From: Jakub Sitnicki <jakub@cloudflare.com>
Date: Fri, 17 Jul 2020 12:35:28 +0200
Subject: udp: Extract helper for selecting socket from reuseport group
Patch-mainline: v5.9-rc1
Git-commit: 7629c73a1466ec2348e9f64c874c19bf13f35f4c
References: bsc#1177028

Prepare for calling into reuseport from __udp4_lib_lookup as well.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200717103536.397595-8-jakub@cloudflare.com
Acked-by: Gary Lin <glin@suse.com>

NOTE from Gary:
  The original commit conflicts with a 5.8-rc7 fix(*1). Follow the merge commit
  to modify this patch. 
 
  (*1) efc6b6f6c3113 udp: Improve load balancing for SO_REUSEPORT.
  (*2) a57066b1a0197 Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
---
 net/ipv4/udp.c |   37 +++++++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 14 deletions(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -408,6 +408,22 @@ static u32 udp_ehashfn(const struct net
 			      udp_ehash_secret + net_hash_mix(net));
 }
 
+static struct sock *lookup_reuseport(struct net *net, struct sock *sk,
+					    struct sk_buff *skb,
+					    __be32 saddr, __be16 sport,
+					    __be32 daddr, unsigned short hnum)
+{
+	struct sock *reuse_sk = NULL;
+	u32 hash;
+
+	if (sk->sk_reuseport && sk->sk_state != TCP_ESTABLISHED) {
+		hash = udp_ehashfn(net, daddr, hnum, saddr, sport);
+		reuse_sk = reuseport_select_sock(sk, hash, skb,
+						 sizeof(struct udphdr));
+	}
+	return reuse_sk;
+}
+
 /* called with rcu_read_lock() */
 static struct sock *udp4_lib_lookup2(struct net *net,
 				     __be32 saddr, __be16 sport,
@@ -416,9 +432,8 @@ static struct sock *udp4_lib_lookup2(str
 				     struct udp_hslot *hslot2,
 				     struct sk_buff *skb)
 {
-	struct sock *sk, *result, *reuseport_result;
+	struct sock *sk, *result;
 	int score, badness;
-	u32 hash = 0;
 
 	result = NULL;
 	badness = 0;
@@ -426,19 +441,13 @@ static struct sock *udp4_lib_lookup2(str
 		score = compute_score(sk, net, saddr, sport,
 				      daddr, hnum, dif, sdif);
 		if (score > badness) {
-			reuseport_result = NULL;
-
-			if (sk->sk_reuseport &&
-			    sk->sk_state != TCP_ESTABLISHED) {
-				hash = udp_ehashfn(net, daddr, hnum,
-						   saddr, sport);
-				reuseport_result = reuseport_select_sock(sk, hash, skb,
-									 sizeof(struct udphdr));
-				if (reuseport_result && !reuseport_has_conns(sk, false))
-					return reuseport_result;
-			}
+			result = lookup_reuseport(net, sk, skb,
+						  saddr, sport, daddr, hnum);
+			/* Fall back to scoring if group has connections */
+			if (result && !reuseport_has_conns(sk, false))
+				return result;
 
-			result = reuseport_result ? : sk;
+			result = result ? : sk;
 			badness = score;
 		}
 	}