How we spent two weeks hunting an NFS bug in the Linux kernel

This post details the debugging of a 'Stale file handle' error in Git when using NFS v4.0. It describes reproducing the bug by keeping a file open while another machine renames it, and how this behavior differs between NFS v4.0 and v4.1. The investigation involved analyzing `strace` and `lsof` output to understand `git gc`'s file handling and using `tcpdump` and Wireshark to analyze NFS traffic. The root cause was identified as a bug in the Linux v4.0 NFS client related to NFS server delegations and their recall, leading to a kernel patch that was backported to stable versions.