net: reduce cycles spend on ICMP replies that gets rate limited

This patch split the global and per (inet)peer ICMP-reply limiter
code, and moves the global limit check to earlier in the packet
processing path.  Thus, avoid spending cycles on ICMP replies that
gets limited/suppressed anyhow.

The global ICMP rate limiter icmp_global_allow() is a good solution,
it just happens too late in the process.  The kernel goes through the
full route lookup (return path) for the ICMP message, before taking
the rate limit decision of not sending the ICMP reply.

Details: The kernels global rate limiter for ICMP messages got added
in commit 4cdf507d5452 ("icmp: add a global rate limitation").  It is
a token bucket limiter with a global lock.  It brilliantly avoids
locking congestion by only updating when 20ms (HZ/50) were elapsed. It
can then avoids taking lock when credit is exhausted (when under
pressure) and time constraint for refill is not yet meet.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 34 insertions, 15 deletions

diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c
index 3036f66..b26ae8b 100644
--- a/net/ipv6/icmp.c
+++ b/net/ipv6/icmp.c
@@ -168,6 +168,30 @@ static bool is_ineligible(const struct sk_buff *skb)
 	return false;
 }
 
+static bool icmpv6_mask_allow(int type)
+{
+	/* Informational messages are not limited. */
+	if (type & ICMPV6_INFOMSG_MASK)
+		return true;
+
+	/* Do not limit pmtu discovery, it would break it. */
+	if (type == ICMPV6_PKT_TOOBIG)
+		return true;
+
+	return false;
+}
+
+static bool icmpv6_global_allow(int type)
+{
+	if (icmpv6_mask_allow(type))
+		return true;
+
+	if (icmp_global_allow())
+		return true;
+
+	return false;
+}
+
 /*
  * Check the ICMP output rate limit
  */
@@ -178,12 +202,7 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	struct dst_entry *dst;
 	bool res = false;
 
-	/* Informational messages are not limited. */
-	if (type & ICMPV6_INFOMSG_MASK)
-		return true;
-
-	/* Do not limit pmtu discovery, it would break it. */
-	if (type == ICMPV6_PKT_TOOBIG)
+	if (icmpv6_mask_allow(type))
 		return true;
 
 	/*
@@ -200,20 +219,16 @@ static bool icmpv6_xrlim_allow(struct sock *sk, u8 type,
 	} else {
 		struct rt6_info *rt = (struct rt6_info *)dst;
 		int tmo = net->ipv6.sysctl.icmpv6_time;
+		struct inet_peer *peer;
 
 		/* Give more bandwidth to wider prefixes. */
 		if (rt->rt6i_dst.plen < 128)
 			tmo >>= ((128 - rt->rt6i_dst.plen)>>5);
 
-		if (icmp_global_allow()) {
-			struct inet_peer *peer;
-
-			peer = inet_getpeer_v6(net->ipv6.peers,
-					       &fl6->daddr, 1);
-			res = inet_peer_xrlim_allow(peer, tmo);
-			if (peer)
-				inet_putpeer(peer);
-		}
+		peer = inet_getpeer_v6(net->ipv6.peers, &fl6->daddr, 1);
+		res = inet_peer_xrlim_allow(peer, tmo);
+		if (peer)
+			inet_putpeer(peer);
 	}
 	dst_release(dst);
 	return res;
@@ -493,6 +508,10 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
 	sk = icmpv6_xmit_lock(net);
 	if (!sk)
 		return;
+
+	if (!icmpv6_global_allow(type))
+		goto out;
+
 	sk->sk_mark = mark;
 	np = inet6_sk(sk);