Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi_disable

[Babu Moger <babu.moger@oracle.com>]

Don,

On 10/17/2016 12:31 PM, Don Zickus wrote:
> On Thu, Oct 13, 2016 at 01:38:01PM -0700, Babu Moger wrote:
>> Currently we do not have a way to enable/disable arch specific
>> watchdog handlers if it was implemented by any of the architectures.
>>
>> This patch introduces new functions arch_watchdog_nmi_enable and
>> arch_watchdog_nmi_disable which can be used to enable/disable architecture
>> specific NMI watchdog handlers. These functions are defined as weak as
>> architectures can override their definitions to enable/disable nmi
>> watchdog behaviour.
> Hi Babu,
>
> This patch tested fine on my x86 box and I am ok with the changes.
>
> I do have one small cosmetic request below for a failure path.  Other than
> that I will give my ack.
Yes. I am testing these changes. If everything goes as expected, I will 
post  v3 version
tomorrow. Thanks Babu

>
> Cheers,
> Don
>
>> Signed-off-by: Babu Moger <babu.moger@oracle.com>
>> ---
>>   kernel/watchdog.c |   65 +++++++++++++++++++++++++++++++++++-----------------
>>   1 files changed, 44 insertions(+), 21 deletions(-)
>>
>> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>> index 9acb29f..d1e84e6 100644
>> --- a/kernel/watchdog.c
>> +++ b/kernel/watchdog.c
>> @@ -46,7 +46,7 @@
>>   
>>   static DEFINE_MUTEX(watchdog_proc_mutex);
>>   
>> -#ifdef CONFIG_HARDLOCKUP_DETECTOR
>> +#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
>>   static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
>>   #else
>>   static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
>> @@ -585,15 +585,11 @@ static void watchdog(unsigned int cpu)
>>    */
>>   static unsigned long cpu0_err;
>>   
>> -static int watchdog_nmi_enable(unsigned int cpu)
>> +static int arch_watchdog_nmi_enable(unsigned int cpu)
>>   {
>>   	struct perf_event_attr *wd_attr;
>>   	struct perf_event *event = per_cpu(watchdog_ev, cpu);
>>   
>> -	/* nothing to do if the hard lockup detector is disabled */
>> -	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
>> -		goto out;
>> -
>>   	/* is it already setup and enabled? */
>>   	if (event && event->state > PERF_EVENT_STATE_OFF)
>>   		goto out;
>> @@ -619,18 +615,6 @@ static int watchdog_nmi_enable(unsigned int cpu)
>>   		goto out_save;
>>   	}
>>   
>> -	/*
>> -	 * Disable the hard lockup detector if _any_ CPU fails to set up
>> -	 * set up the hardware perf event. The watchdog() function checks
>> -	 * the NMI_WATCHDOG_ENABLED bit periodically.
>> -	 *
>> -	 * The barriers are for syncing up watchdog_enabled across all the
>> -	 * cpus, as clear_bit() does not use barriers.
>> -	 */
>> -	smp_mb__before_atomic();
>> -	clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
>> -	smp_mb__after_atomic();
>> -
>>   	/* skip displaying the same error again */
>>   	if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
>>   		return PTR_ERR(event);
> In the arch_watchdog_nmi_enable code is a pr_info on failure
>
> 	pr_info("Shutting down hard lockup detector on all cpus\n");
>
> that should be moved to below..
>
>
>> @@ -658,7 +642,7 @@ out:
>>   	return 0;
>>   }
>>   
>> -static void watchdog_nmi_disable(unsigned int cpu)
>> +static void arch_watchdog_nmi_disable(unsigned int cpu)
>>   {
>>   	struct perf_event *event = per_cpu(watchdog_ev, cpu);
>>   
>> @@ -676,8 +660,13 @@ static void watchdog_nmi_disable(unsigned int cpu)
>>   }
>>   
>>   #else
>> -static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
>> -static void watchdog_nmi_disable(unsigned int cpu) { return; }
>> +/*
>> + * These two functions are mostly architecture specific
>> + * defining them as weak here.
>> + */
>> +int __weak arch_watchdog_nmi_enable(unsigned int cpu) { return 0; }
>> +void __weak arch_watchdog_nmi_disable(unsigned int cpu) { return; }
>> +
>>   #endif /* CONFIG_HARDLOCKUP_DETECTOR */
>>   
>>   static struct smp_hotplug_thread watchdog_threads = {
>> @@ -781,6 +770,40 @@ void lockup_detector_resume(void)
>>   	put_online_cpus();
>>   }
>>   
>> +void watchdog_nmi_disable(unsigned int cpu)
>> +{
>> +	arch_watchdog_nmi_disable(cpu);
>> +}
>> +
>> +int watchdog_nmi_enable(unsigned int cpu)
>> +{
>> +	int err;
>> +
>> +	/* nothing to do if the hard lockup detector is disabled */
>> +	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
>> +		return 0;
>> +
>> +	err = arch_watchdog_nmi_enable(cpu);
>> +
>> +	if (err) {
>> +		/*
>> +		 * Disable the hard lockup detector if _any_ CPU fails to set up
>> +		 * set up the hardware perf event. The watchdog() function checks
>> +		 * the NMI_WATCHDOG_ENABLED bit periodically.
>> +		 *
>> +		 * The barriers are for syncing up watchdog_enabled across all the
>> +		 * cpus, as clear_bit() does not use barriers.
>> +		 */
>> +		smp_mb__before_atomic();
>> +		clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
>> +		smp_mb__after_atomic();
> moved to here:
>
> 		pr_info("Shutting down hard lockup detector on all cpus\n");
>
>
> This lets the failure message be displayed on all arches instead of just
> x86.  Though I guess sparc does not call theirs 'hard lockup detector'.
> Hmm...
>
>
>> +
>> +		return err;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>   static int update_watchdog_all_cpus(void)
>>   {
>>   	int ret;
>> -- 
>> 1.7.1
>>