kernel/watchdog.c

   1 /*
   2  * Detect hard and soft lockups on a system
   3  *
   4  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   5  *
   6  * Note: Most of this code is borrowed heavily from the original softlockup
   7  * detector, so thanks to Ingo for the initial implementation.
   8  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
   9  * to those contributors as well.
  10  */
  11
  12 #define pr_fmt(fmt) "NMI watchdog: " fmt
  13
  14 #include <linux/mm.h>
  15 #include <linux/cpu.h>
  16 #include <linux/nmi.h>
  17 #include <linux/init.h>
  18 #include <linux/module.h>
  19 #include <linux/sysctl.h>
  20 #include <linux/smpboot.h>
  21 #include <linux/sched/rt.h>
  22 #include <uapi/linux/sched/types.h>
  23 #include <linux/tick.h>
  24 #include <linux/workqueue.h>
  25 #include <linux/sched/clock.h>
  26
  27 #include <asm/irq_regs.h>
  28 #include <linux/kvm_para.h>
  29 #include <linux/kthread.h>
  30
  31 static DEFINE_MUTEX(watchdog_proc_mutex);
  32
  33 #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
  34 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
  35 #else
  36 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  37 #endif
  38 int __read_mostly nmi_watchdog_enabled;
  39 int __read_mostly soft_watchdog_enabled;
  40 int __read_mostly watchdog_user_enabled;
  41 int __read_mostly watchdog_thresh = 10;
  42
  43 #ifdef CONFIG_SMP
  44 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  45 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  46 #endif
  47 static struct cpumask watchdog_cpumask __read_mostly;
  48 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  49
  50 /* Helper for online, unparked cpus. */
  51 #define for_each_watchdog_cpu(cpu) \
  52         for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
  53
  54 atomic_t watchdog_park_in_progress = ATOMIC_INIT(0);
  55
  56 /*
  57  * The 'watchdog_running' variable is set to 1 when the watchdog threads
  58  * are registered/started and is set to 0 when the watchdog threads are
  59  * unregistered/stopped, so it is an indicator whether the threads exist.
  60  */
  61 static int __read_mostly watchdog_running;
  62 /*
  63  * If a subsystem has a need to deactivate the watchdog temporarily, it
  64  * can use the suspend/resume interface to achieve this. The content of
  65  * the 'watchdog_suspended' variable reflects this state. Existing threads
  66  * are parked/unparked by the lockup_detector_{suspend|resume} functions
  67  * (see comment blocks pertaining to those functions for further details).
  68  *
  69  * 'watchdog_suspended' also prevents threads from being registered/started
  70  * or unregistered/stopped via parameters in /proc/sys/kernel, so the state
  71  * of 'watchdog_running' cannot change while the watchdog is deactivated
  72  * temporarily (see related code in 'proc' handlers).
  73  */
  74 static int __read_mostly watchdog_suspended;
  75
  76 static u64 __read_mostly sample_period;
  77
  78 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  79 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  80 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  81 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  82 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  83 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  84 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  85 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
  86 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  87 static unsigned long soft_lockup_nmi_warn;
  88
  89 unsigned int __read_mostly softlockup_panic =
  90                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  91
  92 static int __init softlockup_panic_setup(char *str)
  93 {
  94         softlockup_panic = simple_strtoul(str, NULL, 0);
  95
  96         return 1;
  97 }
  98 __setup("softlockup_panic=", softlockup_panic_setup);
  99
 100 static int __init nowatchdog_setup(char *str)
 101 {
 102         watchdog_enabled = 0;
 103         return 1;
 104 }
 105 __setup("nowatchdog", nowatchdog_setup);
 106
 107 static int __init nosoftlockup_setup(char *str)
 108 {
 109         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
 110         return 1;
 111 }
 112 __setup("nosoftlockup", nosoftlockup_setup);
 113
 114 #ifdef CONFIG_SMP
 115 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 116 {
 117         sysctl_softlockup_all_cpu_backtrace =
 118                 !!simple_strtol(str, NULL, 0);
 119         return 1;
 120 }
 121 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 122 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
 123 {
 124         sysctl_hardlockup_all_cpu_backtrace =
 125                 !!simple_strtol(str, NULL, 0);
 126         return 1;
 127 }
 128 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
 129 #endif
 130
 131 /*
 132  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 133  * lockups can have false positives under extreme conditions. So we generally
 134  * want a higher threshold for soft lockups than for hard lockups. So we couple
 135  * the thresholds with a factor: we make the soft threshold twice the amount of
 136  * time the hard threshold is.
 137  */
 138 static int get_softlockup_thresh(void)
 139 {
 140         return watchdog_thresh * 2;
 141 }
 142
 143 /*
 144  * Returns seconds, approximately.  We don't need nanosecond
 145  * resolution, and we don't need to waste time with a big divide when
 146  * 2^30ns == 1.074s.
 147  */
 148 static unsigned long get_timestamp(void)
 149 {
 150         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 151 }
 152
 153 static void set_sample_period(void)
 154 {
 155         /*
 156          * convert watchdog_thresh from seconds to ns
 157          * the divide by 5 is to give hrtimer several chances (two
 158          * or three with the current relation between the soft
 159          * and hard thresholds) to increment before the
 160          * hardlockup detector generates a warning
 161          */
 162         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 163 }
 164
 165 /* Commands for resetting the watchdog */
 166 static void __touch_watchdog(void)
 167 {
 168         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 169 }
 170
 171 /**
 172  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 173  *
 174  * Call when the scheduler may have stalled for legitimate reasons
 175  * preventing the watchdog task from executing - e.g. the scheduler
 176  * entering idle state.  This should only be used for scheduler events.
 177  * Use touch_softlockup_watchdog() for everything else.
 178  */
 179 void touch_softlockup_watchdog_sched(void)
 180 {
 181         /*
 182          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 183          * gets zeroed here, so use the raw_ operation.
 184          */
 185         raw_cpu_write(watchdog_touch_ts, 0);
 186 }
 187
 188 void touch_softlockup_watchdog(void)
 189 {
 190         touch_softlockup_watchdog_sched();
 191         wq_watchdog_touch(raw_smp_processor_id());
 192 }
 193 EXPORT_SYMBOL(touch_softlockup_watchdog);
 194
 195 void touch_all_softlockup_watchdogs(void)
 196 {
 197         int cpu;
 198
 199         /*
 200          * this is done lockless
 201          * do we care if a 0 races with a timestamp?
 202          * all it means is the softlock check starts one cycle later
 203          */
 204         for_each_watchdog_cpu(cpu)
 205                 per_cpu(watchdog_touch_ts, cpu) = 0;
 206         wq_watchdog_touch(-1);
 207 }
 208
 209 void touch_softlockup_watchdog_sync(void)
 210 {
 211         __this_cpu_write(softlockup_touch_sync, true);
 212         __this_cpu_write(watchdog_touch_ts, 0);
 213 }
 214
 215 /* watchdog detector functions */
 216 bool is_hardlockup(void)
 217 {
 218         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 219
 220         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 221                 return true;
 222
 223         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 224         return false;
 225 }
 226
 227 static int is_softlockup(unsigned long touch_ts)
 228 {
 229         unsigned long now = get_timestamp();
 230
 231         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 232                 /* Warn about unreasonable delays. */
 233                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 234                         return now - touch_ts;
 235         }
 236         return 0;
 237 }
 238
 239 static void watchdog_interrupt_count(void)
 240 {
 241         __this_cpu_inc(hrtimer_interrupts);
 242 }
 243
 244 /*
 245  * These two functions are mostly architecture specific
 246  * defining them as weak here.
 247  */
 248 int __weak watchdog_nmi_enable(unsigned int cpu)
 249 {
 250         return 0;
 251 }
 252 void __weak watchdog_nmi_disable(unsigned int cpu)
 253 {
 254 }
 255
 256 static int watchdog_enable_all_cpus(void);
 257 static void watchdog_disable_all_cpus(void);
 258
 259 /* watchdog kicker functions */
 260 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 261 {
 262         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 263         struct pt_regs *regs = get_irq_regs();
 264         int duration;
 265         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 266
 267         if (atomic_read(&watchdog_park_in_progress) != 0)
 268                 return HRTIMER_NORESTART;
 269
 270         /* kick the hardlockup detector */
 271         watchdog_interrupt_count();
 272
 273         /* kick the softlockup detector */
 274         wake_up_process(__this_cpu_read(softlockup_watchdog));
 275
 276         /* .. and repeat */
 277         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 278
 279         if (touch_ts == 0) {
 280                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 281                         /*
 282                          * If the time stamp was touched atomically
 283                          * make sure the scheduler tick is up to date.
 284                          */
 285                         __this_cpu_write(softlockup_touch_sync, false);
 286                         sched_clock_tick();
 287                 }
 288
 289                 /* Clear the guest paused flag on watchdog reset */
 290                 kvm_check_and_clear_guest_paused();
 291                 __touch_watchdog();
 292                 return HRTIMER_RESTART;
 293         }
 294
 295         /* check for a softlockup
 296          * This is done by making sure a high priority task is
 297          * being scheduled.  The task touches the watchdog to
 298          * indicate it is getting cpu time.  If it hasn't then
 299          * this is a good indication some task is hogging the cpu
 300          */
 301         duration = is_softlockup(touch_ts);
 302         if (unlikely(duration)) {
 303                 /*
 304                  * If a virtual machine is stopped by the host it can look to
 305                  * the watchdog like a soft lockup, check to see if the host
 306                  * stopped the vm before we issue the warning
 307                  */
 308                 if (kvm_check_and_clear_guest_paused())
 309                         return HRTIMER_RESTART;
 310
 311                 /* only warn once */
 312                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 313                         /*
 314                          * When multiple processes are causing softlockups the
 315                          * softlockup detector only warns on the first one
 316                          * because the code relies on a full quiet cycle to
 317                          * re-arm.  The second process prevents the quiet cycle
 318                          * and never gets reported.  Use task pointers to detect
 319                          * this.
 320                          */
 321                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 322                             current) {
 323                                 __this_cpu_write(soft_watchdog_warn, false);
 324                                 __touch_watchdog();
 325                         }
 326                         return HRTIMER_RESTART;
 327                 }
 328
 329                 if (softlockup_all_cpu_backtrace) {
 330                         /* Prevent multiple soft-lockup reports if one cpu is already
 331                          * engaged in dumping cpu back traces
 332                          */
 333                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 334                                 /* Someone else will report us. Let's give up */
 335                                 __this_cpu_write(soft_watchdog_warn, true);
 336                                 return HRTIMER_RESTART;
 337                         }
 338                 }
 339
 340                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 341                         smp_processor_id(), duration,
 342                         current->comm, task_pid_nr(current));
 343                 __this_cpu_write(softlockup_task_ptr_saved, current);
 344                 print_modules();
 345                 print_irqtrace_events(current);
 346                 if (regs)
 347                         show_regs(regs);
 348                 else
 349                         dump_stack();
 350
 351                 if (softlockup_all_cpu_backtrace) {
 352                         /* Avoid generating two back traces for current
 353                          * given that one is already made above
 354                          */
 355                         trigger_allbutself_cpu_backtrace();
 356
 357                         clear_bit(0, &soft_lockup_nmi_warn);
 358                         /* Barrier to sync with other cpus */
 359                         smp_mb__after_atomic();
 360                 }
 361
 362                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 363                 if (softlockup_panic)
 364                         panic("softlockup: hung tasks");
 365                 __this_cpu_write(soft_watchdog_warn, true);
 366         } else
 367                 __this_cpu_write(soft_watchdog_warn, false);
 368
 369         return HRTIMER_RESTART;
 370 }
 371
 372 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 373 {
 374         struct sched_param param = { .sched_priority = prio };
 375
 376         sched_setscheduler(current, policy, &param);
 377 }
 378
 379 static void watchdog_enable(unsigned int cpu)
 380 {
 381         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 382
 383         /* kick off the timer for the hardlockup detector */
 384         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 385         hrtimer->function = watchdog_timer_fn;
 386
 387         /* Enable the perf event */
 388         watchdog_nmi_enable(cpu);
 389
 390         /* done here because hrtimer_start can only pin to smp_processor_id() */
 391         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 392                       HRTIMER_MODE_REL_PINNED);
 393
 394         /* initialize timestamp */
 395         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 396         __touch_watchdog();
 397 }
 398
 399 static void watchdog_disable(unsigned int cpu)
 400 {
 401         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 402
 403         watchdog_set_prio(SCHED_NORMAL, 0);
 404         hrtimer_cancel(hrtimer);
 405         /* disable the perf event */
 406         watchdog_nmi_disable(cpu);
 407 }
 408
 409 static void watchdog_cleanup(unsigned int cpu, bool online)
 410 {
 411         watchdog_disable(cpu);
 412 }
 413
 414 static int watchdog_should_run(unsigned int cpu)
 415 {
 416         return __this_cpu_read(hrtimer_interrupts) !=
 417                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 418 }
 419
 420 /*
 421  * The watchdog thread function - touches the timestamp.
 422  *
 423  * It only runs once every sample_period seconds (4 seconds by
 424  * default) to reset the softlockup timestamp. If this gets delayed
 425  * for more than 2*watchdog_thresh seconds then the debug-printout
 426  * triggers in watchdog_timer_fn().
 427  */
 428 static void watchdog(unsigned int cpu)
 429 {
 430         __this_cpu_write(soft_lockup_hrtimer_cnt,
 431                          __this_cpu_read(hrtimer_interrupts));
 432         __touch_watchdog();
 433
 434         /*
 435          * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
 436          * failure path. Check for failures that can occur asynchronously -
 437          * for example, when CPUs are on-lined - and shut down the hardware
 438          * perf event on each CPU accordingly.
 439          *
 440          * The only non-obvious place this bit can be cleared is through
 441          * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
 442          * pr_info here would be too noisy as it would result in a message
 443          * every few seconds if the hardlockup was disabled but the softlockup
 444          * enabled.
 445          */
 446         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 447                 watchdog_nmi_disable(cpu);
 448 }
 449
 450 static struct smp_hotplug_thread watchdog_threads = {
 451         .store                  = &softlockup_watchdog,
 452         .thread_should_run      = watchdog_should_run,
 453         .thread_fn              = watchdog,
 454         .thread_comm            = "watchdog/%u",
 455         .setup                  = watchdog_enable,
 456         .cleanup                = watchdog_cleanup,
 457         .park                   = watchdog_disable,
 458         .unpark                 = watchdog_enable,
 459 };
 460
 461 /*
 462  * park all watchdog threads that are specified in 'watchdog_cpumask'
 463  *
 464  * This function returns an error if kthread_park() of a watchdog thread
 465  * fails. In this situation, the watchdog threads of some CPUs can already
 466  * be parked and the watchdog threads of other CPUs can still be runnable.
 467  * Callers are expected to handle this special condition as appropriate in
 468  * their context.
 469  *
 470  * This function may only be called in a context that is protected against
 471  * races with CPU hotplug - for example, via get_online_cpus().
 472  */
 473 static int watchdog_park_threads(void)
 474 {
 475         int cpu, ret = 0;
 476
 477         atomic_set(&watchdog_park_in_progress, 1);
 478
 479         for_each_watchdog_cpu(cpu) {
 480                 ret = kthread_park(per_cpu(softlockup_watchdog, cpu));
 481                 if (ret)
 482                         break;
 483         }
 484
 485         atomic_set(&watchdog_park_in_progress, 0);
 486
 487         return ret;
 488 }
 489
 490 /*
 491  * unpark all watchdog threads that are specified in 'watchdog_cpumask'
 492  *
 493  * This function may only be called in a context that is protected against
 494  * races with CPU hotplug - for example, via get_online_cpus().
 495  */
 496 static void watchdog_unpark_threads(void)
 497 {
 498         int cpu;
 499
 500         for_each_watchdog_cpu(cpu)
 501                 kthread_unpark(per_cpu(softlockup_watchdog, cpu));
 502 }
 503
 504 /*
 505  * Suspend the hard and soft lockup detector by parking the watchdog threads.
 506  */
 507 int lockup_detector_suspend(void)
 508 {
 509         int ret = 0;
 510
 511         get_online_cpus();
 512         mutex_lock(&watchdog_proc_mutex);
 513         /*
 514          * Multiple suspend requests can be active in parallel (counted by
 515          * the 'watchdog_suspended' variable). If the watchdog threads are
 516          * running, the first caller takes care that they will be parked.
 517          * The state of 'watchdog_running' cannot change while a suspend
 518          * request is active (see related code in 'proc' handlers).
 519          */
 520         if (watchdog_running && !watchdog_suspended)
 521                 ret = watchdog_park_threads();
 522
 523         if (ret == 0)
 524                 watchdog_suspended++;
 525         else {
 526                 watchdog_disable_all_cpus();
 527                 pr_err("Failed to suspend lockup detectors, disabled\n");
 528                 watchdog_enabled = 0;
 529         }
 530
 531         mutex_unlock(&watchdog_proc_mutex);
 532
 533         return ret;
 534 }
 535
 536 /*
 537  * Resume the hard and soft lockup detector by unparking the watchdog threads.
 538  */
 539 void lockup_detector_resume(void)
 540 {
 541         mutex_lock(&watchdog_proc_mutex);
 542
 543         watchdog_suspended--;
 544         /*
 545          * The watchdog threads are unparked if they were previously running
 546          * and if there is no more active suspend request.
 547          */
 548         if (watchdog_running && !watchdog_suspended)
 549                 watchdog_unpark_threads();
 550
 551         mutex_unlock(&watchdog_proc_mutex);
 552         put_online_cpus();
 553 }
 554
 555 static int update_watchdog_all_cpus(void)
 556 {
 557         int ret;
 558
 559         ret = watchdog_park_threads();
 560         if (ret)
 561                 return ret;
 562
 563         watchdog_unpark_threads();
 564
 565         return 0;
 566 }
 567
 568 static int watchdog_enable_all_cpus(void)
 569 {
 570         int err = 0;
 571
 572         if (!watchdog_running) {
 573                 err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
 574                                                              &watchdog_cpumask);
 575                 if (err)
 576                         pr_err("Failed to create watchdog threads, disabled\n");
 577                 else
 578                         watchdog_running = 1;
 579         } else {
 580                 /*
 581                  * Enable/disable the lockup detectors or
 582                  * change the sample period 'on the fly'.
 583                  */
 584                 err = update_watchdog_all_cpus();
 585
 586                 if (err) {
 587                         watchdog_disable_all_cpus();
 588                         pr_err("Failed to update lockup detectors, disabled\n");
 589                 }
 590         }
 591
 592         if (err)
 593                 watchdog_enabled = 0;
 594
 595         return err;
 596 }
 597
 598 static void watchdog_disable_all_cpus(void)
 599 {
 600         if (watchdog_running) {
 601                 watchdog_running = 0;
 602                 smpboot_unregister_percpu_thread(&watchdog_threads);
 603         }
 604 }
 605
 606 #ifdef CONFIG_SYSCTL
 607
 608 /*
 609  * Update the run state of the lockup detectors.
 610  */
 611 static int proc_watchdog_update(void)
 612 {
 613         int err = 0;
 614
 615         /*
 616          * Watchdog threads won't be started if they are already active.
 617          * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
 618          * care of this. If those threads are already active, the sample
 619          * period will be updated and the lockup detectors will be enabled
 620          * or disabled 'on the fly'.
 621          */
 622         if (watchdog_enabled && watchdog_thresh)
 623                 err = watchdog_enable_all_cpus();
 624         else
 625                 watchdog_disable_all_cpus();
 626
 627         return err;
 628
 629 }
 630
 631 /*
 632  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 633  *
 634  * caller             | table->data points to | 'which' contains the flag(s)
 635  * -------------------|-----------------------|-----------------------------
 636  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 637  *                    |                       | with SOFT_WATCHDOG_ENABLED
 638  * -------------------|-----------------------|-----------------------------
 639  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 640  * -------------------|-----------------------|-----------------------------
 641  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 642  */
 643 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 644                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 645 {
 646         int err, old, new;
 647         int *watchdog_param = (int *)table->data;
 648
 649         get_online_cpus();
 650         mutex_lock(&watchdog_proc_mutex);
 651
 652         if (watchdog_suspended) {
 653                 /* no parameter changes allowed while watchdog is suspended */
 654                 err = -EAGAIN;
 655                 goto out;
 656         }
 657
 658         /*
 659          * If the parameter is being read return the state of the corresponding
 660          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
 661          * run state of the lockup detectors.
 662          */
 663         if (!write) {
 664                 *watchdog_param = (watchdog_enabled & which) != 0;
 665                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 666         } else {
 667                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 668                 if (err)
 669                         goto out;
 670
 671                 /*
 672                  * There is a race window between fetching the current value
 673                  * from 'watchdog_enabled' and storing the new value. During
 674                  * this race window, watchdog_nmi_enable() can sneak in and
 675                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
 676                  * The 'cmpxchg' detects this race and the loop retries.
 677                  */
 678                 do {
 679                         old = watchdog_enabled;
 680                         /*
 681                          * If the parameter value is not zero set the
 682                          * corresponding bit(s), else clear it(them).
 683                          */
 684                         if (*watchdog_param)
 685                                 new = old | which;
 686                         else
 687                                 new = old & ~which;
 688                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
 689
 690                 /*
 691                  * Update the run state of the lockup detectors. There is _no_
 692                  * need to check the value returned by proc_watchdog_update()
 693                  * and to restore the previous value of 'watchdog_enabled' as
 694                  * both lockup detectors are disabled if proc_watchdog_update()
 695                  * returns an error.
 696                  */
 697                 if (old == new)
 698                         goto out;
 699
 700                 err = proc_watchdog_update();
 701         }
 702 out:
 703         mutex_unlock(&watchdog_proc_mutex);
 704         put_online_cpus();
 705         return err;
 706 }
 707
 708 /*
 709  * /proc/sys/kernel/watchdog
 710  */
 711 int proc_watchdog(struct ctl_table *table, int write,
 712                   void __user *buffer, size_t *lenp, loff_t *ppos)
 713 {
 714         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 715                                     table, write, buffer, lenp, ppos);
 716 }
 717
 718 /*
 719  * /proc/sys/kernel/nmi_watchdog
 720  */
 721 int proc_nmi_watchdog(struct ctl_table *table, int write,
 722                       void __user *buffer, size_t *lenp, loff_t *ppos)
 723 {
 724         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 725                                     table, write, buffer, lenp, ppos);
 726 }
 727
 728 /*
 729  * /proc/sys/kernel/soft_watchdog
 730  */
 731 int proc_soft_watchdog(struct ctl_table *table, int write,
 732                         void __user *buffer, size_t *lenp, loff_t *ppos)
 733 {
 734         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 735                                     table, write, buffer, lenp, ppos);
 736 }
 737
 738 /*
 739  * /proc/sys/kernel/watchdog_thresh
 740  */
 741 int proc_watchdog_thresh(struct ctl_table *table, int write,
 742                          void __user *buffer, size_t *lenp, loff_t *ppos)
 743 {
 744         int err, old, new;
 745
 746         get_online_cpus();
 747         mutex_lock(&watchdog_proc_mutex);
 748
 749         if (watchdog_suspended) {
 750                 /* no parameter changes allowed while watchdog is suspended */
 751                 err = -EAGAIN;
 752                 goto out;
 753         }
 754
 755         old = ACCESS_ONCE(watchdog_thresh);
 756         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 757
 758         if (err || !write)
 759                 goto out;
 760
 761         /*
 762          * Update the sample period. Restore on failure.
 763          */
 764         new = ACCESS_ONCE(watchdog_thresh);
 765         if (old == new)
 766                 goto out;
 767
 768         set_sample_period();
 769         err = proc_watchdog_update();
 770         if (err) {
 771                 watchdog_thresh = old;
 772                 set_sample_period();
 773         }
 774 out:
 775         mutex_unlock(&watchdog_proc_mutex);
 776         put_online_cpus();
 777         return err;
 778 }
 779
 780 /*
 781  * The cpumask is the mask of possible cpus that the watchdog can run
 782  * on, not the mask of cpus it is actually running on.  This allows the
 783  * user to specify a mask that will include cpus that have not yet
 784  * been brought online, if desired.
 785  */
 786 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 787                           void __user *buffer, size_t *lenp, loff_t *ppos)
 788 {
 789         int err;
 790
 791         get_online_cpus();
 792         mutex_lock(&watchdog_proc_mutex);
 793
 794         if (watchdog_suspended) {
 795                 /* no parameter changes allowed while watchdog is suspended */
 796                 err = -EAGAIN;
 797                 goto out;
 798         }
 799
 800         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 801         if (!err && write) {
 802                 /* Remove impossible cpus to keep sysctl output cleaner. */
 803                 cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
 804                             cpu_possible_mask);
 805
 806                 if (watchdog_running) {
 807                         /*
 808                          * Failure would be due to being unable to allocate
 809                          * a temporary cpumask, so we are likely not in a
 810                          * position to do much else to make things better.
 811                          */
 812                         if (smpboot_update_cpumask_percpu_thread(
 813                                     &watchdog_threads, &watchdog_cpumask) != 0)
 814                                 pr_err("cpumask update failed\n");
 815                 }
 816         }
 817 out:
 818         mutex_unlock(&watchdog_proc_mutex);
 819         put_online_cpus();
 820         return err;
 821 }
 822
 823 #endif /* CONFIG_SYSCTL */
 824
 825 void __init lockup_detector_init(void)
 826 {
 827         set_sample_period();
 828
 829 #ifdef CONFIG_NO_HZ_FULL
 830         if (tick_nohz_full_enabled()) {
 831                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 832                 cpumask_copy(&watchdog_cpumask, housekeeping_mask);
 833         } else
 834                 cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 835 #else
 836         cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 837 #endif
 838
 839         if (watchdog_enabled)
 840                 watchdog_enable_all_cpus();
 841 }