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/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
  32 int watchdog_user_enabled = 1;
  33 int __read_mostly watchdog_thresh = 10;
  34 #ifdef CONFIG_SMP
  35 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  36 #else
  37 #define sysctl_softlockup_all_cpu_backtrace 0
  38 #endif
  39
  40 static int __read_mostly watchdog_running;
  41 static u64 __read_mostly sample_period;
  42
  43 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  44 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  45 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  46 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  47 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  48 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  49 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  50 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
  51 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  52 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  53 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  54 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  55 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  56 #endif
  57 static unsigned long soft_lockup_nmi_warn;
  58
  59 /* boot commands */
  60 /*
  61  * Should we panic when a soft-lockup or hard-lockup occurs:
  62  */
  63 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  64 static int hardlockup_panic =
  65                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  66
  67 static int __init hardlockup_panic_setup(char *str)
  68 {
  69         if (!strncmp(str, "panic", 5))
  70                 hardlockup_panic = 1;
  71         else if (!strncmp(str, "nopanic", 7))
  72                 hardlockup_panic = 0;
  73         else if (!strncmp(str, "0", 1))
  74                 watchdog_user_enabled = 0;
  75         return 1;
  76 }
  77 __setup("nmi_watchdog=", hardlockup_panic_setup);
  78 #endif
  79
  80 unsigned int __read_mostly softlockup_panic =
  81                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  82
  83 static int __init softlockup_panic_setup(char *str)
  84 {
  85         softlockup_panic = simple_strtoul(str, NULL, 0);
  86
  87         return 1;
  88 }
  89 __setup("softlockup_panic=", softlockup_panic_setup);
  90
  91 static int __init nowatchdog_setup(char *str)
  92 {
  93         watchdog_user_enabled = 0;
  94         return 1;
  95 }
  96 __setup("nowatchdog", nowatchdog_setup);
  97
  98 /* deprecated */
  99 static int __init nosoftlockup_setup(char *str)
 100 {
 101         watchdog_user_enabled = 0;
 102         return 1;
 103 }
 104 __setup("nosoftlockup", nosoftlockup_setup);
 105 /*  */
 106 #ifdef CONFIG_SMP
 107 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 108 {
 109         sysctl_softlockup_all_cpu_backtrace =
 110                 !!simple_strtol(str, NULL, 0);
 111         return 1;
 112 }
 113 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 114 #endif
 115
 116 /*
 117  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 118  * lockups can have false positives under extreme conditions. So we generally
 119  * want a higher threshold for soft lockups than for hard lockups. So we couple
 120  * the thresholds with a factor: we make the soft threshold twice the amount of
 121  * time the hard threshold is.
 122  */
 123 static int get_softlockup_thresh(void)
 124 {
 125         return watchdog_thresh * 2;
 126 }
 127
 128 /*
 129  * Returns seconds, approximately.  We don't need nanosecond
 130  * resolution, and we don't need to waste time with a big divide when
 131  * 2^30ns == 1.074s.
 132  */
 133 static unsigned long get_timestamp(void)
 134 {
 135         return local_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 136 }
 137
 138 static void set_sample_period(void)
 139 {
 140         /*
 141          * convert watchdog_thresh from seconds to ns
 142          * the divide by 5 is to give hrtimer several chances (two
 143          * or three with the current relation between the soft
 144          * and hard thresholds) to increment before the
 145          * hardlockup detector generates a warning
 146          */
 147         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 148 }
 149
 150 /* Commands for resetting the watchdog */
 151 static void __touch_watchdog(void)
 152 {
 153         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 154 }
 155
 156 void touch_softlockup_watchdog(void)
 157 {
 158         /*
 159          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 160          * gets zeroed here, so use the raw_ operation.
 161          */
 162         raw_cpu_write(watchdog_touch_ts, 0);
 163 }
 164 EXPORT_SYMBOL(touch_softlockup_watchdog);
 165
 166 void touch_all_softlockup_watchdogs(void)
 167 {
 168         int cpu;
 169
 170         /*
 171          * this is done lockless
 172          * do we care if a 0 races with a timestamp?
 173          * all it means is the softlock check starts one cycle later
 174          */
 175         for_each_online_cpu(cpu)
 176                 per_cpu(watchdog_touch_ts, cpu) = 0;
 177 }
 178
 179 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 180 void touch_nmi_watchdog(void)
 181 {
 182         /*
 183          * Using __raw here because some code paths have
 184          * preemption enabled.  If preemption is enabled
 185          * then interrupts should be enabled too, in which
 186          * case we shouldn't have to worry about the watchdog
 187          * going off.
 188          */
 189         __raw_get_cpu_var(watchdog_nmi_touch) = true;
 190         touch_softlockup_watchdog();
 191 }
 192 EXPORT_SYMBOL(touch_nmi_watchdog);
 193
 194 #endif
 195
 196 void touch_softlockup_watchdog_sync(void)
 197 {
 198         __raw_get_cpu_var(softlockup_touch_sync) = true;
 199         __raw_get_cpu_var(watchdog_touch_ts) = 0;
 200 }
 201
 202 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 203 /* watchdog detector functions */
 204 static int is_hardlockup(void)
 205 {
 206         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 207
 208         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 209                 return 1;
 210
 211         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 212         return 0;
 213 }
 214 #endif
 215
 216 static int is_softlockup(unsigned long touch_ts)
 217 {
 218         unsigned long now = get_timestamp();
 219
 220         /* Warn about unreasonable delays: */
 221         if (time_after(now, touch_ts + get_softlockup_thresh()))
 222                 return now - touch_ts;
 223
 224         return 0;
 225 }
 226
 227 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 228
 229 static struct perf_event_attr wd_hw_attr = {
 230         .type           = PERF_TYPE_HARDWARE,
 231         .config         = PERF_COUNT_HW_CPU_CYCLES,
 232         .size           = sizeof(struct perf_event_attr),
 233         .pinned         = 1,
 234         .disabled       = 1,
 235 };
 236
 237 /* Callback function for perf event subsystem */
 238 static void watchdog_overflow_callback(struct perf_event *event,
 239                  struct perf_sample_data *data,
 240                  struct pt_regs *regs)
 241 {
 242         /* Ensure the watchdog never gets throttled */
 243         event->hw.interrupts = 0;
 244
 245         if (__this_cpu_read(watchdog_nmi_touch) == true) {
 246                 __this_cpu_write(watchdog_nmi_touch, false);
 247                 return;
 248         }
 249
 250         /* check for a hardlockup
 251          * This is done by making sure our timer interrupt
 252          * is incrementing.  The timer interrupt should have
 253          * fired multiple times before we overflow'd.  If it hasn't
 254          * then this is a good indication the cpu is stuck
 255          */
 256         if (is_hardlockup()) {
 257                 int this_cpu = smp_processor_id();
 258
 259                 /* only print hardlockups once */
 260                 if (__this_cpu_read(hard_watchdog_warn) == true)
 261                         return;
 262
 263                 if (hardlockup_panic)
 264                         panic("Watchdog detected hard LOCKUP on cpu %d",
 265                               this_cpu);
 266                 else
 267                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
 268                              this_cpu);
 269
 270                 __this_cpu_write(hard_watchdog_warn, true);
 271                 return;
 272         }
 273
 274         __this_cpu_write(hard_watchdog_warn, false);
 275         return;
 276 }
 277 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 278
 279 static void watchdog_interrupt_count(void)
 280 {
 281         __this_cpu_inc(hrtimer_interrupts);
 282 }
 283
 284 static int watchdog_nmi_enable(unsigned int cpu);
 285 static void watchdog_nmi_disable(unsigned int cpu);
 286
 287 /* watchdog kicker functions */
 288 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 289 {
 290         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 291         struct pt_regs *regs = get_irq_regs();
 292         int duration;
 293         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 294
 295         /* kick the hardlockup detector */
 296         watchdog_interrupt_count();
 297
 298         /* kick the softlockup detector */
 299         wake_up_process(__this_cpu_read(softlockup_watchdog));
 300
 301         /* .. and repeat */
 302         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 303
 304         if (touch_ts == 0) {
 305                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 306                         /*
 307                          * If the time stamp was touched atomically
 308                          * make sure the scheduler tick is up to date.
 309                          */
 310                         __this_cpu_write(softlockup_touch_sync, false);
 311                         sched_clock_tick();
 312                 }
 313
 314                 /* Clear the guest paused flag on watchdog reset */
 315                 kvm_check_and_clear_guest_paused();
 316                 __touch_watchdog();
 317                 return HRTIMER_RESTART;
 318         }
 319
 320         /* check for a softlockup
 321          * This is done by making sure a high priority task is
 322          * being scheduled.  The task touches the watchdog to
 323          * indicate it is getting cpu time.  If it hasn't then
 324          * this is a good indication some task is hogging the cpu
 325          */
 326         duration = is_softlockup(touch_ts);
 327         if (unlikely(duration)) {
 328                 /*
 329                  * If a virtual machine is stopped by the host it can look to
 330                  * the watchdog like a soft lockup, check to see if the host
 331                  * stopped the vm before we issue the warning
 332                  */
 333                 if (kvm_check_and_clear_guest_paused())
 334                         return HRTIMER_RESTART;
 335
 336                 /* only warn once */
 337                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 338                         /*
 339                          * When multiple processes are causing softlockups the
 340                          * softlockup detector only warns on the first one
 341                          * because the code relies on a full quiet cycle to
 342                          * re-arm.  The second process prevents the quiet cycle
 343                          * and never gets reported.  Use task pointers to detect
 344                          * this.
 345                          */
 346                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 347                             current) {
 348                                 __this_cpu_write(soft_watchdog_warn, false);
 349                                 __touch_watchdog();
 350                         }
 351                         return HRTIMER_RESTART;
 352                 }
 353
 354                 if (softlockup_all_cpu_backtrace) {
 355                         /* Prevent multiple soft-lockup reports if one cpu is already
 356                          * engaged in dumping cpu back traces
 357                          */
 358                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 359                                 /* Someone else will report us. Let's give up */
 360                                 __this_cpu_write(soft_watchdog_warn, true);
 361                                 return HRTIMER_RESTART;
 362                         }
 363                 }
 364
 365                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 366                         smp_processor_id(), duration,
 367                         current->comm, task_pid_nr(current));
 368                 __this_cpu_write(softlockup_task_ptr_saved, current);
 369                 print_modules();
 370                 print_irqtrace_events(current);
 371                 if (regs)
 372                         show_regs(regs);
 373                 else
 374                         dump_stack();
 375
 376                 if (softlockup_all_cpu_backtrace) {
 377                         /* Avoid generating two back traces for current
 378                          * given that one is already made above
 379                          */
 380                         trigger_allbutself_cpu_backtrace();
 381
 382                         clear_bit(0, &soft_lockup_nmi_warn);
 383                         /* Barrier to sync with other cpus */
 384                         smp_mb__after_atomic();
 385                 }
 386
 387                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 388                 if (softlockup_panic)
 389                         panic("softlockup: hung tasks");
 390                 __this_cpu_write(soft_watchdog_warn, true);
 391         } else
 392                 __this_cpu_write(soft_watchdog_warn, false);
 393
 394         return HRTIMER_RESTART;
 395 }
 396
 397 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 398 {
 399         struct sched_param param = { .sched_priority = prio };
 400
 401         sched_setscheduler(current, policy, &param);
 402 }
 403
 404 static void watchdog_enable(unsigned int cpu)
 405 {
 406         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 407
 408         /* kick off the timer for the hardlockup detector */
 409         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 410         hrtimer->function = watchdog_timer_fn;
 411
 412         /* Enable the perf event */
 413         watchdog_nmi_enable(cpu);
 414
 415         /* done here because hrtimer_start can only pin to smp_processor_id() */
 416         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 417                       HRTIMER_MODE_REL_PINNED);
 418
 419         /* initialize timestamp */
 420         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 421         __touch_watchdog();
 422 }
 423
 424 static void watchdog_disable(unsigned int cpu)
 425 {
 426         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 427
 428         watchdog_set_prio(SCHED_NORMAL, 0);
 429         hrtimer_cancel(hrtimer);
 430         /* disable the perf event */
 431         watchdog_nmi_disable(cpu);
 432 }
 433
 434 static void watchdog_cleanup(unsigned int cpu, bool online)
 435 {
 436         watchdog_disable(cpu);
 437 }
 438
 439 static int watchdog_should_run(unsigned int cpu)
 440 {
 441         return __this_cpu_read(hrtimer_interrupts) !=
 442                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 443 }
 444
 445 /*
 446  * The watchdog thread function - touches the timestamp.
 447  *
 448  * It only runs once every sample_period seconds (4 seconds by
 449  * default) to reset the softlockup timestamp. If this gets delayed
 450  * for more than 2*watchdog_thresh seconds then the debug-printout
 451  * triggers in watchdog_timer_fn().
 452  */
 453 static void watchdog(unsigned int cpu)
 454 {
 455         __this_cpu_write(soft_lockup_hrtimer_cnt,
 456                          __this_cpu_read(hrtimer_interrupts));
 457         __touch_watchdog();
 458 }
 459
 460 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 461 /*
 462  * People like the simple clean cpu node info on boot.
 463  * Reduce the watchdog noise by only printing messages
 464  * that are different from what cpu0 displayed.
 465  */
 466 static unsigned long cpu0_err;
 467
 468 static int watchdog_nmi_enable(unsigned int cpu)
 469 {
 470         struct perf_event_attr *wd_attr;
 471         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 472
 473         /* is it already setup and enabled? */
 474         if (event && event->state > PERF_EVENT_STATE_OFF)
 475                 goto out;
 476
 477         /* it is setup but not enabled */
 478         if (event != NULL)
 479                 goto out_enable;
 480
 481         wd_attr = &wd_hw_attr;
 482         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 483
 484         /* Try to register using hardware perf events */
 485         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 486
 487         /* save cpu0 error for future comparision */
 488         if (cpu == 0 && IS_ERR(event))
 489                 cpu0_err = PTR_ERR(event);
 490
 491         if (!IS_ERR(event)) {
 492                 /* only print for cpu0 or different than cpu0 */
 493                 if (cpu == 0 || cpu0_err)
 494                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 495                 goto out_save;
 496         }
 497
 498         /* skip displaying the same error again */
 499         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 500                 return PTR_ERR(event);
 501
 502         /* vary the KERN level based on the returned errno */
 503         if (PTR_ERR(event) == -EOPNOTSUPP)
 504                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 505         else if (PTR_ERR(event) == -ENOENT)
 506                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
 507                          cpu);
 508         else
 509                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 510                         cpu, PTR_ERR(event));
 511         return PTR_ERR(event);
 512
 513         /* success path */
 514 out_save:
 515         per_cpu(watchdog_ev, cpu) = event;
 516 out_enable:
 517         perf_event_enable(per_cpu(watchdog_ev, cpu));
 518 out:
 519         return 0;
 520 }
 521
 522 static void watchdog_nmi_disable(unsigned int cpu)
 523 {
 524         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 525
 526         if (event) {
 527                 perf_event_disable(event);
 528                 per_cpu(watchdog_ev, cpu) = NULL;
 529
 530                 /* should be in cleanup, but blocks oprofile */
 531                 perf_event_release_kernel(event);
 532         }
 533         return;
 534 }
 535 #else
 536 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 537 static void watchdog_nmi_disable(unsigned int cpu) { return; }
 538 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 539
 540 static struct smp_hotplug_thread watchdog_threads = {
 541         .store                  = &softlockup_watchdog,
 542         .thread_should_run      = watchdog_should_run,
 543         .thread_fn              = watchdog,
 544         .thread_comm            = "watchdog/%u",
 545         .setup                  = watchdog_enable,
 546         .cleanup                = watchdog_cleanup,
 547         .park                   = watchdog_disable,
 548         .unpark                 = watchdog_enable,
 549 };
 550
 551 static void restart_watchdog_hrtimer(void *info)
 552 {
 553         struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 554         int ret;
 555
 556         /*
 557          * No need to cancel and restart hrtimer if it is currently executing
 558          * because it will reprogram itself with the new period now.
 559          * We should never see it unqueued here because we are running per-cpu
 560          * with interrupts disabled.
 561          */
 562         ret = hrtimer_try_to_cancel(hrtimer);
 563         if (ret == 1)
 564                 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 565                                 HRTIMER_MODE_REL_PINNED);
 566 }
 567
 568 static void update_timers(int cpu)
 569 {
 570         /*
 571          * Make sure that perf event counter will adopt to a new
 572          * sampling period. Updating the sampling period directly would
 573          * be much nicer but we do not have an API for that now so
 574          * let's use a big hammer.
 575          * Hrtimer will adopt the new period on the next tick but this
 576          * might be late already so we have to restart the timer as well.
 577          */
 578         watchdog_nmi_disable(cpu);
 579         smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
 580         watchdog_nmi_enable(cpu);
 581 }
 582
 583 static void update_timers_all_cpus(void)
 584 {
 585         int cpu;
 586
 587         get_online_cpus();
 588         for_each_online_cpu(cpu)
 589                 update_timers(cpu);
 590         put_online_cpus();
 591 }
 592
 593 static int watchdog_enable_all_cpus(bool sample_period_changed)
 594 {
 595         int err = 0;
 596
 597         if (!watchdog_running) {
 598                 err = smpboot_register_percpu_thread(&watchdog_threads);
 599                 if (err)
 600                         pr_err("Failed to create watchdog threads, disabled\n");
 601                 else
 602                         watchdog_running = 1;
 603         } else if (sample_period_changed) {
 604                 update_timers_all_cpus();
 605         }
 606
 607         return err;
 608 }
 609
 610 /* prepare/enable/disable routines */
 611 /* sysctl functions */
 612 #ifdef CONFIG_SYSCTL
 613 static void watchdog_disable_all_cpus(void)
 614 {
 615         if (watchdog_running) {
 616                 watchdog_running = 0;
 617                 smpboot_unregister_percpu_thread(&watchdog_threads);
 618         }
 619 }
 620
 621 /*
 622  * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 623  */
 624
 625 int proc_dowatchdog(struct ctl_table *table, int write,
 626                     void __user *buffer, size_t *lenp, loff_t *ppos)
 627 {
 628         int err, old_thresh, old_enabled;
 629         static DEFINE_MUTEX(watchdog_proc_mutex);
 630
 631         mutex_lock(&watchdog_proc_mutex);
 632         old_thresh = ACCESS_ONCE(watchdog_thresh);
 633         old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 634
 635         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 636         if (err || !write)
 637                 goto out;
 638
 639         set_sample_period();
 640         /*
 641          * Watchdog threads shouldn't be enabled if they are
 642          * disabled. The 'watchdog_running' variable check in
 643          * watchdog_*_all_cpus() function takes care of this.
 644          */
 645         if (watchdog_user_enabled && watchdog_thresh)
 646                 err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
 647         else
 648                 watchdog_disable_all_cpus();
 649
 650         /* Restore old values on failure */
 651         if (err) {
 652                 watchdog_thresh = old_thresh;
 653                 watchdog_user_enabled = old_enabled;
 654         }
 655 out:
 656         mutex_unlock(&watchdog_proc_mutex);
 657         return err;
 658 }
 659 #endif /* CONFIG_SYSCTL */
 660
 661 void __init lockup_detector_init(void)
 662 {
 663         set_sample_period();
 664
 665         if (watchdog_user_enabled)
 666                 watchdog_enable_all_cpus(false);
 667 }