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

[Babu Moger]

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@xxxxxxxxxx>
> > ---
> >   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