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