jones_supa (887896) writes "A hard to track system lockup bug seems to have appeared in the span of couple of most recent Linux kernel releases. Dave Jones of Red Hat was the one to first report his experience of frequent lockups with 3.18. Later he found out that the issue is present in 3.17 too. The problem was first suspected to be related to Xen. A patch dating back to 2005 was pushed for Xen to fix a vmalloc_fault() path that was similar to what was reported by Dave. The patch had a comment that read "the line below does not always work. Needs investigating!" But it looks like this issue was never properly investigated. Due to the nature of the bug and its difficulty in tracking down, testers might be finding multiple but similar bugs within the kernel. Linus even suggested taking a look in the watchdog code. He also concluded the Xen bug to be a different issue. The bug hunt continues in the Linux Kernel Mailing List."