Re: [PATCH v2 08/13] powerpc/hw_breakpoint: Avoid relying on caller synchronization

Marco Elver
2022-07-01T09:42:05Z

On Fri, 1 Jul 2022 at 10:54, Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
> Hi Marco,
>
> Le 28/06/2022 à 11:58, Marco Elver a écrit :
> > Internal data structures (cpu_bps, task_bps) of powerpc's hw_breakpoint
> > implementation have relied on nr_bp_mutex serializing access to them.
> >
> > Before overhauling synchronization of kernel/events/hw_breakpoint.c,
> > introduce 2 spinlocks to synchronize cpu_bps and task_bps respectively,
> > thus avoiding reliance on callers synchronizing powerpc's hw_breakpoint.
>
> We have an still opened old issue in our database related to
> hw_breakpoint, I was wondering if it could have any link with the
> changes you are doing and whether you could handle it at the same time.
>
> https://github.com/linuxppc/issues/issues/38
>
> Maybe it is completely unrelated, but as your series modifies only
> powerpc and as the issue says that powerpc is the only one to do that, I
> thought it might be worth a hand up.

I see the powerpc issue unrelated to the optimizations in this series;
perhaps by fixing the powerpc issue, it would also become more
optimal. But all I saw is that it just so happens that powerpc relied
on the nr_bp_mutex which is going away.

This series will become even more complex if I decided to add a
powerpc rework on top (notwithstanding the fact I don't have any ppc
hardware at my disposal either). A separate series/patch seems much
more appropriate.

Thanks,
-- Marco