tcp/dccp: do not touch listener sk_refcnt under synflood
When a SYNFLOOD targets a non SO_REUSEPORT listener, multiple
cpus contend on sk->sk_refcnt and sk->sk_wmem_alloc changes.
By letting listeners use SOCK_RCU_FREE infrastructure,
we can relax TCP_LISTEN lookup rules and avoid touching sk_refcnt
Note that we still use SLAB_DESTROY_BY_RCU rules for other sockets,
only listeners are impacted by this change.
Peak performance under SYNFLOOD is increased by ~33% :
On my test machine, I could process 3.2 Mpps instead of 2.4 Mpps
Most consuming functions are now skb_set_owner_w() and sock_wfree()
contending on sk->sk_wmem_alloc when cooking SYNACK and freeing them.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index ad45050..e5f924b 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -628,6 +628,7 @@
net = sk ? sock_net(sk) : dev_net(skb_dst(skb)->dev);
#ifdef CONFIG_TCP_MD5SIG
+ rcu_read_lock();
hash_location = tcp_parse_md5sig_option(th);
if (sk && sk_fullsock(sk)) {
key = tcp_md5_do_lookup(sk, (union tcp_md5_addr *)
@@ -646,16 +647,18 @@
ntohs(th->source), inet_iif(skb));
/* don't send rst if it can't find key */
if (!sk1)
- return;
- rcu_read_lock();
+ goto out;
+
key = tcp_md5_do_lookup(sk1, (union tcp_md5_addr *)
&ip_hdr(skb)->saddr, AF_INET);
if (!key)
- goto release_sk1;
+ goto out;
+
genhash = tcp_v4_md5_hash_skb(newhash, key, NULL, skb);
if (genhash || memcmp(hash_location, newhash, 16) != 0)
- goto release_sk1;
+ goto out;
+
}
if (key) {
@@ -698,11 +701,8 @@
TCP_INC_STATS_BH(net, TCP_MIB_OUTRSTS);
#ifdef CONFIG_TCP_MD5SIG
-release_sk1:
- if (sk1) {
- rcu_read_unlock();
- sock_put(sk1);
- }
+out:
+ rcu_read_unlock();
#endif
}
@@ -1538,11 +1538,12 @@
int tcp_v4_rcv(struct sk_buff *skb)
{
+ struct net *net = dev_net(skb->dev);
const struct iphdr *iph;
const struct tcphdr *th;
+ bool refcounted;
struct sock *sk;
int ret;
- struct net *net = dev_net(skb->dev);
if (skb->pkt_type != PACKET_HOST)
goto discard_it;
@@ -1588,7 +1589,7 @@
lookup:
sk = __inet_lookup_skb(&tcp_hashinfo, skb, __tcp_hdrlen(th), th->source,
- th->dest);
+ th->dest, &refcounted);
if (!sk)
goto no_tcp_socket;
@@ -1609,7 +1610,11 @@
inet_csk_reqsk_queue_drop_and_put(sk, req);
goto lookup;
}
+ /* We own a reference on the listener, increase it again
+ * as we might lose it too soon.
+ */
sock_hold(sk);
+ refcounted = true;
nsk = tcp_check_req(sk, skb, req, false);
if (!nsk) {
reqsk_put(req);
@@ -1665,7 +1670,8 @@
bh_unlock_sock(sk);
put_and_return:
- sock_put(sk);
+ if (refcounted)
+ sock_put(sk);
return ret;
@@ -1688,7 +1694,8 @@
return 0;
discard_and_relse:
- sock_put(sk);
+ if (refcounted)
+ sock_put(sk);
goto discard_it;
do_time_wait:
@@ -1712,6 +1719,7 @@
if (sk2) {
inet_twsk_deschedule_put(inet_twsk(sk));
sk = sk2;
+ refcounted = false;
goto process;
}
/* Fall through to ACK */
@@ -1845,17 +1853,17 @@
*/
static void *listening_get_next(struct seq_file *seq, void *cur)
{
- struct inet_connection_sock *icsk;
- struct hlist_nulls_node *node;
- struct sock *sk = cur;
- struct inet_listen_hashbucket *ilb;
struct tcp_iter_state *st = seq->private;
struct net *net = seq_file_net(seq);
+ struct inet_listen_hashbucket *ilb;
+ struct inet_connection_sock *icsk;
+ struct sock *sk = cur;
if (!sk) {
+get_head:
ilb = &tcp_hashinfo.listening_hash[st->bucket];
spin_lock_bh(&ilb->lock);
- sk = sk_nulls_head(&ilb->head);
+ sk = sk_head(&ilb->head);
st->offset = 0;
goto get_sk;
}
@@ -1863,28 +1871,20 @@
++st->num;
++st->offset;
- sk = sk_nulls_next(sk);
+ sk = sk_next(sk);
get_sk:
- sk_nulls_for_each_from(sk, node) {
+ sk_for_each_from(sk) {
if (!net_eq(sock_net(sk), net))
continue;
- if (sk->sk_family == st->family) {
- cur = sk;
- goto out;
- }
+ if (sk->sk_family == st->family)
+ return sk;
icsk = inet_csk(sk);
}
spin_unlock_bh(&ilb->lock);
st->offset = 0;
- if (++st->bucket < INET_LHTABLE_SIZE) {
- ilb = &tcp_hashinfo.listening_hash[st->bucket];
- spin_lock_bh(&ilb->lock);
- sk = sk_nulls_head(&ilb->head);
- goto get_sk;
- }
- cur = NULL;
-out:
- return cur;
+ if (++st->bucket < INET_LHTABLE_SIZE)
+ goto get_head;
+ return NULL;
}
static void *listening_get_idx(struct seq_file *seq, loff_t *pos)
