linux-kernel - Re: fix BUG: using smp_processor_id() in preemptible code (resend)

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Message-ID: <20100819170358.GD19773@amd.com>
Date:	Thu, 19 Aug 2010 19:03:59 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: fix BUG: using smp_processor_id() in preemptible code (resend)

On Wed, Aug 18, 2010 at 05:11:58AM -0400, Sergey Senozhatsky wrote:
> Should we call smp_processor_id/get_cpu in thermal_throttle_add_dev?
> We know the cpu when calling thermal_throttle_add_dev (in thermal_throttle_cpu_callback and
> thermal_throttle_init_device) so we can pass the cpu number when calling it.
> 
> My second solution is:
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/therm_throt.c b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> index c2a8b26..bcd8499 100644
> --- a/arch/x86/kernel/cpu/mcheck/therm_throt.c
> +++ b/arch/x86/kernel/cpu/mcheck/therm_throt.c
> @@ -202,11 +202,12 @@ static int therm_throt_process(bool new_event, int event, int level)
>  
>  #ifdef CONFIG_SYSFS
>  /* Add/Remove thermal_throttle interface for CPU device: */
> -static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev)
> +static __cpuinit int thermal_throttle_add_dev(struct sys_device *sys_dev,
> +				unsigned int cpu)
>  {
>  	int err;
> -	struct cpuinfo_x86 *c = &cpu_data(smp_processor_id());
> -
> +	struct cpuinfo_x86 *c = &cpu_data(cpu);
> +	
>  	err = sysfs_create_group(&sys_dev->kobj, &thermal_attr_group);
>  	if (err)
>  		return err;
> @@ -251,7 +252,7 @@ thermal_throttle_cpu_callback(struct notifier_block *nfb,
>  	case CPU_UP_PREPARE:
>  	case CPU_UP_PREPARE_FROZEN:
>  		mutex_lock(&therm_cpu_lock);
> -		err = thermal_throttle_add_dev(sys_dev);
> +		err = thermal_throttle_add_dev(sys_dev, cpu);
>  		mutex_unlock(&therm_cpu_lock);
>  		WARN_ON(err);
>  		break;
> @@ -287,7 +288,7 @@ static __init int thermal_throttle_init_device(void)
>  #endif
>  	/* connect live CPUs to sysfs */
>  	for_each_online_cpu(cpu) {
> -		err = thermal_throttle_add_dev(get_cpu_sysdev(cpu));
> +		err = thermal_throttle_add_dev(get_cpu_sysdev(cpu), cpu);
>  		WARN_ON(err);
>  	}
>  #ifdef CONFIG_HOTPLUG_CPU

The notifier is preemtible so it can run on another CPU. So using the
supplied cpu arguemnt in the path looks like the right solution to me.

	Joerg

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