Monitoring components for CPU/segmentation faults

[Christian Helmuth]

Hello Pirmin,

On Tue, Jul 05, 2022 at 15:54:19 CEST, Duss Pirmin wrote:
> While searching for a solution to the problem of misbehaving components I
> stumbled upon
> `test-fault_detection` which gave me the idea to let init monitor the PD/CPU
> session of
> its children and report the error.
> 
> The idea is that a monitor component can then decide what to do about the
> failure.

This is an interesting idea indeed but I'm not quite sure if Init is
the right component for monitoring such errors. Currently, Init
already provides the monitoring of component liveliness by the
"hearbeat" feature. Your current implementation augments this with
info about CPU exceptions but any other details about the
exceptions or even which threads faults is still missing. I'd expect
developers instantly demanding more information from the monitoring
feature, which would bloat Init more and more.

> I have drafted what I envision in [1]. It is not yet complete, as I'm not
> sure on how to
> safely remove the signal handlers if in a config change the monitoring is
> disabled.
> 
> If you think this feature would be useful, I'd create an issue where the
> implementation details
> could be discussed.
> 
> On the other hand maybe someone has an other idea how a similar
> functionality can be achieved.

Please go forward and open the issue, and maybe leave open if Init
(while a natural first attempt) is the right place to implement the
feature finally. In past offline discussions we identified POSIX
components as the most valuable target for monitoring. We envisioned
to extend the LibC runtime by a local exception handler for the
component, which could optionally reveal more details about the fault
and even provide a stack backtrace. Back then, I always thought about
logging the information, after your proposal I'm convinced using a
Report session is much more appropriate.

Regards
-- 
Christian Helmuth
Genode Labs

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