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SubjectRe: [PATCH 4/4] cpu/hotplug: Fix CPU down rollback
On Thu, Jan 21, 2021 at 03:57:03PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 11, 2021 at 05:10:47PM +0000, vincent.donnefort@arm.com wrote:
> > From: Vincent Donnefort <vincent.donnefort@arm.com>
> >
> > After the AP brought itself down to CPUHP_TEARDOWN_CPU, the BP will finish
> > the job. The steps left are as followed:
> >
> > +--------------------+
> > | CPUHP_TEARDOWN_CPU | -> If fails state is CPUHP_TEARDOWN_CPU
> > +--------------------+
> > | ATOMIC STATES | -> Cannot Fail
> > +--------------------+
> > | CPUHP_BRINGUP_CPU | -> Cannot fail
> > +--------------------+
> > | ... |
> > | ... | -> Can fail and rollback
>
> These are the PREPARE/DEAD states, right? It would be _really_ daft for
> a DEAD notifier to fail. But yeah, I suppose that if it does, it will
> indeed end up in CPUHP_AP_ONLINE_IDLE.
>
> Do we want to WARN when a DEAD notifier fails?
>
>

Indeed, I couldn't find a dead callback which can return an error. So I
suppose we could go for another strategy here, that would be to not allow
failure for the dead states (i.e states < BRINGUP_CPU when hotunplug). In
that case, the fail interface should probably disallow selecting those
states and a WARN here would be good.

--
Vincent

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