net: speedup udp receive path

Since commit 95766fff ([UDP]: Add memory accounting.), 
each received packet needs one extra sock_lock()/sock_release() pair.

This added latency because of possible backlog handling. Then later,
ticket spinlocks added yet another latency source in case of DDOS.

This patch introduces lock_sock_bh() and unlock_sock_bh()
synchronization primitives, avoiding one atomic operation and backlog
processing.

skb_free_datagram_locked() uses them instead of full blown
lock_sock()/release_sock(). skb is orphaned inside locked section for
proper socket memory reclaim, and finally freed outside of it.

UDP receive path now take the socket spinlock only once.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 15 insertions, 11 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 5574a5ddf908..95b851f3d713 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -229,9 +229,13 @@ EXPORT_SYMBOL(skb_free_datagram);
 
 void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb)
 {
-        lock_sock(sk);
-        skb_free_datagram(sk, skb);
-        release_sock(sk);
+        lock_sock_bh(sk);
+        skb_orphan(skb);
+        sk_mem_reclaim_partial(sk);
+        unlock_sock_bh(sk);
+
+        /* skb is now orphaned, might be freed outside of locked section */
+        consume_skb(skb);
 }
 EXPORT_SYMBOL(skb_free_datagram_locked);
 
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 63eb56b2d873..1f86965ba7d7 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1062,10 +1062,10 @@ static unsigned int first_packet_length(struct sock *sk)
         spin_unlock_bh(&rcvq->lock);
 
         if (!skb_queue_empty(&list_kill)) {
-                lock_sock(sk);
+                lock_sock_bh(sk);
                 __skb_queue_purge(&list_kill);
                 sk_mem_reclaim_partial(sk);
-                release_sock(sk);
+                unlock_sock_bh(sk);
         }
         return res;
 }
@@ -1196,10 +1196,10 @@ out:
         return err;
 
 csum_copy_err:
-        lock_sock(sk);
+        lock_sock_bh(sk);
         if (!skb_kill_datagram(sk, skb, flags))
                 UDP_INC_STATS_USER(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
-        release_sock(sk);
+        unlock_sock_bh(sk);
 
         if (noblock)
                 return -EAGAIN;
@@ -1624,9 +1624,9 @@ int udp_rcv(struct sk_buff *skb)
 
 void udp_destroy_sock(struct sock *sk)
 {
-        lock_sock(sk);
+        lock_sock_bh(sk);
         udp_flush_pending_frames(sk);
-        release_sock(sk);
+        unlock_sock_bh(sk);
 }
 
 /*
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3ead20ad9d07..91c60f0090a4 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -424,7 +424,7 @@ out:
         return err;
 
 csum_copy_err:
-        lock_sock(sk);
+        lock_sock_bh(sk);
         if (!skb_kill_datagram(sk, skb, flags)) {
                 if (is_udp4)
                         UDP_INC_STATS_USER(sock_net(sk),
@@ -433,7 +433,7 @@ csum_copy_err:
                         UDP6_INC_STATS_USER(sock_net(sk),
                                         UDP_MIB_INERRORS, is_udplite);
         }
-        release_sock(sk);
+        unlock_sock_bh(sk);
 
         if (flags & MSG_DONTWAIT)
                 return -EAGAIN;