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
  26#include <asm/irq_regs.h>
  27#include <linux/kvm_para.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 u64 get_sample_period(void)
 117{
 118        /*
 119         * convert watchdog_thresh from seconds to ns
 120         * the divide by 5 is to give hrtimer several chances (two
 121         * or three with the current relation between the soft
 122         * and hard thresholds) to increment before the
 123         * hardlockup detector generates a warning
 124         */
 125        return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 126}
 127
 128/* Commands for resetting the watchdog */
 129static void __touch_watchdog(void)
 130{
 131        int this_cpu = smp_processor_id();
 132
 133        __this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));
 134}
 135
 136void touch_softlockup_watchdog(void)
 137{
 138        __this_cpu_write(watchdog_touch_ts, 0);
 139}
 140EXPORT_SYMBOL(touch_softlockup_watchdog);
 141
 142void touch_all_softlockup_watchdogs(void)
 143{
 144        int cpu;
 145
 146        /*
 147         * this is done lockless
 148         * do we care if a 0 races with a timestamp?
 149         * all it means is the softlock check starts one cycle later
 150         */
 151        for_each_online_cpu(cpu)
 152                per_cpu(watchdog_touch_ts, cpu) = 0;
 153}
 154
 155#ifdef CONFIG_HARDLOCKUP_DETECTOR
 156void touch_nmi_watchdog(void)
 157{
 158        if (watchdog_enabled) {
 159                unsigned cpu;
 160
 161                for_each_present_cpu(cpu) {
 162                        if (per_cpu(watchdog_nmi_touch, cpu) != true)
 163                                per_cpu(watchdog_nmi_touch, cpu) = true;
 164                }
 165        }
 166        touch_softlockup_watchdog();
 167}
 168EXPORT_SYMBOL(touch_nmi_watchdog);
 169
 170#endif
 171
 172void touch_softlockup_watchdog_sync(void)
 173{
 174        __raw_get_cpu_var(softlockup_touch_sync) = true;
 175        __raw_get_cpu_var(watchdog_touch_ts) = 0;
 176}
 177
 178#ifdef CONFIG_HARDLOCKUP_DETECTOR
 179/* watchdog detector functions */
 180static int is_hardlockup(void)
 181{
 182        unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 183
 184        if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 185                return 1;
 186
 187        __this_cpu_write(hrtimer_interrupts_saved, hrint);
 188        return 0;
 189}
 190#endif
 191
 192static int is_softlockup(unsigned long touch_ts)
 193{
 194        unsigned long now = get_timestamp(smp_processor_id());
 195
 196        /* Warn about unreasonable delays: */
 197        if (time_after(now, touch_ts + get_softlockup_thresh()))
 198                return now - touch_ts;
 199
 200        return 0;
 201}
 202
 203#ifdef CONFIG_HARDLOCKUP_DETECTOR
 204
 205static struct perf_event_attr wd_hw_attr = {
 206        .type           = PERF_TYPE_HARDWARE,
 207        .config         = PERF_COUNT_HW_CPU_CYCLES,
 208        .size           = sizeof(struct perf_event_attr),
 209        .pinned         = 1,
 210        .disabled       = 1,
 211};
 212
 213/* Callback function for perf event subsystem */
 214static void watchdog_overflow_callback(struct perf_event *event,
 215                 struct perf_sample_data *data,
 216                 struct pt_regs *regs)
 217{
 218        /* Ensure the watchdog never gets throttled */
 219        event->hw.interrupts = 0;
 220
 221        if (__this_cpu_read(watchdog_nmi_touch) == true) {
 222                __this_cpu_write(watchdog_nmi_touch, false);
 223                return;
 224        }
 225
 226        /* check for a hardlockup
 227         * This is done by making sure our timer interrupt
 228         * is incrementing.  The timer interrupt should have
 229         * fired multiple times before we overflow'd.  If it hasn't
 230         * then this is a good indication the cpu is stuck
 231         */
 232        if (is_hardlockup()) {
 233                int this_cpu = smp_processor_id();
 234
 235                /* only print hardlockups once */
 236                if (__this_cpu_read(hard_watchdog_warn) == true)
 237                        return;
 238
 239                if (hardlockup_panic)
 240                        panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 241                else
 242                        WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 243
 244                __this_cpu_write(hard_watchdog_warn, true);
 245                return;
 246        }
 247
 248        __this_cpu_write(hard_watchdog_warn, false);
 249        return;
 250}
 251static void watchdog_interrupt_count(void)
 252{
 253        __this_cpu_inc(hrtimer_interrupts);
 254}
 255#else
 256static inline void watchdog_interrupt_count(void) { return; }
 257#endif /* CONFIG_HARDLOCKUP_DETECTOR */
 258
 259/* watchdog kicker functions */
 260static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 261{
 262        unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 263        struct pt_regs *regs = get_irq_regs();
 264        int duration;
 265
 266        /* kick the hardlockup detector */
 267        watchdog_interrupt_count();
 268
 269        /* kick the softlockup detector */
 270        wake_up_process(__this_cpu_read(softlockup_watchdog));
 271
 272        /* .. and repeat */
 273        hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
 274
 275        if (touch_ts == 0) {
 276                if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 277                        /*
 278                         * If the time stamp was touched atomically
 279                         * make sure the scheduler tick is up to date.
 280                         */
 281                        __this_cpu_write(softlockup_touch_sync, false);
 282                        sched_clock_tick();
 283                }
 284
 285                /* Clear the guest paused flag on watchdog reset */
 286                kvm_check_and_clear_guest_paused();
 287                __touch_watchdog();
 288                return HRTIMER_RESTART;
 289        }
 290
 291        /* check for a softlockup
 292         * This is done by making sure a high priority task is
 293         * being scheduled.  The task touches the watchdog to
 294         * indicate it is getting cpu time.  If it hasn't then
 295         * this is a good indication some task is hogging the cpu
 296         */
 297        duration = is_softlockup(touch_ts);
 298        if (unlikely(duration)) {
 299                /*
 300                 * If a virtual machine is stopped by the host it can look to
 301                 * the watchdog like a soft lockup, check to see if the host
 302                 * stopped the vm before we issue the warning
 303                 */
 304                if (kvm_check_and_clear_guest_paused())
 305                        return HRTIMER_RESTART;
 306
 307                /* only warn once */
 308                if (__this_cpu_read(soft_watchdog_warn) == true)
 309                        return HRTIMER_RESTART;
 310
 311                printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 312                        smp_processor_id(), duration,
 313                        current->comm, task_pid_nr(current));
 314                print_modules();
 315                print_irqtrace_events(current);
 316                if (regs)
 317                        show_regs(regs);
 318                else
 319                        dump_stack();
 320
 321                if (softlockup_panic)
 322                        panic("softlockup: hung tasks");
 323                __this_cpu_write(soft_watchdog_warn, true);
 324        } else
 325                __this_cpu_write(soft_watchdog_warn, false);
 326
 327        return HRTIMER_RESTART;
 328}
 329
 330
 331/*
 332 * The watchdog thread - touches the timestamp.
 333 */
 334static int watchdog(void *unused)
 335{
 336        struct sched_param param = { .sched_priority = 0 };
 337        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 338
 339        /* initialize timestamp */
 340        __touch_watchdog();
 341
 342        /* kick off the timer for the hardlockup detector */
 343        /* done here because hrtimer_start can only pin to smp_processor_id() */
 344        hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
 345                      HRTIMER_MODE_REL_PINNED);
 346
 347        set_current_state(TASK_INTERRUPTIBLE);
 348        /*
 349         * Run briefly (kicked by the hrtimer callback function) once every
 350         * get_sample_period() seconds (4 seconds by default) to reset the
 351         * softlockup timestamp. If this gets delayed for more than
 352         * 2*watchdog_thresh seconds then the debug-printout triggers in
 353         * watchdog_timer_fn().
 354         */
 355        while (!kthread_should_stop()) {
 356                __touch_watchdog();
 357                schedule();
 358
 359                if (kthread_should_stop())
 360                        break;
 361
 362                set_current_state(TASK_INTERRUPTIBLE);
 363        }
 364        /*
 365         * Drop the policy/priority elevation during thread exit to avoid a
 366         * scheduling latency spike.
 367         */
 368        __set_current_state(TASK_RUNNING);
 369        sched_setscheduler(current, SCHED_NORMAL, &param);
 370        return 0;
 371}
 372
 373
 374#ifdef CONFIG_HARDLOCKUP_DETECTOR
 375/*
 376 * People like the simple clean cpu node info on boot.
 377 * Reduce the watchdog noise by only printing messages
 378 * that are different from what cpu0 displayed.
 379 */
 380static unsigned long cpu0_err;
 381
 382static int watchdog_nmi_enable(int cpu)
 383{
 384        struct perf_event_attr *wd_attr;
 385        struct perf_event *event = per_cpu(watchdog_ev, cpu);
 386
 387        /* is it already setup and enabled? */
 388        if (event && event->state > PERF_EVENT_STATE_OFF)
 389                goto out;
 390
 391        /* it is setup but not enabled */
 392        if (event != NULL)
 393                goto out_enable;
 394
 395        wd_attr = &wd_hw_attr;
 396        wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 397
 398        /* Try to register using hardware perf events */
 399        event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 400
 401        /* save cpu0 error for future comparision */
 402        if (cpu == 0 && IS_ERR(event))
 403                cpu0_err = PTR_ERR(event);
 404
 405        if (!IS_ERR(event)) {
 406                /* only print for cpu0 or different than cpu0 */
 407                if (cpu == 0 || cpu0_err)
 408                        pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 409                goto out_save;
 410        }
 411
 412        /* skip displaying the same error again */
 413        if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 414                return PTR_ERR(event);
 415
 416        /* vary the KERN level based on the returned errno */
 417        if (PTR_ERR(event) == -EOPNOTSUPP)
 418                pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 419        else if (PTR_ERR(event) == -ENOENT)
 420                pr_warning("disabled (cpu%i): hardware events not enabled\n",
 421                         cpu);
 422        else
 423                pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 424                        cpu, PTR_ERR(event));
 425        return PTR_ERR(event);
 426
 427        /* success path */
 428out_save:
 429        per_cpu(watchdog_ev, cpu) = event;
 430out_enable:
 431        perf_event_enable(per_cpu(watchdog_ev, cpu));
 432out:
 433        return 0;
 434}
 435
 436static void watchdog_nmi_disable(int cpu)
 437{
 438        struct perf_event *event = per_cpu(watchdog_ev, cpu);
 439
 440        if (event) {
 441                perf_event_disable(event);
 442                per_cpu(watchdog_ev, cpu) = NULL;
 443
 444                /* should be in cleanup, but blocks oprofile */
 445                perf_event_release_kernel(event);
 446        }
 447        return;
 448}
 449#else
 450static int watchdog_nmi_enable(int cpu) { return 0; }
 451static void watchdog_nmi_disable(int cpu) { return; }
 452#endif /* CONFIG_HARDLOCKUP_DETECTOR */
 453
 454/* prepare/enable/disable routines */
 455static void watchdog_prepare_cpu(int cpu)
 456{
 457        struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
 458
 459        WARN_ON(per_cpu(softlockup_watchdog, cpu));
 460        hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 461        hrtimer->function = watchdog_timer_fn;
 462}
 463
 464static int watchdog_enable(int cpu)
 465{
 466        struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
 467        int err = 0;
 468
 469        /* enable the perf event */
 470        err = watchdog_nmi_enable(cpu);
 471
 472        /* Regardless of err above, fall through and start softlockup */
 473
 474        /* create the watchdog thread */
 475        if (!p) {
 476                struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 477                p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu);
 478                if (IS_ERR(p)) {
 479                        pr_err("softlockup watchdog for %i failed\n", cpu);
 480                        if (!err) {
 481                                /* if hardlockup hasn't already set this */
 482                                err = PTR_ERR(p);
 483                                /* and disable the perf event */
 484                                watchdog_nmi_disable(cpu);
 485                        }
 486                        goto out;
 487                }
 488                sched_setscheduler(p, SCHED_FIFO, &param);
 489                kthread_bind(p, cpu);
 490                per_cpu(watchdog_touch_ts, cpu) = 0;
 491                per_cpu(softlockup_watchdog, cpu) = p;
 492                wake_up_process(p);
 493        }
 494
 495out:
 496        return err;
 497}
 498
 499static void watchdog_disable(int cpu)
 500{
 501        struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
 502        struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
 503
 504        /*
 505         * cancel the timer first to stop incrementing the stats
 506         * and waking up the kthread
 507         */
 508        hrtimer_cancel(hrtimer);
 509
 510        /* disable the perf event */
 511        watchdog_nmi_disable(cpu);
 512
 513        /* stop the watchdog thread */
 514        if (p) {
 515                per_cpu(softlockup_watchdog, cpu) = NULL;
 516                kthread_stop(p);
 517        }
 518}
 519
 520/* sysctl functions */
 521#ifdef CONFIG_SYSCTL
 522static void watchdog_enable_all_cpus(void)
 523{
 524        int cpu;
 525
 526        watchdog_enabled = 0;
 527
 528        for_each_online_cpu(cpu)
 529                if (!watchdog_enable(cpu))
 530                        /* if any cpu succeeds, watchdog is considered
 531                           enabled for the system */
 532                        watchdog_enabled = 1;
 533
 534        if (!watchdog_enabled)
 535                pr_err("failed to be enabled on some cpus\n");
 536
 537}
 538
 539static void watchdog_disable_all_cpus(void)
 540{
 541        int cpu;
 542
 543        for_each_online_cpu(cpu)
 544                watchdog_disable(cpu);
 545
 546        /* if all watchdogs are disabled, then they are disabled for the system */
 547        watchdog_enabled = 0;
 548}
 549
 550
 551/*
 552 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 553 */
 554
 555int proc_dowatchdog(struct ctl_table *table, int write,
 556                    void __user *buffer, size_t *lenp, loff_t *ppos)
 557{
 558        int ret;
 559
 560        ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 561        if (ret || !write)
 562                goto out;
 563
 564        if (watchdog_enabled && watchdog_thresh)
 565                watchdog_enable_all_cpus();
 566        else
 567                watchdog_disable_all_cpus();
 568
 569out:
 570        return ret;
 571}
 572#endif /* CONFIG_SYSCTL */
 573
 574
 575/*
 576 * Create/destroy watchdog threads as CPUs come and go:
 577 */
 578static int __cpuinit
 579cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 580{
 581        int hotcpu = (unsigned long)hcpu;
 582
 583        switch (action) {
 584        case CPU_UP_PREPARE:
 585        case CPU_UP_PREPARE_FROZEN:
 586                watchdog_prepare_cpu(hotcpu);
 587                break;
 588        case CPU_ONLINE:
 589        case CPU_ONLINE_FROZEN:
 590                if (watchdog_enabled)
 591                        watchdog_enable(hotcpu);
 592                break;
 593#ifdef CONFIG_HOTPLUG_CPU
 594        case CPU_UP_CANCELED:
 595        case CPU_UP_CANCELED_FROZEN:
 596                watchdog_disable(hotcpu);
 597                break;
 598        case CPU_DEAD:
 599        case CPU_DEAD_FROZEN:
 600                watchdog_disable(hotcpu);
 601                break;
 602#endif /* CONFIG_HOTPLUG_CPU */
 603        }
 604
 605        /*
 606         * hardlockup and softlockup are not important enough
 607         * to block cpu bring up.  Just always succeed and
 608         * rely on printk output to flag problems.
 609         */
 610        return NOTIFY_OK;
 611}
 612
 613static struct notifier_block __cpuinitdata cpu_nfb = {
 614        .notifier_call = cpu_callback
 615};
 616
 617void __init lockup_detector_init(void)
 618{
 619        void *cpu = (void *)(long)smp_processor_id();
 620        int err;
 621
 622        err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 623        WARN_ON(notifier_to_errno(err));
 624
 625        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 626        register_cpu_notifier(&cpu_nfb);
 627
 628        return;
 629}
 630
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