linux-kernel - Re: [patch 24/29] lockup_detector/perf: Implement init time perf validation

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Date:   Thu, 7 Sep 2017 11:58:35 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Ulrich Obergfell <uobergfe@...hat.com>
Subject: Re: [patch 24/29] lockup_detector/perf: Implement init time perf
 validation

On Thu, Aug 31, 2017 at 09:16:22AM +0200, Thomas Gleixner wrote:
> The watchdog tries to create perf events even after it figured out that
> perf is not functional or the requested event is not supported.
> 
> That's braindead as this can be done once at init time and if not supported
> the NMI watchdog can be turned off unconditonally.
> 
> Implement the perf hardlockup detector functionality for that. This creates
> a new event create function, which will replace the unholy mess of the
> existing one in later patches.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/nmi.h   |    8 ++++++--
>  kernel/watchdog_hld.c |   37 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 43 insertions(+), 2 deletions(-)
> 
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -93,14 +93,18 @@ extern void hardlockup_detector_perf_sto
>  extern void hardlockup_detector_perf_restart(void);
>  extern void hardlockup_detector_perf_disable(void);
>  extern void hardlockup_detector_perf_cleanup(void);
> +extern int hardlockup_detector_perf_init(void);
>  #else
>  static inline void hardlockup_detector_perf_stop(void) { }
>  static inline void hardlockup_detector_perf_restart(void) { }
>  static inline void hardlockup_detector_perf_disable(void) { }
>  static inline void hardlockup_detector_perf_cleanup(void) { }
> -#if !defined(CONFIG_HAVE_NMI_WATCHDOG)
> +# if !defined(CONFIG_HAVE_NMI_WATCHDOG)
> +static int hardlockup_detector_perf_init(void) { return -ENODEV; }
>  static inline void arch_touch_nmi_watchdog(void) {}
> -#endif
> +# else
> +static int hardlockup_detector_perf_init(void) { return 0; }

hardlockup_detector_perf_init needs to be 'inline' otherwise fails to
compile with CONFIG_HARDLOCKUP_DETECTOR_PERF turned off.


Cheers,
Don

> +# endif
>  #endif
>  
>  void watchdog_nmi_reconfigure(bool run);
> --- a/kernel/watchdog_hld.c
> +++ b/kernel/watchdog_hld.c
> @@ -238,6 +238,27 @@ int watchdog_nmi_enable(unsigned int cpu
>  	return 0;
>  }
>  
> +static int hardlockup_detector_event_create(void)
> +{
> +	unsigned int cpu = smp_processor_id();
> +	struct perf_event_attr *wd_attr;
> +	struct perf_event *evt;
> +
> +	wd_attr = &wd_hw_attr;
> +	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
> +
> +	/* Try to register using hardware perf events */
> +	evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
> +					       watchdog_overflow_callback, NULL);
> +	if (IS_ERR(evt)) {
> +		pr_info("Perf event create on CPU %d failed with %ld\n", cpu,
> +			PTR_ERR(evt));
> +		return PTR_ERR(evt);
> +	}
> +	this_cpu_write(watchdog_ev, evt);
> +	return 0;
> +}
> +
>  /**
>   * hardlockup_detector_perf_disable - Disable the local event
>   */
> @@ -315,3 +336,19 @@ void __init hardlockup_detector_perf_res
>  			perf_event_enable(event);
>  	}
>  }
> +
> +/**
> + * hardlockup_detector_perf_init - Probe whether NMI event is available at all
> + */
> +int __init hardlockup_detector_perf_init(void)
> +{
> +	int ret = hardlockup_detector_event_create();
> +
> +	if (ret) {
> +		pr_info("Perf NMI watchdog permanetely disabled\n");
> +	} else {
> +		perf_event_release_kernel(this_cpu_read(watchdog_ev));
> +		this_cpu_write(watchdog_ev, NULL);
> +	}
> +	return ret;
> +}
> 
>