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

[Eugene Grosbein]

22.10.2018 21:21, Andriy Gapon wrote:

>>>>> 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.
>>>
>>>
>>
>> So, if I understand correctly (and please correct me if I am wrong), the
>> majority of the text in the errata note is correct, however needs to be
>> tweaked to remove "upgrading from 10.x...".  Is this generally correct?

Yes.

> This is just a typical foot-shooting (and a shortcoming of the kernel build
> system that allows such foot-shooting to happen).
> I think that there can be other ways in which you can specify inconsistent
> kernel options and/or an incorrect subset of modules in MODULES_OVERRIDE to
> create missing dependencies for critical modules.
> Do we want to issue an errata for each possible misconfiguration?

OTOH, we have option krpc in sys/conf/options but it is not mentioned elsewhere:
not in the Handbook nor in the sys/conf/NOTES or GENERIC. Not a bit of our documentation mentions
that ZFS requires KRPC for last 10 years.

One can call it foot-shooting if it is against documentation but that's not the case.