4.15.0-15 mdadm: CREATE group disk not found

[Márton Kiss]

4.15.0-15-generic (buildd@lcy01-amd64-018) producing the following errors during boot process:

Begin: Waiting for root file system ... Begin: Running /scripts/local-block ... mdadm: CREATE group disk not found
mdadm: No devices listed in conf file were found.
done.
Begin: Running /scripts/local-block ... mdadm: CREATE group disk not found
mdadm: No devices listed in conf file were found.
done.
Begin: Running /scripts/local-block ... mdadm: CREATE group disk not found
mdadm: No devices listed in conf file were found.
done.
...
BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands.

(initramfs) 

It is a Lenovo SR550, and the 4.15.0-13 was booting properly. (Boot log attached)

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1766577

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Joseph Salisbury (jsalisbury)]

Would it be possible for you to test the proposed kernel and post back if it resolves this bug?
See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed.

Thank you in advance!

[Joseph Salisbury (jsalisbury)]

We think this will be fixed in 4.15.0-19 or newer, so if you can test and post back that would be great.

[Juerg Haefliger (juergh)]

4.15.0-19 works OK, 4.15.0-18 is broken.

The problems was introduced in -14 with the following 2 commits:
  * 9403a13fd07e blk-mq: simplify queue mapping & schedule with each possisble CPU
  * f0aff9ccc834 genirq/affinity: assign vectors to all possible CPUs
which where reverted in -19:
  * 97fda9a81481 Revert "genirq/affinity: assign vectors to all possible CPUs"
  * 18a15d75c403 Revert "blk-mq: simplify queue mapping & schedule with each possisble CPU"

[Juerg Haefliger (juergh)]

Marking this as a duplicate of #1765232.

[Green Tea (greentea21)]

Is this issue possible to happen on Ubuntu 16.04.06, 4.15.0-45 kernel?
I saw a very similar log as #1

The boot hangs as #1, but not always happened, after reboot it can successfully boot into OS.

I am not doing any raid, keep mdadm config/setting default.