The upcoming Linux 7.1 kernel cycle is set to retire UDP-Lite support. The UDP-Lite protocol allowed for partial checksums where potentially damaged/corrupted packets are still delivered to the application. Since the Linux 2.6.20 days there has been UDP-Lite support but the kernel is now set to retire it given breakage that has persisted for years and cleaning up the networking code can yield a performance advantage for non-UDP-Lite users.

Kuniyuki Iwashima of Amazon/AWS took to retiring the UDP-Lite code. He explained of the issues that went unchecked for years and the performance benefit to removing UDP-Lite from the kernel:

"In 2023, syzbot found a null-ptr-deref bug triggered when UDP-Lite attempted to charge an skb after the total memory usage for UDP-Lite _and_ UDP exceeded a system-wide threshold, net.ipv4.udp_mem.

Since this threshold is shared with UDP, the bug would have been easy to trigger if any real-world applications were using UDP-Lite; however, only syzbot ever stumbled upon it.

The bug had persisted since 2016, suggesting that UDP-Lite had remained unused for 7 years at that point.

The bug was fixed in commit ad42a35bdfc6 ("udplite: Fix NULL pointer dereference in __sk_mem_raise_allocated()."), and we added another commit be28c14ac8bb ("udplite: Print deprecation notice.") to announce the deprecation plan.

Since then, no one has complained, so it is time to officially retire UDP-Lite.

This series first removes IPv6 and IPv4 UDP-Lite sockets, then gradually cleans up the remaining dead/unnecessary code within the UDP stack.

By removing a bunch of conditionals for UDP-Lite from the fast path, udp_rr with 20,000 flows sees a 10% increase in pps (13.3 Mpps -> 14.7 Mpps) on an AMD EPYC 7B12 (Zen 2) 64-Core Processor platform.

With FDO, the baseline is much higher and the delta was ~3%, 20.1 Mpps -> 20.7 Mpps

"

So per that messaging, the UDP-Lite code really hasn't been used in years and doing away with it can net some measurable (+3~10% packets per second) for other UDP workloads.

It was back in 2023 that a deprecation notice was put in place for UDP-Lite calling for its removal in 2025. With no complaints and now into 2026 (and past the Linux 6.18 LTS of 2025), it's time for removal.

[1]This merge now in net-next is retiring UDP-Lite with the plan to merge it for Linux 7.1.



[1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d6e0f04bf22d9b25b530c5e04f82664eac942719