A bug that was randomly hanging nbdkit tests was fixed after an extensive and frustrating investigation. At first, developers suspected a QEMU bug, but it was eventually concluded that the problem was likely in the Linux guest kernel. However, tracking down the kernel bug required a slow process of bisecting the kernel with a large number of commits. In the end, a hardware-speed dependent race condition was identified, and a fix was suggested by Thomas Gleixner. Although the patch that introduced the bug had already gone into several stable trees, the bug is now fixed.
https://rwmj.wordpress.com/2023/06/18/follow-up-to-i-booted-linux-292612-times/