Comment # 7 on bug 927725 from lynda t

Works for kernel-default, not for kernel-xen

Upgrading kernel to

    4.0.0-4.g27299c0

Machine boots to !Xen, kernel-default

    uname -rm
        4.0.0-4.g27299c0-default x86_64

efi is mounted  and in use correctly

    mount | grep -i efi
        efivarfs on /sys/firmware/efi/efivars type efivarfs
(rw,nosuid,nodev,noexec,relatime)
        systemd-1 on /boot/efi type autofs
(rw,relatime,fd=42,pgrp=1,timeout=300,minproto=5,maxproto=5,direct)

But, boot to kernel-xen fails 100% reproducibly to EmergencyMode

    ...
    [  OK  ] Started File System Check on Root Device.
             Starting Remount Root and Kernel File Systems...
    [  OK  ] Started Remount Root and Kernel File Systems.
    [  OK  ] Reached target Local File Systems (Pre).
             Mounting /sys/kernel/debug...
    [  OK  ] Mounted /sys/kernel/debug.
    [ TIME ] Timed out waiting for device dev-vg0-HOME.device.
    [DEPEND] Dependency failed for /usr/local/src.
    [DEPEND] Dependency failed for Local File Systems.
    Welcome to emergency mode! After logging in, type "journalctl -xb" to view
    system logs, "systemctl reboot" to reboot, "systemctl default" to try again
    to boot into default mode.
    Give root password for maintenance
    (or press Control-D to continue): 
    [~]$uname -rm
        4.0.0-4.g27299c0-xen x86_64

A quick look at the console logs, in current !debug loglevel, shows a LOT of
these,

    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-sysctl[819]: Overwriting earlier assignment
of n
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-sysctl[819]: Overwriting earlier assignment
of n
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-sysctl[819]: Overwriting earlier assignment
of k
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac
    Apr 25 08:34:11 xen01 systemd-udevd[781]: maximum number (72) of children
reac

efi partition is not mounted, and not mountable

    mount | grep -i efi
        efivarfs on /sys/firmware/efi/efivars type efivarfs
(rw,nosuid,nodev,noexec,relatime)

To recover, manual reboot still required

    (XEN) [2015-04-25 15:46:23] Manual reset required ('noreboot' specified)