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 #define SOFTLOCKUP_RESET        ULONG_MAX
 158
 159 #ifdef CONFIG_SMP
 160 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 161 #endif
 162
 163 static struct cpumask watchdog_allowed_mask __read_mostly;
 164
 165 /* Global variables, exported for sysctl */
 166 unsigned int __read_mostly softlockup_panic =
 167                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 168
 169 static bool softlockup_initialized __read_mostly;
 170 static u64 __read_mostly sample_period;
 171
 172 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 173 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 174 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 175 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 176 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 177 static unsigned long soft_lockup_nmi_warn;
 178
 179 static int __init softlockup_panic_setup(char *str)
 180 {
 181         softlockup_panic = simple_strtoul(str, NULL, 0);
 182         return 1;
 183 }
 184 __setup("softlockup_panic=", softlockup_panic_setup);
 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 /* Commands for resetting the watchdog */
 245 static void update_touch_ts(void)
 246 {
 247         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 248 }
 249
 250 /**
 251  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 252  *
 253  * Call when the scheduler may have stalled for legitimate reasons
 254  * preventing the watchdog task from executing - e.g. the scheduler
 255  * entering idle state.  This should only be used for scheduler events.
 256  * Use touch_softlockup_watchdog() for everything else.
 257  */
 258 notrace void touch_softlockup_watchdog_sched(void)
 259 {
 260         /*
 261          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 262          * gets zeroed here, so use the raw_ operation.
 263          */
 264         raw_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 265 }
 266
 267 notrace void touch_softlockup_watchdog(void)
 268 {
 269         touch_softlockup_watchdog_sched();
 270         wq_watchdog_touch(raw_smp_processor_id());
 271 }
 272 EXPORT_SYMBOL(touch_softlockup_watchdog);
 273
 274 void touch_all_softlockup_watchdogs(void)
 275 {
 276         int cpu;
 277
 278         /*
 279          * watchdog_mutex cannpt be taken here, as this might be called
 280          * from (soft)interrupt context, so the access to
 281          * watchdog_allowed_cpumask might race with a concurrent update.
 282          *
 283          * The watchdog time stamp can race against a concurrent real
 284          * update as well, the only side effect might be a cycle delay for
 285          * the softlockup check.
 286          */
 287         for_each_cpu(cpu, &watchdog_allowed_mask)
 288                 per_cpu(watchdog_touch_ts, cpu) = SOFTLOCKUP_RESET;
 289         wq_watchdog_touch(-1);
 290 }
 291
 292 void touch_softlockup_watchdog_sync(void)
 293 {
 294         __this_cpu_write(softlockup_touch_sync, true);
 295         __this_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 296 }
 297
 298 static int is_softlockup(unsigned long touch_ts)
 299 {
 300         unsigned long now = get_timestamp();
 301
 302         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 303                 /* Warn about unreasonable delays. */
 304                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 305                         return now - touch_ts;
 306         }
 307         return 0;
 308 }
 309
 310 /* watchdog detector functions */
 311 bool is_hardlockup(void)
 312 {
 313         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 314
 315         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 316                 return true;
 317
 318         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 319         return false;
 320 }
 321
 322 static void watchdog_interrupt_count(void)
 323 {
 324         __this_cpu_inc(hrtimer_interrupts);
 325 }
 326
 327 static DEFINE_PER_CPU(struct completion, softlockup_completion);
 328 static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
 329
 330 /*
 331  * The watchdog thread function - touches the timestamp.
 332  *
 333  * It only runs once every sample_period seconds (4 seconds by
 334  * default) to reset the softlockup timestamp. If this gets delayed
 335  * for more than 2*watchdog_thresh seconds then the debug-printout
 336  * triggers in watchdog_timer_fn().
 337  */
 338 static int softlockup_fn(void *data)
 339 {
 340         update_touch_ts();
 341         complete(this_cpu_ptr(&softlockup_completion));
 342
 343         return 0;
 344 }
 345
 346 /* watchdog kicker functions */
 347 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 348 {
 349         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 350         struct pt_regs *regs = get_irq_regs();
 351         int duration;
 352         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 353
 354         if (!watchdog_enabled)
 355                 return HRTIMER_NORESTART;
 356
 357         /* kick the hardlockup detector */
 358         watchdog_interrupt_count();
 359
 360         /* kick the softlockup detector */
 361         if (completion_done(this_cpu_ptr(&softlockup_completion))) {
 362                 reinit_completion(this_cpu_ptr(&softlockup_completion));
 363                 stop_one_cpu_nowait(smp_processor_id(),
 364                                 softlockup_fn, NULL,
 365                                 this_cpu_ptr(&softlockup_stop_work));
 366         }
 367
 368         /* .. and repeat */
 369         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 370
 371         if (touch_ts == SOFTLOCKUP_RESET) {
 372                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 373                         /*
 374                          * If the time stamp was touched atomically
 375                          * make sure the scheduler tick is up to date.
 376                          */
 377                         __this_cpu_write(softlockup_touch_sync, false);
 378                         sched_clock_tick();
 379                 }
 380
 381                 /* Clear the guest paused flag on watchdog reset */
 382                 kvm_check_and_clear_guest_paused();
 383                 update_touch_ts();
 384                 return HRTIMER_RESTART;
 385         }
 386
 387         /* check for a softlockup
 388          * This is done by making sure a high priority task is
 389          * being scheduled.  The task touches the watchdog to
 390          * indicate it is getting cpu time.  If it hasn't then
 391          * this is a good indication some task is hogging the cpu
 392          */
 393         duration = is_softlockup(touch_ts);
 394         if (unlikely(duration)) {
 395                 /*
 396                  * If a virtual machine is stopped by the host it can look to
 397                  * the watchdog like a soft lockup, check to see if the host
 398                  * stopped the vm before we issue the warning
 399                  */
 400                 if (kvm_check_and_clear_guest_paused())
 401                         return HRTIMER_RESTART;
 402
 403                 /*
 404                  * Prevent multiple soft-lockup reports if one cpu is already
 405                  * engaged in dumping all cpu back traces.
 406                  */
 407                 if (softlockup_all_cpu_backtrace) {
 408                         if (test_and_set_bit_lock(0, &soft_lockup_nmi_warn))
 409                                 return HRTIMER_RESTART;
 410                 }
 411
 412                 /* Start period for the next softlockup warning. */
 413                 update_touch_ts();
 414
 415                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 416                         smp_processor_id(), duration,
 417                         current->comm, task_pid_nr(current));
 418                 print_modules();
 419                 print_irqtrace_events(current);
 420                 if (regs)
 421                         show_regs(regs);
 422                 else
 423                         dump_stack();
 424
 425                 if (softlockup_all_cpu_backtrace) {
 426                         trigger_allbutself_cpu_backtrace();
 427                         clear_bit_unlock(0, &soft_lockup_nmi_warn);
 428                 }
 429
 430                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 431                 if (softlockup_panic)
 432                         panic("softlockup: hung tasks");
 433         }
 434
 435         return HRTIMER_RESTART;
 436 }
 437
 438 static void watchdog_enable(unsigned int cpu)
 439 {
 440         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 441         struct completion *done = this_cpu_ptr(&softlockup_completion);
 442
 443         WARN_ON_ONCE(cpu != smp_processor_id());
 444
 445         init_completion(done);
 446         complete(done);
 447
 448         /*
 449          * Start the timer first to prevent the NMI watchdog triggering
 450          * before the timer has a chance to fire.
 451          */
 452         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 453         hrtimer->function = watchdog_timer_fn;
 454         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 455                       HRTIMER_MODE_REL_PINNED_HARD);
 456
 457         /* Initialize timestamp */
 458         update_touch_ts();
 459         /* Enable the perf event */
 460         if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
 461                 watchdog_nmi_enable(cpu);
 462 }
 463
 464 static void watchdog_disable(unsigned int cpu)
 465 {
 466         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 467
 468         WARN_ON_ONCE(cpu != smp_processor_id());
 469
 470         /*
 471          * Disable the perf event first. That prevents that a large delay
 472          * between disabling the timer and disabling the perf event causes
 473          * the perf NMI to detect a false positive.
 474          */
 475         watchdog_nmi_disable(cpu);
 476         hrtimer_cancel(hrtimer);
 477         wait_for_completion(this_cpu_ptr(&softlockup_completion));
 478 }
 479
 480 static int softlockup_stop_fn(void *data)
 481 {
 482         watchdog_disable(smp_processor_id());
 483         return 0;
 484 }
 485
 486 static void softlockup_stop_all(void)
 487 {
 488         int cpu;
 489
 490         if (!softlockup_initialized)
 491                 return;
 492
 493         for_each_cpu(cpu, &watchdog_allowed_mask)
 494                 smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);
 495
 496         cpumask_clear(&watchdog_allowed_mask);
 497 }
 498
 499 static int softlockup_start_fn(void *data)
 500 {
 501         watchdog_enable(smp_processor_id());
 502         return 0;
 503 }
 504
 505 static void softlockup_start_all(void)
 506 {
 507         int cpu;
 508
 509         cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
 510         for_each_cpu(cpu, &watchdog_allowed_mask)
 511                 smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);
 512 }
 513
 514 int lockup_detector_online_cpu(unsigned int cpu)
 515 {
 516         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 517                 watchdog_enable(cpu);
 518         return 0;
 519 }
 520
 521 int lockup_detector_offline_cpu(unsigned int cpu)
 522 {
 523         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 524                 watchdog_disable(cpu);
 525         return 0;
 526 }
 527
 528 static void __lockup_detector_reconfigure(void)
 529 {
 530         cpus_read_lock();
 531         watchdog_nmi_stop();
 532
 533         softlockup_stop_all();
 534         set_sample_period();
 535         lockup_detector_update_enable();
 536         if (watchdog_enabled && watchdog_thresh)
 537                 softlockup_start_all();
 538
 539         watchdog_nmi_start();
 540         cpus_read_unlock();
 541         /*
 542          * Must be called outside the cpus locked section to prevent
 543          * recursive locking in the perf code.
 544          */
 545         __lockup_detector_cleanup();
 546 }
 547
 548 void lockup_detector_reconfigure(void)
 549 {
 550         mutex_lock(&watchdog_mutex);
 551         __lockup_detector_reconfigure();
 552         mutex_unlock(&watchdog_mutex);
 553 }
 554
 555 /*
 556  * Create the watchdog thread infrastructure and configure the detector(s).
 557  *
 558  * The threads are not unparked as watchdog_allowed_mask is empty.  When
 559  * the threads are successfully initialized, take the proper locks and
 560  * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
 561  */
 562 static __init void lockup_detector_setup(void)
 563 {
 564         /*
 565          * If sysctl is off and watchdog got disabled on the command line,
 566          * nothing to do here.
 567          */
 568         lockup_detector_update_enable();
 569
 570         if (!IS_ENABLED(CONFIG_SYSCTL) &&
 571             !(watchdog_enabled && watchdog_thresh))
 572                 return;
 573
 574         mutex_lock(&watchdog_mutex);
 575         __lockup_detector_reconfigure();
 576         softlockup_initialized = true;
 577         mutex_unlock(&watchdog_mutex);
 578 }
 579
 580 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
 581 static void __lockup_detector_reconfigure(void)
 582 {
 583         cpus_read_lock();
 584         watchdog_nmi_stop();
 585         lockup_detector_update_enable();
 586         watchdog_nmi_start();
 587         cpus_read_unlock();
 588 }
 589 void lockup_detector_reconfigure(void)
 590 {
 591         __lockup_detector_reconfigure();
 592 }
 593 static inline void lockup_detector_setup(void)
 594 {
 595         __lockup_detector_reconfigure();
 596 }
 597 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 598
 599 static void __lockup_detector_cleanup(void)
 600 {
 601         lockdep_assert_held(&watchdog_mutex);
 602         hardlockup_detector_perf_cleanup();
 603 }
 604
 605 /**
 606  * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 607  *
 608  * Caller must not hold the cpu hotplug rwsem.
 609  */
 610 void lockup_detector_cleanup(void)
 611 {
 612         mutex_lock(&watchdog_mutex);
 613         __lockup_detector_cleanup();
 614         mutex_unlock(&watchdog_mutex);
 615 }
 616
 617 /**
 618  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 619  *
 620  * Special interface for parisc. It prevents lockup detector warnings from
 621  * the default pm_poweroff() function which busy loops forever.
 622  */
 623 void lockup_detector_soft_poweroff(void)
 624 {
 625         watchdog_enabled = 0;
 626 }
 627
 628 #ifdef CONFIG_SYSCTL
 629
 630 /* Propagate any changes to the watchdog threads */
 631 static void proc_watchdog_update(void)
 632 {
 633         /* Remove impossible cpus to keep sysctl output clean. */
 634         cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
 635         __lockup_detector_reconfigure();
 636 }
 637
 638 /*
 639  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 640  *
 641  * caller             | table->data points to      | 'which'
 642  * -------------------|----------------------------|--------------------------
 643  * proc_watchdog      | watchdog_user_enabled      | NMI_WATCHDOG_ENABLED |
 644  *                    |                            | SOFT_WATCHDOG_ENABLED
 645  * -------------------|----------------------------|--------------------------
 646  * proc_nmi_watchdog  | nmi_watchdog_user_enabled  | NMI_WATCHDOG_ENABLED
 647  * -------------------|----------------------------|--------------------------
 648  * proc_soft_watchdog | soft_watchdog_user_enabled | SOFT_WATCHDOG_ENABLED
 649  */
 650 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 651                                 void *buffer, size_t *lenp, loff_t *ppos)
 652 {
 653         int err, old, *param = table->data;
 654
 655         mutex_lock(&watchdog_mutex);
 656
 657         if (!write) {
 658                 /*
 659                  * On read synchronize the userspace interface. This is a
 660                  * racy snapshot.
 661                  */
 662                 *param = (watchdog_enabled & which) != 0;
 663                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 664         } else {
 665                 old = READ_ONCE(*param);
 666                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 667                 if (!err && old != READ_ONCE(*param))
 668                         proc_watchdog_update();
 669         }
 670         mutex_unlock(&watchdog_mutex);
 671         return err;
 672 }
 673
 674 /*
 675  * /proc/sys/kernel/watchdog
 676  */
 677 int proc_watchdog(struct ctl_table *table, int write,
 678                   void *buffer, size_t *lenp, loff_t *ppos)
 679 {
 680         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 681                                     table, write, buffer, lenp, ppos);
 682 }
 683
 684 /*
 685  * /proc/sys/kernel/nmi_watchdog
 686  */
 687 int proc_nmi_watchdog(struct ctl_table *table, int write,
 688                       void *buffer, size_t *lenp, loff_t *ppos)
 689 {
 690         if (!nmi_watchdog_available && write)
 691                 return -ENOTSUPP;
 692         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 693                                     table, write, buffer, lenp, ppos);
 694 }
 695
 696 /*
 697  * /proc/sys/kernel/soft_watchdog
 698  */
 699 int proc_soft_watchdog(struct ctl_table *table, int write,
 700                         void *buffer, size_t *lenp, loff_t *ppos)
 701 {
 702         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 703                                     table, write, buffer, lenp, ppos);
 704 }
 705
 706 /*
 707  * /proc/sys/kernel/watchdog_thresh
 708  */
 709 int proc_watchdog_thresh(struct ctl_table *table, int write,
 710                          void *buffer, size_t *lenp, loff_t *ppos)
 711 {
 712         int err, old;
 713
 714         mutex_lock(&watchdog_mutex);
 715
 716         old = READ_ONCE(watchdog_thresh);
 717         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 718
 719         if (!err && write && old != READ_ONCE(watchdog_thresh))
 720                 proc_watchdog_update();
 721
 722         mutex_unlock(&watchdog_mutex);
 723         return err;
 724 }
 725
 726 /*
 727  * The cpumask is the mask of possible cpus that the watchdog can run
 728  * on, not the mask of cpus it is actually running on.  This allows the
 729  * user to specify a mask that will include cpus that have not yet
 730  * been brought online, if desired.
 731  */
 732 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 733                           void *buffer, size_t *lenp, loff_t *ppos)
 734 {
 735         int err;
 736
 737         mutex_lock(&watchdog_mutex);
 738
 739         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 740         if (!err && write)
 741                 proc_watchdog_update();
 742
 743         mutex_unlock(&watchdog_mutex);
 744         return err;
 745 }
 746 #endif /* CONFIG_SYSCTL */
 747
 748 void __init lockup_detector_init(void)
 749 {
 750         if (tick_nohz_full_enabled())
 751                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 752
 753         cpumask_copy(&watchdog_cpumask,
 754                      housekeeping_cpumask(HK_FLAG_TIMER));
 755
 756         if (!watchdog_nmi_probe())
 757                 nmi_watchdog_available = true;
 758         lockup_detector_setup();
 759 }