Re: [patch V2 25/29] lockup_detector: Implement init time detection of perf

[Don Zickus]

On Tue, Sep 12, 2017 at 09:37:19PM +0200, Thomas Gleixner wrote:
> Use the init time detection of the perf NMI watchdog to determine whether
> the perf NMI watchdog is functional. If not disable it permanentely. It
> won't come back magically at runtime.
> 
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Don Zickus <dzickus@xxxxxxxxxx>
> Cc: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Sebastian Siewior <bigeasy@xxxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Link: http://lkml.kernel.org/r/20170831073054.997264122@xxxxxxxxxxxxx
> 
> ---
>  kernel/watchdog.c |   13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -44,6 +44,7 @@ int __read_mostly watchdog_user_enabled
>  int __read_mostly nmi_watchdog_user_enabled = NMI_WATCHDOG_DEFAULT;
>  int __read_mostly soft_watchdog_user_enabled = 1;
>  int __read_mostly watchdog_thresh = 10;
> +int __read_mostly nmi_watchdog_available;
>  
>  struct cpumask watchdog_allowed_mask __read_mostly;
>  static bool softlockup_threads_initialized __read_mostly;
> @@ -114,6 +115,12 @@ void __weak watchdog_nmi_disable(unsigne
>  	hardlockup_detector_perf_disable();
>  }
>  
> +/* Return 0, if a NMI watchdog is available. Error code otherwise */
> +int __weak __init void watchdog_nmi_probe(void)

^^^ compile error, can't have 'int' and 'void'.  Removing 'void' fixes it.

Cheers,
Don

> +{
> +	return hardlockup_detector_perf_init();
> +}
> +
>  /**
>   * watchdog_nmi_reconfigure - Optional function to reconfigure NMI watchdogs
>   * @run:	If false stop the watchdogs on all enabled CPUs
> @@ -145,7 +152,7 @@ static void lockup_detector_update_enabl
>  	watchdog_enabled = 0;
>  	if (!watchdog_user_enabled)
>  		return;
> -	if (nmi_watchdog_user_enabled)
> +	if (nmi_watchdog_available && nmi_watchdog_user_enabled)
>  		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
>  	if (soft_watchdog_user_enabled)
>  		watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
> @@ -692,6 +699,8 @@ int proc_watchdog(struct ctl_table *tabl
>  int proc_nmi_watchdog(struct ctl_table *table, int write,
>  		      void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
> +	if (!nmi_watchdog_available && write)
> +		return -ENOTSUPP;
>  	return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
>  				    table, write, buffer, lenp, ppos);
>  }
> @@ -764,5 +773,7 @@ void __init lockup_detector_init(void)
>  	cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
>  #endif
>  
> +	if (!watchdog_nmi_probe())
> +		nmi_watchdog_available = true;
>  	softlockup_init_threads();
>  }
> 
>