------- Comment From [email protected] 2016-07-14 08:43 EDT-------
As an alternate solution, try this:

1) Modify /usr/share/initramfs-tools/scripts/init-top/udev

Replace line
udevadm trigger --action=add
with
udevadm trigger --type=subsystems --action=add
udevadm trigger --type=devices --action=add

2) Modify /etc/default/kdump-tools

Replace existing KDUMP_CMDLINE_APPEND= lines with
KDUMP_CMDLINE_APPEND="cio_ignore=all,!condev"

3) Rebuild the kdump initramfs

/etc/kernel/postinst.d/kdump-tools

4) Check if kdump works

echo c > /proc/sysrq-trigger

Explanation:

- Ubuntu 16.04 uses zdev to configure z Systems specific devices
- zdev also handles cio_ignore configuration via a Udev rule that triggers
when the CCW bus is registered (see /etc/udev/rules.d/41-cio-ignore.rules)
- Because of the way that Ubuntu's initramfs tools trigger coldplug of
Uevents, the Uevent for the CCW bus is not generated and the cio_ignore
rule is not triggered. I consider this a bug in Ubuntu's udev package
because systemd provides a corresponding coldplug unit file (see
/lib/systemd/system/systemd-udev-trigger.service) that performs the steps
as proposed in 1)
- With cio_ignore handling covered by the udev rule, KDUMP can use the
command line in 2) to blacklist all devices except the console. The
latter needs to be excluded as the kernel would otherwise not boot on
a z/VM guest

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https://bugs.launchpad.net/bugs/1570775

Title:
  makekdump should re-exec with cio_ignore on s390x

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