[PATCH 5.10 087/406] udp: re-score reuseport groups when connected sockets are present

Greg Kroah-Hartman
2023-09-17T19:23:06Z

From: Lorenz Bauer <lmb@isovalent.com>

[ Upstream commit f0ea27e7bfe1c34e1f451a63eb68faa1d4c3a86d ]

Contrary to TCP, UDP reuseport groups can contain TCP_ESTABLISHED
sockets. To support these properly we remember whether a group has
a connected socket and skip the fast reuseport early-return. In
effect we continue scoring all reuseport sockets and then choose the
one with the highest score.

The current code fails to re-calculate the score for the result of
lookup_reuseport. According to Kuniyuki Iwashima:

1) SO_INCOMING_CPU is set
-> selected sk might have +1 score

2) BPF prog returns ESTABLISHED and/or SO_INCOMING_CPU sk
-> selected sk will have more than 8

Using the old score could trigger more lookups depending on the
order that sockets are created.

sk -> sk (SO_INCOMING_CPU) -> sk (ESTABLISHED)
| |
`-> select the next SO_INCOMING_CPU sk
|
`-> select itself (We should save this lookup)

Fixes: efc6b6f6c311 ("udp: Improve load balancing for SO_REUSEPORT.")
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/r/20230720-so-reuseport-v6-1-7021b683cdae@isovalent.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/udp.c | 20 +++++++++++++++-----
net/ipv6/udp.c | 19 ++++++++++++++-----
2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index f0db66e415bd6..913966e7703fc 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -443,14 +443,24 @@ static struct sock *udp4_lib_lookup2(struct net *net,
score = compute_score(sk, net, saddr, sport,
daddr, hnum, dif, sdif);
if (score > badness) {
- result = lookup_reuseport(net, sk, skb,
- saddr, sport, daddr, hnum);
+ badness = score;
+ result = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
+ if (!result) {
+ result = sk;
+ continue;
+ }
+
/* Fall back to scoring if group has connections */
- if (result && !reuseport_has_conns(sk))
+ if (!reuseport_has_conns(sk))
return result;

- result = result ? : sk;
- badness = score;
+ /* Reuseport logic returned an error, keep original score. */
+ if (IS_ERR(result))
+ continue;
+
+ badness = compute_score(result, net, saddr, sport,
+ daddr, hnum, dif, sdif);
+
}
}
return result;
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 788bb19f32e99..5385037209a6b 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -189,14 +189,23 @@ static struct sock *udp6_lib_lookup2(struct net *net,
score = compute_score(sk, net, saddr, sport,
daddr, hnum, dif, sdif);
if (score > badness) {
- result = lookup_reuseport(net, sk, skb,
- saddr, sport, daddr, hnum);
+ badness = score;
+ result = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
+ if (!result) {
+ result = sk;
+ continue;
+ }
+
/* Fall back to scoring if group has connections */
- if (result && !reuseport_has_conns(sk))
+ if (!reuseport_has_conns(sk))
return result;

- result = result ? : sk;
- badness = score;
+ /* Reuseport logic returned an error, keep original score. */
+ if (IS_ERR(result))
+ continue;
+
+ badness = compute_score(sk, net, saddr, sport,
+ daddr, hnum, dif, sdif);
}
}
return result;
--
2.40.1