ZFS fails with error 6 on upgrade to 11.1

[Sebastian Schwarz]

On 2017-07-28 Goran Tepšić wrote:
> Try booting your OS or livecd like mfsBSD to import pool to alternate root
> and running 'zpool upgrade ssd', maybe that'll do the trick.

I gave that a try:

> # zpool upgrade ssd
> This system supports ZFS pool feature flags
> 
> Enabled the following features on 'ssd':
>   multi_vdev_crash_dump
>   sha512
>   skein
> # zpool upgrade hdd
> This system supports ZFS pool feature flags
> 
> Enabled the following features on 'ssd':
>   multi_vdev_crash_dump
>   sha512
>   skein

Then I rebooted but I'm still getting the same error.

> I don't know anything about Linux ZFS system but I'd expect
> them t be incompatible afterall.

Well, I'm booting off the pool with 11.0 just fine.  It's 11.1
that's giving me trouble.