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