Linux 7.1 To Retire UDP-Lite – Allows For Better Performance With Cleansed Code

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 Google 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.

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