linux-kernel - Re: [PATCH] perf: fix possible divide-by-zero in perf_swevent

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Date:	Thu, 26 Aug 2010 14:12:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dongdong Deng <dongdong.deng@...driver.com>
Cc:	mingo@...e.hu, fweisbec@...il.com, acme@...hat.com,
	paulus@...ba.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf: fix possible divide-by-zero in
 perf_swevent_overflow()

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?

> This patch checks event->hw.last_period before invoke
> perf_swevent_set_period() and replaces "event->hw" with "hwc".
> 
> Signed-off-by: Dongdong Deng <dongdong.deng@...driver.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Paul Mackerras <paulus@...ba.org>
> ---
>  kernel/perf_event.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 403d180..ccba741 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -4050,8 +4050,8 @@ static void perf_swevent_overflow(struct perf_event *event, u64 overflow,
>  	struct hw_perf_event *hwc = &event->hw;
>  	int throttle = 0;
>  
> -	data->period = event->hw.last_period;
> -	if (!overflow)
> +	data->period = hwc->last_period;
> +	if (!overflow && hwc->last_period)
>  		overflow = perf_swevent_set_period(event);
>  
>  	if (hwc->interrupts == MAX_INTERRUPTS)


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