linux-kernel - Re: [PATCH v4 14/24] PM / devfreq: tegra30: Ensure that target freq won't overflow

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Message-ID: <e6b53ba0-ac98-bda6-b087-553088a43d9f@samsung.com>
Date:   Tue, 16 Jul 2019 21:30:39 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:     linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 14/24] PM / devfreq: tegra30: Ensure that target freq
 won't overflow

On 19. 7. 8. 오전 7:32, Dmitry Osipenko wrote:
> Potentially very high boosting could cause an integer overflow for a
> highly clocked memory after conversion to MHz.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra30-devfreq.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/devfreq/tegra30-devfreq.c b/drivers/devfreq/tegra30-devfreq.c
> index 2f59c78930bd..0de1efdaabf4 100644
> --- a/drivers/devfreq/tegra30-devfreq.c
> +++ b/drivers/devfreq/tegra30-devfreq.c
> @@ -460,6 +460,7 @@ static unsigned long actmon_update_target(struct tegra_devfreq *tegra,
>  	unsigned long target_freq;
>  
>  	target_freq = dev->avg_count / ACTMON_SAMPLING_PERIOD + dev->boost_freq;
> +	target_freq = min(target_freq, ULONG_MAX / KHZ);

Did you meet this corner case?
If have to change it, you better to use 'tegra->max_freq' as following:
	min(target_freq, tegra->max_freq);

>  	target_freq = tegra_actmon_account_cpu_freq(tegra, dev, target_freq);
>  
>  	return target_freq;
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics