linux-kernel - Re: [Patch-next] Trival fixes in thermal_throttle_add

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Message-ID: <4C7EF175.1090005@np.css.fujitsu.com>
Date:	Thu, 02 Sep 2010 09:36:05 +0900
From:	Jin Dongming <jin.dongming@...css.fujitsu.com>
To:	Jean Delvare <khali@...ux-fr.org>
CC:	Fenghua Yu <fenghua.yu@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	"H. Peter Anvin" <hpa@...ux.jf.intel.com>,
	LKLM <linux-kernel@...r.kernel.org>,
	"lm-sensors@...sensors.org" <lm-sensors@...sensors.org>,
	mingo Redhat <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Patch-next] Trival fixes in thermal_throttle_add_dev().

Hi Jean and Fenghua,

Sorry for replying late.

(2010/09/01 4:30), Jean Delvare wrote:
> On Tue, 31 Aug 2010 10:04:43 -0700, Fenghua Yu wrote:
>> On Tue, Aug 31, 2010 at 12:07:25AM -0700, Jean Delvare wrote:
>>> On Mon, 30 Aug 2010 18:02:52 -0700, Fenghua Yu wrote:
>>>> On Mon, Aug 30, 2010 at 05:55:48PM -0700, Jin Dongming wrote:
>>>>> diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
>>>>> index d9368ee..79d563a 100644
>>>>> --- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
>>>>> +++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
>>>>> @@ -216,14 +216,27 @@ static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev,
>>>>>  		err = sysfs_add_file_to_group(&sys_dev->kobj,
>>>>>  					      &attr_core_power_limit_count.attr,
>>>>>  					      thermal_attr_group.name);
>>>>> -	if (cpu_has(c, X86_FEATURE_PTS))
>>>>> +	if (err)
>>>>> +		goto error;
>>>>> +
>>>>> +	if (cpu_has(c, X86_FEATURE_PTS)) {
>>>>>  		err = sysfs_add_file_to_group(&sys_dev->kobj,
>>>>>  					      &attr_package_throttle_count.attr,
>>>>>  					      thermal_attr_group.name);
>>>>> +		if (err)
>>>>> +			goto error;
>>>>> +
>>>>>  		if (cpu_has(c, X86_FEATURE_PLN))
>>>>>  			err = sysfs_add_file_to_group(&sys_dev->kobj,
>>>>>  					&attr_package_power_limit_count.attr,
>>>>>  					thermal_attr_group.name);
>>>>> +		if (err)
>>>>> +			goto error;
>>>>> +	}
>>>>> +
>>>>> +	return 0;
>>>>> +error:
>>>>> +	sysfs_remove_group(&sys_dev->kobj, &thermal_attr_group);
>>>>>  
>>>>>  	return err;
>>>>>  }
>>>>
>>>> This fix is incorrect. In this patch, a previous error prevents from adding any
>>>> further devices. There shouldn't be such dependency among the devices.
>>>
>>> I don't quite follow you. Did you mean to write that a previous error
>>> prevents from creating further _attributes_ for the same device? This
>>> would be true.
>>>
>>> Now I don't think this is a problem because 1* such errors should never
>>> happen anyway and 2* if they do happen then further attempts to create
>>> the other attributes are unlikely to succeed either.
>>
>> I don't think there is dependency among the count files, i.e. failure to add a
>> count file to the group shouldn't impact other files. Other filles can still be
>> added to the group. In this case, user application only sees part of count
>> numbers. And kernel may just warn on the failure instead of providing nothing
>> to user.
>>
>> In the patch, any failure to add a file will remove the whole group. This is
>> too strict. Kernel doesn't provide any count number to user application.
> 
> Oh, my bad. I missed the call to sysfs_remove_group() when reviewing
> the code. I agree with you that it shouldn't be added.
> 
>> Agree with you that such errors should never happen anyway. So original code
>> works fine.
> 
> The original code works indeed (except for the missing curly braces)
> but is confusing for the reader (which is why I raised the point and we
> are discussing it now). If you are voluntarily ignoring errors, you
> should add a comment saying so. And it is also a good practice to use a
> dummy variable to store the error value you'll ignore, so that the
> intent is clear.
> 
I agree with your option. So I will cancel error handling of this patch and
resend a patch just for missing { and } only.

And I think Fenghua could make a new patch for a comment.

Best Regards,
Jin Dongming

>> If to be picky to the error handling, a patch may just ignore returning errors
>> from sysfs_add_file_to_group.
> 
> This is an option, yes. Unfortunately this also means that such errors
> won't be even logged, while I think this would be desirable.
> 
>> Or use err |= sysfs_add_file_to_group to collect
>> all errors and return err but without calling sysfs_remove_group.
> 
> Please never use |= on non-bitwise values, it can only lead to bugs and
> confusion.
> 


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