Re: [PATCH] perf: fix possible divide-by-zero in perf_swevent_overflow()

[DDD]

Peter Zijlstra wrote:
> On Fri, 2010-08-27 at 20:21 +0800, DDD wrote:
>
> > > > Maybe the root cause was from kgdb/hw_breakpoint_layer,
> > > Yeah, I think there's a bug in the hw_breakpoint stuff, does something
> > > like the below fix it?
>
> > Thanks for your patch, but I still could reproduce the problem with your 
> > patch.
>
> Frederic, any clue as to what makes hw breakpoints go funny and have
> last_period == 0?

Hi Peter,

Thanks for you take care of it, I have got the root cause of it now.

It is the kgdb using hw_breakpoint_layer's API problem, and I have a RFC 
patch for it.(maybe it is not correctly), I will contact with Jason to 
fix this problem.

Thank you very much,
Dongdong

> > > ---
> > >  kernel/hw_breakpoint.c |   13 ++++++++++++-
> > >  1 files changed, 12 insertions(+), 1 deletions(-)
> > >
> > > diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
> > > index d71a987..f57ebee 100644
> > > --- a/kernel/hw_breakpoint.c
> > > +++ b/kernel/hw_breakpoint.c
> > > @@ -600,9 +600,20 @@ static int __init init_hw_breakpoint(void)
> > >  }
> > >  core_initcall(init_hw_breakpoint);
> > >  
> > > +static int hw_breakpoint_enable(struct perf_event *event)
> > > +{
> > > +     struct hw_perf_event *hwc = &event->hw;
> > > +
> > > +     if (hwc->sample_period) {
> > > +             hwc->last_period = hwc->sample_period;
> > > +             perf_swevent_set_period(event);
> > > +     }
> > > +
> > > +     return arch_install_hw_breakpoint(event);
> > > +}
> > >  
> > >  struct pmu perf_ops_bp = {
> > > -     .enable         = arch_install_hw_breakpoint,
> > > +     .enable         = hw_breakpoint_enable,
> > >       .disable        = arch_uninstall_hw_breakpoint,
> > >       .read           = hw_breakpoint_pmu_read,
> > >  };

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