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

From: Deepthi Dharwar <[email-masked]>
Date: Mon, 21 May 2012 10:25:07 +0530

Hi Ben,

On 05/21/2012 06:17 AM, Benjamin Herrenschmidt wrote:

> 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 ?

  In the current design disable and enable device are called
  when the cpu comes online. This is to make sure that we clean up and
  re-register again. All the counters are reset.

  Not calling cpu disable when cpu goes offline currently, would only
  retain the counters right now.

  But I could add a offline check and disable the device there, if that
  results in cleaner design.  I will test and send across the patch with
  couple more pseries-idle fixes soon.

  Thanks for your review comments !

> 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)
> 
> 
> _______________________________________________
> Linuxppc-dev mailing list
> [email-masked]
> https://lists.ozlabs.org/listinfo/linuxppc-dev
>