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Message-ID: <20250920111059.500c2b8f@kernel.org> Date: Sat, 20 Sep 2025 11:10:59 -0700 From: Jakub Kicinski <kuba@...nel.org> To: Eric Dumazet <edumazet@...gle.com> Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Willem de Bruijn <willemb@...gle.com>, Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com Subject: Re: [PATCH v2 net-next] udp: remove busylock and add per NUMA queues On Sat, 20 Sep 2025 08:02:27 +0000 Eric Dumazet wrote: > busylock was protecting UDP sockets against packet floods, > but unfortunately was not protecting the host itself. > > Under stress, many cpus could spin while acquiring the busylock, > and NIC had to drop packets. Or packets would be dropped > in cpu backlog if RPS/RFS were in place. > > This patch replaces the busylock by intermediate > lockless queues. (One queue per NUMA node). > > This means that fewer number of cpus have to acquire > the UDP receive queue lock. > > Most of the cpus can either: > - immediately drop the packet. > - or queue it in their NUMA aware lockless queue. > > Then one of the cpu is chosen to process this lockless queue > in a batch. > > The batch only contains packets that were cooked on the same > NUMA node, thus with very limited latency impact. Occasionally hitting a UaF like this: https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/306342/3-fcnal-ipv6-sh/stderr decoded: https://netdev-3.bots.linux.dev/vmksft-net-dbg/results/306342/vm-crash-thr2-0 -- pw-bot: cr
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