kernel/watchdog.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Detect hard and soft lockups on a system
   4  *
   5  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   6  *
   7  * Note: Most of this code is borrowed heavily from the original softlockup
   8  * detector, so thanks to Ingo for the initial implementation.
   9  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
  10  * to those contributors as well.
  11  */
  12
  13 #define pr_fmt(fmt) "watchdog: " fmt
  14
  15 #include <linux/mm.h>
  16 #include <linux/cpu.h>
  17 #include <linux/nmi.h>
  18 #include <linux/init.h>
  19 #include <linux/module.h>
  20 #include <linux/sysctl.h>
  21 #include <linux/tick.h>
  22 #include <linux/sched/clock.h>
  23 #include <linux/sched/debug.h>
  24 #include <linux/sched/isolation.h>
  25 #include <linux/stop_machine.h>
  26
  27 #include <asm/irq_regs.h>
  28 #include <linux/kvm_para.h>
  29
  30 static DEFINE_MUTEX(watchdog_mutex);
  31
  32 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
  33 # define WATCHDOG_DEFAULT       (SOFT_WATCHDOG_ENABLED | NMI_WATCHDOG_ENABLED)
  34 # define NMI_WATCHDOG_DEFAULT   1
  35 #else
  36 # define WATCHDOG_DEFAULT       (SOFT_WATCHDOG_ENABLED)
  37 # define NMI_WATCHDOG_DEFAULT   0
  38 #endif
  39
  40 unsigned long __read_mostly watchdog_enabled;
  41 int __read_mostly watchdog_user_enabled = 1;
  42 int __read_mostly nmi_watchdog_user_enabled = NMI_WATCHDOG_DEFAULT;
  43 int __read_mostly soft_watchdog_user_enabled = 1;
  44 int __read_mostly watchdog_thresh = 10;
  45 static int __read_mostly nmi_watchdog_available;
  46
  47 struct cpumask watchdog_cpumask __read_mostly;
  48 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  49
  50 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  51
  52 # ifdef CONFIG_SMP
  53 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  54 # endif /* CONFIG_SMP */
  55
  56 /*
  57  * Should we panic when a soft-lockup or hard-lockup occurs:
  58  */
  59 unsigned int __read_mostly hardlockup_panic =
  60                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  61 /*
  62  * We may not want to enable hard lockup detection by default in all cases,
  63  * for example when running the kernel as a guest on a hypervisor. In these
  64  * cases this function can be called to disable hard lockup detection. This
  65  * function should only be executed once by the boot processor before the
  66  * kernel command line parameters are parsed, because otherwise it is not
  67  * possible to override this in hardlockup_panic_setup().
  68  */
  69 void __init hardlockup_detector_disable(void)
  70 {
  71         nmi_watchdog_user_enabled = 0;
  72 }
  73
  74 static int __init hardlockup_panic_setup(char *str)
  75 {
  76         if (!strncmp(str, "panic", 5))
  77                 hardlockup_panic = 1;
  78         else if (!strncmp(str, "nopanic", 7))
  79                 hardlockup_panic = 0;
  80         else if (!strncmp(str, "0", 1))
  81                 nmi_watchdog_user_enabled = 0;
  82         else if (!strncmp(str, "1", 1))
  83                 nmi_watchdog_user_enabled = 1;
  84         return 1;
  85 }
  86 __setup("nmi_watchdog=", hardlockup_panic_setup);
  87
  88 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
  89
  90 /*
  91  * These functions can be overridden if an architecture implements its
  92  * own hardlockup detector.
  93  *
  94  * watchdog_nmi_enable/disable can be implemented to start and stop when
  95  * softlockup watchdog threads start and stop. The arch must select the
  96  * SOFTLOCKUP_DETECTOR Kconfig.
  97  */
  98 int __weak watchdog_nmi_enable(unsigned int cpu)
  99 {
 100         hardlockup_detector_perf_enable();
 101         return 0;
 102 }
 103
 104 void __weak watchdog_nmi_disable(unsigned int cpu)
 105 {
 106         hardlockup_detector_perf_disable();
 107 }
 108
 109 /* Return 0, if a NMI watchdog is available. Error code otherwise */
 110 int __weak __init watchdog_nmi_probe(void)
 111 {
 112         return hardlockup_detector_perf_init();
 113 }
 114
 115 /**
 116  * watchdog_nmi_stop - Stop the watchdog for reconfiguration
 117  *
 118  * The reconfiguration steps are:
 119  * watchdog_nmi_stop();
 120  * update_variables();
 121  * watchdog_nmi_start();
 122  */
 123 void __weak watchdog_nmi_stop(void) { }
 124
 125 /**
 126  * watchdog_nmi_start - Start the watchdog after reconfiguration
 127  *
 128  * Counterpart to watchdog_nmi_stop().
 129  *
 130  * The following variables have been updated in update_variables() and
 131  * contain the currently valid configuration:
 132  * - watchdog_enabled
 133  * - watchdog_thresh
 134  * - watchdog_cpumask
 135  */
 136 void __weak watchdog_nmi_start(void) { }
 137
 138 /**
 139  * lockup_detector_update_enable - Update the sysctl enable bit
 140  *
 141  * Caller needs to make sure that the NMI/perf watchdogs are off, so this
 142  * can't race with watchdog_nmi_disable().
 143  */
 144 static void lockup_detector_update_enable(void)
 145 {
 146         watchdog_enabled = 0;
 147         if (!watchdog_user_enabled)
 148                 return;
 149         if (nmi_watchdog_available && nmi_watchdog_user_enabled)
 150                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
 151         if (soft_watchdog_user_enabled)
 152                 watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
 153 }
 154
 155 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 156
 157 /*
 158  * Delay the soflockup report when running a known slow code.
 159  * It does _not_ affect the timestamp of the last successdul reschedule.
 160  */
 161 #define SOFTLOCKUP_DELAY_REPORT ULONG_MAX
 162
 163 #ifdef CONFIG_SMP
 164 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 165 #endif
 166
 167 static struct cpumask watchdog_allowed_mask __read_mostly;
 168
 169 /* Global variables, exported for sysctl */
 170 unsigned int __read_mostly softlockup_panic =
 171                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 172
 173 static bool softlockup_initialized __read_mostly;
 174 static u64 __read_mostly sample_period;
 175
 176 /* Timestamp taken after the last successful reschedule. */
 177 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 178 /* Timestamp of the last softlockup report. */
 179 static DEFINE_PER_CPU(unsigned long, watchdog_report_ts);
 180 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 181 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 182 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 183 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 184 static unsigned long soft_lockup_nmi_warn;
 185
 186 static int __init nowatchdog_setup(char *str)
 187 {
 188         watchdog_user_enabled = 0;
 189         return 1;
 190 }
 191 __setup("nowatchdog", nowatchdog_setup);
 192
 193 static int __init nosoftlockup_setup(char *str)
 194 {
 195         soft_watchdog_user_enabled = 0;
 196         return 1;
 197 }
 198 __setup("nosoftlockup", nosoftlockup_setup);
 199
 200 static int __init watchdog_thresh_setup(char *str)
 201 {
 202         get_option(&str, &watchdog_thresh);
 203         return 1;
 204 }
 205 __setup("watchdog_thresh=", watchdog_thresh_setup);
 206
 207 static void __lockup_detector_cleanup(void);
 208
 209 /*
 210  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 211  * lockups can have false positives under extreme conditions. So we generally
 212  * want a higher threshold for soft lockups than for hard lockups. So we couple
 213  * the thresholds with a factor: we make the soft threshold twice the amount of
 214  * time the hard threshold is.
 215  */
 216 static int get_softlockup_thresh(void)
 217 {
 218         return watchdog_thresh * 2;
 219 }
 220
 221 /*
 222  * Returns seconds, approximately.  We don't need nanosecond
 223  * resolution, and we don't need to waste time with a big divide when
 224  * 2^30ns == 1.074s.
 225  */
 226 static unsigned long get_timestamp(void)
 227 {
 228         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 229 }
 230
 231 static void set_sample_period(void)
 232 {
 233         /*
 234          * convert watchdog_thresh from seconds to ns
 235          * the divide by 5 is to give hrtimer several chances (two
 236          * or three with the current relation between the soft
 237          * and hard thresholds) to increment before the
 238          * hardlockup detector generates a warning
 239          */
 240         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 241         watchdog_update_hrtimer_threshold(sample_period);
 242 }
 243
 244 static void update_report_ts(void)
 245 {
 246         __this_cpu_write(watchdog_report_ts, get_timestamp());
 247 }
 248
 249 /* Commands for resetting the watchdog */
 250 static void update_touch_ts(void)
 251 {
 252         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 253         update_report_ts();
 254 }
 255
 256 /**
 257  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 258  *
 259  * Call when the scheduler may have stalled for legitimate reasons
 260  * preventing the watchdog task from executing - e.g. the scheduler
 261  * entering idle state.  This should only be used for scheduler events.
 262  * Use touch_softlockup_watchdog() for everything else.
 263  */
 264 notrace void touch_softlockup_watchdog_sched(void)
 265 {
 266         /*
 267          * Preemption can be enabled.  It doesn't matter which CPU's watchdog
 268          * report period gets restarted here, so use the raw_ operation.
 269          */
 270         raw_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
 271 }
 272
 273 notrace void touch_softlockup_watchdog(void)
 274 {
 275         touch_softlockup_watchdog_sched();
 276         wq_watchdog_touch(raw_smp_processor_id());
 277 }
 278 EXPORT_SYMBOL(touch_softlockup_watchdog);
 279
 280 void touch_all_softlockup_watchdogs(void)
 281 {
 282         int cpu;
 283
 284         /*
 285          * watchdog_mutex cannpt be taken here, as this might be called
 286          * from (soft)interrupt context, so the access to
 287          * watchdog_allowed_cpumask might race with a concurrent update.
 288          *
 289          * The watchdog time stamp can race against a concurrent real
 290          * update as well, the only side effect might be a cycle delay for
 291          * the softlockup check.
 292          */
 293         for_each_cpu(cpu, &watchdog_allowed_mask) {
 294                 per_cpu(watchdog_report_ts, cpu) = SOFTLOCKUP_DELAY_REPORT;
 295                 wq_watchdog_touch(cpu);
 296         }
 297 }
 298
 299 void touch_softlockup_watchdog_sync(void)
 300 {
 301         __this_cpu_write(softlockup_touch_sync, true);
 302         __this_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
 303 }
 304
 305 static int is_softlockup(unsigned long touch_ts, unsigned long period_ts)
 306 {
 307         unsigned long now = get_timestamp();
 308
 309         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 310                 /* Warn about unreasonable delays. */
 311                 if (time_after(now, period_ts + get_softlockup_thresh()))
 312                         return now - touch_ts;
 313         }
 314         return 0;
 315 }
 316
 317 /* watchdog detector functions */
 318 bool is_hardlockup(void)
 319 {
 320         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 321
 322         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 323                 return true;
 324
 325         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 326         return false;
 327 }
 328
 329 static void watchdog_interrupt_count(void)
 330 {
 331         __this_cpu_inc(hrtimer_interrupts);
 332 }
 333
 334 static DEFINE_PER_CPU(struct completion, softlockup_completion);
 335 static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
 336
 337 /*
 338  * The watchdog thread function - touches the timestamp.
 339  *
 340  * It only runs once every sample_period seconds (4 seconds by
 341  * default) to reset the softlockup timestamp. If this gets delayed
 342  * for more than 2*watchdog_thresh seconds then the debug-printout
 343  * triggers in watchdog_timer_fn().
 344  */
 345 static int softlockup_fn(void *data)
 346 {
 347         update_touch_ts();
 348         complete(this_cpu_ptr(&softlockup_completion));
 349
 350         return 0;
 351 }
 352
 353 /* watchdog kicker functions */
 354 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 355 {
 356         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 357         unsigned long period_ts = __this_cpu_read(watchdog_report_ts);
 358         struct pt_regs *regs = get_irq_regs();
 359         int duration;
 360         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 361
 362         if (!watchdog_enabled)
 363                 return HRTIMER_NORESTART;
 364
 365         /* kick the hardlockup detector */
 366         watchdog_interrupt_count();
 367
 368         /* kick the softlockup detector */
 369         if (completion_done(this_cpu_ptr(&softlockup_completion))) {
 370                 reinit_completion(this_cpu_ptr(&softlockup_completion));
 371                 stop_one_cpu_nowait(smp_processor_id(),
 372                                 softlockup_fn, NULL,
 373                                 this_cpu_ptr(&softlockup_stop_work));
 374         }
 375
 376         /* .. and repeat */
 377         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 378
 379         /*
 380          * If a virtual machine is stopped by the host it can look to
 381          * the watchdog like a soft lockup. Check to see if the host
 382          * stopped the vm before we process the timestamps.
 383          */
 384         kvm_check_and_clear_guest_paused();
 385
 386         /* Reset the interval when touched by known problematic code. */
 387         if (period_ts == SOFTLOCKUP_DELAY_REPORT) {
 388                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 389                         /*
 390                          * If the time stamp was touched atomically
 391                          * make sure the scheduler tick is up to date.
 392                          */
 393                         __this_cpu_write(softlockup_touch_sync, false);
 394                         sched_clock_tick();
 395                 }
 396
 397                 update_report_ts();
 398                 return HRTIMER_RESTART;
 399         }
 400
 401         /* check for a softlockup
 402          * This is done by making sure a high priority task is
 403          * being scheduled.  The task touches the watchdog to
 404          * indicate it is getting cpu time.  If it hasn't then
 405          * this is a good indication some task is hogging the cpu
 406          */
 407         duration = is_softlockup(touch_ts, period_ts);
 408         if (unlikely(duration)) {
 409                 /*
 410                  * Prevent multiple soft-lockup reports if one cpu is already
 411                  * engaged in dumping all cpu back traces.
 412                  */
 413                 if (softlockup_all_cpu_backtrace) {
 414                         if (test_and_set_bit_lock(0, &soft_lockup_nmi_warn))
 415                                 return HRTIMER_RESTART;
 416                 }
 417
 418                 /* Start period for the next softlockup warning. */
 419                 update_report_ts();
 420
 421                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 422                         smp_processor_id(), duration,
 423                         current->comm, task_pid_nr(current));
 424                 print_modules();
 425                 print_irqtrace_events(current);
 426                 if (regs)
 427                         show_regs(regs);
 428                 else
 429                         dump_stack();
 430
 431                 if (softlockup_all_cpu_backtrace) {
 432                         trigger_allbutself_cpu_backtrace();
 433                         clear_bit_unlock(0, &soft_lockup_nmi_warn);
 434                 }
 435
 436                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 437                 if (softlockup_panic)
 438                         panic("softlockup: hung tasks");
 439         }
 440
 441         return HRTIMER_RESTART;
 442 }
 443
 444 static void watchdog_enable(unsigned int cpu)
 445 {
 446         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 447         struct completion *done = this_cpu_ptr(&softlockup_completion);
 448
 449         WARN_ON_ONCE(cpu != smp_processor_id());
 450
 451         init_completion(done);
 452         complete(done);
 453
 454         /*
 455          * Start the timer first to prevent the NMI watchdog triggering
 456          * before the timer has a chance to fire.
 457          */
 458         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 459         hrtimer->function = watchdog_timer_fn;
 460         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 461                       HRTIMER_MODE_REL_PINNED_HARD);
 462
 463         /* Initialize timestamp */
 464         update_touch_ts();
 465         /* Enable the perf event */
 466         if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
 467                 watchdog_nmi_enable(cpu);
 468 }
 469
 470 static void watchdog_disable(unsigned int cpu)
 471 {
 472         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 473
 474         WARN_ON_ONCE(cpu != smp_processor_id());
 475
 476         /*
 477          * Disable the perf event first. That prevents that a large delay
 478          * between disabling the timer and disabling the perf event causes
 479          * the perf NMI to detect a false positive.
 480          */
 481         watchdog_nmi_disable(cpu);
 482         hrtimer_cancel(hrtimer);
 483         wait_for_completion(this_cpu_ptr(&softlockup_completion));
 484 }
 485
 486 static int softlockup_stop_fn(void *data)
 487 {
 488         watchdog_disable(smp_processor_id());
 489         return 0;
 490 }
 491
 492 static void softlockup_stop_all(void)
 493 {
 494         int cpu;
 495
 496         if (!softlockup_initialized)
 497                 return;
 498
 499         for_each_cpu(cpu, &watchdog_allowed_mask)
 500                 smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);
 501
 502         cpumask_clear(&watchdog_allowed_mask);
 503 }
 504
 505 static int softlockup_start_fn(void *data)
 506 {
 507         watchdog_enable(smp_processor_id());
 508         return 0;
 509 }
 510
 511 static void softlockup_start_all(void)
 512 {
 513         int cpu;
 514
 515         cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
 516         for_each_cpu(cpu, &watchdog_allowed_mask)
 517                 smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);
 518 }
 519
 520 int lockup_detector_online_cpu(unsigned int cpu)
 521 {
 522         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 523                 watchdog_enable(cpu);
 524         return 0;
 525 }
 526
 527 int lockup_detector_offline_cpu(unsigned int cpu)
 528 {
 529         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 530                 watchdog_disable(cpu);
 531         return 0;
 532 }
 533
 534 static void lockup_detector_reconfigure(void)
 535 {
 536         cpus_read_lock();
 537         watchdog_nmi_stop();
 538
 539         softlockup_stop_all();
 540         set_sample_period();
 541         lockup_detector_update_enable();
 542         if (watchdog_enabled && watchdog_thresh)
 543                 softlockup_start_all();
 544
 545         watchdog_nmi_start();
 546         cpus_read_unlock();
 547         /*
 548          * Must be called outside the cpus locked section to prevent
 549          * recursive locking in the perf code.
 550          */
 551         __lockup_detector_cleanup();
 552 }
 553
 554 /*
 555  * Create the watchdog thread infrastructure and configure the detector(s).
 556  *
 557  * The threads are not unparked as watchdog_allowed_mask is empty.  When
 558  * the threads are successfully initialized, take the proper locks and
 559  * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
 560  */
 561 static __init void lockup_detector_setup(void)
 562 {
 563         /*
 564          * If sysctl is off and watchdog got disabled on the command line,
 565          * nothing to do here.
 566          */
 567         lockup_detector_update_enable();
 568
 569         if (!IS_ENABLED(CONFIG_SYSCTL) &&
 570             !(watchdog_enabled && watchdog_thresh))
 571                 return;
 572
 573         mutex_lock(&watchdog_mutex);
 574         lockup_detector_reconfigure();
 575         softlockup_initialized = true;
 576         mutex_unlock(&watchdog_mutex);
 577 }
 578
 579 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
 580 static void lockup_detector_reconfigure(void)
 581 {
 582         cpus_read_lock();
 583         watchdog_nmi_stop();
 584         lockup_detector_update_enable();
 585         watchdog_nmi_start();
 586         cpus_read_unlock();
 587 }
 588 static inline void lockup_detector_setup(void)
 589 {
 590         lockup_detector_reconfigure();
 591 }
 592 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 593
 594 static void __lockup_detector_cleanup(void)
 595 {
 596         lockdep_assert_held(&watchdog_mutex);
 597         hardlockup_detector_perf_cleanup();
 598 }
 599
 600 /**
 601  * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 602  *
 603  * Caller must not hold the cpu hotplug rwsem.
 604  */
 605 void lockup_detector_cleanup(void)
 606 {
 607         mutex_lock(&watchdog_mutex);
 608         __lockup_detector_cleanup();
 609         mutex_unlock(&watchdog_mutex);
 610 }
 611
 612 /**
 613  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 614  *
 615  * Special interface for parisc. It prevents lockup detector warnings from
 616  * the default pm_poweroff() function which busy loops forever.
 617  */
 618 void lockup_detector_soft_poweroff(void)
 619 {
 620         watchdog_enabled = 0;
 621 }
 622
 623 #ifdef CONFIG_SYSCTL
 624
 625 /* Propagate any changes to the watchdog threads */
 626 static void proc_watchdog_update(void)
 627 {
 628         /* Remove impossible cpus to keep sysctl output clean. */
 629         cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
 630         lockup_detector_reconfigure();
 631 }
 632
 633 /*
 634  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 635  *
 636  * caller             | table->data points to      | 'which'
 637  * -------------------|----------------------------|--------------------------
 638  * proc_watchdog      | watchdog_user_enabled      | NMI_WATCHDOG_ENABLED |
 639  *                    |                            | SOFT_WATCHDOG_ENABLED
 640  * -------------------|----------------------------|--------------------------
 641  * proc_nmi_watchdog  | nmi_watchdog_user_enabled  | NMI_WATCHDOG_ENABLED
 642  * -------------------|----------------------------|--------------------------
 643  * proc_soft_watchdog | soft_watchdog_user_enabled | SOFT_WATCHDOG_ENABLED
 644  */
 645 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 646                                 void *buffer, size_t *lenp, loff_t *ppos)
 647 {
 648         int err, old, *param = table->data;
 649
 650         mutex_lock(&watchdog_mutex);
 651
 652         if (!write) {
 653                 /*
 654                  * On read synchronize the userspace interface. This is a
 655                  * racy snapshot.
 656                  */
 657                 *param = (watchdog_enabled & which) != 0;
 658                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 659         } else {
 660                 old = READ_ONCE(*param);
 661                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 662                 if (!err && old != READ_ONCE(*param))
 663                         proc_watchdog_update();
 664         }
 665         mutex_unlock(&watchdog_mutex);
 666         return err;
 667 }
 668
 669 /*
 670  * /proc/sys/kernel/watchdog
 671  */
 672 int proc_watchdog(struct ctl_table *table, int write,
 673                   void *buffer, size_t *lenp, loff_t *ppos)
 674 {
 675         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 676                                     table, write, buffer, lenp, ppos);
 677 }
 678
 679 /*
 680  * /proc/sys/kernel/nmi_watchdog
 681  */
 682 int proc_nmi_watchdog(struct ctl_table *table, int write,
 683                       void *buffer, size_t *lenp, loff_t *ppos)
 684 {
 685         if (!nmi_watchdog_available && write)
 686                 return -ENOTSUPP;
 687         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 688                                     table, write, buffer, lenp, ppos);
 689 }
 690
 691 /*
 692  * /proc/sys/kernel/soft_watchdog
 693  */
 694 int proc_soft_watchdog(struct ctl_table *table, int write,
 695                         void *buffer, size_t *lenp, loff_t *ppos)
 696 {
 697         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 698                                     table, write, buffer, lenp, ppos);
 699 }
 700
 701 /*
 702  * /proc/sys/kernel/watchdog_thresh
 703  */
 704 int proc_watchdog_thresh(struct ctl_table *table, int write,
 705                          void *buffer, size_t *lenp, loff_t *ppos)
 706 {
 707         int err, old;
 708
 709         mutex_lock(&watchdog_mutex);
 710
 711         old = READ_ONCE(watchdog_thresh);
 712         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 713
 714         if (!err && write && old != READ_ONCE(watchdog_thresh))
 715                 proc_watchdog_update();
 716
 717         mutex_unlock(&watchdog_mutex);
 718         return err;
 719 }
 720
 721 /*
 722  * The cpumask is the mask of possible cpus that the watchdog can run
 723  * on, not the mask of cpus it is actually running on.  This allows the
 724  * user to specify a mask that will include cpus that have not yet
 725  * been brought online, if desired.
 726  */
 727 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 728                           void *buffer, size_t *lenp, loff_t *ppos)
 729 {
 730         int err;
 731
 732         mutex_lock(&watchdog_mutex);
 733
 734         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 735         if (!err && write)
 736                 proc_watchdog_update();
 737
 738         mutex_unlock(&watchdog_mutex);
 739         return err;
 740 }
 741 #endif /* CONFIG_SYSCTL */
 742
 743 void __init lockup_detector_init(void)
 744 {
 745         if (tick_nohz_full_enabled())
 746                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 747
 748         cpumask_copy(&watchdog_cpumask,
 749                      housekeeping_cpumask(HK_FLAG_TIMER));
 750
 751         if (!watchdog_nmi_probe())
 752                 nmi_watchdog_available = true;
 753         lockup_detector_setup();
 754 }