krpc: unbootable ZFS-on-root after major upgrade to 11.2

[Eugene Grosbein]

22.10.2018 21:03, Glen Barber wrote:

t's strange that this is a 10.x vs 11.x issue.
>>> I see that zfs has the krpc dependency since r193128.
>>> And the call to xdrmem_create is there since r168404.
>>
>> You are right. I was mis-informed and have not verified enough a report from local user.
>>
>> Glen, maybe that errata record should be deleted. The problem is real but it is long-standing
>> and present in 10.x too.
>>
> 
> Could you elaborate more on the failure case you originally reported
> first?  If the problem is real, my feeling is that the errata entry
> should stay, just worded differently to reflect the failure case here.

zfs.ko depends on krpc.ko. The KRPC code in compiled in GENERIC kernel as dependency
of NFS client/server code. The problem arises if all of these are true:

1) a system uses custom kernel with NFS options removed;
2) there is no krpc.ko available due to MODULES_OVERRIDE excluding it;
3) the system boots off ZFS pool.

In such case, loader cannot resolve dependency and fails to load zfs.ko
and kernel fails to mount root breaking boot sequence.