Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

Guilherme G. Piccoli
2022-05-03T17:58:10Z

On 03/05/2022 14:44, Michael Kelley (LINUX) wrote:
> [...]
>>
>> Hi Michael, thanks for your feedback! I agree that your idea could work,
>> but...there is one downside: imagine the kmsg_dump() approach is not set
>> in some Hyper-V guest, then we would rely in the regular notification
>> mechanism [hv_die_panic_notify_crash()], right?
>> But...you want then to run this notifier in the informational list,
>> which...won't execute *by default* before kdump if no kmsg_dump() is
>> set. So, this logic is convoluted when you mix it with the default level
>> concept + kdump.
>
> Yes, you are right. But to me that speaks as much to the linkage
> between the informational list and kmsg_dump() being the core
> problem. But as I described in my reply to Patch 24, I can live with
> the linkage as-is.

Thanks for the feedback Michael!

> [...]
>> I feel the panic notification mechanism does really fit with a
>> hypervisor list, it's a good match with the nature of the list, which
>> aims at informing the panic notification to the hypervisor/FW.
>> Of course we can modify it if you prefer...but please take into account
>> the kdump case and how it complicates the logic.
>
> I agree that the runtime effect of one list vs. the other is nil. The
> code works and can stay as you written it.
>
> I was trying to align from a conceptual standpoint. It was a bit
> unexpected that one path would be on the hypervisor list, and the
> other path effectively on the informational list. When I see
> conceptual mismatches like that, I tend to want to understand why,
> and if there is something more fundamental that is out-of-whack.
>

Totally agree with you here, I am like that as well - try to really
understand the details, this is very important specially in this patch
set, since it's a refactor and affects every user of the notifiers
infrastructure.

Again, just to double-say it: feel free to suggest any change for the
Hyper-V portion (might as well for any patch in the series, indeed) -
you and the other Hyper-V maintainers own this code and I'd be glad to
align with your needs, you are honor citizens in the panic notifiers
area, being one the most heavy users for that =)

Cheers,

Guilherme