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