Linux kernel optimization causes QUIC bug

A recent optimization in the Linux kernel, intended to improve TCP performance, has inadvertently created a bug within the QUIC protocol implementation used by Cloudflare. This bug causes the congestion window to become permanently pinned at its minimum, preventing recovery after congestion events. The issue surfaced during specific testing scenarios involving heavy packet loss, where the QUIC implementation failed to ramp up bandwidth utilization even after the loss subsided. Cloudflare has identified a potential fix, highlighting the complex interplay between kernel-level optimizations and application-layer protocols.