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 bool hardlockup_detector_enabled = true;
  63 /*
  64  * We may not want to enable hard lockup detection by default in all cases,
  65  * for example when running the kernel as a guest on a hypervisor. In these
  66  * cases this function can be called to disable hard lockup detection. This
  67  * function should only be executed once by the boot processor before the
  68  * kernel command line parameters are parsed, because otherwise it is not
  69  * possible to override this in hardlockup_panic_setup().
  70  */
  71 void watchdog_enable_hardlockup_detector(bool val)
  72 {
  73         hardlockup_detector_enabled = val;
  74 }
  75
  76 bool watchdog_hardlockup_detector_is_enabled(void)
  77 {
  78         return hardlockup_detector_enabled;
  79 }
  80
  81 static int __init hardlockup_panic_setup(char *str)
  82 {
  83         if (!strncmp(str, "panic", 5))
  84                 hardlockup_panic = 1;
  85         else if (!strncmp(str, "nopanic", 7))
  86                 hardlockup_panic = 0;
  87         else if (!strncmp(str, "0", 1))
  88                 watchdog_user_enabled = 0;
  89         else if (!strncmp(str, "1", 1) || !strncmp(str, "2", 1)) {
  90                 /*
  91                  * Setting 'nmi_watchdog=1' or 'nmi_watchdog=2' (legacy option)
  92                  * has the same effect.
  93                  */
  94                 watchdog_user_enabled = 1;
  95                 watchdog_enable_hardlockup_detector(true);
  96         }
  97         return 1;
  98 }
  99 __setup("nmi_watchdog=", hardlockup_panic_setup);
 100 #endif
 101
 102 unsigned int __read_mostly softlockup_panic =
 103                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 104
 105 static int __init softlockup_panic_setup(char *str)
 106 {
 107         softlockup_panic = simple_strtoul(str, NULL, 0);
 108
 109         return 1;
 110 }
 111 __setup("softlockup_panic=", softlockup_panic_setup);
 112
 113 static int __init nowatchdog_setup(char *str)
 114 {
 115         watchdog_user_enabled = 0;
 116         return 1;
 117 }
 118 __setup("nowatchdog", nowatchdog_setup);
 119
 120 /* deprecated */
 121 static int __init nosoftlockup_setup(char *str)
 122 {
 123         watchdog_user_enabled = 0;
 124         return 1;
 125 }
 126 __setup("nosoftlockup", nosoftlockup_setup);
 127 /*  */
 128 #ifdef CONFIG_SMP
 129 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 130 {
 131         sysctl_softlockup_all_cpu_backtrace =
 132                 !!simple_strtol(str, NULL, 0);
 133         return 1;
 134 }
 135 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 136 #endif
 137
 138 /*
 139  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 140  * lockups can have false positives under extreme conditions. So we generally
 141  * want a higher threshold for soft lockups than for hard lockups. So we couple
 142  * the thresholds with a factor: we make the soft threshold twice the amount of
 143  * time the hard threshold is.
 144  */
 145 static int get_softlockup_thresh(void)
 146 {
 147         return watchdog_thresh * 2;
 148 }
 149
 150 /*
 151  * Returns seconds, approximately.  We don't need nanosecond
 152  * resolution, and we don't need to waste time with a big divide when
 153  * 2^30ns == 1.074s.
 154  */
 155 static unsigned long get_timestamp(void)
 156 {
 157         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 158 }
 159
 160 static void set_sample_period(void)
 161 {
 162         /*
 163          * convert watchdog_thresh from seconds to ns
 164          * the divide by 5 is to give hrtimer several chances (two
 165          * or three with the current relation between the soft
 166          * and hard thresholds) to increment before the
 167          * hardlockup detector generates a warning
 168          */
 169         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 170 }
 171
 172 /* Commands for resetting the watchdog */
 173 static void __touch_watchdog(void)
 174 {
 175         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 176 }
 177
 178 void touch_softlockup_watchdog(void)
 179 {
 180         /*
 181          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 182          * gets zeroed here, so use the raw_ operation.
 183          */
 184         raw_cpu_write(watchdog_touch_ts, 0);
 185 }
 186 EXPORT_SYMBOL(touch_softlockup_watchdog);
 187
 188 void touch_all_softlockup_watchdogs(void)
 189 {
 190         int cpu;
 191
 192         /*
 193          * this is done lockless
 194          * do we care if a 0 races with a timestamp?
 195          * all it means is the softlock check starts one cycle later
 196          */
 197         for_each_online_cpu(cpu)
 198                 per_cpu(watchdog_touch_ts, cpu) = 0;
 199 }
 200
 201 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 202 void touch_nmi_watchdog(void)
 203 {
 204         /*
 205          * Using __raw here because some code paths have
 206          * preemption enabled.  If preemption is enabled
 207          * then interrupts should be enabled too, in which
 208          * case we shouldn't have to worry about the watchdog
 209          * going off.
 210          */
 211         raw_cpu_write(watchdog_nmi_touch, true);
 212         touch_softlockup_watchdog();
 213 }
 214 EXPORT_SYMBOL(touch_nmi_watchdog);
 215
 216 #endif
 217
 218 void touch_softlockup_watchdog_sync(void)
 219 {
 220         __this_cpu_write(softlockup_touch_sync, true);
 221         __this_cpu_write(watchdog_touch_ts, 0);
 222 }
 223
 224 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 225 /* watchdog detector functions */
 226 static int is_hardlockup(void)
 227 {
 228         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 229
 230         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 231                 return 1;
 232
 233         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 234         return 0;
 235 }
 236 #endif
 237
 238 static int is_softlockup(unsigned long touch_ts)
 239 {
 240         unsigned long now = get_timestamp();
 241
 242         /* Warn about unreasonable delays: */
 243         if (time_after(now, touch_ts + get_softlockup_thresh()))
 244                 return now - touch_ts;
 245
 246         return 0;
 247 }
 248
 249 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 250
 251 static DEFINE_RAW_SPINLOCK(watchdog_output_lock);
 252
 253 static struct perf_event_attr wd_hw_attr = {
 254         .type           = PERF_TYPE_HARDWARE,
 255         .config         = PERF_COUNT_HW_CPU_CYCLES,
 256         .size           = sizeof(struct perf_event_attr),
 257         .pinned         = 1,
 258         .disabled       = 1,
 259 };
 260
 261 /* Callback function for perf event subsystem */
 262 static void watchdog_overflow_callback(struct perf_event *event,
 263                  struct perf_sample_data *data,
 264                  struct pt_regs *regs)
 265 {
 266         /* Ensure the watchdog never gets throttled */
 267         event->hw.interrupts = 0;
 268
 269         if (__this_cpu_read(watchdog_nmi_touch) == true) {
 270                 __this_cpu_write(watchdog_nmi_touch, false);
 271                 return;
 272         }
 273
 274         /* check for a hardlockup
 275          * This is done by making sure our timer interrupt
 276          * is incrementing.  The timer interrupt should have
 277          * fired multiple times before we overflow'd.  If it hasn't
 278          * then this is a good indication the cpu is stuck
 279          */
 280         if (is_hardlockup()) {
 281                 int this_cpu = smp_processor_id();
 282
 283                 /* only print hardlockups once */
 284                 if (__this_cpu_read(hard_watchdog_warn) == true)
 285                         return;
 286                 /*
 287                  * If early-printk is enabled then make sure we do not
 288                  * lock up in printk() and kill console logging:
 289                  */
 290                 printk_kill();
 291
 292                 if (hardlockup_panic) {
 293                         panic("Watchdog detected hard LOCKUP on cpu %d",
 294                               this_cpu);
 295                 } else {
 296                         raw_spin_lock(&watchdog_output_lock);
 297                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
 298                              this_cpu);
 299                         raw_spin_unlock(&watchdog_output_lock);
 300                 }
 301
 302                 __this_cpu_write(hard_watchdog_warn, true);
 303                 return;
 304         }
 305
 306         __this_cpu_write(hard_watchdog_warn, false);
 307         return;
 308 }
 309 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 310
 311 static void watchdog_interrupt_count(void)
 312 {
 313         __this_cpu_inc(hrtimer_interrupts);
 314 }
 315
 316 static int watchdog_nmi_enable(unsigned int cpu);
 317 static void watchdog_nmi_disable(unsigned int cpu);
 318
 319 /* watchdog kicker functions */
 320 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 321 {
 322         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 323         struct pt_regs *regs = get_irq_regs();
 324         int duration;
 325         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 326
 327         /* kick the hardlockup detector */
 328         watchdog_interrupt_count();
 329
 330         /* kick the softlockup detector */
 331         wake_up_process(__this_cpu_read(softlockup_watchdog));
 332
 333         /* .. and repeat */
 334         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 335
 336         if (touch_ts == 0) {
 337                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 338                         /*
 339                          * If the time stamp was touched atomically
 340                          * make sure the scheduler tick is up to date.
 341                          */
 342                         __this_cpu_write(softlockup_touch_sync, false);
 343                         sched_clock_tick();
 344                 }
 345
 346                 /* Clear the guest paused flag on watchdog reset */
 347                 kvm_check_and_clear_guest_paused();
 348                 __touch_watchdog();
 349                 return HRTIMER_RESTART;
 350         }
 351
 352         /* check for a softlockup
 353          * This is done by making sure a high priority task is
 354          * being scheduled.  The task touches the watchdog to
 355          * indicate it is getting cpu time.  If it hasn't then
 356          * this is a good indication some task is hogging the cpu
 357          */
 358         duration = is_softlockup(touch_ts);
 359         if (unlikely(duration)) {
 360                 /*
 361                  * If a virtual machine is stopped by the host it can look to
 362                  * the watchdog like a soft lockup, check to see if the host
 363                  * stopped the vm before we issue the warning
 364                  */
 365                 if (kvm_check_and_clear_guest_paused())
 366                         return HRTIMER_RESTART;
 367
 368                 /* only warn once */
 369                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 370                         /*
 371                          * When multiple processes are causing softlockups the
 372                          * softlockup detector only warns on the first one
 373                          * because the code relies on a full quiet cycle to
 374                          * re-arm.  The second process prevents the quiet cycle
 375                          * and never gets reported.  Use task pointers to detect
 376                          * this.
 377                          */
 378                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 379                             current) {
 380                                 __this_cpu_write(soft_watchdog_warn, false);
 381                                 __touch_watchdog();
 382                         }
 383                         return HRTIMER_RESTART;
 384                 }
 385
 386                 if (softlockup_all_cpu_backtrace) {
 387                         /* Prevent multiple soft-lockup reports if one cpu is already
 388                          * engaged in dumping cpu back traces
 389                          */
 390                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 391                                 /* Someone else will report us. Let's give up */
 392                                 __this_cpu_write(soft_watchdog_warn, true);
 393                                 return HRTIMER_RESTART;
 394                         }
 395                 }
 396
 397                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 398                         smp_processor_id(), duration,
 399                         current->comm, task_pid_nr(current));
 400                 __this_cpu_write(softlockup_task_ptr_saved, current);
 401                 print_modules();
 402                 print_irqtrace_events(current);
 403                 if (regs)
 404                         show_regs(regs);
 405                 else
 406                         dump_stack();
 407
 408                 if (softlockup_all_cpu_backtrace) {
 409                         /* Avoid generating two back traces for current
 410                          * given that one is already made above
 411                          */
 412                         trigger_allbutself_cpu_backtrace();
 413
 414                         clear_bit(0, &soft_lockup_nmi_warn);
 415                         /* Barrier to sync with other cpus */
 416                         smp_mb__after_atomic();
 417                 }
 418
 419                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 420                 if (softlockup_panic)
 421                         panic("softlockup: hung tasks");
 422                 __this_cpu_write(soft_watchdog_warn, true);
 423         } else
 424                 __this_cpu_write(soft_watchdog_warn, false);
 425
 426         return HRTIMER_RESTART;
 427 }
 428
 429 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 430 {
 431         struct sched_param param = { .sched_priority = prio };
 432
 433         sched_setscheduler(current, policy, &param);
 434 }
 435
 436 static void watchdog_enable(unsigned int cpu)
 437 {
 438         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 439
 440         /* kick off the timer for the hardlockup detector */
 441         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 442         hrtimer->function = watchdog_timer_fn;
 443         hrtimer->irqsafe = 1;
 444
 445         /* Enable the perf event */
 446         watchdog_nmi_enable(cpu);
 447
 448         /* done here because hrtimer_start can only pin to smp_processor_id() */
 449         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 450                       HRTIMER_MODE_REL_PINNED);
 451
 452         /* initialize timestamp */
 453         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 454         __touch_watchdog();
 455 }
 456
 457 static void watchdog_disable(unsigned int cpu)
 458 {
 459         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 460
 461         watchdog_set_prio(SCHED_NORMAL, 0);
 462         hrtimer_cancel(hrtimer);
 463         /* disable the perf event */
 464         watchdog_nmi_disable(cpu);
 465 }
 466
 467 static void watchdog_cleanup(unsigned int cpu, bool online)
 468 {
 469         watchdog_disable(cpu);
 470 }
 471
 472 static int watchdog_should_run(unsigned int cpu)
 473 {
 474         return __this_cpu_read(hrtimer_interrupts) !=
 475                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 476 }
 477
 478 /*
 479  * The watchdog thread function - touches the timestamp.
 480  *
 481  * It only runs once every sample_period seconds (4 seconds by
 482  * default) to reset the softlockup timestamp. If this gets delayed
 483  * for more than 2*watchdog_thresh seconds then the debug-printout
 484  * triggers in watchdog_timer_fn().
 485  */
 486 static void watchdog(unsigned int cpu)
 487 {
 488         __this_cpu_write(soft_lockup_hrtimer_cnt,
 489                          __this_cpu_read(hrtimer_interrupts));
 490         __touch_watchdog();
 491 }
 492
 493 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 494 /*
 495  * People like the simple clean cpu node info on boot.
 496  * Reduce the watchdog noise by only printing messages
 497  * that are different from what cpu0 displayed.
 498  */
 499 static unsigned long cpu0_err;
 500
 501 static int watchdog_nmi_enable(unsigned int cpu)
 502 {
 503         struct perf_event_attr *wd_attr;
 504         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 505
 506         /*
 507          * Some kernels need to default hard lockup detection to
 508          * 'disabled', for example a guest on a hypervisor.
 509          */
 510         if (!watchdog_hardlockup_detector_is_enabled()) {
 511                 event = ERR_PTR(-ENOENT);
 512                 goto handle_err;
 513         }
 514
 515         /* is it already setup and enabled? */
 516         if (event && event->state > PERF_EVENT_STATE_OFF)
 517                 goto out;
 518
 519         /* it is setup but not enabled */
 520         if (event != NULL)
 521                 goto out_enable;
 522
 523         wd_attr = &wd_hw_attr;
 524         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 525
 526         /* Try to register using hardware perf events */
 527         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 528
 529 handle_err:
 530         /* save cpu0 error for future comparision */
 531         if (cpu == 0 && IS_ERR(event))
 532                 cpu0_err = PTR_ERR(event);
 533
 534         if (!IS_ERR(event)) {
 535                 /* only print for cpu0 or different than cpu0 */
 536                 if (cpu == 0 || cpu0_err)
 537                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 538                 goto out_save;
 539         }
 540
 541         /* skip displaying the same error again */
 542         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 543                 return PTR_ERR(event);
 544
 545         /* vary the KERN level based on the returned errno */
 546         if (PTR_ERR(event) == -EOPNOTSUPP)
 547                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 548         else if (PTR_ERR(event) == -ENOENT)
 549                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
 550                          cpu);
 551         else
 552                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 553                         cpu, PTR_ERR(event));
 554         return PTR_ERR(event);
 555
 556         /* success path */
 557 out_save:
 558         per_cpu(watchdog_ev, cpu) = event;
 559 out_enable:
 560         perf_event_enable(per_cpu(watchdog_ev, cpu));
 561 out:
 562         return 0;
 563 }
 564
 565 static void watchdog_nmi_disable(unsigned int cpu)
 566 {
 567         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 568
 569         if (event) {
 570                 perf_event_disable(event);
 571                 per_cpu(watchdog_ev, cpu) = NULL;
 572
 573                 /* should be in cleanup, but blocks oprofile */
 574                 perf_event_release_kernel(event);
 575         }
 576         if (cpu == 0) {
 577                 /* watchdog_nmi_enable() expects this to be zero initially. */
 578                 cpu0_err = 0;
 579         }
 580 }
 581 #else
 582 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 583 static void watchdog_nmi_disable(unsigned int cpu) { return; }
 584 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 585
 586 static struct smp_hotplug_thread watchdog_threads = {
 587         .store                  = &softlockup_watchdog,
 588         .thread_should_run      = watchdog_should_run,
 589         .thread_fn              = watchdog,
 590         .thread_comm            = "watchdog/%u",
 591         .setup                  = watchdog_enable,
 592         .cleanup                = watchdog_cleanup,
 593         .park                   = watchdog_disable,
 594         .unpark                 = watchdog_enable,
 595 };
 596
 597 static void restart_watchdog_hrtimer(void *info)
 598 {
 599         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 600         int ret;
 601
 602         /*
 603          * No need to cancel and restart hrtimer if it is currently executing
 604          * because it will reprogram itself with the new period now.
 605          * We should never see it unqueued here because we are running per-cpu
 606          * with interrupts disabled.
 607          */
 608         ret = hrtimer_try_to_cancel(hrtimer);
 609         if (ret == 1)
 610                 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 611                                 HRTIMER_MODE_REL_PINNED);
 612 }
 613
 614 static void update_timers(int cpu)
 615 {
 616         /*
 617          * Make sure that perf event counter will adopt to a new
 618          * sampling period. Updating the sampling period directly would
 619          * be much nicer but we do not have an API for that now so
 620          * let's use a big hammer.
 621          * Hrtimer will adopt the new period on the next tick but this
 622          * might be late already so we have to restart the timer as well.
 623          */
 624         watchdog_nmi_disable(cpu);
 625         smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
 626         watchdog_nmi_enable(cpu);
 627 }
 628
 629 static void update_timers_all_cpus(void)
 630 {
 631         int cpu;
 632
 633         get_online_cpus();
 634         for_each_online_cpu(cpu)
 635                 update_timers(cpu);
 636         put_online_cpus();
 637 }
 638
 639 static int watchdog_enable_all_cpus(bool sample_period_changed)
 640 {
 641         int err = 0;
 642
 643         if (!watchdog_running) {
 644                 err = smpboot_register_percpu_thread(&watchdog_threads);
 645                 if (err)
 646                         pr_err("Failed to create watchdog threads, disabled\n");
 647                 else
 648                         watchdog_running = 1;
 649         } else if (sample_period_changed) {
 650                 update_timers_all_cpus();
 651         }
 652
 653         return err;
 654 }
 655
 656 /* prepare/enable/disable routines */
 657 /* sysctl functions */
 658 #ifdef CONFIG_SYSCTL
 659 static void watchdog_disable_all_cpus(void)
 660 {
 661         if (watchdog_running) {
 662                 watchdog_running = 0;
 663                 smpboot_unregister_percpu_thread(&watchdog_threads);
 664         }
 665 }
 666
 667 /*
 668  * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
 669  */
 670
 671 int proc_dowatchdog(struct ctl_table *table, int write,
 672                     void __user *buffer, size_t *lenp, loff_t *ppos)
 673 {
 674         int err, old_thresh, old_enabled;
 675         bool old_hardlockup;
 676         static DEFINE_MUTEX(watchdog_proc_mutex);
 677
 678         mutex_lock(&watchdog_proc_mutex);
 679         old_thresh = ACCESS_ONCE(watchdog_thresh);
 680         old_enabled = ACCESS_ONCE(watchdog_user_enabled);
 681         old_hardlockup = watchdog_hardlockup_detector_is_enabled();
 682
 683         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 684         if (err || !write)
 685                 goto out;
 686
 687         set_sample_period();
 688         /*
 689          * Watchdog threads shouldn't be enabled if they are
 690          * disabled. The 'watchdog_running' variable check in
 691          * watchdog_*_all_cpus() function takes care of this.
 692          */
 693         if (watchdog_user_enabled && watchdog_thresh) {
 694                 /*
 695                  * Prevent a change in watchdog_thresh accidentally overriding
 696                  * the enablement of the hardlockup detector.
 697                  */
 698                 if (watchdog_user_enabled != old_enabled)
 699                         watchdog_enable_hardlockup_detector(true);
 700                 err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
 701         } else
 702                 watchdog_disable_all_cpus();
 703
 704         /* Restore old values on failure */
 705         if (err) {
 706                 watchdog_thresh = old_thresh;
 707                 watchdog_user_enabled = old_enabled;
 708                 watchdog_enable_hardlockup_detector(old_hardlockup);
 709         }
 710 out:
 711         mutex_unlock(&watchdog_proc_mutex);
 712         return err;
 713 }
 714 #endif /* CONFIG_SYSCTL */
 715
 716 void __init lockup_detector_init(void)
 717 {
 718         set_sample_period();
 719
 720         if (watchdog_user_enabled)
 721                 watchdog_enable_all_cpus(false);
 722 }