linux-kernel - Re: [PATCH v2] x86/therm_throt.c: Fix error handling in thermal_throttle_add

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Date:	Fri, 10 Sep 2010 10:19:37 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	"Fenghua Yu" <fenghua.yu@...el.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "H Peter Anvin" <hpa@...or.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Guenter Roeck" <guenter.roeck@...csson.com>,
	"Jin Dongming" <jin.dongming@...css.fujitsu.com>,
	"Hidetoshi Seto" <seto.hidetoshi@...fujitsu.com>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"lm-sensors" <lm-sensors@...sensors.org>
Subject: Re: [PATCH v2] x86/therm_throt.c: Fix error handling in
 thermal_throttle_add_dev

On Tue,  7 Sep 2010 17:25:50 -0700, Fenghua Yu wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> 
> When sysfs_add_file_to_group fails, thermal_throttle_add_dev removes the
> created group and returns with the error code and the driver cleans up and
> returns with the error code. Thus the driver either installs all devices
> successfully or doesn't install any device at all.

I don't think this makes any sense. While I generally agree with the
idea that a given device (actually, CPU feature) should either be fully
available or not available at all, I don't get the point of preventing
the driver from loading because one device couldn't be initialized for
whatever reason. I don't know of any other driver behaving this way.

What's the rationale? I think Ingo's wording was inaccurate and when he
wrote "we should either initialize a driver fully - or not intialize it
at all" he really meant "device" not "driver. Ingo?

> 
> Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> ---
>  arch/x86/kernel/cpu/mcheck/therm_throt.c |   36 ++++++++++++++++++++++++++---
>  1 files changed, 32 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> index c2a8b26..5099e90 100644
> --- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
> +++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> @@ -211,19 +211,33 @@ static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev)
>  	if (err)
>  		return err;
>  
> -	if (cpu_has(c, X86_FEATURE_PLN))
> +	if (cpu_has(c, X86_FEATURE_PLN)) {
>  		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 (cpu_has(c, X86_FEATURE_PLN))
> +		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;
>  }
>  

I'm fine with the above...

> @@ -275,6 +289,7 @@ static struct notifier_block thermal_throttle_cpu_notifier __cpuinitdata =
>  static __init int thermal_throttle_init_device(void)
>  {
>  	unsigned int cpu = 0;
> +	int i;
>  	int err;
>  
>  	if (!atomic_read(&therm_throt_en))
> @@ -288,13 +303,26 @@ static __init int thermal_throttle_init_device(void)
>  	/* connect live CPUs to sysfs */
>  	for_each_online_cpu(cpu) {
>  		err = thermal_throttle_add_dev(get_cpu_sysdev(cpu));
> -		WARN_ON(err);
> +		if (err)
> +			goto error;
>  	}
>  #ifdef CONFIG_HOTPLUG_CPU
>  	mutex_unlock(&therm_cpu_lock);
>  #endif
>  
>  	return 0;
> +error:
> +	WARN_ON(err);
> +
> +	/* cleanup. */
> +	for (i = 0; i < cpu; i++)
> +		thermal_throttle_remove_dev(get_cpu_sysdev(i));
> +#ifdef CONFIG_HOTPLUG_CPU
> +	mutex_unlock(&therm_cpu_lock);
> +#endif
> +	unregister_hotcpu_notifier(&thermal_throttle_cpu_notifier);
> +
> +	return err;
>  }
>  device_initcall(thermal_throttle_init_device);
>  

... but not with this!

-- 
Jean Delvare
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