Re: [PATCH 8/9] perf/breakpoint: Split breakpoint "check" and "commit"

Joel Fernandes
2018-05-15T15:18:59Z

On Tue, May 15, 2018 at 03:53:00PM +0200, Frederic Weisbecker wrote:
> On Mon, May 07, 2018 at 12:46:06AM +0000, Joel Fernandes wrote:
> > On Sun, May 6, 2018 at 12:22 PM Frederic Weisbecker <frederic@kernel.org>
> > wrote:
> >
> > > arch_validate_hwbkpt_settings() mixes up attribute check and commit into
> > > a single code entity. Therefore the validation may return an error due to
> > > incorrect atributes while still leaving halfway modified architecture
> > > breakpoint struct.
> >
> > > Now that we have split its logic on all archs, we can remove this
> > > misdesigned function and call directly the arch check and commit
> > > functions instead. This allows us to later avoid commiting
> > > a breakpoint to architecture when its slot couldn't be allocated.
> >
> > [...]
> > > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> > > index 6e28d28..6896ceeb 100644
> > > --- a/kernel/events/hw_breakpoint.c
> > > +++ b/kernel/events/hw_breakpoint.c
> > > @@ -402,11 +402,12 @@ int dbg_release_bp_slot(struct perf_event *bp)
> >
> > > static int validate_hw_breakpoint(struct perf_event *bp)
> > > {
> > > - int ret;
> > > + int err;
> >
> > > - ret = arch_validate_hwbkpt_settings(bp);
> > > - if (ret)
> > > - return ret;
> > > + err = hw_breakpoint_arch_check(bp, &bp->attr);
> > > + if (err)
> > > + return err;
> > > + hw_breakpoint_arch_commit(bp);
> >
> > minor nit:
> > To preserve bisectability, shouldn't this be the following in this and
> > earlier patches?
> >
> > err = hw_breakpoint_arch_check(bp, &bp->attr);
> > hw_breakpoint_arch_commit(bp);
> > if (err)
> > return err;
> >
> > And then in patch 9/9 you can fix it the right way?
>
> I don't see how it was breaking bisectability.

Sorry may be I used wrong words, I meant keeping the restructure patch as
just for restvructuring and then changing the logic later. But I'm Ok with
what you have, and also like Peter's __weak thing suggestion.

> Anyway I'm rewriting it entirely to use:
>
> struct arch_hw_breakpoint hw;
> int err;
>
> err = hw_breakpoint_arch_parse(bp, attr, &hw);
> if (err)
> return err;

Cool, if you don't mind do CC me on patches, Thanks.

Just to update you about my email address change, the new one is: joel@joelfernandes.org

thanks,

- Joel