Commit 5a465a0da13e ("udp: Fix multiple wraparounds of sk->sk_rmem_alloc.") allowed to slightly overshoot sk->sk_rmem_alloc, when many cpus are trying to feed packets to a common UDP socket. This patch, combined with the following one reduces false sharing on the victim socket under DDOS. Signed-off-by: Eric Dumazet --- net/ipv4/udp.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index cca41c569f37621404829e096306ba7d78ce4d43..edd846fee90ff7850356a5cb3400ce96856e5429 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1739,8 +1739,8 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb) if (rcvbuf > INT_MAX >> 1) goto drop; - /* Always allow at least one packet for small buffer. */ - if (rmem > rcvbuf) + /* Accept the packet if queue is empty. */ + if (rmem) goto drop; } -- 2.51.0.384.g4c02a37b29-goog