blob: 3a09ea1b1d3d5e6e284d058052403ac1396804ca [file] [log] [blame]
* Detect hard 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/nmi.h>
#include <linux/module.h>
#include <linux/sched/debug.h>
#include <asm/irq_regs.h>
#include <linux/perf_event.h>
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
static unsigned long hardlockup_allcpu_dumped;
void arch_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);
static DEFINE_PER_CPU(ktime_t, last_timestamp);
static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
void watchdog_update_hrtimer_threshold(u64 period)
* The hrtimer runs with a period of (watchdog_threshold * 2) / 5
* So it runs effectively with 2.5 times the rate of the NMI
* watchdog. That means the hrtimer should fire 2-3 times before
* the NMI watchdog expires. The NMI watchdog on x86 is based on
* unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
* might run way faster than expected and the NMI fires in a
* smaller period than the one deduced from the nominal CPU
* frequency. Depending on the Turbo-Mode factor this might be fast
* enough to get the NMI period smaller than the hrtimer watchdog
* period and trigger false positives.
* The sample threshold is used to check in the NMI handler whether
* the minimum time between two NMI samples has elapsed. That
* prevents false positives.
* Set this to 4/5 of the actual watchdog threshold period so the
* hrtimer is guaranteed to fire at least once within the real
* watchdog threshold.
watchdog_hrtimer_sample_threshold = period * 2;
static bool watchdog_check_timestamp(void)
ktime_t delta, now = ktime_get_mono_fast_ns();
delta = now - __this_cpu_read(last_timestamp);
if (delta < watchdog_hrtimer_sample_threshold) {
* If ktime is jiffies based, a stalled timer would prevent
* jiffies from being incremented and the filter would look
* at a stale timestamp and never trigger.
if (__this_cpu_inc_return(nmi_rearmed) < 10)
return false;
__this_cpu_write(nmi_rearmed, 0);
__this_cpu_write(last_timestamp, now);
return true;
static inline bool watchdog_check_timestamp(void)
return true;
static struct perf_event_attr wd_hw_attr = {
.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 (atomic_read(&watchdog_park_in_progress) != 0)
if (__this_cpu_read(watchdog_nmi_touch) == true) {
__this_cpu_write(watchdog_nmi_touch, false);
if (!watchdog_check_timestamp())
/* 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)
pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
if (regs)
* Perform all-CPU dump only once to avoid multiple hardlockups
* generating interleaving traces
if (sysctl_hardlockup_all_cpu_backtrace &&
!test_and_set_bit(0, &hardlockup_allcpu_dumped))
if (hardlockup_panic)
nmi_panic(regs, "Hard LOCKUP");
__this_cpu_write(hard_watchdog_warn, true);
__this_cpu_write(hard_watchdog_warn, false);
* 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 firstcpu_err;
static atomic_t watchdog_cpus;
int watchdog_nmi_enable(unsigned int cpu)
struct perf_event_attr *wd_attr;
struct perf_event *event = per_cpu(watchdog_ev, cpu);
int firstcpu = 0;
/* 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;
if (atomic_inc_return(&watchdog_cpus) == 1)
firstcpu = 1;
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 the first cpu's error for future comparision */
if (firstcpu && IS_ERR(event))
firstcpu_err = PTR_ERR(event);
if (!IS_ERR(event)) {
/* only print for the first cpu initialized */
if (firstcpu || firstcpu_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.
clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
/* skip displaying the same error again */
if (!firstcpu && (PTR_ERR(event) == firstcpu_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",
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 */
per_cpu(watchdog_ev, cpu) = event;
perf_event_enable(per_cpu(watchdog_ev, cpu));
return 0;
void watchdog_nmi_disable(unsigned int cpu)
struct perf_event *event = per_cpu(watchdog_ev, cpu);
if (event) {
per_cpu(watchdog_ev, cpu) = NULL;
/* should be in cleanup, but blocks oprofile */
/* watchdog_nmi_enable() expects this to be zero initially. */
if (atomic_dec_and_test(&watchdog_cpus))
firstcpu_err = 0;