Initial import

1 files changed, 890 insertions, 0 deletions

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
new file mode 100644
index 000000000..581a68a04
--- /dev/null
+++ b/kernel/watchdog.c
@@ -0,0 +1,890 @@
+/*
+ * Detect hard and soft lockups on a system
+ *
+ * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
+ *
+ * Note: Most of this code is borrowed heavily from the original softlockup
+ * detector, so thanks to Ingo for the initial implementation.
+ * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
+ * to those contributors as well.
+ */
+
+#define pr_fmt(fmt) "NMI watchdog: " fmt
+
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/nmi.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+#include <linux/smpboot.h>
+#include <linux/sched/rt.h>
+
+#include <asm/irq_regs.h>
+#include <linux/kvm_para.h>
+#include <linux/perf_event.h>
+
+/*
+ * The run state of the lockup detectors is controlled by the content of the
+ * 'watchdog_enabled' variable. Each lockup detector has its dedicated bit -
+ * bit 0 for the hard lockup detector and bit 1 for the soft lockup detector.
+ *
+ * 'watchdog_user_enabled', 'nmi_watchdog_enabled' and 'soft_watchdog_enabled'
+ * are variables that are only used as an 'interface' between the parameters
+ * in /proc/sys/kernel and the internal state bits in 'watchdog_enabled'. The
+ * 'watchdog_thresh' variable is handled differently because its value is not
+ * boolean, and the lockup detectors are 'suspended' while 'watchdog_thresh'
+ * is equal zero.
+ */
+#define NMI_WATCHDOG_ENABLED_BIT   0
+#define SOFT_WATCHDOG_ENABLED_BIT  1
+#define NMI_WATCHDOG_ENABLED      (1 << NMI_WATCHDOG_ENABLED_BIT)
+#define SOFT_WATCHDOG_ENABLED     (1 << SOFT_WATCHDOG_ENABLED_BIT)
+
+static DEFINE_MUTEX(watchdog_proc_mutex);
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
+#else
+static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
+#endif
+int __read_mostly nmi_watchdog_enabled;
+int __read_mostly soft_watchdog_enabled;
+int __read_mostly watchdog_user_enabled;
+int __read_mostly watchdog_thresh = 10;
+
+#ifdef CONFIG_SMP
+int __read_mostly sysctl_softlockup_all_cpu_backtrace;
+#else
+#define sysctl_softlockup_all_cpu_backtrace 0
+#endif
+
+static int __read_mostly watchdog_running;
+static u64 __read_mostly sample_period;
+
+static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
+static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
+static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
+static DEFINE_PER_CPU(bool, softlockup_touch_sync);
+static DEFINE_PER_CPU(bool, soft_watchdog_warn);
+static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
+static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
+static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+static DEFINE_PER_CPU(bool, hard_watchdog_warn);
+static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
+static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
+static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
+#endif
+static unsigned long soft_lockup_nmi_warn;
+
+/* boot commands */
+/*
+ * Should we panic when a soft-lockup or hard-lockup occurs:
+ */
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+static int hardlockup_panic =
+			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
+/*
+ * We may not want to enable hard lockup detection by default in all cases,
+ * for example when running the kernel as a guest on a hypervisor. In these
+ * cases this function can be called to disable hard lockup detection. This
+ * function should only be executed once by the boot processor before the
+ * kernel command line parameters are parsed, because otherwise it is not
+ * possible to override this in hardlockup_panic_setup().
+ */
+void hardlockup_detector_disable(void)
+{
+	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
+}
+
+static int __init hardlockup_panic_setup(char *str)
+{
+	if (!strncmp(str, "panic", 5))
+		hardlockup_panic = 1;
+	else if (!strncmp(str, "nopanic", 7))
+		hardlockup_panic = 0;
+	else if (!strncmp(str, "0", 1))
+		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
+	else if (!strncmp(str, "1", 1))
+		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
+	return 1;
+}
+__setup("nmi_watchdog=", hardlockup_panic_setup);
+#endif
+
+unsigned int __read_mostly softlockup_panic =
+			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
+
+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 nowatchdog_setup(char *str)
+{
+	watchdog_enabled = 0;
+	return 1;
+}
+__setup("nowatchdog", nowatchdog_setup);
+
+static int __init nosoftlockup_setup(char *str)
+{
+	watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
+	return 1;
+}
+__setup("nosoftlockup", nosoftlockup_setup);
+
+#ifdef CONFIG_SMP
+static int __init softlockup_all_cpu_backtrace_setup(char *str)
+{
+	sysctl_softlockup_all_cpu_backtrace =
+		!!simple_strtol(str, NULL, 0);
+	return 1;
+}
+__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
+#endif
+
+/*
+ * Hard-lockup warnings should be triggered after just a few seconds. Soft-
+ * lockups can have false positives under extreme conditions. So we generally
+ * want a higher threshold for soft lockups than for hard lockups. So we couple
+ * the thresholds with a factor: we make the soft threshold twice the amount of
+ * time the hard threshold is.
+ */
+static int get_softlockup_thresh(void)
+{
+	return watchdog_thresh * 2;
+}
+
+/*
+ * 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(void)
+{
+	return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
+}
+
+static void set_sample_period(void)
+{
+	/*
+	 * convert watchdog_thresh from seconds to ns
+	 * the divide by 5 is to give hrtimer several chances (two
+	 * or three with the current relation between the soft
+	 * and hard thresholds) to increment before the
+	 * hardlockup detector generates a warning
+	 */
+	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
+}
+
+/* Commands for resetting the watchdog */
+static void __touch_watchdog(void)
+{
+	__this_cpu_write(watchdog_touch_ts, get_timestamp());
+}
+
+void touch_softlockup_watchdog(void)
+{
+	/*
+	 * Preemption can be enabled.  It doesn't matter which CPU's timestamp
+	 * gets zeroed here, so use the raw_ operation.
+	 */
+	raw_cpu_write(watchdog_touch_ts, 0);
+}
+EXPORT_SYMBOL(touch_softlockup_watchdog);
+
+void touch_all_softlockup_watchdogs(void)
+{
+	int cpu;
+
+	/*
+	 * this is done lockless
+	 * do we care if a 0 races with a timestamp?
+	 * all it means is the softlock check starts one cycle later
+	 */
+	for_each_online_cpu(cpu)
+		per_cpu(watchdog_touch_ts, cpu) = 0;
+}
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+void touch_nmi_watchdog(void)
+{
+	/*
+	 * Using __raw here because some code paths have
+	 * preemption enabled.  If preemption is enabled
+	 * then interrupts should be enabled too, in which
+	 * case we shouldn't have to worry about the watchdog
+	 * going off.
+	 */
+	raw_cpu_write(watchdog_nmi_touch, true);
+	touch_softlockup_watchdog();
+}
+EXPORT_SYMBOL(touch_nmi_watchdog);
+
+#endif
+
+void touch_softlockup_watchdog_sync(void)
+{
+	__this_cpu_write(softlockup_touch_sync, true);
+	__this_cpu_write(watchdog_touch_ts, 0);
+}
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+/* watchdog detector functions */
+static int is_hardlockup(void)
+{
+	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
+
+	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
+		return 1;
+
+	__this_cpu_write(hrtimer_interrupts_saved, hrint);
+	return 0;
+}
+#endif
+
+static int is_softlockup(unsigned long touch_ts)
+{
+	unsigned long now = get_timestamp();
+
+	if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) {
+		/* Warn about unreasonable delays. */
+		if (time_after(now, touch_ts + get_softlockup_thresh()))
+			return now - touch_ts;
+	}
+	return 0;
+}
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+
+static 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,
+};
+
+/* Callback function for perf event subsystem */
+static void watchdog_overflow_callback(struct perf_event *event,
+		 struct perf_sample_data *data,
+		 struct pt_regs *regs)
+{
+	/* Ensure the watchdog never gets throttled */
+	event->hw.interrupts = 0;
+
+	if (__this_cpu_read(watchdog_nmi_touch) == true) {
+		__this_cpu_write(watchdog_nmi_touch, false);
+		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()) {
+		int this_cpu = smp_processor_id();
+
+		/* only print hardlockups once */
+		if (__this_cpu_read(hard_watchdog_warn) == true)
+			return;
+
+		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);
+
+		__this_cpu_write(hard_watchdog_warn, true);
+		return;
+	}
+
+	__this_cpu_write(hard_watchdog_warn, false);
+	return;
+}
+#endif /* CONFIG_HARDLOCKUP_DETECTOR */
+
+static void watchdog_interrupt_count(void)
+{
+	__this_cpu_inc(hrtimer_interrupts);
+}
+
+static int watchdog_nmi_enable(unsigned int cpu);
+static void watchdog_nmi_disable(unsigned int cpu);
+
+/* watchdog kicker functions */
+static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
+{
+	unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
+	struct pt_regs *regs = get_irq_regs();
+	int duration;
+	int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
+
+	/* kick the hardlockup detector */
+	watchdog_interrupt_count();
+
+	/* kick the softlockup detector */
+	wake_up_process(__this_cpu_read(softlockup_watchdog));
+
+	/* .. and repeat */
+	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
+
+	if (touch_ts == 0) {
+		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
+			/*
+			 * If the time stamp was touched atomically
+			 * make sure the scheduler tick is up to date.
+			 */
+			__this_cpu_write(softlockup_touch_sync, false);
+			sched_clock_tick();
+		}
+
+		/* Clear the guest paused flag on watchdog reset */
+		kvm_check_and_clear_guest_paused();
+		__touch_watchdog();
+		return HRTIMER_RESTART;
+	}
+
+	/* 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);
+	if (unlikely(duration)) {
+		/*
+		 * If a virtual machine is stopped by the host it can look to
+		 * the watchdog like a soft lockup, check to see if the host
+		 * stopped the vm before we issue the warning
+		 */
+		if (kvm_check_and_clear_guest_paused())
+			return HRTIMER_RESTART;
+
+		/* only warn once */
+		if (__this_cpu_read(soft_watchdog_warn) == true) {
+			/*
+			 * When multiple processes are causing softlockups the
+			 * softlockup detector only warns on the first one
+			 * because the code relies on a full quiet cycle to
+			 * re-arm.  The second process prevents the quiet cycle
+			 * and never gets reported.  Use task pointers to detect
+			 * this.
+			 */
+			if (__this_cpu_read(softlockup_task_ptr_saved) !=
+			    current) {
+				__this_cpu_write(soft_watchdog_warn, false);
+				__touch_watchdog();
+			}
+			return HRTIMER_RESTART;
+		}
+
+		if (softlockup_all_cpu_backtrace) {
+			/* Prevent multiple soft-lockup reports if one cpu is already
+			 * engaged in dumping cpu back traces
+			 */
+			if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
+				/* Someone else will report us. Let's give up */
+				__this_cpu_write(soft_watchdog_warn, true);
+				return HRTIMER_RESTART;
+			}
+		}
+
+		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
+			smp_processor_id(), duration,
+			current->comm, task_pid_nr(current));
+		__this_cpu_write(softlockup_task_ptr_saved, current);
+		print_modules();
+		print_irqtrace_events(current);
+		if (regs)
+			show_regs(regs);
+		else
+			dump_stack();
+
+		if (softlockup_all_cpu_backtrace) {
+			/* Avoid generating two back traces for current
+			 * given that one is already made above
+			 */
+			trigger_allbutself_cpu_backtrace();
+
+			clear_bit(0, &soft_lockup_nmi_warn);
+			/* Barrier to sync with other cpus */
+			smp_mb__after_atomic();
+		}
+
+		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
+		if (softlockup_panic)
+			panic("softlockup: hung tasks");
+		__this_cpu_write(soft_watchdog_warn, true);
+	} else
+		__this_cpu_write(soft_watchdog_warn, false);
+
+	return HRTIMER_RESTART;
+}
+
+static void watchdog_set_prio(unsigned int policy, unsigned int prio)
+{
+	struct sched_param param = { .sched_priority = prio };
+
+	sched_setscheduler(current, policy, &param);
+}
+
+static void watchdog_enable(unsigned int cpu)
+{
+	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
+
+	/* kick off the timer for the hardlockup detector */
+	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer->function = watchdog_timer_fn;
+
+	/* Enable the perf event */
+	watchdog_nmi_enable(cpu);
+
+	/* done here because hrtimer_start can only pin to smp_processor_id() */
+	hrtimer_start(hrtimer, ns_to_ktime(sample_period),
+		      HRTIMER_MODE_REL_PINNED);
+
+	/* initialize timestamp */
+	watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
+	__touch_watchdog();
+}
+
+static void watchdog_disable(unsigned int cpu)
+{
+	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
+
+	watchdog_set_prio(SCHED_NORMAL, 0);
+	hrtimer_cancel(hrtimer);
+	/* disable the perf event */
+	watchdog_nmi_disable(cpu);
+}
+
+static void watchdog_cleanup(unsigned int cpu, bool online)
+{
+	watchdog_disable(cpu);
+}
+
+static int watchdog_should_run(unsigned int cpu)
+{
+	return __this_cpu_read(hrtimer_interrupts) !=
+		__this_cpu_read(soft_lockup_hrtimer_cnt);
+}
+
+/*
+ * The watchdog thread function - touches the timestamp.
+ *
+ * It only runs once every sample_period seconds (4 seconds by
+ * default) to reset the softlockup timestamp. If this gets delayed
+ * for more than 2*watchdog_thresh seconds then the debug-printout
+ * triggers in watchdog_timer_fn().
+ */
+static void watchdog(unsigned int cpu)
+{
+	__this_cpu_write(soft_lockup_hrtimer_cnt,
+			 __this_cpu_read(hrtimer_interrupts));
+	__touch_watchdog();
+
+	/*
+	 * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
+	 * failure path. Check for failures that can occur asynchronously -
+	 * for example, when CPUs are on-lined - and shut down the hardware
+	 * perf event on each CPU accordingly.
+	 *
+	 * The only non-obvious place this bit can be cleared is through
+	 * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
+	 * pr_info here would be too noisy as it would result in a message
+	 * every few seconds if the hardlockup was disabled but the softlockup
+	 * enabled.
+	 */
+	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
+		watchdog_nmi_disable(cpu);
+}
+
+#ifdef CONFIG_HARDLOCKUP_DETECTOR
+/*
+ * People like the simple clean cpu node info on boot.
+ * Reduce the watchdog noise by only printing messages
+ * that are different from what cpu0 displayed.
+ */
+static unsigned long cpu0_err;
+
+static int 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;
+
+	/* it is setup but not enabled */
+	if (event != NULL)
+		goto out_enable;
+
+	wd_attr = &wd_hw_attr;
+	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
+
+	/* Try to register using hardware perf events */
+	event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
+
+	/* save cpu0 error for future comparision */
+	if (cpu == 0 && IS_ERR(event))
+		cpu0_err = PTR_ERR(event);
+
+	if (!IS_ERR(event)) {
+		/* only print for cpu0 or different than cpu0 */
+		if (cpu == 0 || cpu0_err)
+			pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
+		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);
+
+	/* vary the KERN level based on the returned errno */
+	if (PTR_ERR(event) == -EOPNOTSUPP)
+		pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
+	else if (PTR_ERR(event) == -ENOENT)
+		pr_warn("disabled (cpu%i): hardware events not enabled\n",
+			 cpu);
+	else
+		pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
+			cpu, PTR_ERR(event));
+
+	pr_info("Shutting down hard lockup detector on all cpus\n");
+
+	return PTR_ERR(event);
+
+	/* success path */
+out_save:
+	per_cpu(watchdog_ev, cpu) = event;
+out_enable:
+	perf_event_enable(per_cpu(watchdog_ev, cpu));
+out:
+	return 0;
+}
+
+static void watchdog_nmi_disable(unsigned int cpu)
+{
+	struct perf_event *event = per_cpu(watchdog_ev, cpu);
+
+	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 (cpu == 0) {
+		/* watchdog_nmi_enable() expects this to be zero initially. */
+		cpu0_err = 0;
+	}
+}
+
+void watchdog_nmi_enable_all(void)
+{
+	int cpu;
+
+	mutex_lock(&watchdog_proc_mutex);
+
+	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
+		goto unlock;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		watchdog_nmi_enable(cpu);
+	put_online_cpus();
+
+unlock:
+	mutex_unlock(&watchdog_proc_mutex);
+}
+
+void watchdog_nmi_disable_all(void)
+{
+	int cpu;
+
+	mutex_lock(&watchdog_proc_mutex);
+
+	if (!watchdog_running)
+		goto unlock;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		watchdog_nmi_disable(cpu);
+	put_online_cpus();
+
+unlock:
+	mutex_unlock(&watchdog_proc_mutex);
+}
+#else
+static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
+static void watchdog_nmi_disable(unsigned int cpu) { return; }
+void watchdog_nmi_enable_all(void) {}
+void watchdog_nmi_disable_all(void) {}
+#endif /* CONFIG_HARDLOCKUP_DETECTOR */
+
+static struct smp_hotplug_thread watchdog_threads = {
+	.store			= &softlockup_watchdog,
+	.thread_should_run	= watchdog_should_run,
+	.thread_fn		= watchdog,
+	.thread_comm		= "watchdog/%u",
+	.setup			= watchdog_enable,
+	.cleanup		= watchdog_cleanup,
+	.park			= watchdog_disable,
+	.unpark			= watchdog_enable,
+};
+
+static void restart_watchdog_hrtimer(void *info)
+{
+	struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
+	int ret;
+
+	/*
+	 * No need to cancel and restart hrtimer if it is currently executing
+	 * because it will reprogram itself with the new period now.
+	 * We should never see it unqueued here because we are running per-cpu
+	 * with interrupts disabled.
+	 */
+	ret = hrtimer_try_to_cancel(hrtimer);
+	if (ret == 1)
+		hrtimer_start(hrtimer, ns_to_ktime(sample_period),
+				HRTIMER_MODE_REL_PINNED);
+}
+
+static void update_watchdog(int cpu)
+{
+	/*
+	 * Make sure that perf event counter will adopt to a new
+	 * sampling period. Updating the sampling period directly would
+	 * be much nicer but we do not have an API for that now so
+	 * let's use a big hammer.
+	 * Hrtimer will adopt the new period on the next tick but this
+	 * might be late already so we have to restart the timer as well.
+	 */
+	watchdog_nmi_disable(cpu);
+	smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
+	watchdog_nmi_enable(cpu);
+}
+
+static void update_watchdog_all_cpus(void)
+{
+	int cpu;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		update_watchdog(cpu);
+	put_online_cpus();
+}
+
+static int watchdog_enable_all_cpus(void)
+{
+	int err = 0;
+
+	if (!watchdog_running) {
+		err = smpboot_register_percpu_thread(&watchdog_threads);
+		if (err)
+			pr_err("Failed to create watchdog threads, disabled\n");
+		else
+			watchdog_running = 1;
+	} else {
+		/*
+		 * Enable/disable the lockup detectors or
+		 * change the sample period 'on the fly'.
+		 */
+		update_watchdog_all_cpus();
+	}
+
+	return err;
+}
+
+/* prepare/enable/disable routines */
+/* sysctl functions */
+#ifdef CONFIG_SYSCTL
+static void watchdog_disable_all_cpus(void)
+{
+	if (watchdog_running) {
+		watchdog_running = 0;
+		smpboot_unregister_percpu_thread(&watchdog_threads);
+	}
+}
+
+/*
+ * Update the run state of the lockup detectors.
+ */
+static int proc_watchdog_update(void)
+{
+	int err = 0;
+
+	/*
+	 * Watchdog threads won't be started if they are already active.
+	 * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
+	 * care of this. If those threads are already active, the sample
+	 * period will be updated and the lockup detectors will be enabled
+	 * or disabled 'on the fly'.
+	 */
+	if (watchdog_enabled && watchdog_thresh)
+		err = watchdog_enable_all_cpus();
+	else
+		watchdog_disable_all_cpus();
+
+	return err;
+
+}
+
+/*
+ * common function for watchdog, nmi_watchdog and soft_watchdog parameter
+ *
+ * caller             | table->data points to | 'which' contains the flag(s)
+ * -------------------|-----------------------|-----------------------------
+ * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
+ *                    |                       | with SOFT_WATCHDOG_ENABLED
+ * -------------------|-----------------------|-----------------------------
+ * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
+ * -------------------|-----------------------|-----------------------------
+ * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
+ */
+static int proc_watchdog_common(int which, struct ctl_table *table, int write,
+				void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int err, old, new;
+	int *watchdog_param = (int *)table->data;
+
+	mutex_lock(&watchdog_proc_mutex);
+
+	/*
+	 * If the parameter is being read return the state of the corresponding
+	 * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
+	 * run state of the lockup detectors.
+	 */
+	if (!write) {
+		*watchdog_param = (watchdog_enabled & which) != 0;
+		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	} else {
+		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+		if (err)
+			goto out;
+
+		/*
+		 * There is a race window between fetching the current value
+		 * from 'watchdog_enabled' and storing the new value. During
+		 * this race window, watchdog_nmi_enable() can sneak in and
+		 * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
+		 * The 'cmpxchg' detects this race and the loop retries.
+		 */
+		do {
+			old = watchdog_enabled;
+			/*
+			 * If the parameter value is not zero set the
+			 * corresponding bit(s), else clear it(them).
+			 */
+			if (*watchdog_param)
+				new = old | which;
+			else
+				new = old & ~which;
+		} while (cmpxchg(&watchdog_enabled, old, new) != old);
+
+		/*
+		 * Update the run state of the lockup detectors.
+		 * Restore 'watchdog_enabled' on failure.
+		 */
+		err = proc_watchdog_update();
+		if (err)
+			watchdog_enabled = old;
+	}
+out:
+	mutex_unlock(&watchdog_proc_mutex);
+	return err;
+}
+
+/*
+ * /proc/sys/kernel/watchdog
+ */
+int proc_watchdog(struct ctl_table *table, int write,
+		  void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
+				    table, write, buffer, lenp, ppos);
+}
+
+/*
+ * /proc/sys/kernel/nmi_watchdog
+ */
+int proc_nmi_watchdog(struct ctl_table *table, int write,
+		      void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
+				    table, write, buffer, lenp, ppos);
+}
+
+/*
+ * /proc/sys/kernel/soft_watchdog
+ */
+int proc_soft_watchdog(struct ctl_table *table, int write,
+			void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
+				    table, write, buffer, lenp, ppos);
+}
+
+/*
+ * /proc/sys/kernel/watchdog_thresh
+ */
+int proc_watchdog_thresh(struct ctl_table *table, int write,
+			 void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	int err, old;
+
+	mutex_lock(&watchdog_proc_mutex);
+
+	old = ACCESS_ONCE(watchdog_thresh);
+	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+
+	if (err || !write)
+		goto out;
+
+	/*
+	 * Update the sample period.
+	 * Restore 'watchdog_thresh' on failure.
+	 */
+	set_sample_period();
+	err = proc_watchdog_update();
+	if (err)
+		watchdog_thresh = old;
+out:
+	mutex_unlock(&watchdog_proc_mutex);
+	return err;
+}
+#endif /* CONFIG_SYSCTL */
+
+void __init lockup_detector_init(void)
+{
+	set_sample_period();
+
+	if (watchdog_enabled)
+		watchdog_enable_all_cpus();
+}