linux-kernel - Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi

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Date:   Mon, 17 Oct 2016 13:31:57 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Babu Moger <babu.moger@...cle.com>
Cc:     mingo@...nel.org, akpm@...ux-foundation.org, ak@...ux.intel.com,
        jkosina@...e.cz, baiyaowei@...s.chinamobile.com,
        atomlin@...hat.com, uobergfe@...hat.com, tj@...nel.org,
        hidehiro.kawai.ez@...achi.com, johunt@...mai.com,
        davem@...emloft.net, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, sam@...nborg.org
Subject: Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and
 arch_watchdog_nmi_disable

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.

Cheers,
Don

> 
> Signed-off-by: Babu Moger <babu.moger@...cle.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
>