[PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[Pan Xinhui]

From: Pan Xinhui <xinhuix.pan@intel.com>

This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
return error when failing to set minfreq").It attempt to return an error
on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
Actually we just need check if new_policy->min > new_policy->max.
Because at least one of max/min is copied from cpufreq_get_policy().

For example, when we echo xxx > .../scaling_min_freq, new_policy is
copied from policy in cpufreq_get_policy. new_policy->max is same with
policy->max. new_policy->min is set to a new value.

Let me explain it in deduction method, first statment in if ():
new_policy->min > policy->max
policy->max == new_policy->max
==> new_policy->min > new_policy->max

second statment in if():
new_policy->max < policy->min
policy->max < policy->min
==>new_policy->min > new_policy->max (induction method)

So we have proved that we only need check if new_policy->min >
new_policy->max.

After apply this patch, we can also modify ->min and ->max in same time
if new freq range is very much different from current freq range. For
example, if current freq range is 480000-960000, then we want to set
this range to 1120000-2240000, we would fail in the past because
new_policy->min > policy->max. As long as the cpufreq range is valid, we
has no reason to reject the user. So correct the check.

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
---
 drivers/cpufreq/cpufreq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6424e05..8772346 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2276,7 +2276,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 
 	memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
 
-	if (new_policy->min > policy->max || new_policy->max < policy->min)
+	if (new_policy->min > new_policy->max)
 		return -EINVAL;
 
 	/* verify the cpu speed can be set within this limit */
-- 
1.9.1

Re: [PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[Viresh Kumar]

On 28-07-15, 11:34, Pan Xinhui wrote:
> From: Pan Xinhui <xinhuix.pan@intel.com>
> 
> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
> return error when failing to set minfreq").It attempt to return an error
> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
> Actually we just need check if new_policy->min > new_policy->max.
> Because at least one of max/min is copied from cpufreq_get_policy().
> 
> For example, when we echo xxx > .../scaling_min_freq, new_policy is
> copied from policy in cpufreq_get_policy. new_policy->max is same with
> policy->max. new_policy->min is set to a new value.
> 
> Let me explain it in deduction method, first statment in if ():
> new_policy->min > policy->max
> policy->max == new_policy->max
> ==> new_policy->min > new_policy->max
> 
> second statment in if():
> new_policy->max < policy->min
> policy->max < policy->min
> ==>new_policy->min > new_policy->max (induction method)
> 
> So we have proved that we only need check if new_policy->min >
> new_policy->max.
> 
> After apply this patch, we can also modify ->min and ->max in same time
> if new freq range is very much different from current freq range. For
> example, if current freq range is 480000-960000, then we want to set
> this range to 1120000-2240000, we would fail in the past because
> new_policy->min > policy->max. As long as the cpufreq range is valid, we
> has no reason to reject the user. So correct the check.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>

Does this patch depend on the other patch you sent where you are
trying to update both min/max in the same call to
cpufreq_set_policy()? If so, they should have been part of the same
series in proper order, as you have sent them as separate patches.

Now, if we don't consider your first patch at all, then this patch is
obviously wrong. We need to take care of both the checks.

-- 
viresh

Re: [PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[Pan Xinhui]

hi, Viresh
	thanks for your quick reply! :)
On 2015年07月28日 12:41, Viresh Kumar wrote:
> On 28-07-15, 11:34, Pan Xinhui wrote:
>> From: Pan Xinhui <xinhuix.pan@intel.com>
>>
>> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
>> return error when failing to set minfreq").It attempt to return an error
>> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
>> Actually we just need check if new_policy->min > new_policy->max.
>> Because at least one of max/min is copied from cpufreq_get_policy().
>>
>> For example, when we echo xxx > .../scaling_min_freq, new_policy is
>> copied from policy in cpufreq_get_policy. new_policy->max is same with
>> policy->max. new_policy->min is set to a new value.
>>
>> Let me explain it in deduction method, first statment in if ():
>> new_policy->min > policy->max
>> policy->max == new_policy->max
>> ==> new_policy->min > new_policy->max
>>
>> second statment in if():
>> new_policy->max < policy->min
>> policy->max < policy->min
>> ==>new_policy->min > new_policy->max (induction method)
>>
>> So we have proved that we only need check if new_policy->min >
>> new_policy->max.
>>
>> After apply this patch, we can also modify ->min and ->max in same time
>> if new freq range is very much different from current freq range. For
>> example, if current freq range is 480000-960000, then we want to set
>> this range to 1120000-2240000, we would fail in the past because
>> new_policy->min > policy->max. As long as the cpufreq range is valid, we
>> has no reason to reject the user. So correct the check.
>>
>> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
> 
> Does this patch depend on the other patch you sent where you are
> trying to update both min/max in the same call to
> cpufreq_set_policy()? If so, they should have been part of the same
> series in proper order, as you have sent them as separate patches.
>

Thanks for pointing out my mistakes. I will send them in a same series with proper order.
Sorry for that.
 
> Now, if we don't consider your first patch at all, then this patch is
> obviously wrong. We need to take care of both the checks.
> 
Agree, we need take care of every checks. BUT, As We have proved, it's equal to check if (new_policy->min > new_policy->max). I don't why it's wrong.
with/without this patch, echo 0 > .../scaling_min_freq has no error. min freq is just set to the limit min freq. I prefer to treat it as a feature. :)
So I don't add new_policy->min < policy->cpuinfo.min_freq || new_policy->max > policy->cpuinfo.max_freq.

We have ->verify callback, no need to worry about that an out-of-limit cpufreq will harm kernel.
This check is just to tell userspace that *the cpufreq you are trying to set is wrong, pls double check.*

thanks
xinhui

Re: [PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[Viresh Kumar]

On 28-07-15, 11:34, Pan Xinhui wrote:
> From: Pan Xinhui <xinhuix.pan@intel.com>
> 
> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
> return error when failing to set minfreq").It attempt to return an error
> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
> Actually we just need check if new_policy->min > new_policy->max.
> Because at least one of max/min is copied from cpufreq_get_policy().
> 
> For example, when we echo xxx > .../scaling_min_freq, new_policy is
> copied from policy in cpufreq_get_policy. new_policy->max is same with
> policy->max. new_policy->min is set to a new value.
> 
> Let me explain it in deduction method, first statment in if ():
> new_policy->min > policy->max
> policy->max == new_policy->max
> ==> new_policy->min > new_policy->max
> 
> second statment in if():
> new_policy->max < policy->min
> policy->max < policy->min
> ==>new_policy->min > new_policy->max (induction method)
> 
> So we have proved that we only need check if new_policy->min >
> new_policy->max.
> 
> After apply this patch, we can also modify ->min and ->max in same time
> if new freq range is very much different from current freq range. For
> example, if current freq range is 480000-960000, then we want to set
> this range to 1120000-2240000, we would fail in the past because
> new_policy->min > policy->max. As long as the cpufreq range is valid, we
> has no reason to reject the user. So correct the check.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
> ---
>  drivers/cpufreq/cpufreq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 6424e05..8772346 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2276,7 +2276,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  
>  	memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
>  
> -	if (new_policy->min > policy->max || new_policy->max < policy->min)
> +	if (new_policy->min > new_policy->max)
>  		return -EINVAL;

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh

Re: [PATCH] cpufreq: Correct a freq check in cpufreq_set_policy

[Rafael J. Wysocki]

On Tuesday, July 28, 2015 11:34:21 AM Pan Xinhui wrote:
> From: Pan Xinhui <xinhuix.pan@intel.com>
> 
> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
> return error when failing to set minfreq").It attempt to return an error
> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
> Actually we just need check if new_policy->min > new_policy->max.
> Because at least one of max/min is copied from cpufreq_get_policy().
> 
> For example, when we echo xxx > .../scaling_min_freq, new_policy is
> copied from policy in cpufreq_get_policy. new_policy->max is same with
> policy->max. new_policy->min is set to a new value.
> 
> Let me explain it in deduction method, first statment in if ():
> new_policy->min > policy->max
> policy->max == new_policy->max
> ==> new_policy->min > new_policy->max
> 
> second statment in if():
> new_policy->max < policy->min
> policy->max < policy->min
> ==>new_policy->min > new_policy->max (induction method)
> 
> So we have proved that we only need check if new_policy->min >
> new_policy->max.
> 
> After apply this patch, we can also modify ->min and ->max in same time
> if new freq range is very much different from current freq range. For
> example, if current freq range is 480000-960000, then we want to set
> this range to 1120000-2240000, we would fail in the past because
> new_policy->min > policy->max. As long as the cpufreq range is valid, we
> has no reason to reject the user. So correct the check.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
> ---
>  drivers/cpufreq/cpufreq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 6424e05..8772346 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -2276,7 +2276,7 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  
>  	memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
>  
> -	if (new_policy->min > policy->max || new_policy->max < policy->min)

Please add a comment here mentioning the fact that this *relies* on new_policy
being a copy of policy with one field updated.

> +	if (new_policy->min > new_policy->max)
>  		return -EINVAL;
>  
>  	/* verify the cpu speed can be set within this limit */
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

[PATCH V2] cpufreq: Correct a freq check in cpufreq_set_policy

[Pan Xinhui]

From: Pan Xinhui <xinhuix.pan@intel.com>

This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
return error when failing to set minfreq").It attempt to return an error
on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
Actually we just need check if new_policy->min > new_policy->max.
Because at least one of max/min is copied from cpufreq_get_policy().

For example, when we echo xxx > .../scaling_min_freq, new_policy is
copied from policy in cpufreq_get_policy. new_policy->max is same with
policy->max. new_policy->min is set to a new value.

Let me explain it in deduction method, first statement in if ():
new_policy->min > policy->max
policy->max == new_policy->max
==> new_policy->min > new_policy->max

second statement in if():
new_policy->max < policy->min
policy->max < policy->min
==>new_policy->min > new_policy->max (induction method)

So we have proved that we only need check if new_policy->min >
new_policy->max.

After apply this patch, we can also modify ->min and ->max at same time
if new freq range is very much different from current freq range. For
example, if current freq range is 480000-960000, then we want to set
this range to 1120000-2240000, we would fail in the past because
new_policy->min > policy->max. As long as the cpufreq range is valid, we
has no reason to reject the user. So correct the check to avoid such
case.

Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>
---
Change from V1:
	just update comments.
---
 drivers/cpufreq/cpufreq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 26063af..a32f50b 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -2245,7 +2245,11 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 
 	memcpy(&new_policy->cpuinfo, &policy->cpuinfo, sizeof(policy->cpuinfo));
 
-	if (new_policy->min > policy->max || new_policy->max < policy->min)
+	/*
+	* This check works well when we store new min/max freq attributes,
+	* because new_policy is a copy of policy with one field updated.
+	*/
+	if (new_policy->min > new_policy->max)
 		return -EINVAL;
 
 	/* verify the cpu speed can be set within this limit */
-- 
1.9.1

Re: [PATCH V2] cpufreq: Correct a freq check in cpufreq_set_policy

[Rafael J. Wysocki]

On Thursday, July 30, 2015 06:10:40 PM Pan Xinhui wrote:
> From: Pan Xinhui <xinhuix.pan@intel.com>
> 
> This check was originally added by commit 9c9a43ed2734 ("[CPUFREQ]
> return error when failing to set minfreq").It attempt to return an error
> on obviously incorrect limits when we echo xxx >.../scaling_max,min_freq
> Actually we just need check if new_policy->min > new_policy->max.
> Because at least one of max/min is copied from cpufreq_get_policy().
> 
> For example, when we echo xxx > .../scaling_min_freq, new_policy is
> copied from policy in cpufreq_get_policy. new_policy->max is same with
> policy->max. new_policy->min is set to a new value.
> 
> Let me explain it in deduction method, first statement in if ():
> new_policy->min > policy->max
> policy->max == new_policy->max
> ==> new_policy->min > new_policy->max
> 
> second statement in if():
> new_policy->max < policy->min
> policy->max < policy->min
> ==>new_policy->min > new_policy->max (induction method)
> 
> So we have proved that we only need check if new_policy->min >
> new_policy->max.
> 
> After apply this patch, we can also modify ->min and ->max at same time
> if new freq range is very much different from current freq range. For
> example, if current freq range is 480000-960000, then we want to set
> this range to 1120000-2240000, we would fail in the past because
> new_policy->min > policy->max. As long as the cpufreq range is valid, we
> has no reason to reject the user. So correct the check to avoid such
> case.
> 
> Signed-off-by: Pan Xinhui <xinhuix.pan@intel.com>

Queued up for 4.3, thanks!


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.