netdev - [PATCH net-next] udp: no longer touch sk->sk

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Message-ID: <20240307220016.3147666-1-edumazet@google.com>
Date: Thu,  7 Mar 2024 22:00:16 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>, Martin KaFai Lau <kafai@...com>, Joe Stringer <joe@...d.net.nz>, 
	Alexei Starovoitov <ast@...nel.org>, Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
	Kuniyuki Iwashima <kuniyu@...zon.com>
Subject: [PATCH net-next] udp: no longer touch sk->sk_refcnt in early demux

After commits ca065d0cf80f ("udp: no longer use SLAB_DESTROY_BY_RCU")
and 7ae215d23c12 ("bpf: Don't refcount LISTEN sockets in sk_assign()")
UDP early demux no longer need to grab a refcount on the UDP socket.

This save two atomic operations per incoming packet for connected
sockets.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Martin KaFai Lau <kafai@...com>
Cc: Joe Stringer <joe@...d.net.nz>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 net/ipv4/udp.c | 5 +++--
 net/ipv6/udp.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index a8acea17b4e5344d022ae8f8eb674d1a36f8035a..e43ad1d846bdc2ddf5767606b78bbd055f692aa8 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2570,11 +2570,12 @@ int udp_v4_early_demux(struct sk_buff *skb)
 					     uh->source, iph->saddr, dif, sdif);
 	}
 
-	if (!sk || !refcount_inc_not_zero(&sk->sk_refcnt))
+	if (!sk)
 		return 0;
 
 	skb->sk = sk;
-	skb->destructor = sock_efree;
+	DEBUG_NET_WARN_ON_ONCE(sk_is_refcounted(sk));
+	skb->destructor = sock_pfree;
 	dst = rcu_dereference(sk->sk_rx_dst);
 
 	if (dst)
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 3f2249b4cd5f6a594dd9768e29f20f0d9a57faed..fad6667fad6644db8c679ae9b723ccda15edaede 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -1101,11 +1101,12 @@ void udp_v6_early_demux(struct sk_buff *skb)
 	else
 		return;
 
-	if (!sk || !refcount_inc_not_zero(&sk->sk_refcnt))
+	if (!sk)
 		return;
 
 	skb->sk = sk;
-	skb->destructor = sock_efree;
+	DEBUG_NET_WARN_ON_ONCE(sk_is_refcounted(sk));
+	skb->destructor = sock_pfree;
 	dst = rcu_dereference(sk->sk_rx_dst);
 
 	if (dst)
-- 
2.44.0.278.ge034bb2e1d-goog