[34-longterm 000/196] v2.6.34.11 longterm review

Posted by Paul Gortmaker

Paul Gortmaker

[34-longterm 196/196] net: sk_add_backlog() take rmem_alloc into account
March 13, 2012 01:30AM

From: Eric Dumazet <[email protected]>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit c377411f2494a931ff7facdbb3a6839b1266bcf6 upstream.

Current socket backlog limit is not enough to really stop DDOS attacks,
because user thread spend many time to process a full backlog each
round, and user might crazy spin on socket lock.

We should add backlog size and receive_queue size (aka rmem_alloc) to
pace writers, and let user run without being slow down too much.

Introduce a sk_rcvqueues_full() helper, to avoid taking socket lock in
stress situations.

Under huge stress from a multiqueue/RPS enabled NIC, a single flow udp
receiver can now process ~200.000 pps (instead of ~100 pps before the
patch) on a 8 core machine.

Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Paul Gortmaker <[email protected]>
---
include/net/sock.h | 13 +++++++++++--
net/core/sock.c | 5 ++++-
net/ipv4/udp.c | 4 ++++
net/ipv6/udp.c | 8 ++++++++
net/sctp/socket.c | 3 ---
5 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 721c7b3..b365fc2 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -255,7 +255,6 @@ struct sock {
struct sk_buff *head;
struct sk_buff *tail;
int len;
- int limit;
} sk_backlog;
wait_queue_head_t *sk_sleep;
struct dst_entry *sk_dst_cache;
@@ -604,10 +603,20 @@ static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
skb->next = NULL;
}

+/*
+ * Take into account size of receive queue and backlog queue
+ */
+static inline bool sk_rcvqueues_full(const struct sock *sk, const struct sk_buff *skb)
+{
+ unsigned int qsize = sk->sk_backlog.len + atomic_read(&sk->sk_rmem_alloc);
+
+ return qsize + skb->truesize > sk->sk_rcvbuf;
+}
+
/* The per-socket spinlock must be held here. */
static inline __must_check int sk_add_backlog(struct sock *sk, struct sk_buff *skb)
{
- if (sk->sk_backlog.len >= max(sk->sk_backlog.limit, sk->sk_rcvbuf << 1))
+ if (sk_rcvqueues_full(sk, skb))
return -ENOBUFS;

__sk_add_backlog(sk, skb);
diff --git a/net/core/sock.c b/net/core/sock.c
index cf3b9aa..78b7087 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -327,6 +327,10 @@ int sk_receive_skb(struct sock *sk, struct sk_buff *skb, const int nested)

skb->dev = NULL;

+ if (sk_rcvqueues_full(sk, skb)) {
+ atomic_inc(&sk->sk_drops);
+ goto discard_and_relse;
+ }
if (nested)
bh_lock_sock_nested(sk);
else
@@ -1885,7 +1889,6 @@ void sock_init_data(struct socket *sock, struct sock *sk)
sk->sk_allocation = GFP_KERNEL;
sk->sk_rcvbuf = sysctl_rmem_default;
sk->sk_sndbuf = sysctl_wmem_default;
- sk->sk_backlog.limit = sk->sk_rcvbuf << 1;
sk->sk_state = TCP_CLOSE;
sk_set_socket(sk, sock);

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index fd510bc..ff6a18e 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1410,6 +1410,10 @@ int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
goto drop;
}

+
+ if (sk_rcvqueues_full(sk, skb))
+ goto drop;
+
rc = 0;

bh_lock_sock(sk);
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 402a61c..479f926 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -590,6 +590,10 @@ static void flush_stack(struct sock **stack, unsigned int count,

sk = stack;
if (skb1) {
+ if (sk_rcvqueues_full(sk, skb)) {
+ kfree_skb(skb1);
+ goto drop;
+ }
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
udpv6_queue_rcv_skb(sk, skb1);
@@ -765,6 +769,10 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,

/* deliver */

+ if (sk_rcvqueues_full(sk, skb)) {
+ sock_put(sk);
+ goto discard;
+ }
bh_lock_sock(sk);
if (!sock_owned_by_user(sk))
udpv6_queue_rcv_skb(sk, skb);
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 7f28df5..8375609 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -3720,9 +3720,6 @@ SCTP_STATIC int sctp_init_sock(struct sock *sk)

SCTP_DBG_OBJCNT_INC(sock);

- /* Set socket backlog limit. */
- sk->sk_backlog.limit = sysctl_sctp_rmem[1];
-
local_bh_disable();
percpu_counter_inc(&sctp_sockets_allocated);
sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
--
1.7.9.3

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