Question: Move BPF_SK_LOOKUP ahead of connected UDP sk lookup?
From: Philo Lu <lulie@linux.alibaba.com>
Date: 2024-08-20 12:31:05
Also in:
bpf
Subsystem:
networking [general], the rest, user datagram protocol (udp) · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Willem de Bruijn
Hi all, I wonder if it is feasible to move BPF_SK_LOOKUP ahead of connected UDP sk lookup? That is something like: (i.e., move connected udp socket lookup behind bpf sk lookup prog)
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ddb86baaea6c8..9a1408775bcb1 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -493,13 +493,6 @@ struct sock *__udp4_lib_lookup(const struct net
*net, __be32 saddr,
slot2 = hash2 & udptable->mask;
hslot2 = &udptable->hash2[slot2];
- /* Lookup connected or non-wildcard socket */
- result = udp4_lib_lookup2(net, saddr, sport,
- daddr, hnum, dif, sdif,
- hslot2, skb);
- if (!IS_ERR_OR_NULL(result) && result->sk_state == TCP_ESTABLISHED)
- goto done;
-
/* Lookup redirect from BPF */
if (static_branch_unlikely(&bpf_sk_lookup_enabled) &&
udptable == net->ipv4.udp_table) {
@@ -512,6 +505,13 @@ struct sock *__udp4_lib_lookup(const struct net
*net, __be32 saddr,
}
}
+ /* Lookup connected or non-wildcard socket */
+ result = udp4_lib_lookup2(net, saddr, sport,
+ daddr, hnum, dif, sdif,
+ hslot2, skb);
+ if (!IS_ERR_OR_NULL(result) && result->sk_state == TCP_ESTABLISHED)
+ goto done;
+
/* Got non-wildcard socket or error on first lookup */
if (result)
goto done;
This will be useful, e.g., if there are many concurrent udp sockets of a same ip:port, where udp4_lib_lookup2() may induce high softirq overhead, because it computes score for all sockets of the ip:port. With bpf sk_lookup prog, we can implement 4-tuple hash for udp socket lookup to solve the problem (if bpf prog runs before udp4_lib_lookup2). Currently, in udp, bpf sk lookup runs after connected socket lookup. IIUC, this is because the early version of SK_LOOKUP[0] modified local_ip/local_port to redirect socket. This may interact wrongly with udp lookup because udp uses score to select socket, and setting local_ip/local_port cannot guarantee the result socket selected. However, now we get socket directly from map in bpf sk_lookup prog, so the above problem no longer exists. So is there any other problem on it？Or I'll try to work on it and commit patches later. [0]https://lore.kernel.org/bpf/20190618130050.8344-1-jakub@cloudflare.com/ (local) Thank you for your time. -- Philo