Subject: Re: [PATCH] cpuidle: (POWER) Replace pseries_notify_cpuidle_add call with a elegant notifier to fix lockdep problem in start_secondary

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 21 May 2012 10:47:01 +1000

On Fri, 2012-05-18 at 18:58 +0530, Deepthi Dharwar wrote:
> The following patch is to remove the pseries_notify_add_cpu() call
> and replace it by a hot plug notifier.
> This would prevent cpuidle resources being
> released and allocated each time cpu comes online on pseries.
> The earlier design was causing a lockdep problem
> in start_secondary as reported on this thread
>         -https://lkml.org/lkml/2012/5/17/2
> 
> This applies on 3.4-rc7
> 
> Signed-off-by: Deepthi Dharwar <[email-masked]>
> ---

Any reason why you don't do cpuidle_disable_device() when the
CPU is going offline and cpuidle_enable_device() when it's coming
back ?

I'm applying the patch for now since it fixes a real problem but
if the above makes sense, please send a followup fix.

Cheers,
Ben.

>  arch/powerpc/include/asm/processor.h            |    2 --
>  arch/powerpc/platforms/pseries/processor_idle.c |   25
> +++++++++++++++++------
>  arch/powerpc/platforms/pseries/smp.c            |    1 -
>  3 files changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/processor.h
> b/arch/powerpc/include/asm/processor.h
> index 8e2d037..c6bc22b 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -390,10 +390,8 @@ void cpu_idle_wait(void);
> 
>  #ifdef CONFIG_PSERIES_IDLE
>  extern void update_smt_snooze_delay(int snooze);
> -extern int pseries_notify_cpuidle_add_cpu(int cpu);
>  #else
>  static inline void update_smt_snooze_delay(int snooze) {}
> -static inline int pseries_notify_cpuidle_add_cpu(int cpu) { return 0; }
>  #endif
> 
>  extern void flush_instruction_cache(void);
> diff --git a/arch/powerpc/platforms/pseries/processor_idle.c
> b/arch/powerpc/platforms/pseries/processor_idle.c
> index 41a34bc..d1a7dc0 100644
> --- a/arch/powerpc/platforms/pseries/processor_idle.c
> +++ b/arch/powerpc/platforms/pseries/processor_idle.c
> @@ -11,6 +11,7 @@
>  #include <linux/moduleparam.h>
>  #include <linux/cpuidle.h>
>  #include <linux/cpu.h>
> +#include <linux/notifier.h>
> 
>  #include <asm/paca.h>
>  #include <asm/reg.h>
> @@ -186,17 +187,28 @@ static struct cpuidle_state
> shared_states[MAX_IDLE_STATE_COUNT] = {
>  		.enter = &shared_cede_loop },
>  };
> 
> -int pseries_notify_cpuidle_add_cpu(int cpu)
> +static int pseries_cpuidle_add_cpu_notifier(struct notifier_block *n,
> +			unsigned long action, void *hcpu)
>  {
> +	int hotcpu = (unsigned long)hcpu;
>  	struct cpuidle_device *dev =
> -			per_cpu_ptr(pseries_cpuidle_devices, cpu);
> -	if (dev && cpuidle_get_driver()) {
> -		cpuidle_disable_device(dev);
> -		cpuidle_enable_device(dev);
> +			per_cpu_ptr(pseries_cpuidle_devices, hotcpu);
> +
> +	switch (action & 0xf) {
> +	case CPU_ONLINE:
> +		if (dev && cpuidle_get_driver()) {
> +			cpuidle_disable_device(dev);
> +			cpuidle_enable_device(dev);
> +		}
> +		break;
>  	}
> -	return 0;
> +	return NOTIFY_OK;
>  }
> 
> +static struct notifier_block setup_hotplug_notifier = {
> +	.notifier_call = pseries_cpuidle_add_cpu_notifier,
> +};
> +
>  /*
>   * pseries_cpuidle_driver_init()
>   */
> @@ -321,6 +333,7 @@ static int __init pseries_processor_idle_init(void)
>  		return retval;
>  	}
> 
> +	register_cpu_notifier(&setup_hotplug_notifier);
>  	printk(KERN_DEBUG "pseries_idle_driver registered\n");
> 
>  	return 0;
> diff --git a/arch/powerpc/platforms/pseries/smp.c
> b/arch/powerpc/platforms/pseries/smp.c
> index e16bb8d..71706bc 100644
> --- a/arch/powerpc/platforms/pseries/smp.c
> +++ b/arch/powerpc/platforms/pseries/smp.c
> @@ -147,7 +147,6 @@ static void __devinit smp_xics_setup_cpu(int cpu)
>  	set_cpu_current_state(cpu, CPU_STATE_ONLINE);
>  	set_default_offline_state(cpu);
>  #endif
> -	pseries_notify_cpuidle_add_cpu(cpu);
>  }
> 
>  static int __devinit smp_pSeries_kick_cpu(int nr)