_lock);
+        local_bh_enable();
 }
 
 static struct clusterip_config *
@@ -108,7 +116,7 @@ __clusterip_config_find(__be32 clusterip)
 {
         struct clusterip_config *c;
 
-        list_for_each_entry(c, &clusterip_configs, list) {
+        list_for_each_entry_rcu(c, &clusterip_configs, list) {
                 if (c->clusterip == clusterip)
                         return c;
         }
@@ -121,16 +129,15 @@ clusterip_config_find_get(__be32 clusterip, int entry)
 {
         struct clusterip_config *c;
 
-        read_lock_bh(&clusterip_lock);
+        rcu_read_lock_bh();
         c = __clusterip_config_find(clusterip);
-        if (!c) {
-                read_unlock_bh(&clusterip_lock);
-                return NULL;
+        if (c) {
+                if (unlikely(!atomic_inc_not_zero(&c->refcount)))
+                        c = NULL;
+                else if (entry)
+                        atomic_inc(&c->entries);
         }
-        atomic_inc(&c->refcount);
-        if (entry)
-                atomic_inc(&c->entries);
-        read_unlock_bh(&clusterip_lock);
+        rcu_read_unlock_bh();
 
         return c;
 }
@@ -181,9 +188,9 @@ clusterip_config_init(const struct ipt_clusterip_tgt_info *i, __be32 ip,
         }
 #endif
 
-        write_lock_bh(&clusterip_lock);
-        list_add(&c->list, &clusterip_configs);
-        write_unlock_bh(&clusterip_lock);
+        spin_lock_bh(&clusterip_lock);
+        list_add_rcu(&c->list, &clusterip_configs);
+        spin_unlock_bh(&clusterip_lock);
 
         return c;
 }
@@ -733,6 +740,9 @@ static void __exit clusterip_tg_exit(void)
 #endif
         nf_unregister_hook(&cip_arp_ops);
         xt_unregister_target(&clusterip_tg_reg);
+
+        /* Wait for completion of call_rcu_bh()'s (clusterip_config_rcu_free) */
+        rcu_barrier_bh();
 }
 
 module_init(clusterip_tg_init);