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

[Dmitry Osipenko]

16.07.2019 15:30, Chanwoo Choi ÐÐÑÐÑ:
> On 19. 7. 8. ìì 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@xxxxxxxxx>
>> ---
>>  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?

I can't recall that, technically it could happen and I don't feel
comfortable by having potential integer overflows anyway.

> If have to change it, you better to use 'tegra->max_freq' as following:
> 	min(target_freq, tegra->max_freq);

The 'tegra->max_freq' will work here, but 'ULONG_MAX / KHZ' is a
constant value which is also correct and doesn't case any harm.

Probably will be even more expressive to write this as:

	target_freq = dev->avg_freq + dev->boost_freq;
	target_freq = tegra_actmon_account_cpu_freq(tegra, dev, target_freq);

	return min(target_freq, tegra->max_freq);


Thank you very much for the reviews!