linux/kernel/watchdog.c
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   1/*
   2 * Detect hard and soft lockups on a system
   3 *
   4 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   5 *
   6 * Note: Most of this code is borrowed heavily from the original softlockup
   7 * detector, so thanks to Ingo for the initial implementation.
   8 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
   9 * to those contributors as well.
  10 */
  11
  12#define pr_fmt(fmt) "NMI watchdog: " fmt
  13
  14#include <linux/mm.h>
  15#include <linux/cpu.h>
  16#include <linux/nmi.h>
  17#include <linux/init.h>
  18#include <linux/delay.h>
  19#include <linux/freezer.h>
  20#include <linux/kthread.h>
  21#include <linux/lockdep.h>
  22#include <linux/notifier.h>
  23#include <linux/module.h>
  24#include <linux/sysctl.h>
  25#include <linux/smpboot.h>
  26#include <linux/sched/rt.h>
  27
  28#include <asm/irq_regs.h>
  29#include <linux/kvm_para.h>
  30#include <linux/perf_event.h>
  31
  32int watchdog_user_enabled = 1;
  33int __read_mostly watchdog_thresh = 10;
  34static int __read_mostly watchdog_running;
  35static u64 __read_mostly sample_period;
  36
  37static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  38static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  39static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  40static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  41static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  42static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  43static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  44#ifdef CONFIG_HARDLOCKUP_DETECTOR
  45static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  46static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  47static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  48static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  49#endif
  50
  51/* boot commands */
  52/*
  53 * Should we panic when a soft-lockup or hard-lockup occurs:
  54 */
  55#ifdef CONFIG_HARDLOCKUP_DETECTOR
  56static int hardlockup_panic =
  57                        CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  58
  59static int __init hardlockup_panic_setup(char *str)
  60{
  61        if (!strncmp(str, "panic", 5))
  62                hardlockup_panic = 1;
  63        else if (!strncmp(str, "nopanic", 7))
  64                hardlockup_panic = 0;
  65        else if (!strncmp(str, "0", 1))
  66                watchdog_user_enabled = 0;
  67        return 1;
  68}
  69__setup("nmi_watchdog=", hardlockup_panic_setup);
  70#endif
  71
  72unsigned int __read_mostly softlockup_panic =
  73                        CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  74
  75static int __init softlockup_panic_setup(char *str)
  76{
  77        softlockup_panic = simple_strtoul(str, NULL, 0);
  78
  79        return 1;
  80}
  81__setup("softlockup_panic=", softlockup_panic_setup);
  82
  83static int __init nowatchdog_setup(char *str)
  84{
  85        watchdog_user_enabled = 0;
  86        return 1;
  87}
  88__setup("nowatchdog", nowatchdog_setup);
  89
  90/* deprecated */
  91static int __init nosoftlockup_setup(char *str)
  92{
  93        watchdog_user_enabled = 0;
  94        return 1;
  95}
  96__setup("nosoftlockup", nosoftlockup_setup);
  97/*  */
  98
  99/*
 100 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 101 * lockups can have false positives under extreme conditions. So we generally
 102 * want a higher threshold for soft lockups than for hard lockups. So we couple
 103 * the thresholds with a factor: we make the soft threshold twice the amount of
 104 * time the hard threshold is.
 105 */
 106static int get_softlockup_thresh(void)
 107{
 108        return watchdog_thresh * 2;
 109}
 110
 111/*
 112 * Returns seconds, approximately.  We don't need nanosecond
 113 * resolution, and we don't need to waste time with a big divide when
 114 * 2^30ns == 1.074s.
 115 */
 116static unsigned long get_timestamp(void)
 117{
 118        return local_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 119}
 120
 121static void set_sample_period(void)
 122{
 123        /*
 124         * convert watchdog_thresh from seconds to ns
 125         * the divide by 5 is to give hrtimer several chances (two
 126         * or three with the current relation between the soft
 127         * and hard thresholds) to increment before the
 128         * hardlockup detector generates a warning
 129         */
 130        sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 131}
 132
 133/* Commands for resetting the watchdog */
 134static void __touch_watchdog(void)
 135{
 136        __this_cpu_write(watchdog_touch_ts, get_timestamp());
 137}
 138
 139void touch_softlockup_watchdog(void)
 140{
 141        __this_cpu_write(watchdog_touch_ts, 0);
 142}
 143EXPORT_SYMBOL(touch_softlockup_watchdog);
 144
 145void touch_all_softlockup_watchdogs(void)
 146{
 147        int cpu;
 148
 149        /*
 150         * this is done lockless
 151         * do we care if a 0 races with a timestamp?
 152         * all it means is the softlock check starts one cycle later
 153         */
 154        for_each_online_cpu(cpu)
 155                per_cpu(watchdog_touch_ts, cpu) = 0;
 156}
 157
 158#ifdef CONFIG_HARDLOCKUP_DETECTOR
 159void touch_nmi_watchdog(void)
 160{
 161        if (watchdog_user_enabled) {
 162                unsigned cpu;
 163
 164                for_each_present_cpu(cpu) {
 165                        if (per_cpu(watchdog_nmi_touch, cpu) != true)
 166                                per_cpu(watchdog_nmi_touch, cpu) = true;
 167                }
 168        }
 169        touch_softlockup_watchdog();
 170}
 171EXPORT_SYMBOL(touch_nmi_watchdog);
 172
 173#endif
 174
 175void touch_softlockup_watchdog_sync(void)
 176{
 177        __raw_get_cpu_var(softlockup_touch_sync) = true;
 178        __raw_get_cpu_var(watchdog_touch_ts) = 0;
 179}
 180
 181#ifdef CONFIG_HARDLOCKUP_DETECTOR
 182/* watchdog detector functions */
 183static int is_hardlockup(void)
 184{
 185        unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 186
 187        if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 188                return 1;
 189
 190        __this_cpu_write(hrtimer_interrupts_saved, hrint);
 191        return 0;
 192}
 193#endif
 194
 195static int is_softlockup(unsigned long touch_ts)
 196{
 197        unsigned long now = get_timestamp();
 198
 199        /* Warn about unreasonable delays: */
 200        if (time_after(now, touch_ts + get_softlockup_thresh()))
 201                return now - touch_ts;
 202
 203        return 0;
 204}
 205
 206#ifdef CONFIG_HARDLOCKUP_DETECTOR
 207
 208static struct perf_event_attr wd_hw_attr = {
 209        .type           = PERF_TYPE_HARDWARE,
 210        .config         = PERF_COUNT_HW_CPU_CYCLES,
 211        .size           = sizeof(struct perf_event_attr),
 212        .pinned         = 1,
 213        .disabled       = 1,
 214};
 215
 216/* Callback function for perf event subsystem */
 217static void watchdog_overflow_callback(struct perf_event *event,
 218                 struct perf_sample_data *data,
 219                 struct pt_regs *regs)
 220{
 221        /* Ensure the watchdog never gets throttled */
 222        event->hw.interrupts = 0;
 223
 224        if (__this_cpu_read(watchdog_nmi_touch) == true) {
 225                __this_cpu_write(watchdog_nmi_touch, false);
 226                return;
 227        }
 228
 229        /* check for a hardlockup
 230         * This is done by making sure our timer interrupt
 231         * is incrementing.  The timer interrupt should have
 232         * fired multiple times before we overflow'd.  If it hasn't
 233         * then this is a good indication the cpu is stuck
 234         */
 235        if (is_hardlockup()) {
 236                int this_cpu = smp_processor_id();
 237
 238                /* only print hardlockups once */
 239                if (__this_cpu_read(hard_watchdog_warn) == true)
 240                        return;
 241
 242                if (hardlockup_panic)
 243                        panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 244                else
 245                        WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 246
 247                __this_cpu_write(hard_watchdog_warn, true);
 248                return;
 249        }
 250
 251        __this_cpu_write(hard_watchdog_warn, false);
 252        return;
 253}
 254#endif /* CONFIG_HARDLOCKUP_DETECTOR */
 255
 256static void watchdog_interrupt_count(void)
 257{
 258        __this_cpu_inc(hrtimer_interrupts);
 259}
 260
 261static int watchdog_nmi_enable(unsigned int cpu);
 262static void watchdog_nmi_disable(unsigned int cpu);
 263
 264/* watchdog kicker functions */
 265static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 266{
 267        unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 268        struct pt_regs *regs = get_irq_regs();
 269        int duration;
 270
 271        /* kick the hardlockup detector */
 272        watchdog_interrupt_count();
 273
 274        /* kick the softlockup detector */
 275        wake_up_process(__this_cpu_read(softlockup_watchdog));
 276
 277        /* .. and repeat */
 278        hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 279
 280        if (touch_ts == 0) {
 281                if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 282                        /*
 283                         * If the time stamp was touched atomically
 284                         * make sure the scheduler tick is up to date.
 285                         */
 286                        __this_cpu_write(softlockup_touch_sync, false);
 287                        sched_clock_tick();
 288                }
 289
 290                /* Clear the guest paused flag on watchdog reset */
 291                kvm_check_and_clear_guest_paused();
 292                __touch_watchdog();
 293                return HRTIMER_RESTART;
 294        }
 295
 296        /* check for a softlockup
 297         * This is done by making sure a high priority task is
 298         * being scheduled.  The task touches the watchdog to
 299         * indicate it is getting cpu time.  If it hasn't then
 300         * this is a good indication some task is hogging the cpu
 301         */
 302        duration = is_softlockup(touch_ts);
 303        if (unlikely(duration)) {
 304                /*
 305                 * If a virtual machine is stopped by the host it can look to
 306                 * the watchdog like a soft lockup, check to see if the host
 307                 * stopped the vm before we issue the warning
 308                 */
 309                if (kvm_check_and_clear_guest_paused())
 310                        return HRTIMER_RESTART;
 311
 312                /* only warn once */
 313                if (__this_cpu_read(soft_watchdog_warn) == true)
 314                        return HRTIMER_RESTART;
 315
 316                printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 317                        smp_processor_id(), duration,
 318                        current->comm, task_pid_nr(current));
 319                print_modules();
 320                print_irqtrace_events(current);
 321                if (regs)
 322                        show_regs(regs);
 323                else
 324                        dump_stack();
 325
 326                if (softlockup_panic)
 327                        panic("softlockup: hung tasks");
 328                __this_cpu_write(soft_watchdog_warn, true);
 329        } else
 330                __this_cpu_write(soft_watchdog_warn, false);
 331
 332        return HRTIMER_RESTART;
 333}
 334
 335static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 336{
 337        struct sched_param param = { .sched_priority = prio };
 338
 339        sched_setscheduler(current, policy, &param);
 340}
 341
 342static void watchdog_enable(unsigned int cpu)
 343{
 344        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 345
 346        /* kick off the timer for the hardlockup detector */
 347        hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 348        hrtimer->function = watchdog_timer_fn;
 349
 350        /* Enable the perf event */
 351        watchdog_nmi_enable(cpu);
 352
 353        /* done here because hrtimer_start can only pin to smp_processor_id() */
 354        hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 355                      HRTIMER_MODE_REL_PINNED);
 356
 357        /* initialize timestamp */
 358        watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 359        __touch_watchdog();
 360}
 361
 362static void watchdog_disable(unsigned int cpu)
 363{
 364        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 365
 366        watchdog_set_prio(SCHED_NORMAL, 0);
 367        hrtimer_cancel(hrtimer);
 368        /* disable the perf event */
 369        watchdog_nmi_disable(cpu);
 370}
 371
 372static void watchdog_cleanup(unsigned int cpu, bool online)
 373{
 374        watchdog_disable(cpu);
 375}
 376
 377static int watchdog_should_run(unsigned int cpu)
 378{
 379        return __this_cpu_read(hrtimer_interrupts) !=
 380                __this_cpu_read(soft_lockup_hrtimer_cnt);
 381}
 382
 383/*
 384 * The watchdog thread function - touches the timestamp.
 385 *
 386 * It only runs once every sample_period seconds (4 seconds by
 387 * default) to reset the softlockup timestamp. If this gets delayed
 388 * for more than 2*watchdog_thresh seconds then the debug-printout
 389 * triggers in watchdog_timer_fn().
 390 */
 391static void watchdog(unsigned int cpu)
 392{
 393        __this_cpu_write(soft_lockup_hrtimer_cnt,
 394                         __this_cpu_read(hrtimer_interrupts));
 395        __touch_watchdog();
 396}
 397
 398#ifdef CONFIG_HARDLOCKUP_DETECTOR
 399/*
 400 * People like the simple clean cpu node info on boot.
 401 * Reduce the watchdog noise by only printing messages
 402 * that are different from what cpu0 displayed.
 403 */
 404static unsigned long cpu0_err;
 405
 406static int watchdog_nmi_enable(unsigned int cpu)
 407{
 408        struct perf_event_attr *wd_attr;
 409        struct perf_event *event = per_cpu(watchdog_ev, cpu);
 410
 411        /* is it already setup and enabled? */
 412        if (event && event->state > PERF_EVENT_STATE_OFF)
 413                goto out;
 414
 415        /* it is setup but not enabled */
 416        if (event != NULL)
 417                goto out_enable;
 418
 419        wd_attr = &wd_hw_attr;
 420        wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 421
 422        /* Try to register using hardware perf events */
 423        event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 424
 425        /* save cpu0 error for future comparision */
 426        if (cpu == 0 && IS_ERR(event))
 427                cpu0_err = PTR_ERR(event);
 428
 429        if (!IS_ERR(event)) {
 430                /* only print for cpu0 or different than cpu0 */
 431                if (cpu == 0 || cpu0_err)
 432                        pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 433                goto out_save;
 434        }
 435
 436        /* skip displaying the same error again */
 437        if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 438                return PTR_ERR(event);
 439
 440        /* vary the KERN level based on the returned errno */
 441        if (PTR_ERR(event) == -EOPNOTSUPP)
 442                pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 443        else if (PTR_ERR(event) == -ENOENT)
 444                pr_warning("disabled (cpu%i): hardware events not enabled\n",
 445                         cpu);
 446        else
 447                pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 448                        cpu, PTR_ERR(event));
 449        return PTR_ERR(event);
 450
 451        /* success path */
 452out_save:
 453        per_cpu(watchdog_ev, cpu) = event;
 454out_enable:
 455        perf_event_enable(per_cpu(watchdog_ev, cpu));
 456out:
 457        return 0;
 458}
 459
 460static void watchdog_nmi_disable(unsigned int cpu)
 461{
 462        struct perf_event *event = per_cpu(watchdog_ev, cpu);
 463
 464        if (event) {
 465                perf_event_disable(event);
 466                per_cpu(watchdog_ev, cpu) = NULL;
 467
 468                /* should be in cleanup, but blocks oprofile */
 469                perf_event_release_kernel(event);
 470        }
 471        return;
 472}
 473#else
 474static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 475static void watchdog_nmi_disable(unsigned int cpu) { return; }
 476#endif /* CONFIG_HARDLOCKUP_DETECTOR */
 477
 478static struct smp_hotplug_thread watchdog_threads = {
 479        .store                  = &softlockup_watchdog,
 480        .thread_should_run      = watchdog_should_run,
 481        .thread_fn              = watchdog,
 482        .thread_comm            = "watchdog/%u",
 483        .setup                  = watchdog_enable,
 484        .cleanup                = watchdog_cleanup,
 485        .park                   = watchdog_disable,
 486        .unpark                 = watchdog_enable,
 487};
 488
 489static void restart_watchdog_hrtimer(void *info)
 490{
 491        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 492        int ret;
 493
 494        /*
 495         * No need to cancel and restart hrtimer if it is currently executing
 496         * because it will reprogram itself with the new period now.
 497         * We should never see it unqueued here because we are running per-cpu
 498         * with interrupts disabled.
 499         */
 500        ret = hrtimer_try_to_cancel(hrtimer);
 501        if (ret == 1)
 502                hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 503                                HRTIMER_MODE_REL_PINNED);
 504}
 505
 506static void update_timers(int cpu)
 507{
 508        struct call_single_data data = {.func = restart_watchdog_hrtimer};
 509        /*
 510         * Make sure that perf event counter will adopt to a new
 511         * sampling period. Updating the sampling period directly would
 512         * be much nicer but we do not have an API for that now so
 513         * let's use a big hammer.
 514         * Hrtimer will adopt the new period on the next tick but this
 515         * might be late already so we have to restart the timer as well.
 516         */
 517        watchdog_nmi_disable(cpu);
 518        __smp_call_function_single(cpu, &data, 1);
 519        watchdog_nmi_enable(cpu);
 520}
 521
 522static void update_timers_all_cpus(void)
 523{
 524        int cpu;
 525
 526        get_online_cpus();
 527        preempt_disable();
 528        for_each_online_cpu(cpu)
 529                update_timers(cpu);
 530        preempt_enable();
 531        put_online_cpus();
 532}
 533
 534static int watchdog_enable_all_cpus(bool sample_period_changed)
 535{
 536        int err = 0;
 537
 538        if (!watchdog_running) {
 539                err = smpboot_register_percpu_thread(&watchdog_threads);
 540                if (err)
 541                        pr_err("Failed to create watchdog threads, disabled\n");
 542                else
 543                        watchdog_running = 1;
 544        } else if (sample_period_changed) {
 545                update_timers_all_cpus();
 546        }
 547
 548        return err;
 549}
 550
 551/* prepare/enable/disable routines */
 552/* sysctl functions */
 553#ifdef CONFIG_SYSCTL
 554static void watchdog_disable_all_cpus(void)
 555{
 556        if (watchdog_running) {
 557                watchdog_running = 0;
 558                smpboot_unregister_percpu_thread(&watchdog_threads);
 559        }
 560}
 561
 562/*
 563 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 564 */
 565
 566int proc_dowatchdog(struct ctl_table *table, int write,
 567                    void __user *buffer, size_t *lenp, loff_t *ppos)
 568{
 569        int err, old_thresh, old_enabled;
 570        static DEFINE_MUTEX(watchdog_proc_mutex);
 571
 572        mutex_lock(&watchdog_proc_mutex);
 573        old_thresh = ACCESS_ONCE(watchdog_thresh);
 574        old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 575
 576        err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 577        if (err || !write)
 578                goto out;
 579
 580        set_sample_period();
 581        /*
 582         * Watchdog threads shouldn't be enabled if they are
 583         * disabled. The 'watchdog_running' variable check in
 584         * watchdog_*_all_cpus() function takes care of this.
 585         */
 586        if (watchdog_user_enabled && watchdog_thresh)
 587                err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
 588        else
 589                watchdog_disable_all_cpus();
 590
 591        /* Restore old values on failure */
 592        if (err) {
 593                watchdog_thresh = old_thresh;
 594                watchdog_user_enabled = old_enabled;
 595        }
 596out:
 597        mutex_unlock(&watchdog_proc_mutex);
 598        return err;
 599}
 600#endif /* CONFIG_SYSCTL */
 601
 602void __init lockup_detector_init(void)
 603{
 604        set_sample_period();
 605
 606        if (watchdog_user_enabled)
 607                watchdog_enable_all_cpus(false);
 608}
 609
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