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) "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 #include <uapi/linux/sched/types.h>
  23 #include <linux/tick.h>
  24 #include <linux/workqueue.h>
  25 #include <linux/sched/clock.h>
  26 #include <linux/sched/debug.h>
  27
  28 #include <asm/irq_regs.h>
  29 #include <linux/kvm_para.h>
  30 #include <linux/kthread.h>
  31
  32 static DEFINE_MUTEX(watchdog_mutex);
  33
  34 int __read_mostly nmi_watchdog_enabled;
  35
  36 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
  37 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED |
  38                                                 NMI_WATCHDOG_ENABLED;
  39 #else
  40 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  41 #endif
  42
  43 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  44 /*
  45  * Should we panic when a soft-lockup or hard-lockup occurs:
  46  */
  47 unsigned int __read_mostly hardlockup_panic =
  48                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  49 /*
  50  * We may not want to enable hard lockup detection by default in all cases,
  51  * for example when running the kernel as a guest on a hypervisor. In these
  52  * cases this function can be called to disable hard lockup detection. This
  53  * function should only be executed once by the boot processor before the
  54  * kernel command line parameters are parsed, because otherwise it is not
  55  * possible to override this in hardlockup_panic_setup().
  56  */
  57 void __init hardlockup_detector_disable(void)
  58 {
  59         watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  60 }
  61
  62 static int __init hardlockup_panic_setup(char *str)
  63 {
  64         if (!strncmp(str, "panic", 5))
  65                 hardlockup_panic = 1;
  66         else if (!strncmp(str, "nopanic", 7))
  67                 hardlockup_panic = 0;
  68         else if (!strncmp(str, "0", 1))
  69                 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  70         else if (!strncmp(str, "1", 1))
  71                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
  72         return 1;
  73 }
  74 __setup("nmi_watchdog=", hardlockup_panic_setup);
  75
  76 # ifdef CONFIG_SMP
  77 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  78
  79 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
  80 {
  81         sysctl_hardlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
  82         return 1;
  83 }
  84 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
  85 # endif /* CONFIG_SMP */
  86 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
  87
  88 int __read_mostly watchdog_user_enabled;
  89 int __read_mostly watchdog_thresh = 10;
  90
  91 struct cpumask watchdog_cpumask __read_mostly;
  92 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  93
  94 /*
  95  * These functions can be overridden if an architecture implements its
  96  * own hardlockup detector.
  97  *
  98  * watchdog_nmi_enable/disable can be implemented to start and stop when
  99  * softlockup watchdog threads start and stop. The arch must select the
 100  * SOFTLOCKUP_DETECTOR Kconfig.
 101  */
 102 int __weak watchdog_nmi_enable(unsigned int cpu)
 103 {
 104         return 0;
 105 }
 106
 107 void __weak watchdog_nmi_disable(unsigned int cpu)
 108 {
 109         hardlockup_detector_perf_disable();
 110 }
 111
 112 /*
 113  * watchdog_nmi_reconfigure can be implemented to be notified after any
 114  * watchdog configuration change. The arch hardlockup watchdog should
 115  * respond to the following variables:
 116  * - nmi_watchdog_enabled
 117  * - watchdog_thresh
 118  * - watchdog_cpumask
 119  * - sysctl_hardlockup_all_cpu_backtrace
 120  * - hardlockup_panic
 121  */
 122 void __weak watchdog_nmi_reconfigure(void) { }
 123
 124 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 125
 126 /* Global variables, exported for sysctl */
 127 unsigned int __read_mostly softlockup_panic =
 128                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 129 int __read_mostly soft_watchdog_enabled;
 130
 131 struct cpumask watchdog_allowed_mask __read_mostly;
 132 static bool softlockup_threads_initialized __read_mostly;
 133
 134 static u64 __read_mostly sample_period;
 135
 136 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 137 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
 138 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 139 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 140 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 141 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 142 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
 143 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
 144 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 145 static unsigned long soft_lockup_nmi_warn;
 146
 147 static int __init softlockup_panic_setup(char *str)
 148 {
 149         softlockup_panic = simple_strtoul(str, NULL, 0);
 150         return 1;
 151 }
 152 __setup("softlockup_panic=", softlockup_panic_setup);
 153
 154 static int __init nowatchdog_setup(char *str)
 155 {
 156         watchdog_enabled = 0;
 157         return 1;
 158 }
 159 __setup("nowatchdog", nowatchdog_setup);
 160
 161 static int __init nosoftlockup_setup(char *str)
 162 {
 163         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
 164         return 1;
 165 }
 166 __setup("nosoftlockup", nosoftlockup_setup);
 167
 168 #ifdef CONFIG_SMP
 169 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 170
 171 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 172 {
 173         sysctl_softlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
 174         return 1;
 175 }
 176 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 177 #endif
 178
 179 static void __lockup_detector_cleanup(void);
 180
 181 /*
 182  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 183  * lockups can have false positives under extreme conditions. So we generally
 184  * want a higher threshold for soft lockups than for hard lockups. So we couple
 185  * the thresholds with a factor: we make the soft threshold twice the amount of
 186  * time the hard threshold is.
 187  */
 188 static int get_softlockup_thresh(void)
 189 {
 190         return watchdog_thresh * 2;
 191 }
 192
 193 /*
 194  * Returns seconds, approximately.  We don't need nanosecond
 195  * resolution, and we don't need to waste time with a big divide when
 196  * 2^30ns == 1.074s.
 197  */
 198 static unsigned long get_timestamp(void)
 199 {
 200         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 201 }
 202
 203 static void set_sample_period(void)
 204 {
 205         /*
 206          * convert watchdog_thresh from seconds to ns
 207          * the divide by 5 is to give hrtimer several chances (two
 208          * or three with the current relation between the soft
 209          * and hard thresholds) to increment before the
 210          * hardlockup detector generates a warning
 211          */
 212         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 213         watchdog_update_hrtimer_threshold(sample_period);
 214 }
 215
 216 /* Commands for resetting the watchdog */
 217 static void __touch_watchdog(void)
 218 {
 219         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 220 }
 221
 222 /**
 223  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 224  *
 225  * Call when the scheduler may have stalled for legitimate reasons
 226  * preventing the watchdog task from executing - e.g. the scheduler
 227  * entering idle state.  This should only be used for scheduler events.
 228  * Use touch_softlockup_watchdog() for everything else.
 229  */
 230 void touch_softlockup_watchdog_sched(void)
 231 {
 232         /*
 233          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 234          * gets zeroed here, so use the raw_ operation.
 235          */
 236         raw_cpu_write(watchdog_touch_ts, 0);
 237 }
 238
 239 void touch_softlockup_watchdog(void)
 240 {
 241         touch_softlockup_watchdog_sched();
 242         wq_watchdog_touch(raw_smp_processor_id());
 243 }
 244 EXPORT_SYMBOL(touch_softlockup_watchdog);
 245
 246 void touch_all_softlockup_watchdogs(void)
 247 {
 248         int cpu;
 249
 250         /*
 251          * watchdog_mutex cannpt be taken here, as this might be called
 252          * from (soft)interrupt context, so the access to
 253          * watchdog_allowed_cpumask might race with a concurrent update.
 254          *
 255          * The watchdog time stamp can race against a concurrent real
 256          * update as well, the only side effect might be a cycle delay for
 257          * the softlockup check.
 258          */
 259         for_each_cpu(cpu, &watchdog_allowed_mask)
 260                 per_cpu(watchdog_touch_ts, cpu) = 0;
 261         wq_watchdog_touch(-1);
 262 }
 263
 264 void touch_softlockup_watchdog_sync(void)
 265 {
 266         __this_cpu_write(softlockup_touch_sync, true);
 267         __this_cpu_write(watchdog_touch_ts, 0);
 268 }
 269
 270 static int is_softlockup(unsigned long touch_ts)
 271 {
 272         unsigned long now = get_timestamp();
 273
 274         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 275                 /* Warn about unreasonable delays. */
 276                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 277                         return now - touch_ts;
 278         }
 279         return 0;
 280 }
 281
 282 /* watchdog detector functions */
 283 bool is_hardlockup(void)
 284 {
 285         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 286
 287         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 288                 return true;
 289
 290         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 291         return false;
 292 }
 293
 294 static void watchdog_interrupt_count(void)
 295 {
 296         __this_cpu_inc(hrtimer_interrupts);
 297 }
 298
 299 /* watchdog kicker functions */
 300 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 301 {
 302         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 303         struct pt_regs *regs = get_irq_regs();
 304         int duration;
 305         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 306
 307         if (!watchdog_enabled)
 308                 return HRTIMER_NORESTART;
 309
 310         /* kick the hardlockup detector */
 311         watchdog_interrupt_count();
 312
 313         /* kick the softlockup detector */
 314         wake_up_process(__this_cpu_read(softlockup_watchdog));
 315
 316         /* .. and repeat */
 317         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 318
 319         if (touch_ts == 0) {
 320                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 321                         /*
 322                          * If the time stamp was touched atomically
 323                          * make sure the scheduler tick is up to date.
 324                          */
 325                         __this_cpu_write(softlockup_touch_sync, false);
 326                         sched_clock_tick();
 327                 }
 328
 329                 /* Clear the guest paused flag on watchdog reset */
 330                 kvm_check_and_clear_guest_paused();
 331                 __touch_watchdog();
 332                 return HRTIMER_RESTART;
 333         }
 334
 335         /* check for a softlockup
 336          * This is done by making sure a high priority task is
 337          * being scheduled.  The task touches the watchdog to
 338          * indicate it is getting cpu time.  If it hasn't then
 339          * this is a good indication some task is hogging the cpu
 340          */
 341         duration = is_softlockup(touch_ts);
 342         if (unlikely(duration)) {
 343                 /*
 344                  * If a virtual machine is stopped by the host it can look to
 345                  * the watchdog like a soft lockup, check to see if the host
 346                  * stopped the vm before we issue the warning
 347                  */
 348                 if (kvm_check_and_clear_guest_paused())
 349                         return HRTIMER_RESTART;
 350
 351                 /* only warn once */
 352                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 353                         /*
 354                          * When multiple processes are causing softlockups the
 355                          * softlockup detector only warns on the first one
 356                          * because the code relies on a full quiet cycle to
 357                          * re-arm.  The second process prevents the quiet cycle
 358                          * and never gets reported.  Use task pointers to detect
 359                          * this.
 360                          */
 361                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 362                             current) {
 363                                 __this_cpu_write(soft_watchdog_warn, false);
 364                                 __touch_watchdog();
 365                         }
 366                         return HRTIMER_RESTART;
 367                 }
 368
 369                 if (softlockup_all_cpu_backtrace) {
 370                         /* Prevent multiple soft-lockup reports if one cpu is already
 371                          * engaged in dumping cpu back traces
 372                          */
 373                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 374                                 /* Someone else will report us. Let's give up */
 375                                 __this_cpu_write(soft_watchdog_warn, true);
 376                                 return HRTIMER_RESTART;
 377                         }
 378                 }
 379
 380                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 381                         smp_processor_id(), duration,
 382                         current->comm, task_pid_nr(current));
 383                 __this_cpu_write(softlockup_task_ptr_saved, current);
 384                 print_modules();
 385                 print_irqtrace_events(current);
 386                 if (regs)
 387                         show_regs(regs);
 388                 else
 389                         dump_stack();
 390
 391                 if (softlockup_all_cpu_backtrace) {
 392                         /* Avoid generating two back traces for current
 393                          * given that one is already made above
 394                          */
 395                         trigger_allbutself_cpu_backtrace();
 396
 397                         clear_bit(0, &soft_lockup_nmi_warn);
 398                         /* Barrier to sync with other cpus */
 399                         smp_mb__after_atomic();
 400                 }
 401
 402                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 403                 if (softlockup_panic)
 404                         panic("softlockup: hung tasks");
 405                 __this_cpu_write(soft_watchdog_warn, true);
 406         } else
 407                 __this_cpu_write(soft_watchdog_warn, false);
 408
 409         return HRTIMER_RESTART;
 410 }
 411
 412 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 413 {
 414         struct sched_param param = { .sched_priority = prio };
 415
 416         sched_setscheduler(current, policy, &param);
 417 }
 418
 419 static void watchdog_enable(unsigned int cpu)
 420 {
 421         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 422
 423         /*
 424          * Start the timer first to prevent the NMI watchdog triggering
 425          * before the timer has a chance to fire.
 426          */
 427         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 428         hrtimer->function = watchdog_timer_fn;
 429         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 430                       HRTIMER_MODE_REL_PINNED);
 431
 432         /* Initialize timestamp */
 433         __touch_watchdog();
 434         /* Enable the perf event */
 435         watchdog_nmi_enable(cpu);
 436
 437         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 438 }
 439
 440 static void watchdog_disable(unsigned int cpu)
 441 {
 442         struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
 443
 444         watchdog_set_prio(SCHED_NORMAL, 0);
 445         /*
 446          * Disable the perf event first. That prevents that a large delay
 447          * between disabling the timer and disabling the perf event causes
 448          * the perf NMI to detect a false positive.
 449          */
 450         watchdog_nmi_disable(cpu);
 451         hrtimer_cancel(hrtimer);
 452 }
 453
 454 static void watchdog_cleanup(unsigned int cpu, bool online)
 455 {
 456         watchdog_disable(cpu);
 457 }
 458
 459 static int watchdog_should_run(unsigned int cpu)
 460 {
 461         return __this_cpu_read(hrtimer_interrupts) !=
 462                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 463 }
 464
 465 /*
 466  * The watchdog thread function - touches the timestamp.
 467  *
 468  * It only runs once every sample_period seconds (4 seconds by
 469  * default) to reset the softlockup timestamp. If this gets delayed
 470  * for more than 2*watchdog_thresh seconds then the debug-printout
 471  * triggers in watchdog_timer_fn().
 472  */
 473 static void watchdog(unsigned int cpu)
 474 {
 475         __this_cpu_write(soft_lockup_hrtimer_cnt,
 476                          __this_cpu_read(hrtimer_interrupts));
 477         __touch_watchdog();
 478 }
 479
 480 static struct smp_hotplug_thread watchdog_threads = {
 481         .store                  = &softlockup_watchdog,
 482         .thread_should_run      = watchdog_should_run,
 483         .thread_fn              = watchdog,
 484         .thread_comm            = "watchdog/%u",
 485         .setup                  = watchdog_enable,
 486         .cleanup                = watchdog_cleanup,
 487         .park                   = watchdog_disable,
 488         .unpark                 = watchdog_enable,
 489 };
 490
 491 static void softlockup_update_smpboot_threads(void)
 492 {
 493         lockdep_assert_held(&watchdog_mutex);
 494
 495         if (!softlockup_threads_initialized)
 496                 return;
 497
 498         smpboot_update_cpumask_percpu_thread(&watchdog_threads,
 499                                              &watchdog_allowed_mask);
 500         __lockup_detector_cleanup();
 501 }
 502
 503 /* Temporarily park all watchdog threads */
 504 static void softlockup_park_all_threads(void)
 505 {
 506         cpumask_clear(&watchdog_allowed_mask);
 507         softlockup_update_smpboot_threads();
 508 }
 509
 510 /*
 511  * Park threads which are not longer enabled and unpark threads which have
 512  * been newly enabled.
 513  */
 514 static void softlockup_update_threads(void)
 515 {
 516         cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
 517         softlockup_update_smpboot_threads();
 518 }
 519
 520 static void softlockup_reconfigure_threads(bool enabled)
 521 {
 522         softlockup_park_all_threads();
 523         set_sample_period();
 524         if (enabled)
 525                 softlockup_update_threads();
 526 }
 527
 528 /*
 529  * Create the watchdog thread infrastructure.
 530  *
 531  * The threads are not unparked as watchdog_allowed_mask is empty.  When
 532  * the threads are sucessfully initialized, take the proper locks and
 533  * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
 534  */
 535 static __init void softlockup_init_threads(void)
 536 {
 537         int ret;
 538
 539         /*
 540          * If sysctl is off and watchdog got disabled on the command line,
 541          * nothing to do here.
 542          */
 543         if (!IS_ENABLED(CONFIG_SYSCTL) &&
 544             !(watchdog_enabled && watchdog_thresh))
 545                 return;
 546
 547         ret = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
 548                                                      &watchdog_allowed_mask);
 549         if (ret) {
 550                 pr_err("Failed to initialize soft lockup detector threads\n");
 551                 return;
 552         }
 553
 554         mutex_lock(&watchdog_mutex);
 555         softlockup_threads_initialized = true;
 556         softlockup_reconfigure_threads(watchdog_enabled && watchdog_thresh);
 557         mutex_unlock(&watchdog_mutex);
 558 }
 559
 560 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
 561 static inline int watchdog_park_threads(void) { return 0; }
 562 static inline void watchdog_unpark_threads(void) { }
 563 static inline int watchdog_enable_all_cpus(void) { return 0; }
 564 static inline void watchdog_disable_all_cpus(void) { }
 565 static inline void softlockup_init_threads(void) { }
 566 static inline void softlockup_update_threads(void) { }
 567 static inline void softlockup_reconfigure_threads(bool enabled) { }
 568 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
 569
 570 static void __lockup_detector_cleanup(void)
 571 {
 572         lockdep_assert_held(&watchdog_mutex);
 573         hardlockup_detector_perf_cleanup();
 574 }
 575
 576 /**
 577  * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 578  *
 579  * Caller must not hold the cpu hotplug rwsem.
 580  */
 581 void lockup_detector_cleanup(void)
 582 {
 583         mutex_lock(&watchdog_mutex);
 584         __lockup_detector_cleanup();
 585         mutex_unlock(&watchdog_mutex);
 586 }
 587
 588 /**
 589  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 590  *
 591  * Special interface for parisc. It prevents lockup detector warnings from
 592  * the default pm_poweroff() function which busy loops forever.
 593  */
 594 void lockup_detector_soft_poweroff(void)
 595 {
 596         watchdog_enabled = 0;
 597 }
 598
 599 #ifdef CONFIG_SYSCTL
 600
 601 /*
 602  * Update the run state of the lockup detectors.
 603  */
 604 static void proc_watchdog_update(void)
 605 {
 606         softlockup_reconfigure_threads(watchdog_enabled && watchdog_thresh);
 607         watchdog_nmi_reconfigure();
 608 }
 609
 610 /*
 611  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 612  *
 613  * caller             | table->data points to | 'which' contains the flag(s)
 614  * -------------------|-----------------------|-----------------------------
 615  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 616  *                    |                       | with SOFT_WATCHDOG_ENABLED
 617  * -------------------|-----------------------|-----------------------------
 618  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 619  * -------------------|-----------------------|-----------------------------
 620  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 621  */
 622 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 623                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 624 {
 625         int err, old, new;
 626         int *watchdog_param = (int *)table->data;
 627
 628         cpu_hotplug_disable();
 629         mutex_lock(&watchdog_mutex);
 630
 631         /*
 632          * If the parameter is being read return the state of the corresponding
 633          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
 634          * run state of the lockup detectors.
 635          */
 636         if (!write) {
 637                 *watchdog_param = (watchdog_enabled & which) != 0;
 638                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 639         } else {
 640                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 641                 if (err)
 642                         goto out;
 643
 644                 /*
 645                  * There is a race window between fetching the current value
 646                  * from 'watchdog_enabled' and storing the new value. During
 647                  * this race window, watchdog_nmi_enable() can sneak in and
 648                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
 649                  * The 'cmpxchg' detects this race and the loop retries.
 650                  */
 651                 do {
 652                         old = watchdog_enabled;
 653                         /*
 654                          * If the parameter value is not zero set the
 655                          * corresponding bit(s), else clear it(them).
 656                          */
 657                         if (*watchdog_param)
 658                                 new = old | which;
 659                         else
 660                                 new = old & ~which;
 661                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
 662
 663                 if (old != new)
 664                         proc_watchdog_update();
 665         }
 666 out:
 667         mutex_unlock(&watchdog_mutex);
 668         cpu_hotplug_enable();
 669         return err;
 670 }
 671
 672 /*
 673  * /proc/sys/kernel/watchdog
 674  */
 675 int proc_watchdog(struct ctl_table *table, int write,
 676                   void __user *buffer, size_t *lenp, loff_t *ppos)
 677 {
 678         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 679                                     table, write, buffer, lenp, ppos);
 680 }
 681
 682 /*
 683  * /proc/sys/kernel/nmi_watchdog
 684  */
 685 int proc_nmi_watchdog(struct ctl_table *table, int write,
 686                       void __user *buffer, size_t *lenp, loff_t *ppos)
 687 {
 688         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 689                                     table, write, buffer, lenp, ppos);
 690 }
 691
 692 /*
 693  * /proc/sys/kernel/soft_watchdog
 694  */
 695 int proc_soft_watchdog(struct ctl_table *table, int write,
 696                         void __user *buffer, size_t *lenp, loff_t *ppos)
 697 {
 698         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 699                                     table, write, buffer, lenp, ppos);
 700 }
 701
 702 /*
 703  * /proc/sys/kernel/watchdog_thresh
 704  */
 705 int proc_watchdog_thresh(struct ctl_table *table, int write,
 706                          void __user *buffer, size_t *lenp, loff_t *ppos)
 707 {
 708         int err, old;
 709
 710         cpu_hotplug_disable();
 711         mutex_lock(&watchdog_mutex);
 712
 713         old = READ_ONCE(watchdog_thresh);
 714         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 715
 716         if (!err && write && old != READ_ONCE(watchdog_thresh))
 717                 proc_watchdog_update();
 718
 719         mutex_unlock(&watchdog_mutex);
 720         cpu_hotplug_enable();
 721         return err;
 722 }
 723
 724 static void proc_watchdog_cpumask_update(void)
 725 {
 726         /* Remove impossible cpus to keep sysctl output clean. */
 727         cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
 728
 729         softlockup_update_threads();
 730         watchdog_nmi_reconfigure();
 731 }
 732
 733 /*
 734  * The cpumask is the mask of possible cpus that the watchdog can run
 735  * on, not the mask of cpus it is actually running on.  This allows the
 736  * user to specify a mask that will include cpus that have not yet
 737  * been brought online, if desired.
 738  */
 739 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 740                           void __user *buffer, size_t *lenp, loff_t *ppos)
 741 {
 742         int err;
 743
 744         cpu_hotplug_disable();
 745         mutex_lock(&watchdog_mutex);
 746
 747         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 748         if (!err && write)
 749                 proc_watchdog_cpumask_update();
 750
 751         mutex_unlock(&watchdog_mutex);
 752         cpu_hotplug_enable();
 753         return err;
 754 }
 755 #endif /* CONFIG_SYSCTL */
 756
 757 void __init lockup_detector_init(void)
 758 {
 759 #ifdef CONFIG_NO_HZ_FULL
 760         if (tick_nohz_full_enabled()) {
 761                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 762                 cpumask_copy(&watchdog_cpumask, housekeeping_mask);
 763         } else
 764                 cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 765 #else
 766         cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 767 #endif
 768
 769         softlockup_init_threads();
 770 }