> It's likely held alive by some random file descriptor someone has open. > IOW, try and walk all /proc/<pid>/fd/<nr> in that case and see whether > anything keeps it alive. Thanks for the suggestion, but I've already tried the equivalent of that by using a debugger to find the superblock in question and then walking all open fds and comparing the superblock pointer. I've validated that this approach works in a synthetic example where I create a new namespace, mount the filesystem under /mnt, run a program to open /mnt/foo and lazy unmount /mnt. Walking procfs seems less precise. I've tried iterating through /proc/*/fd/* and comparing the Device entry of stat -L, also without luck.
