kernel/watchdog.c

   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/module.h>
  19 #include <linux/sysctl.h>
  20 #include <linux/smpboot.h>
  21 #include <linux/sched/rt.h>
  22
  23 #include <asm/irq_regs.h>
  24 #include <linux/kvm_para.h>
  25 #include <linux/perf_event.h>
  26
  27 int watchdog_user_enabled = 1;
  28 int __read_mostly watchdog_thresh = 10;
  29 #ifdef CONFIG_SMP
  30 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  31 #else
  32 #define sysctl_softlockup_all_cpu_backtrace 0
  33 #endif
  34
  35 static int __read_mostly watchdog_running;
  36 static u64 __read_mostly sample_period;
  37
  38 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  39 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  40 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  41 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  42 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  43 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  44 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  45 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
  46 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  47 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  48 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  49 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  50 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  51 #endif
  52 static unsigned long soft_lockup_nmi_warn;
  53
  54 /* boot commands */
  55 /*
  56  * Should we panic when a soft-lockup or hard-lockup occurs:
  57  */
  58 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  59 static int hardlockup_panic =
  60                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  61
  62 static int __init hardlockup_panic_setup(char *str)
  63 {
  64         if (!strncmp(str, "panic", 5))
  65                 hardlockup_panic = 1;
  66         else if (!strncmp(str, "nopanic", 7))
  67                 hardlockup_panic = 0;
  68         else if (!strncmp(str, "0", 1))
  69                 watchdog_user_enabled = 0;
  70         return 1;
  71 }
  72 __setup("nmi_watchdog=", hardlockup_panic_setup);
  73 #endif
  74
  75 unsigned int __read_mostly softlockup_panic =
  76                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  77
  78 static int __init softlockup_panic_setup(char *str)
  79 {
  80         softlockup_panic = simple_strtoul(str, NULL, 0);
  81
  82         return 1;
  83 }
  84 __setup("softlockup_panic=", softlockup_panic_setup);
  85
  86 static int __init nowatchdog_setup(char *str)
  87 {
  88         watchdog_user_enabled = 0;
  89         return 1;
  90 }
  91 __setup("nowatchdog", nowatchdog_setup);
  92
  93 /* deprecated */
  94 static int __init nosoftlockup_setup(char *str)
  95 {
  96         watchdog_user_enabled = 0;
  97         return 1;
  98 }
  99 __setup("nosoftlockup", nosoftlockup_setup);
 100 /*  */
 101 #ifdef CONFIG_SMP
 102 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 103 {
 104         sysctl_softlockup_all_cpu_backtrace =
 105                 !!simple_strtol(str, NULL, 0);
 106         return 1;
 107 }
 108 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 109 #endif
 110
 111 /*
 112  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 113  * lockups can have false positives under extreme conditions. So we generally
 114  * want a higher threshold for soft lockups than for hard lockups. So we couple
 115  * the thresholds with a factor: we make the soft threshold twice the amount of
 116  * time the hard threshold is.
 117  */
 118 static int get_softlockup_thresh(void)
 119 {
 120         return watchdog_thresh * 2;
 121 }
 122
 123 /*
 124  * Returns seconds, approximately.  We don't need nanosecond
 125  * resolution, and we don't need to waste time with a big divide when
 126  * 2^30ns == 1.074s.
 127  */
 128 static unsigned long get_timestamp(void)
 129 {
 130         return local_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 131 }
 132
 133 static void set_sample_period(void)
 134 {
 135         /*
 136          * convert watchdog_thresh from seconds to ns
 137          * the divide by 5 is to give hrtimer several chances (two
 138          * or three with the current relation between the soft
 139          * and hard thresholds) to increment before the
 140          * hardlockup detector generates a warning
 141          */
 142         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 143 }
 144
 145 /* Commands for resetting the watchdog */
 146 static void __touch_watchdog(void)
 147 {
 148         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 149 }
 150
 151 void touch_softlockup_watchdog(void)
 152 {
 153         /*
 154          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 155          * gets zeroed here, so use the raw_ operation.
 156          */
 157         raw_cpu_write(watchdog_touch_ts, 0);
 158 }
 159 EXPORT_SYMBOL(touch_softlockup_watchdog);
 160
 161 void touch_all_softlockup_watchdogs(void)
 162 {
 163         int cpu;
 164
 165         /*
 166          * this is done lockless
 167          * do we care if a 0 races with a timestamp?
 168          * all it means is the softlock check starts one cycle later
 169          */
 170         for_each_online_cpu(cpu)
 171                 per_cpu(watchdog_touch_ts, cpu) = 0;
 172 }
 173
 174 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 175 void touch_nmi_watchdog(void)
 176 {
 177         /*
 178          * Using __raw here because some code paths have
 179          * preemption enabled.  If preemption is enabled
 180          * then interrupts should be enabled too, in which
 181          * case we shouldn't have to worry about the watchdog
 182          * going off.
 183          */
 184         __raw_get_cpu_var(watchdog_nmi_touch) = true;
 185         touch_softlockup_watchdog();
 186 }
 187 EXPORT_SYMBOL(touch_nmi_watchdog);
 188
 189 #endif
 190
 191 void touch_softlockup_watchdog_sync(void)
 192 {
 193         __raw_get_cpu_var(softlockup_touch_sync) = true;
 194         __raw_get_cpu_var(watchdog_touch_ts) = 0;
 195 }
 196
 197 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 198 /* watchdog detector functions */
 199 static int is_hardlockup(void)
 200 {
 201         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 202
 203         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 204                 return 1;
 205
 206         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 207         return 0;
 208 }
 209 #endif
 210
 211 static int is_softlockup(unsigned long touch_ts)
 212 {
 213         unsigned long now = get_timestamp();
 214
 215         /* Warn about unreasonable delays: */
 216         if (time_after(now, touch_ts + get_softlockup_thresh()))
 217                 return now - touch_ts;
 218
 219         return 0;
 220 }
 221
 222 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 223
 224 static struct perf_event_attr wd_hw_attr = {
 225         .type           = PERF_TYPE_HARDWARE,
 226         .config         = PERF_COUNT_HW_CPU_CYCLES,
 227         .size           = sizeof(struct perf_event_attr),
 228         .pinned         = 1,
 229         .disabled       = 1,
 230 };
 231
 232 /* Callback function for perf event subsystem */
 233 static void watchdog_overflow_callback(struct perf_event *event,
 234                  struct perf_sample_data *data,
 235                  struct pt_regs *regs)
 236 {
 237         /* Ensure the watchdog never gets throttled */
 238         event->hw.interrupts = 0;
 239
 240         if (__this_cpu_read(watchdog_nmi_touch) == true) {
 241                 __this_cpu_write(watchdog_nmi_touch, false);
 242                 return;
 243         }
 244
 245         /* check for a hardlockup
 246          * This is done by making sure our timer interrupt
 247          * is incrementing.  The timer interrupt should have
 248          * fired multiple times before we overflow'd.  If it hasn't
 249          * then this is a good indication the cpu is stuck
 250          */
 251         if (is_hardlockup()) {
 252                 int this_cpu = smp_processor_id();
 253
 254                 /* only print hardlockups once */
 255                 if (__this_cpu_read(hard_watchdog_warn) == true)
 256                         return;
 257
 258                 if (hardlockup_panic)
 259                         panic("Watchdog detected hard LOCKUP on cpu %d",
 260                               this_cpu);
 261                 else
 262                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
 263                              this_cpu);
 264
 265                 __this_cpu_write(hard_watchdog_warn, true);
 266                 return;
 267         }
 268
 269         __this_cpu_write(hard_watchdog_warn, false);
 270         return;
 271 }
 272 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 273
 274 static void watchdog_interrupt_count(void)
 275 {
 276         __this_cpu_inc(hrtimer_interrupts);
 277 }
 278
 279 static int watchdog_nmi_enable(unsigned int cpu);
 280 static void watchdog_nmi_disable(unsigned int cpu);
 281
 282 /* watchdog kicker functions */
 283 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 284 {
 285         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 286         struct pt_regs *regs = get_irq_regs();
 287         int duration;
 288         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 289
 290         /* kick the hardlockup detector */
 291         watchdog_interrupt_count();
 292
 293         /* kick the softlockup detector */
 294         wake_up_process(__this_cpu_read(softlockup_watchdog));
 295
 296         /* .. and repeat */
 297         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 298
 299         if (touch_ts == 0) {
 300                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 301                         /*
 302                          * If the time stamp was touched atomically
 303                          * make sure the scheduler tick is up to date.
 304                          */
 305                         __this_cpu_write(softlockup_touch_sync, false);
 306                         sched_clock_tick();
 307                 }
 308
 309                 /* Clear the guest paused flag on watchdog reset */
 310                 kvm_check_and_clear_guest_paused();
 311                 __touch_watchdog();
 312                 return HRTIMER_RESTART;
 313         }
 314
 315         /* check for a softlockup
 316          * This is done by making sure a high priority task is
 317          * being scheduled.  The task touches the watchdog to
 318          * indicate it is getting cpu time.  If it hasn't then
 319          * this is a good indication some task is hogging the cpu
 320          */
 321         duration = is_softlockup(touch_ts);
 322         if (unlikely(duration)) {
 323                 /*
 324                  * If a virtual machine is stopped by the host it can look to
 325                  * the watchdog like a soft lockup, check to see if the host
 326                  * stopped the vm before we issue the warning
 327                  */
 328                 if (kvm_check_and_clear_guest_paused())
 329                         return HRTIMER_RESTART;
 330
 331                 /* only warn once */
 332                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 333                         /*
 334                          * When multiple processes are causing softlockups the
 335                          * softlockup detector only warns on the first one
 336                          * because the code relies on a full quiet cycle to
 337                          * re-arm.  The second process prevents the quiet cycle
 338                          * and never gets reported.  Use task pointers to detect
 339                          * this.
 340                          */
 341                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 342                             current) {
 343                                 __this_cpu_write(soft_watchdog_warn, false);
 344                                 __touch_watchdog();
 345                         }
 346                         return HRTIMER_RESTART;
 347                 }
 348
 349                 if (softlockup_all_cpu_backtrace) {
 350                         /* Prevent multiple soft-lockup reports if one cpu is already
 351                          * engaged in dumping cpu back traces
 352                          */
 353                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 354                                 /* Someone else will report us. Let's give up */
 355                                 __this_cpu_write(soft_watchdog_warn, true);
 356                                 return HRTIMER_RESTART;
 357                         }
 358                 }
 359
 360                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 361                         smp_processor_id(), duration,
 362                         current->comm, task_pid_nr(current));
 363                 __this_cpu_write(softlockup_task_ptr_saved, current);
 364                 print_modules();
 365                 print_irqtrace_events(current);
 366                 if (regs)
 367                         show_regs(regs);
 368                 else
 369                         dump_stack();
 370
 371                 if (softlockup_all_cpu_backtrace) {
 372                         /* Avoid generating two back traces for current
 373                          * given that one is already made above
 374                          */
 375                         trigger_allbutself_cpu_backtrace();
 376
 377                         clear_bit(0, &soft_lockup_nmi_warn);
 378                         /* Barrier to sync with other cpus */
 379                         smp_mb__after_atomic();
 380                 }
 381
 382                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 383                 if (softlockup_panic)
 384                         panic("softlockup: hung tasks");
 385                 __this_cpu_write(soft_watchdog_warn, true);
 386         } else
 387                 __this_cpu_write(soft_watchdog_warn, false);
 388
 389         return HRTIMER_RESTART;
 390 }
 391
 392 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 393 {
 394         struct sched_param param = { .sched_priority = prio };
 395
 396         sched_setscheduler(current, policy, &param);
 397 }
 398
 399 static void watchdog_enable(unsigned int cpu)
 400 {
 401         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 402
 403         /* kick off the timer for the hardlockup detector */
 404         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 405         hrtimer->function = watchdog_timer_fn;
 406
 407         /* Enable the perf event */
 408         watchdog_nmi_enable(cpu);
 409
 410         /* done here because hrtimer_start can only pin to smp_processor_id() */
 411         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 412                       HRTIMER_MODE_REL_PINNED);
 413
 414         /* initialize timestamp */
 415         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 416         __touch_watchdog();
 417 }
 418
 419 static void watchdog_disable(unsigned int cpu)
 420 {
 421         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 422
 423         watchdog_set_prio(SCHED_NORMAL, 0);
 424         hrtimer_cancel(hrtimer);
 425         /* disable the perf event */
 426         watchdog_nmi_disable(cpu);
 427 }
 428
 429 static void watchdog_cleanup(unsigned int cpu, bool online)
 430 {
 431         watchdog_disable(cpu);
 432 }
 433
 434 static int watchdog_should_run(unsigned int cpu)
 435 {
 436         return __this_cpu_read(hrtimer_interrupts) !=
 437                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 438 }
 439
 440 /*
 441  * The watchdog thread function - touches the timestamp.
 442  *
 443  * It only runs once every sample_period seconds (4 seconds by
 444  * default) to reset the softlockup timestamp. If this gets delayed
 445  * for more than 2*watchdog_thresh seconds then the debug-printout
 446  * triggers in watchdog_timer_fn().
 447  */
 448 static void watchdog(unsigned int cpu)
 449 {
 450         __this_cpu_write(soft_lockup_hrtimer_cnt,
 451                          __this_cpu_read(hrtimer_interrupts));
 452         __touch_watchdog();
 453 }
 454
 455 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 456 /*
 457  * People like the simple clean cpu node info on boot.
 458  * Reduce the watchdog noise by only printing messages
 459  * that are different from what cpu0 displayed.
 460  */
 461 static unsigned long cpu0_err;
 462
 463 static int watchdog_nmi_enable(unsigned int cpu)
 464 {
 465         struct perf_event_attr *wd_attr;
 466         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 467
 468         /* is it already setup and enabled? */
 469         if (event && event->state > PERF_EVENT_STATE_OFF)
 470                 goto out;
 471
 472         /* it is setup but not enabled */
 473         if (event != NULL)
 474                 goto out_enable;
 475
 476         wd_attr = &wd_hw_attr;
 477         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 478
 479         /* Try to register using hardware perf events */
 480         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 481
 482         /* save cpu0 error for future comparision */
 483         if (cpu == 0 && IS_ERR(event))
 484                 cpu0_err = PTR_ERR(event);
 485
 486         if (!IS_ERR(event)) {
 487                 /* only print for cpu0 or different than cpu0 */
 488                 if (cpu == 0 || cpu0_err)
 489                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 490                 goto out_save;
 491         }
 492
 493         /* skip displaying the same error again */
 494         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 495                 return PTR_ERR(event);
 496
 497         /* vary the KERN level based on the returned errno */
 498         if (PTR_ERR(event) == -EOPNOTSUPP)
 499                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 500         else if (PTR_ERR(event) == -ENOENT)
 501                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
 502                          cpu);
 503         else
 504                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 505                         cpu, PTR_ERR(event));
 506         return PTR_ERR(event);
 507
 508         /* success path */
 509 out_save:
 510         per_cpu(watchdog_ev, cpu) = event;
 511 out_enable:
 512         perf_event_enable(per_cpu(watchdog_ev, cpu));
 513 out:
 514         return 0;
 515 }
 516
 517 static void watchdog_nmi_disable(unsigned int cpu)
 518 {
 519         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 520
 521         if (event) {
 522                 perf_event_disable(event);
 523                 per_cpu(watchdog_ev, cpu) = NULL;
 524
 525                 /* should be in cleanup, but blocks oprofile */
 526                 perf_event_release_kernel(event);
 527         }
 528         if (cpu == 0) {
 529                 /* watchdog_nmi_enable() expects this to be zero initially. */
 530                 cpu0_err = 0;
 531         }
 532 }
 533 #else
 534 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 535 static void watchdog_nmi_disable(unsigned int cpu) { return; }
 536 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 537
 538 static struct smp_hotplug_thread watchdog_threads = {
 539         .store                  = &softlockup_watchdog,
 540         .thread_should_run      = watchdog_should_run,
 541         .thread_fn              = watchdog,
 542         .thread_comm            = "watchdog/%u",
 543         .setup                  = watchdog_enable,
 544         .cleanup                = watchdog_cleanup,
 545         .park                   = watchdog_disable,
 546         .unpark                 = watchdog_enable,
 547 };
 548
 549 static void restart_watchdog_hrtimer(void *info)
 550 {
 551         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 552         int ret;
 553
 554         /*
 555          * No need to cancel and restart hrtimer if it is currently executing
 556          * because it will reprogram itself with the new period now.
 557          * We should never see it unqueued here because we are running per-cpu
 558          * with interrupts disabled.
 559          */
 560         ret = hrtimer_try_to_cancel(hrtimer);
 561         if (ret == 1)
 562                 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 563                                 HRTIMER_MODE_REL_PINNED);
 564 }
 565
 566 static void update_timers(int cpu)
 567 {
 568         /*
 569          * Make sure that perf event counter will adopt to a new
 570          * sampling period. Updating the sampling period directly would
 571          * be much nicer but we do not have an API for that now so
 572          * let's use a big hammer.
 573          * Hrtimer will adopt the new period on the next tick but this
 574          * might be late already so we have to restart the timer as well.
 575          */
 576         watchdog_nmi_disable(cpu);
 577         smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
 578         watchdog_nmi_enable(cpu);
 579 }
 580
 581 static void update_timers_all_cpus(void)
 582 {
 583         int cpu;
 584
 585         get_online_cpus();
 586         for_each_online_cpu(cpu)
 587                 update_timers(cpu);
 588         put_online_cpus();
 589 }
 590
 591 static int watchdog_enable_all_cpus(bool sample_period_changed)
 592 {
 593         int err = 0;
 594
 595         if (!watchdog_running) {
 596                 err = smpboot_register_percpu_thread(&watchdog_threads);
 597                 if (err)
 598                         pr_err("Failed to create watchdog threads, disabled\n");
 599                 else
 600                         watchdog_running = 1;
 601         } else if (sample_period_changed) {
 602                 update_timers_all_cpus();
 603         }
 604
 605         return err;
 606 }
 607
 608 /* prepare/enable/disable routines */
 609 /* sysctl functions */
 610 #ifdef CONFIG_SYSCTL
 611 static void watchdog_disable_all_cpus(void)
 612 {
 613         if (watchdog_running) {
 614                 watchdog_running = 0;
 615                 smpboot_unregister_percpu_thread(&watchdog_threads);
 616         }
 617 }
 618
 619 /*
 620  * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 621  */
 622
 623 int proc_dowatchdog(struct ctl_table *table, int write,
 624                     void __user *buffer, size_t *lenp, loff_t *ppos)
 625 {
 626         int err, old_thresh, old_enabled;
 627         static DEFINE_MUTEX(watchdog_proc_mutex);
 628
 629         mutex_lock(&watchdog_proc_mutex);
 630         old_thresh = ACCESS_ONCE(watchdog_thresh);
 631         old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 632
 633         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 634         if (err || !write)
 635                 goto out;
 636
 637         set_sample_period();
 638         /*
 639          * Watchdog threads shouldn't be enabled if they are
 640          * disabled. The 'watchdog_running' variable check in
 641          * watchdog_*_all_cpus() function takes care of this.
 642          */
 643         if (watchdog_user_enabled && watchdog_thresh)
 644                 err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
 645         else
 646                 watchdog_disable_all_cpus();
 647
 648         /* Restore old values on failure */
 649         if (err) {
 650                 watchdog_thresh = old_thresh;
 651                 watchdog_user_enabled = old_enabled;
 652         }
 653 out:
 654         mutex_unlock(&watchdog_proc_mutex);
 655         return err;
 656 }
 657 #endif /* CONFIG_SYSCTL */
 658
 659 void __init lockup_detector_init(void)
 660 {
 661         set_sample_period();
 662
 663         if (watchdog_user_enabled)
 664                 watchdog_enable_all_cpus(false);
 665 }