netfilter: xt_hashlimit: RCU conversion

xt_hashlimit uses a central lock per hash table and suffers from
contention on some workloads. (Multiqueue NIC or if RPS is enabled)

After RCU conversion, central lock is only used when a writer wants to
add or delete an entry.

For 'readers', updating an existing entry, they use an individual lock
per entry.

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

1 files changed, 47 insertions, 23 deletions

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 5470bb097c4..453178d25cb 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -81,12 +81,14 @@ struct dsthash_ent {
         struct dsthash_dst dst;
 
         /* modified structure members in the end */
+        spinlock_t lock;
         unsigned long expires;          /* precalculated expiry time */
         struct {
                 unsigned long prev;     /* last modification */
                 u_int32_t credit;
                 u_int32_t credit_cap, cost;
         } rateinfo;
+        struct rcu_head rcu;
 };
 
 struct xt_hashlimit_htable {
@@ -143,9 +145,11 @@ dsthash_find(const struct xt_hashlimit_htable *ht,
         u_int32_t hash = hash_dst(ht, dst);
 
         if (!hlist_empty(&ht->hash[hash])) {
-                hlist_for_each_entry(ent, pos, &ht->hash[hash], node)
-                        if (dst_cmp(ent, dst))
+                hlist_for_each_entry_rcu(ent, pos, &ht->hash[hash], node)
+                        if (dst_cmp(ent, dst)) {
+                                spin_lock(&ent->lock);
                                 return ent;
+                        }
         }
         return NULL;
 }
@@ -157,9 +161,10 @@ dsthash_alloc_init(struct xt_hashlimit_htable *ht,
 {
         struct dsthash_ent *ent;
 
+        spin_lock(&ht->lock);
         /* initialize hash with random val at the time we allocate
          * the first hashtable entry */
-        if (!ht->rnd_initialized) {
+        if (unlikely(!ht->rnd_initialized)) {
                 get_random_bytes(&ht->rnd, sizeof(ht->rnd));
                 ht->rnd_initialized = true;
         }
@@ -168,27 +173,36 @@ dsthash_alloc_init(struct xt_hashlimit_htable *ht,
                 /* FIXME: do something. question is what.. */
                 if (net_ratelimit())
                         pr_err("max count of %u reached\n", ht->cfg.max);
-                return NULL;
-        }
-
-        ent = kmem_cache_alloc(hashlimit_cachep, GFP_ATOMIC);
+                ent = NULL;
+        } else
+                ent = kmem_cache_alloc(hashlimit_cachep, GFP_ATOMIC);
         if (!ent) {
                 if (net_ratelimit())
                         pr_err("cannot allocate dsthash_ent\n");
-                return NULL;
-        }
-        memcpy(&ent->dst, dst, sizeof(ent->dst));
+        } else {
+                memcpy(&ent->dst, dst, sizeof(ent->dst));
+                spin_lock_init(&ent->lock);
 
-        hlist_add_head(&ent->node, &ht->hash[hash_dst(ht, dst)]);
-        ht->count++;
+                spin_lock(&ent->lock);
+                hlist_add_head_rcu(&ent->node, &ht->hash[hash_dst(ht, dst)]);
+                ht->count++;
+        }
+        spin_unlock(&ht->lock);
         return ent;
 }
 
+static void dsthash_free_rcu(struct rcu_head *head)
+{
+        struct dsthash_ent *ent = container_of(head, struct dsthash_ent, rcu);
+
+        kmem_cache_free(hashlimit_cachep, ent);
+}
+
 static inline void
 dsthash_free(struct xt_hashlimit_htable *ht, struct dsthash_ent *ent)
 {
-        hlist_del(&ent->node);
-        kmem_cache_free(hashlimit_cachep, ent);
+        hlist_del_rcu(&ent->node);
+        call_rcu_bh(&ent->rcu, dsthash_free_rcu);
         ht->count--;
 }
 static void htable_gc(unsigned long htlong);
@@ -512,15 +526,14 @@ hashlimit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
         if (hashlimit_init_dst(hinfo, &dst, skb, par->thoff) < 0)
                 goto hotdrop;
 
-        spin_lock_bh(&hinfo->lock);
+        rcu_read_lock_bh();
         dh = dsthash_find(hinfo, &dst);
         if (dh == NULL) {
                 dh = dsthash_alloc_init(hinfo, &dst);
                 if (dh == NULL) {
-                        spin_unlock_bh(&hinfo->lock);
+                        rcu_read_unlock_bh();
                         goto hotdrop;
                 }
-
                 dh->expires = jiffies + msecs_to_jiffies(hinfo->cfg.expire);
                 dh->rateinfo.prev = jiffies;
                 dh->rateinfo.credit = user2credits(hinfo->cfg.avg *
@@ -537,11 +550,13 @@ hashlimit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
         if (dh->rateinfo.credit >= dh->rateinfo.cost) {
                 /* below the limit */
                 dh->rateinfo.credit -= dh->rateinfo.cost;
-                spin_unlock_bh(&hinfo->lock);
+                spin_unlock(&dh->lock);
+                rcu_read_unlock_bh();
                 return !(info->cfg.mode & XT_HASHLIMIT_INVERT);
         }
 
-        spin_unlock_bh(&hinfo->lock);
+        spin_unlock(&dh->lock);
+        rcu_read_unlock_bh();
         /* default match is underlimit - so over the limit, we need to invert */
         return info->cfg.mode & XT_HASHLIMIT_INVERT;
 
@@ -666,12 +681,15 @@ static void dl_seq_stop(struct seq_file *s, void *v)
 static int dl_seq_real_show(struct dsthash_ent *ent, u_int8_t family,
                                    struct seq_file *s)
 {
+        int res;
+
+        spin_lock(&ent->lock);
         /* recalculate to show accurate numbers */
         rateinfo_recalc(ent, jiffies);
 
         switch (family) {
         case NFPROTO_IPV4:
-                return seq_printf(s, "%ld %pI4:%u->%pI4:%u %u %u %u\n",
+                res = seq_printf(s, "%ld %pI4:%u->%pI4:%u %u %u %u\n",
                                  (long)(ent->expires - jiffies)/HZ,
                                  &ent->dst.ip.src,
                                  ntohs(ent->dst.src_port),
@@ -679,9 +697,10 @@ static int dl_seq_real_show(struct dsthash_ent *ent, u_int8_t family,
                                  ntohs(ent->dst.dst_port),
                                  ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                  ent->rateinfo.cost);
+                break;
 #if defined(CONFIG_IP6_NF_IPTABLES) || defined(CONFIG_IP6_NF_IPTABLES_MODULE)
         case NFPROTO_IPV6:
-                return seq_printf(s, "%ld %pI6:%u->%pI6:%u %u %u %u\n",
+                res = seq_printf(s, "%ld %pI6:%u->%pI6:%u %u %u %u\n",
                                  (long)(ent->expires - jiffies)/HZ,
                                  &ent->dst.ip6.src,
                                  ntohs(ent->dst.src_port),
@@ -689,11 +708,14 @@ static int dl_seq_real_show(struct dsthash_ent *ent, u_int8_t family,
                                  ntohs(ent->dst.dst_port),
                                  ent->rateinfo.credit, ent->rateinfo.credit_cap,
                                  ent->rateinfo.cost);
+                break;
 #endif
         default:
                 BUG();
-                return 0;
+                res = 0;
         }
+        spin_unlock(&ent->lock);
+        return res;
 }
 
 static int dl_seq_show(struct seq_file *s, void *v)
@@ -817,9 +839,11 @@ err1:
 
 static void __exit hashlimit_mt_exit(void)
 {
-        kmem_cache_destroy(hashlimit_cachep);
         xt_unregister_matches(hashlimit_mt_reg, ARRAY_SIZE(hashlimit_mt_reg));
         unregister_pernet_subsys(&hashlimit_net_ops);
+
+        rcu_barrier_bh();
+        kmem_cache_destroy(hashlimit_cachep);
 }
 
 module_init(hashlimit_mt_init);