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