tcp: md5: remove spinlock usage in fast path

TCP md5 code uses per cpu variables but protects access to them with
a shared spinlock, which is a contention point.

[ tcp_md5sig_pool_lock is locked twice per incoming packet ]

Makes things much simpler, by allocating crypto structures once, first
time a socket needs md5 keys, and not deallocating them as they are
really small.

Next step would be to allow crypto allocations being done in a NUMA
aware way.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e1c3723..bf1cc3d 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1283,11 +1283,13 @@ static inline struct tcp_md5sig_key *tcp_md5_do_lookup(struct sock *sk,
 #define tcp_twsk_md5_key(twsk) NULL
 #endif
 
-extern struct tcp_md5sig_pool __percpu *tcp_alloc_md5sig_pool(struct sock *);
-extern void tcp_free_md5sig_pool(void);
+extern bool tcp_alloc_md5sig_pool(void);
 
 extern struct tcp_md5sig_pool  *tcp_get_md5sig_pool(void);
-extern void tcp_put_md5sig_pool(void);
+static inline void tcp_put_md5sig_pool(void)
+{
+       local_bh_enable();
+}
 
 extern int tcp_md5_hash_header(struct tcp_md5sig_pool *, const struct tcphdr *);
 extern int tcp_md5_hash_skb_data(struct tcp_md5sig_pool *, const struct sk_buff *,

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index dcb116d..53d9c12 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3095,9 +3095,8 @@ int tcp_gro_complete(struct sk_buff *skb)
 EXPORT_SYMBOL(tcp_gro_complete);
 
 #ifdef CONFIG_TCP_MD5SIG
-static unsigned long tcp_md5sig_users;
-static struct tcp_md5sig_pool __percpu *tcp_md5sig_pool;
-static DEFINE_SPINLOCK(tcp_md5sig_pool_lock);
+static struct tcp_md5sig_pool __percpu *tcp_md5sig_pool __read_mostly;
+static DEFINE_MUTEX(tcp_md5sig_mutex);
 
 static void __tcp_free_md5sig_pool(struct tcp_md5sig_pool __percpu *pool)
 {
@@ -3112,30 +3111,14 @@ static void __tcp_free_md5sig_pool(struct tcp_md5sig_pool __percpu *pool)
        free_percpu(pool);
 }
 
-void tcp_free_md5sig_pool(void)
-{
-       struct tcp_md5sig_pool __percpu *pool = NULL;
-
-       spin_lock_bh(&tcp_md5sig_pool_lock);
-       if (--tcp_md5sig_users == 0) {
-               pool = tcp_md5sig_pool;
-               tcp_md5sig_pool = NULL;
-       }
-       spin_unlock_bh(&tcp_md5sig_pool_lock);
-       if (pool)
-               __tcp_free_md5sig_pool(pool);
-}
-EXPORT_SYMBOL(tcp_free_md5sig_pool);
-
-static struct tcp_md5sig_pool __percpu *
-__tcp_alloc_md5sig_pool(struct sock *sk)
+static void __tcp_alloc_md5sig_pool(void)
 {
        int cpu;
        struct tcp_md5sig_pool __percpu *pool;
 
        pool = alloc_percpu(struct tcp_md5sig_pool);
        if (!pool)
-               return NULL;
+               return;
 
        for_each_possible_cpu(cpu) {
                struct crypto_hash *hash;
@@ -3146,53 +3129,27 @@ __tcp_alloc_md5sig_pool(struct sock *sk)
 
                per_cpu_ptr(pool, cpu)->md5_desc.tfm = hash;
        }
-       return pool;
+       /* before setting tcp_md5sig_pool, we must commit all writes
+        * to memory. See ACCESS_ONCE() in tcp_get_md5sig_pool()
+        */
+       smp_wmb();
+       tcp_md5sig_pool = pool;
+       return;
 out_free:
        __tcp_free_md5sig_pool(pool);
-       return NULL;
 }
 
-struct tcp_md5sig_pool __percpu *tcp_alloc_md5sig_pool(struct sock *sk)
+bool tcp_alloc_md5sig_pool(void)
 {
-       struct tcp_md5sig_pool __percpu *pool;
-       bool alloc = false;
-
-retry:
-       spin_lock_bh(&tcp_md5sig_pool_lock);
-       pool = tcp_md5sig_pool;
-       if (tcp_md5sig_users++ == 0) {
-               alloc = true;
-               spin_unlock_bh(&tcp_md5sig_pool_lock);
-       } else if (!pool) {
-               tcp_md5sig_users--;
-               spin_unlock_bh(&tcp_md5sig_pool_lock);
-               cpu_relax();
-               goto retry;
-       } else
-               spin_unlock_bh(&tcp_md5sig_pool_lock);
-
-       if (alloc) {
-               /* we cannot hold spinlock here because this may sleep. */
-               struct tcp_md5sig_pool __percpu *p;
-
-               p = __tcp_alloc_md5sig_pool(sk);
-               spin_lock_bh(&tcp_md5sig_pool_lock);
-               if (!p) {
-                       tcp_md5sig_users--;
-                       spin_unlock_bh(&tcp_md5sig_pool_lock);
-                       return NULL;
-               }
-               pool = tcp_md5sig_pool;
-               if (pool) {
-                       /* oops, it has already been assigned. */
-                       spin_unlock_bh(&tcp_md5sig_pool_lock);
-                       __tcp_free_md5sig_pool(p);
-               } else {
-                       tcp_md5sig_pool = pool = p;
-                       spin_unlock_bh(&tcp_md5sig_pool_lock);
-               }
+       if (unlikely(!tcp_md5sig_pool)) {
+               mutex_lock(&tcp_md5sig_mutex);
+
+               if (!tcp_md5sig_pool)
+                       __tcp_alloc_md5sig_pool();
+
+               mutex_unlock(&tcp_md5sig_mutex);
        }
-       return pool;
+       return tcp_md5sig_pool != NULL;
 }
 EXPORT_SYMBOL(tcp_alloc_md5sig_pool);
 
@@ -3209,28 +3166,15 @@ struct tcp_md5sig_pool *tcp_get_md5sig_pool(void)
        struct tcp_md5sig_pool __percpu *p;
 
        local_bh_disable();
-
-       spin_lock(&tcp_md5sig_pool_lock);
-       p = tcp_md5sig_pool;
-       if (p)
-               tcp_md5sig_users++;
-       spin_unlock(&tcp_md5sig_pool_lock);
-
+       p = ACCESS_ONCE(tcp_md5sig_pool);
        if (p)
-               return this_cpu_ptr(p);
+               return __this_cpu_ptr(p);
 
        local_bh_enable();
        return NULL;
 }
 EXPORT_SYMBOL(tcp_get_md5sig_pool);
 
-void tcp_put_md5sig_pool(void)
-{
-       local_bh_enable();
-       tcp_free_md5sig_pool();
-}
-EXPORT_SYMBOL(tcp_put_md5sig_pool);
-
 int tcp_md5_hash_header(struct tcp_md5sig_pool *hp,
                        const struct tcphdr *th)
 {

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7196523..d20ede0 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1026,7 +1026,7 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
        key = sock_kmalloc(sk, sizeof(*key), gfp);
        if (!key)
                return -ENOMEM;
-       if (hlist_empty(&md5sig->head) && !tcp_alloc_md5sig_pool(sk)) {
+       if (!tcp_alloc_md5sig_pool()) {
                sock_kfree_s(sk, key, sizeof(*key));
                return -ENOMEM;
        }
@@ -1044,9 +1044,7 @@ EXPORT_SYMBOL(tcp_md5_do_add);
 
 int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr, int family)
 {
-       struct tcp_sock *tp = tcp_sk(sk);
        struct tcp_md5sig_key *key;
-       struct tcp_md5sig_info *md5sig;
 
        key = tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&addr, AF_INET);
        if (!key)
@@ -1054,10 +1052,6 @@ int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr, int family)
        hlist_del_rcu(&key->node);
        atomic_sub(sizeof(*key), &sk->sk_omem_alloc);
        kfree_rcu(key, rcu);
-       md5sig = rcu_dereference_protected(tp->md5sig_info,
-                                          sock_owned_by_user(sk));
-       if (hlist_empty(&md5sig->head))
-               tcp_free_md5sig_pool();
        return 0;
 }
 EXPORT_SYMBOL(tcp_md5_do_del);
@@ -1071,8 +1065,6 @@ static void tcp_clear_md5_list(struct sock *sk)
 
        md5sig = rcu_dereference_protected(tp->md5sig_info, 1);
 
-       if (!hlist_empty(&md5sig->head))
-               tcp_free_md5sig_pool();
        hlist_for_each_entry_safe(key, n, &md5sig->head, node) {
                hlist_del_rcu(&key->node);
                atomic_sub(sizeof(*key), &sk->sk_omem_alloc);

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 0f01788..ab1c086 100644 (file)
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -317,7 +317,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
                        key = tp->af_specific->md5_lookup(sk, sk);
                        if (key != NULL) {
                                tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
-                               if (tcptw->tw_md5_key && tcp_alloc_md5sig_pool(sk) == NULL)
+                               if (tcptw->tw_md5_key && !tcp_alloc_md5sig_pool())
                                        BUG();
                        }
                } while (0);
@@ -358,10 +358,8 @@ void tcp_twsk_destructor(struct sock *sk)
 #ifdef CONFIG_TCP_MD5SIG
        struct tcp_timewait_sock *twsk = tcp_twsk(sk);
 
-       if (twsk->tw_md5_key) {
-               tcp_free_md5sig_pool();
+       if (twsk->tw_md5_key)
                kfree_rcu(twsk->tw_md5_key, rcu);
-       }
 #endif
 }
 EXPORT_SYMBOL_GPL(tcp_twsk_destructor);