netdev - [PATCH net-next 06/10] udp: update sk_rmem

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Message-ID: <20250916160951.541279-7-edumazet@google.com>
Date: Tue, 16 Sep 2025 16:09:47 +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: Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 06/10] udp: update sk_rmem_alloc before busylock acquisition

Avoid piling too many producers on the busylock
by updating sk_rmem_alloc before busylock acquisition.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/udp.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index edd846fee90ff7850356a5cb3400ce96856e5429..658ae87827991a78c25c2172d52e772c94ea217f 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1753,13 +1753,16 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	if (rmem > (rcvbuf >> 1)) {
 		skb_condense(skb);
 		size = skb->truesize;
+		rmem = atomic_add_return(size, &sk->sk_rmem_alloc);
+		if (rmem > rcvbuf)
+			goto uncharge_drop;
 		busy = busylock_acquire(sk);
+	} else {
+		atomic_add(size, &sk->sk_rmem_alloc);
 	}
 
 	udp_set_dev_scratch(skb);
 
-	atomic_add(size, &sk->sk_rmem_alloc);
-
 	spin_lock(&list->lock);
 	err = udp_rmem_schedule(sk, size);
 	if (err) {
-- 
2.51.0.384.g4c02a37b29-goog