Re: [watchdog] combine nmi_watchdog and softlockup

[Don Zickus <dzickus@redhat.com>]

On Tue, Mar 23, 2010 at 05:33:38PM -0400, Don Zickus wrote:
> The new nmi_watchdog (which uses the perf event subsystem) is very
> similar in structure to the softlockup detector.  Using Ingo's suggestion,
> I combined the two functionalities into one file, kernel/watchdog.c.
> 
> Now both the nmi_watchdog (or hardlockup detector) and softlockup detector
> sit on top of the perf event subsystem, which is run every 60 seconds or so
> to see if there are any lockups.

I raised some questions privately to Ingo, he asked I re-iterate them with
Peter Z. and Frederic W. cc'd.

> Ok thanks.  When you get a chance I had a couple of questions I was hoping
> you could answer for me.
>
> - does the hrtimer stuff look ok?
>
> - any thoughts on how to achieve arch-independent way of calculating a
>   sample period for perf events?  otherwise i am stuck with an arch hook.
>
> - I wanted to merge the hung task detector code into watchdog.c.  The main
>   logic of the code is to walk the task list which i thought about doing
>   in the watchdog kthread.  I assume that is the right way to go, but i was a
>   little confused on how the scheduler worked.  I thought the watchdog kthread
>   would be scheduled very frequently (being a high priority task) but it seems
>   to only schedule when the code wakes it up.  Is that right?

Cheers,
Don

>
> ---
>  arch/x86/kernel/apic/hw_nmi.c |    2 +-
>  include/linux/nmi.h           |    2 +-
>  kernel/Makefile               |    2 +-
>  kernel/sysctl.c               |    2 +-
>  kernel/watchdog.c             |  526 +++++++++++++++++++++++++++++++++++++++++
>  lib/Kconfig.debug             |   24 ++-
>  6 files changed, 546 insertions(+), 12 deletions(-)
>  create mode 100644 kernel/watchdog.c
> 
> diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
> index e8b78a0..79425f9 100644
> --- a/arch/x86/kernel/apic/hw_nmi.c
> +++ b/arch/x86/kernel/apic/hw_nmi.c
> @@ -89,7 +89,7 @@ int hw_nmi_is_cpu_stuck(struct pt_regs *regs)
>  
>  u64 hw_nmi_get_sample_period(void)
>  {
> -	return cpu_khz * 1000;
> +	return (u64)(cpu_khz) * 1000 * 60;
>  }
>  
>  #ifdef ARCH_HAS_NMI_WATCHDOG
> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
> index 22cc796..a501de9 100644
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -54,7 +54,7 @@ static inline bool trigger_all_cpu_backtrace(void)
>  #ifdef CONFIG_NMI_WATCHDOG
>  int hw_nmi_is_cpu_stuck(struct pt_regs *);
>  u64 hw_nmi_get_sample_period(void);
> -extern int nmi_watchdog_enabled;
> +extern int watchdog_enabled;
>  struct ctl_table;
>  extern int proc_nmi_enabled(struct ctl_table *, int ,
>  			void __user *, size_t *, loff_t *);
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 8a5abe5..c8e3e7c 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -76,7 +76,7 @@ obj-$(CONFIG_AUDIT_TREE) += audit_tree.o
>  obj-$(CONFIG_KPROBES) += kprobes.o
>  obj-$(CONFIG_KGDB) += kgdb.o
>  obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
> -obj-$(CONFIG_NMI_WATCHDOG) += nmi_watchdog.o
> +obj-$(CONFIG_NMI_WATCHDOG) += watchdog.o
>  obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o
>  obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
>  obj-$(CONFIG_SECCOMP) += seccomp.o
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ac72c9e..6066e3d 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -699,7 +699,7 @@ static struct ctl_table kern_table[] = {
>  #if defined(CONFIG_NMI_WATCHDOG)
>  	{
>  		.procname       = "nmi_watchdog",
> -		.data           = &nmi_watchdog_enabled,
> +		.data           = &watchdog_enabled,
>  		.maxlen         = sizeof (int),
>  		.mode           = 0644,
>  		.proc_handler   = proc_nmi_enabled,
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> new file mode 100644
> index 0000000..7334565
> --- /dev/null
> +++ b/kernel/watchdog.c
> @@ -0,0 +1,526 @@
> +/*
> + * Detect Hard/Soft Lockups using the NMI
> + *
> + * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
> + *
> + * this code detects hard lockups: incidents in where on a CPU
> + * the kernel does not respond to anything except NMI.
> + *
> + * Note: Most of this code is borrowed heavily from softlockup.c,
> + * so thanks to Ingo for the initial implementation.
> + * Some chunks also taken from arch/x86/kernel/apic/nmi.c, thanks
> + * to those contributors as well.
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/cpu.h>
> +#include <linux/nmi.h>
> +#include <linux/init.h>
> +#include <linux/delay.h>
> +#include <linux/freezer.h>
> +#include <linux/kthread.h>
> +#include <linux/lockdep.h>
> +#include <linux/notifier.h>
> +#include <linux/module.h>
> +#include <linux/sysctl.h>
> +
> +#include <asm/irq_regs.h>
> +#include <linux/perf_event.h>
> +
> +int watchdog_enabled;
> +int __read_mostly softlockup_thresh = 60;
> +
> +static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
> +static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
> +static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
> +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
> +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
> +static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
> +
> +static int __read_mostly did_panic;
> +static int __initdata no_watchdog;
> +
> +
> +/* boot commands */
> +/*
> + * Should we panic when a soft-lockup or hard-lockup occurs:
> + */
> +static int hardlockup_panic;
> +
> +unsigned int __read_mostly softlockup_panic =
> +			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
> +
> +static int __init hardlockup_panic_setup(char *str)
> +{
> +	if (!strncmp(str, "panic", 5))
> +		hardlockup_panic = 1;
> +	return 1;
> +}
> +__setup("nmi_watchdog=", hardlockup_panic_setup);
> +
> +static int __init softlockup_panic_setup(char *str)
> +{
> +	softlockup_panic = simple_strtoul(str, NULL, 0);
> +
> +	return 1;
> +}
> +__setup("softlockup_panic=", softlockup_panic_setup);
> +
> +static int __init no_watchdog_setup(char *str)
> +{
> +	no_watchdog = 1;
> +	return 1;
> +}
> +__setup("no_watchdog", no_watchdog_setup);
> +
> +/* deprecated */
> +static int __init nosoftlockup_setup(char *str)
> +{
> +	no_watchdog = 1;
> +	return 1;
> +}
> +__setup("nosoftlockup", nosoftlockup_setup);
> +static int __init nonmi_watchdog_setup(char *str)
> +{
> +	no_watchdog = 1;
> +	return 1;
> +}
> +__setup("nonmi_watchdog", nonmi_watchdog_setup);
> +/*  */
> +
> +
> +/*
> + * Returns seconds, approximately.  We don't need nanosecond
> + * resolution, and we don't need to waste time with a big divide when
> + * 2^30ns == 1.074s.
> + */
> +static unsigned long get_timestamp(int this_cpu)
> +{
> +	return cpu_clock(this_cpu) >> 30LL;  /* 2^30 ~= 10^9 */
> +}
> +
> +static unsigned long get_sample_period(void)
> +{
> +	/*
> +	 * convert softlockup_thresh from seconds to ns
> +	 * the divide by 5 is to give hrtimer 5 chances to
> +	 * increment before the hardlockup detector generates
> +	 * a warning
> +	 */
> +	return softlockup_thresh / 5 * NSEC_PER_SEC;
> +}
> +
> +/* Commands for resetting the watchdog */
> +static void __touch_watchdog(void)
> +{
> +	int this_cpu = raw_smp_processor_id();
> +
> +	__raw_get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
> +}
> +
> +void touch_watchdog(void)
> +{
> +	__raw_get_cpu_var(watchdog_touch_ts) = 0;
> +}
> +EXPORT_SYMBOL(touch_watchdog);
> +
> +void touch_all_watchdog(void)
> +{
> +	int cpu;
> +
> +	for_each_online_cpu(cpu)
> +		per_cpu(watchdog_touch_ts, cpu) = 0;
> +}
> +
> +void touch_nmi_watchdog(void)
> +{
> +	touch_watchdog();
> +}
> +EXPORT_SYMBOL(touch_nmi_watchdog);
> +
> +void touch_all_nmi_watchdog(void)
> +{
> +	touch_all_watchdog();
> +}
> +/* end of deprecated functions */
> +
> +/* watchdog detector functions */
> +static int is_hardlockup(int cpu)
> +{
> +	unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);
> +
> +	if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
> +		return 1;
> +
> +	per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
> +	return 0;
> +}
> +
> +static int is_softlockup(unsigned long touch_ts, int cpu)
> +{
> +	unsigned long now = get_timestamp(cpu);
> +
> +	/* Warn about unreasonable delays: */
> +	if (now > (touch_ts + softlockup_thresh)) {
> +		return now - touch_ts;
> +	}
> +
> +	return 0;
> +}
> +
> +static int
> +watchdog_panic(struct notifier_block *this, unsigned long event, void *ptr)
> +{
> +	did_panic = 1;
> +
> +	return NOTIFY_DONE;
> +}
> +
> +static struct notifier_block panic_block = {
> +	.notifier_call = watchdog_panic,
> +};
> +
> +struct perf_event_attr wd_hw_attr = {
> +	.type		= PERF_TYPE_HARDWARE,
> +	.config		= PERF_COUNT_HW_CPU_CYCLES,
> +	.size		= sizeof(struct perf_event_attr),
> +	.pinned		= 1,
> +	.disabled	= 1,
> +};
> +
> +struct perf_event_attr wd_sw_attr = {
> +	.type		= PERF_TYPE_SOFTWARE,
> +	.config		= PERF_COUNT_SW_CPU_CLOCK,
> +	.size		= sizeof(struct perf_event_attr),
> +	.pinned		= 1,
> +	.disabled	= 1,
> +};
> +
> +/* Callback function for perf event subsystem */
> +void watchdog_overflow_callback(struct perf_event *event, int nmi,
> +		 struct perf_sample_data *data,
> +		 struct pt_regs *regs)
> +{
> +	int this_cpu = smp_processor_id();
> +	unsigned long touch_ts = per_cpu(watchdog_touch_ts, this_cpu);
> +	int duration;
> +
> +	if (touch_ts == 0) {
> +		__touch_watchdog();
> +		return;
> +	}
> +
> +	/* check for a hardlockup
> +	 * This is done by making sure our timer interrupt
> +	 * is incrementing.  The timer interrupt should have
> +	 * fired multiple times before we overflow'd.  If it hasn't
> +	 * then this is a good indication the cpu is stuck
> +	 */
> +	if (is_hardlockup(this_cpu)) {
> +		if (hardlockup_panic)
> +			panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> +		else
> +			WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
> +	}
> +
> +	/* check for a softlockup
> +	 * This is done by making sure a high priority task is
> +	 * being scheduled.  The task touches the watchdog to
> +	 * indicate it is getting cpu time.  If it hasn't then
> +	 * this is a good indication some task is hogging the cpu
> +	 */
> +	duration = is_softlockup(touch_ts, this_cpu);
> +	if (duration) {
> +		printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
> +			this_cpu, duration,
> +			current->comm, task_pid_nr(current));
> +		print_modules();
> +		print_irqtrace_events(current);
> +		if (regs)
> +			show_regs(regs);
> +		else
> +			dump_stack();
> +
> +		if (softlockup_panic)
> +			panic("softlockup: hung tasks");
> +	}
> +
> +	return;
> +}
> +
> +/* watchdog kicker functions */
> +static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
> +{
> +	/* kick the hardlockup detector */
> +	__get_cpu_var(hrtimer_interrupts)++;
> +
> +	/* kick the softlockup detector */
> +	wake_up_process(__get_cpu_var(softlockup_watchdog));
> +
> +	/* .. and repeat */
> +	hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
> +
> +	return HRTIMER_RESTART;
> +}
> +
> +
> +/*
> + * The watchdog thread - touches the timestamp.
> + */
> +static int watchdog(void *__bind_cpu)
> +{
> +	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
> +	struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, (unsigned long)__bind_cpu);
> +
> +	sched_setscheduler(current, SCHED_FIFO, &param);
> +
> +	/* initialize timestamp */
> +	__touch_watchdog();
> +
> +	/* kick off the timer for the hardlockup detector */
> +	/* done here because hrtimer_start can only pin to smp_processor_id() */
> +	hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
> +		      HRTIMER_MODE_REL_PINNED);
> +
> +	set_current_state(TASK_INTERRUPTIBLE);
> +	/*
> +	 * Run briefly once per second to reset the softlockup timestamp.
> +	 * If this gets delayed for more than 60 seconds then the
> +	 * debug-printout triggers in softlockup_tick().
> +	 */
> +	while (!kthread_should_stop()) {
> +		__touch_watchdog();
> +		schedule();
> +
> +		if (kthread_should_stop())
> +			break;
> +
> +		set_current_state(TASK_INTERRUPTIBLE);
> +	}
> +	__set_current_state(TASK_RUNNING);
> +
> +	return 0;
> +}
> +
> +
> +/* prepare/enable/disable routines */
> +static int watchdog_prepare_cpu(int cpu)
> +{
> +	struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
> +	struct task_struct *p;
> +
> +	BUG_ON(per_cpu(softlockup_watchdog, cpu));
> +	p = kthread_create(watchdog, (void *)(unsigned long)cpu, "watchdog/%d", cpu);
> +	if (IS_ERR(p)) {
> +		printk(KERN_ERR "softlockup watchdog for %i failed\n", cpu);
> +		return -1;
> +	}
> +	per_cpu(watchdog_touch_ts, cpu) = 0;
> +	per_cpu(softlockup_watchdog, cpu) = p;
> +	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	hrtimer->function = watchdog_timer_fn;
> +
> +	return 0;
> +}
> +
> +static int watchdog_enable(int cpu)
> +{
> +	struct perf_event_attr *wd_attr;
> +	struct perf_event *event = per_cpu(watchdog_ev, cpu);
> +	struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
> +
> +	/* is it already setup and enabled? */
> +	if (event && event->state > PERF_EVENT_STATE_OFF)
> +		goto out;
> +
> +	/* it is setup but not enabled */
> +	if (event != NULL)
> +		goto out_enable;
> +
> +	/* Try to register using hardware perf events first */
> +	wd_attr = &wd_hw_attr;
> +	wd_attr->sample_period = hw_nmi_get_sample_period();
> +	event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback);
> +	if (!IS_ERR(event)) {
> +		printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
> +		goto out_save;
> +	}
> +
> +	/* hardware doesn't exist or not supported, fallback to software events */
> +	printk(KERN_INFO "NMI watchdog: hardware not available, trying software events\n");
> +	wd_attr = &wd_sw_attr;
> +	wd_attr->sample_period = softlockup_thresh * NSEC_PER_SEC;
> +	event = perf_event_create_kernel_counter(wd_attr, cpu, -1, watchdog_overflow_callback);
> +	if (!IS_ERR(event)) {
> +		printk(KERN_INFO "NMI watchdog enabled, takes one software counter.\n");
> +		goto out_save;
> +	}
> +
> +	printk(KERN_ERR "NMI watchdog failed to create perf event on cpu%i: %p\n", cpu, event);
> +	return -1;
> +
> +	/* success path */
> +out_save:
> +	per_cpu(watchdog_ev, cpu) = event;
> +out_enable:
> +	perf_event_enable(per_cpu(watchdog_ev, cpu));
> +out:
> +	/* kick the softlockup thread */
> +	if (p) {
> +		kthread_bind(p, cpu);
> +		wake_up_process(p);
> +	}
> +
> +	/* if any cpu succeeds, watchdog is considered enabled for the system */
> +	watchdog_enabled = 1;
> +
> +	return 0;
> +}
> +
> +static void watchdog_disable(int cpu)
> +{
> +	struct perf_event *event = per_cpu(watchdog_ev, cpu);
> +	struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
> +	struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
> +
> +	/*
> +	 * cancel the timer first to stop incrementing the stats
> +	 * and waking up the kthread
> +	 */
> +	hrtimer_cancel(hrtimer);
> +
> +	if (event) {
> +		perf_event_disable(event);
> +		per_cpu(watchdog_ev, cpu) = NULL;
> +
> +		/* should be in cleanup, but blocks oprofile */
> +		perf_event_release_kernel(event);
> +	}
> +
> +	if (p) {
> +		kthread_bind(p, cpumask_any(cpu_online_mask));
> +		kthread_stop(p);
> +	}
> +}
> +
> +static void watchdog_cleanup(int cpu)
> +{
> +	per_cpu(softlockup_watchdog, cpu) = NULL;
> +}
> +
> +static void watchdog_enable_all_cpus(void)
> +{
> +	int cpu;
> +	int result;
> +
> +	if (watchdog_enabled)
> +		return;
> +
> +	for_each_online_cpu(cpu)
> +		result += watchdog_enable(cpu);
> +
> +	if (result)
> +		printk(KERN_ERR "watchdog: failed to be enabled on some cpus\n");
> +
> +}
> +
> +static void watchdog_disable_all_cpus(void)
> +{
> +	int cpu;
> +
> +	for_each_online_cpu(cpu)
> +		watchdog_disable(cpu);
> +
> +	/* if all watchdogs are disabled, then they are disabled for the system */
> +	watchdog_enabled = 0;
> +}
> +
> +
> +/* sysctl functions */
> +#ifdef CONFIG_SYSCTL
> +/*
> + * proc handler for /proc/sys/kernel/nmi_watchdog
> + */
> +
> +int proc_nmi_enabled(struct ctl_table *table, int write,
> +		     void __user *buffer, size_t *length, loff_t *ppos)
> +{
> +	touch_all_watchdog();
> +	proc_dointvec(table, write, buffer, length, ppos);
> +	if (watchdog_enabled)
> +		watchdog_enable_all_cpus();
> +	else
> +		watchdog_disable_all_cpus();
> +	return 0;
> +}
> +
> +int proc_dowatchdog_thresh(struct ctl_table *table, int write,
> +			     void __user *buffer,
> +			     size_t *lenp, loff_t *ppos)
> +{
> +	touch_all_watchdog();
> +	return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> +}
> +
> +#endif /* CONFIG_SYSCTL */
> +
> +
> +/*
> + * Create/destroy watchdog threads as CPUs come and go:
> + */
> +static int __cpuinit
> +cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
> +{
> +	int hotcpu = (unsigned long)hcpu;
> +
> +	switch (action) {
> +	case CPU_UP_PREPARE:
> +	case CPU_UP_PREPARE_FROZEN:
> +		if (watchdog_prepare_cpu(hotcpu))
> +			return NOTIFY_BAD;
> +		break;
> +	case CPU_ONLINE:
> +	case CPU_ONLINE_FROZEN:
> +		if (watchdog_enable(hotcpu))
> +			return NOTIFY_BAD;
> +		break;
> +#ifdef CONFIG_HOTPLUG_CPU
> +	case CPU_UP_CANCELED:
> +	case CPU_UP_CANCELED_FROZEN:
> +		watchdog_disable(hotcpu);
> +		break;
> +	case CPU_DEAD:
> +	case CPU_DEAD_FROZEN:
> +		watchdog_disable(hotcpu);
> +		watchdog_cleanup(hotcpu);
> +		break;
> +#endif /* CONFIG_HOTPLUG_CPU */
> +	}
> +	return NOTIFY_OK;
> +}
> +
> +static struct notifier_block __cpuinitdata cpu_nfb = {
> +	.notifier_call = cpu_callback
> +};
> +
> +static int __init spawn_watchdog_task(void)
> +{
> +	void *cpu = (void *)(long)smp_processor_id();
> +	int err;
> +
> +	if (no_watchdog)
> +		return 0;
> +
> +	err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
> +	if (err == NOTIFY_BAD) {
> +		BUG();
> +		return 1;
> +	}
> +	cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
> +	register_cpu_notifier(&cpu_nfb);
> +
> +	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
> +
> +	return 0;
> +}
> +early_initcall(spawn_watchdog_task);
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index e2e73cc..518ec79 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -171,20 +171,28 @@ config DETECT_SOFTLOCKUP
>  	   support it.)
>  
>  config NMI_WATCHDOG
> -	bool "Detect Hard Lockups with an NMI Watchdog"
> -	depends on DEBUG_KERNEL && PERF_EVENTS && PERF_EVENTS_NMI
> +	bool "Detect Hard and Soft Lockups"
> +	depends on DEBUG_KERNEL && PERF_EVENTS && PERF_EVENTS_NMI && !DETECT_SOFTLOCKUP
>  	help
>  	  Say Y here to enable the kernel to use the NMI as a watchdog
> -	  to detect hard lockups.  This is useful when a cpu hangs for no
> -	  reason but can still respond to NMIs.  A backtrace is displayed
> -	  for reviewing and reporting.
> +	  to detect hard and soft lockups.
>  
> -	  The overhead should be minimal, just an extra NMI every few
> +	  Softlockups are bugs that cause the kernel to loop in kernel
> +	  mode for more than 60 seconds, without giving other tasks a
> +	  chance to run.  The current stack trace is displayed upon
> +	  detection and the system will stay locked up.
> +
> +	  Hardlockups are bugs that cause the cpu to loop in kernel mode
> +	  for more than 60 seconds, without letting other interrupts a
> +	  chance to run.  The current stack trace is displayed upon detection
> +	  and the system will stay locked up.
> +
> +	  The overhead should me minimal, just an extra NMI every few
>  	  seconds.
>  
>  config BOOTPARAM_SOFTLOCKUP_PANIC
>  	bool "Panic (Reboot) On Soft Lockups"
> -	depends on DETECT_SOFTLOCKUP
> +	depends on DETECT_SOFTLOCKUP || NMI_WATCHDOG
>  	help
>  	  Say Y here to enable the kernel to panic on "soft lockups",
>  	  which are bugs that cause the kernel to loop in kernel
> @@ -201,7 +209,7 @@ config BOOTPARAM_SOFTLOCKUP_PANIC
>  
>  config BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
>  	int
> -	depends on DETECT_SOFTLOCKUP
> +	depends on DETECT_SOFTLOCKUP || NMI_WATCHDOG
>  	range 0 1
>  	default 0 if !BOOTPARAM_SOFTLOCKUP_PANIC
>  	default 1 if BOOTPARAM_SOFTLOCKUP_PANIC
> -- 
> 1.6.5.2
>