Re: [Xen-devel] [PATCH v3 10/10] xen/arm: Enable errata for secondary CPU on hotplug after the boot

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2018-05-11 at 11:54 +0100, Julien Grall wrote:
> On 11/05/18 11:41, Mirela Simonovic wrote:
> "We should really avoid to use panic(...) if this is something the 
> system can survive. In that specific case, it would only affect the 
> current CPU. So it would be better to return an error and let the
> caller 
> decide what to do."
> 
> To summarize:
>       1) Notifiers should only report an error and let the upper
> caller (here 
> notify_cpu_starting()) deciding what to do.
>       2) I am OK with the BUG_ON in notify_cpu_starting() for now.
> 
And, in general, I agree with all this.

However (and I think I'm repeating this concept for, what, the 10th
time now?!?! :-P), in this specific case, the reason why none of the
existing CPU_STARTING callbacks report an error, is that the CPU
bringup process is, AFAICT, built around the assumption that once we
reached CPU_STARTING, things can't fail.

For this very reason, whatever new CPU_STARTING callback is introduced,
in this series or everywhere else, _can't_ fail, and _can't_ return any
error.

If we need to have a CPU_STARTING callback that can fail, we need to
change the CPU bringup process accordingly.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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