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Date: Tue, 9 Apr 2013 10:02:47 -0700
From: Andrew Bresticker <abrestic@...gle.com>
To: Eduardo Valentin <eduardo.valentin@...com>
Cc: Andrew Bresticker <abrestic@...omium.org>,
Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] thermal: fix frequency table lookup bugs
Hi Eduardo,
On Tue, Apr 9, 2013 at 7:55 AM, Eduardo Valentin
<eduardo.valentin@...com> wrote:
> Hi Andrew,
>
>
> On 08-04-2013 19:54, Andrew Bresticker wrote:
>>
>> The loops which are used to perform lookups in CPU frequency tables in
>> cpu_cooling and the Exynos thermal driver do not update the loop counter
>> if they encounter an invalid table entry, leading to an infinite loop in
>> that case.
>>
>> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
>> ---
>> drivers/thermal/cpu_cooling.c | 19 ++++++++++---------
>> drivers/thermal/exynos_thermal.c | 8 ++++----
>> 2 files changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/thermal/cpu_cooling.c b/drivers/thermal/cpu_cooling.c
>> index 836828e..e6db441 100644
>> --- a/drivers/thermal/cpu_cooling.c
>> +++ b/drivers/thermal/cpu_cooling.c
>> @@ -124,14 +124,14 @@ static int is_cpufreq_valid(int cpu)
>> static unsigned int get_cpu_frequency(unsigned int cpu, unsigned long
>> level)
>> {
>> int ret = 0, i = 0;
>> - unsigned long level_index;
>> + unsigned long level_index = 0;
>> bool descend = false;
>> struct cpufreq_frequency_table *table =
>> cpufreq_frequency_get_table(cpu);
>> if (!table)
>> return ret;
>>
>> - while (table[i].frequency != CPUFREQ_TABLE_END) {
>> + for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
>> if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
>> continue;
>
> Wouldn't be easier to just increase the index i before doing a continue?
I think this is cleaner. The code is iterating through an array -- it
should be a for loop.
>
>
>>
>> @@ -143,24 +143,25 @@ static unsigned int get_cpu_frequency(unsigned int
>> cpu, unsigned long level)
>> }
>>
>> /*return if level matched and table in descending order*/
>> - if (descend && i == level)
>> + if (descend && level_index == level)
>> return table[i].frequency;
>
>
> What this has to do with the patch description?
I'm using level_index as the counter of valid frequencies, where as i
is the index into the array. If there are invalid entries, they are
not necessarily equal. The point of this function is to find the
level-th *valid* frequency in the table.
> Besides why would you be comparing level against 0 all the time (you have
> initialized level_index to 0 at this point).
Huh? level_index is clearly incremented below...
>
>> - i++;
>> + level_index++;
>
>
> level_index wont be updated in case of INVALID entry.
That's the point.
>
>
>> }
>> i--;
>> + level_index--;
>>
>> - if (level > i || descend)
>> + if (level > level_index || descend)
>> return ret;
>> - level_index = i - level;
>> + level = level_index - level;
>>
>> /*Scan the table in reverse order and match the level*/
>> - while (i >= 0) {
>> + for (; i >= 0; i--) {
>> if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
>> continue;
>> /*return if level matched*/
>> - if (i == level_index)
>> + if (level_index == level)
>> return table[i].frequency;
>> - i--;
>> + level_index--;
>> }
>
>
> I believe you do more than what you have described in your intention under
> you patch description
I disagree. I'm fixing the loop so that it properly handles invalid
entries and thus the infinite loop problem I mention in the commit
message.
> Can you please split your patch into smaller changes?
I don't think there is a need for separate patches to cpu_cooling.c.
>
>> return ret;
>> }
>> diff --git a/drivers/thermal/exynos_thermal.c
>> b/drivers/thermal/exynos_thermal.c
>> index d5e6267..524b2a0 100644
>> --- a/drivers/thermal/exynos_thermal.c
>> +++ b/drivers/thermal/exynos_thermal.c
>> @@ -237,7 +237,7 @@ static int exynos_get_crit_temp(struct
>> thermal_zone_device *thermal,
>>
>> static int exynos_get_frequency_level(unsigned int cpu, unsigned int
>> freq)
>> {
>> - int i = 0, ret = -EINVAL;
>> + int i, level = 0, ret = -EINVAL;
>> struct cpufreq_frequency_table *table = NULL;
>> #ifdef CONFIG_CPU_FREQ
>> table = cpufreq_frequency_get_table(cpu);
>> @@ -245,12 +245,12 @@ static int exynos_get_frequency_level(unsigned int
>> cpu, unsigned int freq)
>> if (!table)
>> return ret;
>>
>> - while (table[i].frequency != CPUFREQ_TABLE_END) {
>> + for (i = 0; table[i].frequency != CPUFREQ_TABLE_END; i++) {
>> if (table[i].frequency == CPUFREQ_ENTRY_INVALID)
>> continue;
>> if (table[i].frequency == freq)
>> - return i;
>> - i++;
>> + return level;
>> + level++;
>
>
> Can you please send a separate patch on this driver instead?
Sure.
>
>
>
>> }
>> return ret;
>> }
>>
>
Thanks,
Andrew
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