[Skiboot] question about sbe-p9 timer

[Oliver O'Halloran]

On Thu, Feb 13, 2020 at 3:32 AM Thiago Jung Bauermann
<bauerman at linux.ibm.com> wrote:
>
>
> Hello,
>
> I've been studying the timer code in hw/sbe-p9.c and I have a question
> regarding concurrency: I noticed that in almost all cases,
> sbe_last_gen_stamp is accessed with sbe->lock held (where sbe is the
> default chip).
>
> Except in one case: p9_sbe_update_timer_expiry() calls
> p9_sbe_timer_schedule() - which reads sbe_last_gen_stamp - without
> acquiring sbe->lock. Is this a problem that needs to be fixed?

The SBE timer state is protected by a separate lock (sbe_timer_lock)
since it's global state and not tied to a specific SBE. When starting
the timer we take the per-SBE lock for the default SBE since we need
to modify its message queue. Seems ok to me.

>
> --
> Thiago Jung Bauermann
> IBM Linux Technology Center
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