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 static struct cpumask watchdog_allowed_mask __read_mostly;
  48
  49 struct cpumask watchdog_cpumask __read_mostly;
  50 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  51
  52 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  53 /*
  54  * Should we panic when a soft-lockup or hard-lockup occurs:
  55  */
  56 unsigned int __read_mostly hardlockup_panic =
  57                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  58 /*
  59  * We may not want to enable hard lockup detection by default in all cases,
  60  * for example when running the kernel as a guest on a hypervisor. In these
  61  * cases this function can be called to disable hard lockup detection. This
  62  * function should only be executed once by the boot processor before the
  63  * kernel command line parameters are parsed, because otherwise it is not
  64  * possible to override this in hardlockup_panic_setup().
  65  */
  66 void __init hardlockup_detector_disable(void)
  67 {
  68         nmi_watchdog_user_enabled = 0;
  69 }
  70
  71 static int __init hardlockup_panic_setup(char *str)
  72 {
  73         if (!strncmp(str, "panic", 5))
  74                 hardlockup_panic = 1;
  75         else if (!strncmp(str, "nopanic", 7))
  76                 hardlockup_panic = 0;
  77         else if (!strncmp(str, "0", 1))
  78                 nmi_watchdog_user_enabled = 0;
  79         else if (!strncmp(str, "1", 1))
  80                 nmi_watchdog_user_enabled = 1;
  81         return 1;
  82 }
  83 __setup("nmi_watchdog=", hardlockup_panic_setup);
  84
  85 # ifdef CONFIG_SMP
  86 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  87
  88 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
  89 {
  90         sysctl_hardlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
  91         return 1;
  92 }
  93 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
  94 # endif /* CONFIG_SMP */
  95 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
  96
  97 /*
  98  * These functions can be overridden if an architecture implements its
  99  * own hardlockup detector.
 100  *
 101  * watchdog_nmi_enable/disable can be implemented to start and stop when
 102  * softlockup watchdog threads start and stop. The arch must select the
 103  * SOFTLOCKUP_DETECTOR Kconfig.
 104  */
 105 int __weak watchdog_nmi_enable(unsigned int cpu)
 106 {
 107         hardlockup_detector_perf_enable();
 108         return 0;
 109 }
 110
 111 void __weak watchdog_nmi_disable(unsigned int cpu)
 112 {
 113         hardlockup_detector_perf_disable();
 114 }
 115
 116 /* Return 0, if a NMI watchdog is available. Error code otherwise */
 117 int __weak __init watchdog_nmi_probe(void)
 118 {
 119         return hardlockup_detector_perf_init();
 120 }
 121
 122 /**
 123  * watchdog_nmi_stop - Stop the watchdog for reconfiguration
 124  *
 125  * The reconfiguration steps are:
 126  * watchdog_nmi_stop();
 127  * update_variables();
 128  * watchdog_nmi_start();
 129  */
 130 void __weak watchdog_nmi_stop(void) { }
 131
 132 /**
 133  * watchdog_nmi_start - Start the watchdog after reconfiguration
 134  *
 135  * Counterpart to watchdog_nmi_stop().
 136  *
 137  * The following variables have been updated in update_variables() and
 138  * contain the currently valid configuration:
 139  * - watchdog_enabled
 140  * - watchdog_thresh
 141  * - watchdog_cpumask
 142  */
 143 void __weak watchdog_nmi_start(void) { }
 144
 145 /**
 146  * lockup_detector_update_enable - Update the sysctl enable bit
 147  *
 148  * Caller needs to make sure that the NMI/perf watchdogs are off, so this
 149  * can't race with watchdog_nmi_disable().
 150  */
 151 static void lockup_detector_update_enable(void)
 152 {
 153         watchdog_enabled = 0;
 154         if (!watchdog_user_enabled)
 155                 return;
 156         if (nmi_watchdog_available && nmi_watchdog_user_enabled)
 157                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
 158         if (soft_watchdog_user_enabled)
 159                 watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
 160 }
 161
 162 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 163
 164 #define SOFTLOCKUP_RESET        ULONG_MAX
 165
 166 /* Global variables, exported for sysctl */
 167 unsigned int __read_mostly softlockup_panic =
 168                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 169
 170 static bool softlockup_initialized __read_mostly;
 171 static u64 __read_mostly sample_period;
 172
 173 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 174 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 175 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 176 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 177 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 178 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 179 static unsigned long soft_lockup_nmi_warn;
 180
 181 static int __init softlockup_panic_setup(char *str)
 182 {
 183         softlockup_panic = simple_strtoul(str, NULL, 0);
 184         return 1;
 185 }
 186 __setup("softlockup_panic=", softlockup_panic_setup);
 187
 188 static int __init nowatchdog_setup(char *str)
 189 {
 190         watchdog_user_enabled = 0;
 191         return 1;
 192 }
 193 __setup("nowatchdog", nowatchdog_setup);
 194
 195 static int __init nosoftlockup_setup(char *str)
 196 {
 197         soft_watchdog_user_enabled = 0;
 198         return 1;
 199 }
 200 __setup("nosoftlockup", nosoftlockup_setup);
 201
 202 static int __init watchdog_thresh_setup(char *str)
 203 {
 204         get_option(&str, &watchdog_thresh);
 205         return 1;
 206 }
 207 __setup("watchdog_thresh=", watchdog_thresh_setup);
 208
 209 #ifdef CONFIG_SMP
 210 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 211
 212 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 213 {
 214         sysctl_softlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
 215         return 1;
 216 }
 217 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 218 #endif
 219
 220 static void __lockup_detector_cleanup(void);
 221
 222 /*
 223  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 224  * lockups can have false positives under extreme conditions. So we generally
 225  * want a higher threshold for soft lockups than for hard lockups. So we couple
 226  * the thresholds with a factor: we make the soft threshold twice the amount of
 227  * time the hard threshold is.
 228  */
 229 static int get_softlockup_thresh(void)
 230 {
 231         return watchdog_thresh * 2;
 232 }
 233
 234 /*
 235  * Returns seconds, approximately.  We don't need nanosecond
 236  * resolution, and we don't need to waste time with a big divide when
 237  * 2^30ns == 1.074s.
 238  */
 239 static unsigned long get_timestamp(void)
 240 {
 241         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 242 }
 243
 244 static void set_sample_period(void)
 245 {
 246         /*
 247          * convert watchdog_thresh from seconds to ns
 248          * the divide by 5 is to give hrtimer several chances (two
 249          * or three with the current relation between the soft
 250          * and hard thresholds) to increment before the
 251          * hardlockup detector generates a warning
 252          */
 253         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 254         watchdog_update_hrtimer_threshold(sample_period);
 255 }
 256
 257 /* Commands for resetting the watchdog */
 258 static void __touch_watchdog(void)
 259 {
 260         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 261 }
 262
 263 /**
 264  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 265  *
 266  * Call when the scheduler may have stalled for legitimate reasons
 267  * preventing the watchdog task from executing - e.g. the scheduler
 268  * entering idle state.  This should only be used for scheduler events.
 269  * Use touch_softlockup_watchdog() for everything else.
 270  */
 271 notrace void touch_softlockup_watchdog_sched(void)
 272 {
 273         /*
 274          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 275          * gets zeroed here, so use the raw_ operation.
 276          */
 277         raw_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 278 }
 279
 280 notrace void touch_softlockup_watchdog(void)
 281 {
 282         touch_softlockup_watchdog_sched();
 283         wq_watchdog_touch(raw_smp_processor_id());
 284 }
 285 EXPORT_SYMBOL(touch_softlockup_watchdog);
 286
 287 void touch_all_softlockup_watchdogs(void)
 288 {
 289         int cpu;
 290
 291         /*
 292          * watchdog_mutex cannpt be taken here, as this might be called
 293          * from (soft)interrupt context, so the access to
 294          * watchdog_allowed_cpumask might race with a concurrent update.
 295          *
 296          * The watchdog time stamp can race against a concurrent real
 297          * update as well, the only side effect might be a cycle delay for
 298          * the softlockup check.
 299          */
 300         for_each_cpu(cpu, &watchdog_allowed_mask)
 301                 per_cpu(watchdog_touch_ts, cpu) = SOFTLOCKUP_RESET;
 302         wq_watchdog_touch(-1);
 303 }
 304
 305 void touch_softlockup_watchdog_sync(void)
 306 {
 307         __this_cpu_write(softlockup_touch_sync, true);
 308         __this_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET);
 309 }
 310
 311 static int is_softlockup(unsigned long touch_ts)
 312 {
 313         unsigned long now = get_timestamp();
 314
 315         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 316                 /* Warn about unreasonable delays. */
 317                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 318                         return now - touch_ts;
 319         }
 320         return 0;
 321 }
 322
 323 /* watchdog detector functions */
 324 bool is_hardlockup(void)
 325 {
 326         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 327
 328         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 329                 return true;
 330
 331         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 332         return false;
 333 }
 334
 335 static void watchdog_interrupt_count(void)
 336 {
 337         __this_cpu_inc(hrtimer_interrupts);
 338 }
 339
 340 static DEFINE_PER_CPU(struct completion, softlockup_completion);
 341 static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
 342
 343 /*
 344  * The watchdog thread function - touches the timestamp.
 345  *
 346  * It only runs once every sample_period seconds (4 seconds by
 347  * default) to reset the softlockup timestamp. If this gets delayed
 348  * for more than 2*watchdog_thresh seconds then the debug-printout
 349  * triggers in watchdog_timer_fn().
 350  */
 351 static int softlockup_fn(void *data)
 352 {
 353         __touch_watchdog();
 354         complete(this_cpu_ptr(&softlockup_completion));
 355
 356         return 0;
 357 }
 358
 359 /* watchdog kicker functions */
 360 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 361 {
 362         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 363         struct pt_regs *regs = get_irq_regs();
 364         int duration;
 365         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 366
 367         if (!watchdog_enabled)
 368                 return HRTIMER_NORESTART;
 369
 370         /* kick the hardlockup detector */
 371         watchdog_interrupt_count();
 372
 373         /* kick the softlockup detector */
 374         if (completion_done(this_cpu_ptr(&softlockup_completion))) {
 375                 reinit_completion(this_cpu_ptr(&softlockup_completion));
 376                 stop_one_cpu_nowait(smp_processor_id(),
 377                                 softlockup_fn, NULL,
 378                                 this_cpu_ptr(&softlockup_stop_work));
 379         }
 380
 381         /* .. and repeat */
 382         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 383
 384         if (touch_ts == SOFTLOCKUP_RESET) {
 385                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 386                         /*
 387                          * If the time stamp was touched atomically
 388                          * make sure the scheduler tick is up to date.
 389                          */
 390                         __this_cpu_write(softlockup_touch_sync, false);
 391                         sched_clock_tick();
 392                 }
 393
 394                 /* Clear the guest paused flag on watchdog reset */
 395                 kvm_check_and_clear_guest_paused();
 396                 __touch_watchdog();
 397                 return HRTIMER_RESTART;
 398         }
 399
 400         /* check for a softlockup
 401          * This is done by making sure a high priority task is
 402          * being scheduled.  The task touches the watchdog to
 403          * indicate it is getting cpu time.  If it hasn't then
 404          * this is a good indication some task is hogging the cpu
 405          */
 406         duration = is_softlockup(touch_ts);
 407         if (unlikely(duration)) {
 408                 /*
 409                  * If a virtual machine is stopped by the host it can look to
 410                  * the watchdog like a soft lockup, check to see if the host
 411                  * stopped the vm before we issue the warning
 412                  */
 413                 if (kvm_check_and_clear_guest_paused())
 414                         return HRTIMER_RESTART;
 415
 416                 /* only warn once */
 417                 if (__this_cpu_read(soft_watchdog_warn) == true)
 418                         return HRTIMER_RESTART;
 419
 420                 if (softlockup_all_cpu_backtrace) {
 421                         /* Prevent multiple soft-lockup reports if one cpu is already
 422                          * engaged in dumping cpu back traces
 423                          */
 424                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 425                                 /* Someone else will report us. Let's give up */
 426                                 __this_cpu_write(soft_watchdog_warn, true);
 427                                 return HRTIMER_RESTART;
 428                         }
 429                 }
 430
 431                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 432                         smp_processor_id(), duration,
 433                         current->comm, task_pid_nr(current));
 434                 print_modules();
 435                 print_irqtrace_events(current);
 436                 if (regs)
 437                         show_regs(regs);
 438                 else
 439                         dump_stack();
 440
 441                 if (softlockup_all_cpu_backtrace) {
 442                         /* Avoid generating two back traces for current
 443                          * given that one is already made above
 444                          */
 445                         trigger_allbutself_cpu_backtrace();
 446
 447                         clear_bit(0, &soft_lockup_nmi_warn);
 448                         /* Barrier to sync with other cpus */
 449                         smp_mb__after_atomic();
 450                 }
 451
 452                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 453                 if (softlockup_panic)
 454                         panic("softlockup: hung tasks");
 455                 __this_cpu_write(soft_watchdog_warn, true);
 456         } else
 457                 __this_cpu_write(soft_watchdog_warn, false);
 458
 459         return HRTIMER_RESTART;
 460 }
 461
 462 static void watchdog_enable(unsigned int cpu)
 463 {
 464         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 465         struct completion *done = this_cpu_ptr(&softlockup_completion);
 466
 467         WARN_ON_ONCE(cpu != smp_processor_id());
 468
 469         init_completion(done);
 470         complete(done);
 471
 472         /*
 473          * Start the timer first to prevent the NMI watchdog triggering
 474          * before the timer has a chance to fire.
 475          */
 476         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
 477         hrtimer->function = watchdog_timer_fn;
 478         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 479                       HRTIMER_MODE_REL_PINNED_HARD);
 480
 481         /* Initialize timestamp */
 482         __touch_watchdog();
 483         /* Enable the perf event */
 484         if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
 485                 watchdog_nmi_enable(cpu);
 486 }
 487
 488 static void watchdog_disable(unsigned int cpu)
 489 {
 490         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 491
 492         WARN_ON_ONCE(cpu != smp_processor_id());
 493
 494         /*
 495          * Disable the perf event first. That prevents that a large delay
 496          * between disabling the timer and disabling the perf event causes
 497          * the perf NMI to detect a false positive.
 498          */
 499         watchdog_nmi_disable(cpu);
 500         hrtimer_cancel(hrtimer);
 501         wait_for_completion(this_cpu_ptr(&softlockup_completion));
 502 }
 503
 504 static int softlockup_stop_fn(void *data)
 505 {
 506         watchdog_disable(smp_processor_id());
 507         return 0;
 508 }
 509
 510 static void softlockup_stop_all(void)
 511 {
 512         int cpu;
 513
 514         if (!softlockup_initialized)
 515                 return;
 516
 517         for_each_cpu(cpu, &watchdog_allowed_mask)
 518                 smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);
 519
 520         cpumask_clear(&watchdog_allowed_mask);
 521 }
 522
 523 static int softlockup_start_fn(void *data)
 524 {
 525         watchdog_enable(smp_processor_id());
 526         return 0;
 527 }
 528
 529 static void softlockup_start_all(void)
 530 {
 531         int cpu;
 532
 533         cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
 534         for_each_cpu(cpu, &watchdog_allowed_mask)
 535                 smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);
 536 }
 537
 538 int lockup_detector_online_cpu(unsigned int cpu)
 539 {
 540         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 541                 watchdog_enable(cpu);
 542         return 0;
 543 }
 544
 545 int lockup_detector_offline_cpu(unsigned int cpu)
 546 {
 547         if (cpumask_test_cpu(cpu, &watchdog_allowed_mask))
 548                 watchdog_disable(cpu);
 549         return 0;
 550 }
 551
 552 static void lockup_detector_reconfigure(void)
 553 {
 554         cpus_read_lock();
 555         watchdog_nmi_stop();
 556
 557         softlockup_stop_all();
 558         set_sample_period();
 559         lockup_detector_update_enable();
 560         if (watchdog_enabled && watchdog_thresh)
 561                 softlockup_start_all();
 562
 563         watchdog_nmi_start();
 564         cpus_read_unlock();
 565         /*
 566          * Must be called outside the cpus locked section to prevent
 567          * recursive locking in the perf code.
 568          */
 569         __lockup_detector_cleanup();
 570 }
 571
 572 /*
 573  * Create the watchdog thread infrastructure and configure the detector(s).
 574  *
 575  * The threads are not unparked as watchdog_allowed_mask is empty.  When
 576  * the threads are successfully initialized, take the proper locks and
 577  * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
 578  */
 579 static __init void lockup_detector_setup(void)
 580 {
 581         /*
 582          * If sysctl is off and watchdog got disabled on the command line,
 583          * nothing to do here.
 584          */
 585         lockup_detector_update_enable();
 586
 587         if (!IS_ENABLED(CONFIG_SYSCTL) &&
 588             !(watchdog_enabled && watchdog_thresh))
 589                 return;
 590
 591         mutex_lock(&watchdog_mutex);
 592         lockup_detector_reconfigure();
 593         softlockup_initialized = true;
 594         mutex_unlock(&watchdog_mutex);
 595 }
 596
 597 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
 598 static void lockup_detector_reconfigure(void)
 599 {
 600         cpus_read_lock();
 601         watchdog_nmi_stop();
 602         lockup_detector_update_enable();
 603         watchdog_nmi_start();
 604         cpus_read_unlock();
 605 }
 606 static inline void lockup_detector_setup(void)
 607 {
 608         lockup_detector_reconfigure();
 609 }
 610 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 611
 612 static void __lockup_detector_cleanup(void)
 613 {
 614         lockdep_assert_held(&watchdog_mutex);
 615         hardlockup_detector_perf_cleanup();
 616 }
 617
 618 /**
 619  * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 620  *
 621  * Caller must not hold the cpu hotplug rwsem.
 622  */
 623 void lockup_detector_cleanup(void)
 624 {
 625         mutex_lock(&watchdog_mutex);
 626         __lockup_detector_cleanup();
 627         mutex_unlock(&watchdog_mutex);
 628 }
 629
 630 /**
 631  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 632  *
 633  * Special interface for parisc. It prevents lockup detector warnings from
 634  * the default pm_poweroff() function which busy loops forever.
 635  */
 636 void lockup_detector_soft_poweroff(void)
 637 {
 638         watchdog_enabled = 0;
 639 }
 640
 641 #ifdef CONFIG_SYSCTL
 642
 643 /* Propagate any changes to the watchdog threads */
 644 static void proc_watchdog_update(void)
 645 {
 646         /* Remove impossible cpus to keep sysctl output clean. */
 647         cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
 648         lockup_detector_reconfigure();
 649 }
 650
 651 /*
 652  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 653  *
 654  * caller             | table->data points to      | 'which'
 655  * -------------------|----------------------------|--------------------------
 656  * proc_watchdog      | watchdog_user_enabled      | NMI_WATCHDOG_ENABLED |
 657  *                    |                            | SOFT_WATCHDOG_ENABLED
 658  * -------------------|----------------------------|--------------------------
 659  * proc_nmi_watchdog  | nmi_watchdog_user_enabled  | NMI_WATCHDOG_ENABLED
 660  * -------------------|----------------------------|--------------------------
 661  * proc_soft_watchdog | soft_watchdog_user_enabled | SOFT_WATCHDOG_ENABLED
 662  */
 663 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 664                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 665 {
 666         int err, old, *param = table->data;
 667
 668         mutex_lock(&watchdog_mutex);
 669
 670         if (!write) {
 671                 /*
 672                  * On read synchronize the userspace interface. This is a
 673                  * racy snapshot.
 674                  */
 675                 *param = (watchdog_enabled & which) != 0;
 676                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 677         } else {
 678                 old = READ_ONCE(*param);
 679                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 680                 if (!err && old != READ_ONCE(*param))
 681                         proc_watchdog_update();
 682         }
 683         mutex_unlock(&watchdog_mutex);
 684         return err;
 685 }
 686
 687 /*
 688  * /proc/sys/kernel/watchdog
 689  */
 690 int proc_watchdog(struct ctl_table *table, int write,
 691                   void __user *buffer, size_t *lenp, loff_t *ppos)
 692 {
 693         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 694                                     table, write, buffer, lenp, ppos);
 695 }
 696
 697 /*
 698  * /proc/sys/kernel/nmi_watchdog
 699  */
 700 int proc_nmi_watchdog(struct ctl_table *table, int write,
 701                       void __user *buffer, size_t *lenp, loff_t *ppos)
 702 {
 703         if (!nmi_watchdog_available && write)
 704                 return -ENOTSUPP;
 705         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 706                                     table, write, buffer, lenp, ppos);
 707 }
 708
 709 /*
 710  * /proc/sys/kernel/soft_watchdog
 711  */
 712 int proc_soft_watchdog(struct ctl_table *table, int write,
 713                         void __user *buffer, size_t *lenp, loff_t *ppos)
 714 {
 715         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 716                                     table, write, buffer, lenp, ppos);
 717 }
 718
 719 /*
 720  * /proc/sys/kernel/watchdog_thresh
 721  */
 722 int proc_watchdog_thresh(struct ctl_table *table, int write,
 723                          void __user *buffer, size_t *lenp, loff_t *ppos)
 724 {
 725         int err, old;
 726
 727         mutex_lock(&watchdog_mutex);
 728
 729         old = READ_ONCE(watchdog_thresh);
 730         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 731
 732         if (!err && write && old != READ_ONCE(watchdog_thresh))
 733                 proc_watchdog_update();
 734
 735         mutex_unlock(&watchdog_mutex);
 736         return err;
 737 }
 738
 739 /*
 740  * The cpumask is the mask of possible cpus that the watchdog can run
 741  * on, not the mask of cpus it is actually running on.  This allows the
 742  * user to specify a mask that will include cpus that have not yet
 743  * been brought online, if desired.
 744  */
 745 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 746                           void __user *buffer, size_t *lenp, loff_t *ppos)
 747 {
 748         int err;
 749
 750         mutex_lock(&watchdog_mutex);
 751
 752         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 753         if (!err && write)
 754                 proc_watchdog_update();
 755
 756         mutex_unlock(&watchdog_mutex);
 757         return err;
 758 }
 759 #endif /* CONFIG_SYSCTL */
 760
 761 void __init lockup_detector_init(void)
 762 {
 763         if (tick_nohz_full_enabled())
 764                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 765
 766         cpumask_copy(&watchdog_cpumask,
 767                      housekeeping_cpumask(HK_FLAG_TIMER));
 768
 769         if (!watchdog_nmi_probe())
 770                 nmi_watchdog_available = true;
 771         lockup_detector_setup();
 772 }