Handling BMC Reboots when Host is Running

Andrew Geissler geissonator at gmail.com
Thu Mar 23 07:57:54 AEDT 2017

A few updates for everyone on this.  The initial chassis code went in
via this commit and it's 2 next one's -

I've been working this sprint on refactoring host ipmid a bit to be
able to send up different commands (currently our only communication
up to the host is a hard coded soft reboot).  The host interface
proposal is out here - https://gerrit.openbmc-project.xyz/#/c/3098/.
We need this so there's a way to discover if the host is running after
a bmc reboot.

One thing I didn’t really like (and neither did anyone else) with
handling bmc reboots while the chassis is on or if the host is running
is that we have a target fail in the journal when they are not on or
running.  See https://github.com/openbmc/openbmc/issues/1337

Here’s what I did:
Action Target: obmc-chassis-reset.target
  Requires: op-reset-pgood-check.service (check for pgood, service
success if so, fail otherwise)
  Requires: op-reset-set-power-on.service (runs after pgood-check,
creates file indicating pgood on)
  Requires: op-reset-chasiss-on.service (runs after set-power-on,
starts chassis power on target)

There was also a synchronization target, obmc-power-reset-on.target,
which indicated power was on (pgood-check service a success).

If pgood was not on, then the pgood-check service would fail, causing
the other services to not run and the obmc-chassis-reset.target to
fail.  No harm, but confusing to see a target fail in the journal on
the way to BMC_READY.  The cool part was this was all contained to
targets and services with no applications needed.  You could easily
add other services that help determine if the chassis is “on” and
other services once it was found that power was on.

Here’s my new proposal:
Action Target: obmc-chassis-reset.target
   Requires: op-reset-power-check.service - a shell script that
verifies power is on, and creates the file if so

this service always return success (pgood on or off) unless it hits a
real failure
   Requires: op-reset-chassis-on.service     - start the chassis
target - setup service file to only run if “power on” file created.

We have to write a shell script, and we’re not quite as dynamic with
plug and play of services, but we now won’t have a target fail and it
simplifies the process a bit.

With this proposal in mind, I’d like to do something similar with host function

Action Target: obmc-host-reset.target:
   Requires: obmc-chassis-reset.target
   Requires: op-reset-host-check.service - Service runs after the
application that only runs if the chassis power service created the
“power on” file.

This issues the heartbeat command to the host and if the host
responds, it creates the

“host on” file.  This will need to be an application since dbus signal
monitoring is required.

   Requires: op-reset-host-on.service       - start the host start
target - only run if “host on” file created

Xo, wondering if the Zaius issue could be related to what we see on
Witherspoon, https://github.com/openbmc/openbmc/issues/1322?  Either
way we seem to have a similar problem on witherspoon so all of this
above code is moot until we get that figured out.  Testing on
barreleye has been fine though.

Thoughts/Ideas always appreciated,

On Thu, Mar 2, 2017 at 12:04 PM, Xo Wang <xow at google.com> wrote:
> On Wed, Mar 1, 2017 at 5:01 PM, Joel Stanley <joel at jms.id.au> wrote:
>> On Wed, Mar 1, 2017 at 3:33 AM, Andrew Geissler <geissonator at gmail.com> wrote:
>>> My story this sprint, https://github.com/openbmc/openbmc/issues/1094,
>>> is to allow the BMC to be rebooted while the host is up and running.
>> Cool. In addition to this work, we need to make sure the required bits
>> of the Aspeed hardware are not reset to a default state, either by the
>> SoC's reset mechanism, or by the loading of drivers.
>> GPIOs are a good example of this. When we know that the host is
>> already up, any access should read the current state of the GPIO and
>> before it does any toggling. Another is the operation of flash (which
>> will now need to be handled by mboxd).
> FYI, we have an internal bug about Zaius-specific behavior with our
> board-level latches (between BMC and power sequencer) being set
> transparent prior to reading the host power state. This kills power to
> the host every time that the BMC resets.
> I'm currently working on this and it looks like a bug with my earlier
> changes to the glib-based power control daemon.
>> I realise this is outside the scope of your "lets get the targets
>> sorted" work. I thought I'd mention it now so we can be on the look
>> out for strange behaviour as you do your rework.
>> Cheers,
>> Joel
>>> After the BMC reboot, we need to keep the host running and also get to
>>> the appropriate systemd target states to represent this.   The
>>> challenge here is that if we just re-ran the existing targets and
>>> services, we would do things like run P9 vcs workarounds, bit bang the
>>> FSI bus, and even potentially toggle pgood.  We obviously need to
>>> avoid this in order to keep the host up and running.  This divides our
>>> services started during a obmc-host-start.target into 2 categories,
>>> services required to boot the system, and services which are required
>>> to support the host running.  We only want to run the latter in a
>>> situation where the BMC is reset while the host is up and running.
>>> Requirements:
>>> - The applications should have no knowledge of Host state
>>>   - i.e. the service starting or not starting is where we control what runs
>>> - Must handle being able to start and not start any arbitrary service
>>> within the host power on targets
>>>   - Lots of services have dependencies on each other and
>>> synchronization targets, this design has to handle starting services
>>> that depend on other services or targets that may not be required when
>>> the host is running
>>> - The obmc-host-start.target needs to get to the running state when
>>> the host is already running after a BMC reset
>>>   - This will ensure that any re-starts of this target do not harm the
>>> system and that the power off targets will work as expected
>>> Proposal:
>>> Use the ConditionPathExists= systemd unit feature.
>>> From the man page: "Before starting a unit, verify that the specified
>>> condition is true. If it is not true, the starting of the unit will be
>>> (mostly silently) skipped, however all ordering dependencies of it are
>>> still respected. A failing condition will not result in the unit being
>>> moved into a failure state. The condition is checked at the time the
>>> queued start job is to be executed. Use condition expressions in order
>>> to silently skip units that do not apply to the local running system,
>>> for example because the kernel or runtime environment doesn't require
>>> its functionality. "
>>> This will be put in the service files that we do not want to run in
>>> this reset scenario (services required to boot the system).  The first
>>> service we will run on a power on, is a service that detects whether
>>> the host is already running.  If the host is running, then this
>>> service will create a file which will then be used to determine
>>> whether the boot services are run or not.
>>> The nice part about ConditionPathExists= is that it doesn’t execute
>>> the application in the services, but it allows dependencies on that
>>> service to be satisfied so systemd will still start the dependent
>>> services and reach the dependent synchronization targets.
>>> This proposal has not gone off as well as I would have hoped
>>> internally here :)  There’s definitely a desire to not have this at
>>> the service level, but rather at the target level.  I have not found a
>>> solution in this area though that satisfies the above requirements.
>>> Thoughts/ideas are definitely appreciated.
>>> Andrew
> cheers
> xo

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