From: Eric Dumazet <edumazet@google.com>
Date: Tue, 16 Sep 2025 16:09:47 +0000 (+0000)
Subject: udp: update sk_rmem_alloc before busylock acquisition
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=faf7b4aefd5be1d1b460e2161b8f730e03abb9b9;p=users%2Fhch%2Fmisc.git

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@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250916160951.541279-7-edumazet@google.com
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index edd846fee90f..658ae8782799 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) {