Critical BMC process failure recovery

[Andrew Geissler]

> On Oct 20, 2020, at 9:28 AM, Patrick Williams <patrick at stwcx.xyz> wrote:
> 
> Hi Andrew,
> 
> I like the proposal to reuse what systemd already provides.  It does
> look like Lei pointed to some existing bbclass that could be enhanced
> for this purpose so that any recipe can simply 'inherit ...' and maybe
> set a variable to indicate that it is providing "critical services”.

Yeah, looks like currently it opts in every service (except for a few special
cases). I like the idea of putting it on the individual service to
opt itself in. I’ve def seen what James mentions in his response
where you get in situations where the BMC is rebooting itself too
much due to non-critical services failing.

> 
> On Mon, Oct 19, 2020 at 02:53:11PM -0500, Andrew Geissler wrote:
>> Greetings,
>> 
>> I've started initial investigation into two IBM requirements:
>> 
>> - Reboot the BMC if a "critical" process fails and can not recover
>> - Limit the amount of times the BMC reboots for recovery
>>  - Limit should be configurable, i.e. 3 resets within 5 minutes
> 
> I like that it has a time bound on it here.  If the reset didn't have a
> time bound that would be a problem to me because it means that a slow
> memory leak could eventually get the BMCs into this state.
> 
> Do you need to do anything in relationship with the WDT and failover
> settings there?  I'm thinking you'll need to do something to ensure that
> you don't swap flash banks between these resets.  Do you need to do N
> resets on one flash bank and then M on the other?

I’m hoping to keep the flash bank switch a separate discussion. The key
here is to not impact whatever design decision is made there.

We’re still going back and forth a bit on whether we want to continue
with that automatic flash bank switch design point. It sometimes causes
more confusion than it’s worth.

I know we did make this work with our Witherspoon system from
a watchdog perspective. We would reboot a certain amount of times
and swap flash banks after a certain limit was reached. I’m not 
sure how we did it though :)

> 
> It seems that the most likely cause of N resets in a short time is some
> sort of flash corruption, BMC chip error, or a bug aggravated some RWFS
> setting.  None of these are particularly recovered by the reset but at
> least you know your in a bad situation at that point.

Yeah, I would really like some data on how often a reboot of the
BMC really does fix an issue. The focus for us should def be on
avoiding the reboot in the first place. But the reboot is our last
ditch effort.

> 
>>  - If limit reached, display error to panel (if one available) and halt
>>    the BMC.
> 
> And then what?  What is the remediation for this condition?  Are there
> any services, such as SSH, that will continue to run in this state?  I
> hope the only answer for remediation is physical access / power cycle.

I believe the best option (and what we’ve done historically) is to try and
put an error code on the panel and halt in u-boot, requiring physical
access / power cycle to recover.

> 
> -- 
> Patrick Williams