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