Messages in this thread | | | Date | Fri, 27 Aug 2010 20:21:21 +0800 | From | DDD <> | Subject | Re: [PATCH] perf: fix possible divide-by-zero in perf_swevent_overflow() |
| |
Peter Zijlstra wrote: > On Thu, 2010-08-26 at 20:36 +0800, DDD wrote: >> Peter Zijlstra wrote: >>> On Thu, 2010-08-26 at 20:07 +0800, Dongdong Deng wrote: >>>> The event->hw.last_period is possible to zero, thus it will >>>> cause divide_by_zero later in perf_swevent_set_period(). >>> How can it be zero? >> When I am running the kgdbts to test the hw_breakpoint_layer with kgdb, >> I get a call trace as following and this problem is hardly to reproduce. >> >> 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?
hello Peter,
Thanks for your patch, but I still could reproduce the problem with your patch.
Thanks, Dongdong
> > >> but add a checking is good to us and harmless. :-) > > Except that code path is already too bloated and should be reduced not > added to and conditionals are expensive. > > > --- > 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, > }; > >
| |