linux/kernel/watchdog_hld.c
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   1// SPDX-License-Identifier: GPL-2.0
   2/*
   3 * Detect hard lockups on a system
   4 *
   5 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   6 *
   7 * Note: Most of this code is borrowed heavily from the original softlockup
   8 * detector, so thanks to Ingo for the initial implementation.
   9 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
  10 * to those contributors as well.
  11 */
  12
  13#define pr_fmt(fmt) "NMI watchdog: " fmt
  14
  15#include <linux/nmi.h>
  16#include <linux/atomic.h>
  17#include <linux/module.h>
  18#include <linux/sched/debug.h>
  19
  20#include <asm/irq_regs.h>
  21#include <linux/perf_event.h>
  22
  23static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  24static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  25static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  26static DEFINE_PER_CPU(struct perf_event *, dead_event);
  27static struct cpumask dead_events_mask;
  28
  29static unsigned long hardlockup_allcpu_dumped;
  30static atomic_t watchdog_cpus = ATOMIC_INIT(0);
  31
  32notrace void arch_touch_nmi_watchdog(void)
  33{
  34        /*
  35         * Using __raw here because some code paths have
  36         * preemption enabled.  If preemption is enabled
  37         * then interrupts should be enabled too, in which
  38         * case we shouldn't have to worry about the watchdog
  39         * going off.
  40         */
  41        raw_cpu_write(watchdog_nmi_touch, true);
  42}
  43EXPORT_SYMBOL(arch_touch_nmi_watchdog);
  44
  45#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
  46static DEFINE_PER_CPU(ktime_t, last_timestamp);
  47static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
  48static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
  49
  50void watchdog_update_hrtimer_threshold(u64 period)
  51{
  52        /*
  53         * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
  54         *
  55         * So it runs effectively with 2.5 times the rate of the NMI
  56         * watchdog. That means the hrtimer should fire 2-3 times before
  57         * the NMI watchdog expires. The NMI watchdog on x86 is based on
  58         * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
  59         * might run way faster than expected and the NMI fires in a
  60         * smaller period than the one deduced from the nominal CPU
  61         * frequency. Depending on the Turbo-Mode factor this might be fast
  62         * enough to get the NMI period smaller than the hrtimer watchdog
  63         * period and trigger false positives.
  64         *
  65         * The sample threshold is used to check in the NMI handler whether
  66         * the minimum time between two NMI samples has elapsed. That
  67         * prevents false positives.
  68         *
  69         * Set this to 4/5 of the actual watchdog threshold period so the
  70         * hrtimer is guaranteed to fire at least once within the real
  71         * watchdog threshold.
  72         */
  73        watchdog_hrtimer_sample_threshold = period * 2;
  74}
  75
  76static bool watchdog_check_timestamp(void)
  77{
  78        ktime_t delta, now = ktime_get_mono_fast_ns();
  79
  80        delta = now - __this_cpu_read(last_timestamp);
  81        if (delta < watchdog_hrtimer_sample_threshold) {
  82                /*
  83                 * If ktime is jiffies based, a stalled timer would prevent
  84                 * jiffies from being incremented and the filter would look
  85                 * at a stale timestamp and never trigger.
  86                 */
  87                if (__this_cpu_inc_return(nmi_rearmed) < 10)
  88                        return false;
  89        }
  90        __this_cpu_write(nmi_rearmed, 0);
  91        __this_cpu_write(last_timestamp, now);
  92        return true;
  93}
  94#else
  95static inline bool watchdog_check_timestamp(void)
  96{
  97        return true;
  98}
  99#endif
 100
 101static struct perf_event_attr wd_hw_attr = {
 102        .type           = PERF_TYPE_HARDWARE,
 103        .config         = PERF_COUNT_HW_CPU_CYCLES,
 104        .size           = sizeof(struct perf_event_attr),
 105        .pinned         = 1,
 106        .disabled       = 1,
 107};
 108
 109/* Callback function for perf event subsystem */
 110static void watchdog_overflow_callback(struct perf_event *event,
 111                                       struct perf_sample_data *data,
 112                                       struct pt_regs *regs)
 113{
 114        /* Ensure the watchdog never gets throttled */
 115        event->hw.interrupts = 0;
 116
 117        if (__this_cpu_read(watchdog_nmi_touch) == true) {
 118                __this_cpu_write(watchdog_nmi_touch, false);
 119                return;
 120        }
 121
 122        if (!watchdog_check_timestamp())
 123                return;
 124
 125        /* check for a hardlockup
 126         * This is done by making sure our timer interrupt
 127         * is incrementing.  The timer interrupt should have
 128         * fired multiple times before we overflow'd.  If it hasn't
 129         * then this is a good indication the cpu is stuck
 130         */
 131        if (is_hardlockup()) {
 132                int this_cpu = smp_processor_id();
 133
 134                /* only print hardlockups once */
 135                if (__this_cpu_read(hard_watchdog_warn) == true)
 136                        return;
 137
 138                pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n",
 139                         this_cpu);
 140                print_modules();
 141                print_irqtrace_events(current);
 142                if (regs)
 143                        show_regs(regs);
 144                else
 145                        dump_stack();
 146
 147                /*
 148                 * Perform all-CPU dump only once to avoid multiple hardlockups
 149                 * generating interleaving traces
 150                 */
 151                if (sysctl_hardlockup_all_cpu_backtrace &&
 152                                !test_and_set_bit(0, &hardlockup_allcpu_dumped))
 153                        trigger_allbutself_cpu_backtrace();
 154
 155                if (hardlockup_panic)
 156                        nmi_panic(regs, "Hard LOCKUP");
 157
 158                __this_cpu_write(hard_watchdog_warn, true);
 159                return;
 160        }
 161
 162        __this_cpu_write(hard_watchdog_warn, false);
 163        return;
 164}
 165
 166static int hardlockup_detector_event_create(void)
 167{
 168        unsigned int cpu = smp_processor_id();
 169        struct perf_event_attr *wd_attr;
 170        struct perf_event *evt;
 171
 172        wd_attr = &wd_hw_attr;
 173        wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 174
 175        /* Try to register using hardware perf events */
 176        evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
 177                                               watchdog_overflow_callback, NULL);
 178        if (IS_ERR(evt)) {
 179                pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
 180                         PTR_ERR(evt));
 181                return PTR_ERR(evt);
 182        }
 183        this_cpu_write(watchdog_ev, evt);
 184        return 0;
 185}
 186
 187/**
 188 * hardlockup_detector_perf_enable - Enable the local event
 189 */
 190void hardlockup_detector_perf_enable(void)
 191{
 192        if (hardlockup_detector_event_create())
 193                return;
 194
 195        /* use original value for check */
 196        if (!atomic_fetch_inc(&watchdog_cpus))
 197                pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
 198
 199        perf_event_enable(this_cpu_read(watchdog_ev));
 200}
 201
 202/**
 203 * hardlockup_detector_perf_disable - Disable the local event
 204 */
 205void hardlockup_detector_perf_disable(void)
 206{
 207        struct perf_event *event = this_cpu_read(watchdog_ev);
 208
 209        if (event) {
 210                perf_event_disable(event);
 211                this_cpu_write(watchdog_ev, NULL);
 212                this_cpu_write(dead_event, event);
 213                cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
 214                atomic_dec(&watchdog_cpus);
 215        }
 216}
 217
 218/**
 219 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
 220 *
 221 * Called from lockup_detector_cleanup(). Serialized by the caller.
 222 */
 223void hardlockup_detector_perf_cleanup(void)
 224{
 225        int cpu;
 226
 227        for_each_cpu(cpu, &dead_events_mask) {
 228                struct perf_event *event = per_cpu(dead_event, cpu);
 229
 230                /*
 231                 * Required because for_each_cpu() reports  unconditionally
 232                 * CPU0 as set on UP kernels. Sigh.
 233                 */
 234                if (event)
 235                        perf_event_release_kernel(event);
 236                per_cpu(dead_event, cpu) = NULL;
 237        }
 238        cpumask_clear(&dead_events_mask);
 239}
 240
 241/**
 242 * hardlockup_detector_perf_stop - Globally stop watchdog events
 243 *
 244 * Special interface for x86 to handle the perf HT bug.
 245 */
 246void __init hardlockup_detector_perf_stop(void)
 247{
 248        int cpu;
 249
 250        lockdep_assert_cpus_held();
 251
 252        for_each_online_cpu(cpu) {
 253                struct perf_event *event = per_cpu(watchdog_ev, cpu);
 254
 255                if (event)
 256                        perf_event_disable(event);
 257        }
 258}
 259
 260/**
 261 * hardlockup_detector_perf_restart - Globally restart watchdog events
 262 *
 263 * Special interface for x86 to handle the perf HT bug.
 264 */
 265void __init hardlockup_detector_perf_restart(void)
 266{
 267        int cpu;
 268
 269        lockdep_assert_cpus_held();
 270
 271        if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 272                return;
 273
 274        for_each_online_cpu(cpu) {
 275                struct perf_event *event = per_cpu(watchdog_ev, cpu);
 276
 277                if (event)
 278                        perf_event_enable(event);
 279        }
 280}
 281
 282/**
 283 * hardlockup_detector_perf_init - Probe whether NMI event is available at all
 284 */
 285int __init hardlockup_detector_perf_init(void)
 286{
 287        int ret = hardlockup_detector_event_create();
 288
 289        if (ret) {
 290                pr_info("Perf NMI watchdog permanently disabled\n");
 291        } else {
 292                perf_event_release_kernel(this_cpu_read(watchdog_ev));
 293                this_cpu_write(watchdog_ev, NULL);
 294        }
 295        return ret;
 296}
 297