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 #include <linux/sched/debug.h>
  27
  28 #include <asm/irq_regs.h>
  29 #include <linux/kvm_para.h>
  30 #include <linux/kthread.h>
  31
  32 static DEFINE_MUTEX(watchdog_proc_mutex);
  33
  34 #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
  35 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
  36 #else
  37 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  38 #endif
  39 int __read_mostly nmi_watchdog_enabled;
  40 int __read_mostly soft_watchdog_enabled;
  41 int __read_mostly watchdog_user_enabled;
  42 int __read_mostly watchdog_thresh = 10;
  43
  44 #ifdef CONFIG_SMP
  45 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  46 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  47 #endif
  48 static struct cpumask watchdog_cpumask __read_mostly;
  49 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  50
  51 /* Helper for online, unparked cpus. */
  52 #define for_each_watchdog_cpu(cpu) \
  53         for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
  54
  55 atomic_t watchdog_park_in_progress = ATOMIC_INIT(0);
  56
  57 /*
  58  * The 'watchdog_running' variable is set to 1 when the watchdog threads
  59  * are registered/started and is set to 0 when the watchdog threads are
  60  * unregistered/stopped, so it is an indicator whether the threads exist.
  61  */
  62 static int __read_mostly watchdog_running;
  63 /*
  64  * If a subsystem has a need to deactivate the watchdog temporarily, it
  65  * can use the suspend/resume interface to achieve this. The content of
  66  * the 'watchdog_suspended' variable reflects this state. Existing threads
  67  * are parked/unparked by the lockup_detector_{suspend|resume} functions
  68  * (see comment blocks pertaining to those functions for further details).
  69  *
  70  * 'watchdog_suspended' also prevents threads from being registered/started
  71  * or unregistered/stopped via parameters in /proc/sys/kernel, so the state
  72  * of 'watchdog_running' cannot change while the watchdog is deactivated
  73  * temporarily (see related code in 'proc' handlers).
  74  */
  75 static int __read_mostly watchdog_suspended;
  76
  77 static u64 __read_mostly sample_period;
  78
  79 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  80 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  81 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  82 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  83 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  84 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  85 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  86 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
  87 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  88 static unsigned long soft_lockup_nmi_warn;
  89
  90 unsigned int __read_mostly softlockup_panic =
  91                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
  92
  93 static int __init softlockup_panic_setup(char *str)
  94 {
  95         softlockup_panic = simple_strtoul(str, NULL, 0);
  96
  97         return 1;
  98 }
  99 __setup("softlockup_panic=", softlockup_panic_setup);
 100
 101 static int __init nowatchdog_setup(char *str)
 102 {
 103         watchdog_enabled = 0;
 104         return 1;
 105 }
 106 __setup("nowatchdog", nowatchdog_setup);
 107
 108 static int __init nosoftlockup_setup(char *str)
 109 {
 110         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
 111         return 1;
 112 }
 113 __setup("nosoftlockup", nosoftlockup_setup);
 114
 115 #ifdef CONFIG_SMP
 116 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 117 {
 118         sysctl_softlockup_all_cpu_backtrace =
 119                 !!simple_strtol(str, NULL, 0);
 120         return 1;
 121 }
 122 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 123 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
 124 {
 125         sysctl_hardlockup_all_cpu_backtrace =
 126                 !!simple_strtol(str, NULL, 0);
 127         return 1;
 128 }
 129 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
 130 #endif
 131
 132 /*
 133  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 134  * lockups can have false positives under extreme conditions. So we generally
 135  * want a higher threshold for soft lockups than for hard lockups. So we couple
 136  * the thresholds with a factor: we make the soft threshold twice the amount of
 137  * time the hard threshold is.
 138  */
 139 static int get_softlockup_thresh(void)
 140 {
 141         return watchdog_thresh * 2;
 142 }
 143
 144 /*
 145  * Returns seconds, approximately.  We don't need nanosecond
 146  * resolution, and we don't need to waste time with a big divide when
 147  * 2^30ns == 1.074s.
 148  */
 149 static unsigned long get_timestamp(void)
 150 {
 151         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 152 }
 153
 154 static void set_sample_period(void)
 155 {
 156         /*
 157          * convert watchdog_thresh from seconds to ns
 158          * the divide by 5 is to give hrtimer several chances (two
 159          * or three with the current relation between the soft
 160          * and hard thresholds) to increment before the
 161          * hardlockup detector generates a warning
 162          */
 163         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 164 }
 165
 166 /* Commands for resetting the watchdog */
 167 static void __touch_watchdog(void)
 168 {
 169         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 170 }
 171
 172 /**
 173  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 174  *
 175  * Call when the scheduler may have stalled for legitimate reasons
 176  * preventing the watchdog task from executing - e.g. the scheduler
 177  * entering idle state.  This should only be used for scheduler events.
 178  * Use touch_softlockup_watchdog() for everything else.
 179  */
 180 void touch_softlockup_watchdog_sched(void)
 181 {
 182         /*
 183          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 184          * gets zeroed here, so use the raw_ operation.
 185          */
 186         raw_cpu_write(watchdog_touch_ts, 0);
 187 }
 188
 189 void touch_softlockup_watchdog(void)
 190 {
 191         touch_softlockup_watchdog_sched();
 192         wq_watchdog_touch(raw_smp_processor_id());
 193 }
 194 EXPORT_SYMBOL(touch_softlockup_watchdog);
 195
 196 void touch_all_softlockup_watchdogs(void)
 197 {
 198         int cpu;
 199
 200         /*
 201          * this is done lockless
 202          * do we care if a 0 races with a timestamp?
 203          * all it means is the softlock check starts one cycle later
 204          */
 205         for_each_watchdog_cpu(cpu)
 206                 per_cpu(watchdog_touch_ts, cpu) = 0;
 207         wq_watchdog_touch(-1);
 208 }
 209
 210 void touch_softlockup_watchdog_sync(void)
 211 {
 212         __this_cpu_write(softlockup_touch_sync, true);
 213         __this_cpu_write(watchdog_touch_ts, 0);
 214 }
 215
 216 /* watchdog detector functions */
 217 bool is_hardlockup(void)
 218 {
 219         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 220
 221         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 222                 return true;
 223
 224         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 225         return false;
 226 }
 227
 228 static int is_softlockup(unsigned long touch_ts)
 229 {
 230         unsigned long now = get_timestamp();
 231
 232         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 233                 /* Warn about unreasonable delays. */
 234                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 235                         return now - touch_ts;
 236         }
 237         return 0;
 238 }
 239
 240 static void watchdog_interrupt_count(void)
 241 {
 242         __this_cpu_inc(hrtimer_interrupts);
 243 }
 244
 245 /*
 246  * These two functions are mostly architecture specific
 247  * defining them as weak here.
 248  */
 249 int __weak watchdog_nmi_enable(unsigned int cpu)
 250 {
 251         return 0;
 252 }
 253 void __weak watchdog_nmi_disable(unsigned int cpu)
 254 {
 255 }
 256
 257 static int watchdog_enable_all_cpus(void);
 258 static void watchdog_disable_all_cpus(void);
 259
 260 /* watchdog kicker functions */
 261 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 262 {
 263         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 264         struct pt_regs *regs = get_irq_regs();
 265         int duration;
 266         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 267
 268         if (atomic_read(&watchdog_park_in_progress) != 0)
 269                 return HRTIMER_NORESTART;
 270
 271         /* kick the hardlockup detector */
 272         watchdog_interrupt_count();
 273
 274         /* kick the softlockup detector */
 275         wake_up_process(__this_cpu_read(softlockup_watchdog));
 276
 277         /* .. and repeat */
 278         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 279
 280         if (touch_ts == 0) {
 281                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 282                         /*
 283                          * If the time stamp was touched atomically
 284                          * make sure the scheduler tick is up to date.
 285                          */
 286                         __this_cpu_write(softlockup_touch_sync, false);
 287                         sched_clock_tick();
 288                 }
 289
 290                 /* Clear the guest paused flag on watchdog reset */
 291                 kvm_check_and_clear_guest_paused();
 292                 __touch_watchdog();
 293                 return HRTIMER_RESTART;
 294         }
 295
 296         /* check for a softlockup
 297          * This is done by making sure a high priority task is
 298          * being scheduled.  The task touches the watchdog to
 299          * indicate it is getting cpu time.  If it hasn't then
 300          * this is a good indication some task is hogging the cpu
 301          */
 302         duration = is_softlockup(touch_ts);
 303         if (unlikely(duration)) {
 304                 /*
 305                  * If a virtual machine is stopped by the host it can look to
 306                  * the watchdog like a soft lockup, check to see if the host
 307                  * stopped the vm before we issue the warning
 308                  */
 309                 if (kvm_check_and_clear_guest_paused())
 310                         return HRTIMER_RESTART;
 311
 312                 /* only warn once */
 313                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 314                         /*
 315                          * When multiple processes are causing softlockups the
 316                          * softlockup detector only warns on the first one
 317                          * because the code relies on a full quiet cycle to
 318                          * re-arm.  The second process prevents the quiet cycle
 319                          * and never gets reported.  Use task pointers to detect
 320                          * this.
 321                          */
 322                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 323                             current) {
 324                                 __this_cpu_write(soft_watchdog_warn, false);
 325                                 __touch_watchdog();
 326                         }
 327                         return HRTIMER_RESTART;
 328                 }
 329
 330                 if (softlockup_all_cpu_backtrace) {
 331                         /* Prevent multiple soft-lockup reports if one cpu is already
 332                          * engaged in dumping cpu back traces
 333                          */
 334                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 335                                 /* Someone else will report us. Let's give up */
 336                                 __this_cpu_write(soft_watchdog_warn, true);
 337                                 return HRTIMER_RESTART;
 338                         }
 339                 }
 340
 341                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 342                         smp_processor_id(), duration,
 343                         current->comm, task_pid_nr(current));
 344                 __this_cpu_write(softlockup_task_ptr_saved, current);
 345                 print_modules();
 346                 print_irqtrace_events(current);
 347                 if (regs)
 348                         show_regs(regs);
 349                 else
 350                         dump_stack();
 351
 352                 if (softlockup_all_cpu_backtrace) {
 353                         /* Avoid generating two back traces for current
 354                          * given that one is already made above
 355                          */
 356                         trigger_allbutself_cpu_backtrace();
 357
 358                         clear_bit(0, &soft_lockup_nmi_warn);
 359                         /* Barrier to sync with other cpus */
 360                         smp_mb__after_atomic();
 361                 }
 362
 363                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 364                 if (softlockup_panic)
 365                         panic("softlockup: hung tasks");
 366                 __this_cpu_write(soft_watchdog_warn, true);
 367         } else
 368                 __this_cpu_write(soft_watchdog_warn, false);
 369
 370         return HRTIMER_RESTART;
 371 }
 372
 373 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 374 {
 375         struct sched_param param = { .sched_priority = prio };
 376
 377         sched_setscheduler(current, policy, &param);
 378 }
 379
 380 static void watchdog_enable(unsigned int cpu)
 381 {
 382         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 383
 384         /* kick off the timer for the hardlockup detector */
 385         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 386         hrtimer->function = watchdog_timer_fn;
 387
 388         /* Enable the perf event */
 389         watchdog_nmi_enable(cpu);
 390
 391         /* done here because hrtimer_start can only pin to smp_processor_id() */
 392         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 393                       HRTIMER_MODE_REL_PINNED);
 394
 395         /* initialize timestamp */
 396         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 397         __touch_watchdog();
 398 }
 399
 400 static void watchdog_disable(unsigned int cpu)
 401 {
 402         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 403
 404         watchdog_set_prio(SCHED_NORMAL, 0);
 405         hrtimer_cancel(hrtimer);
 406         /* disable the perf event */
 407         watchdog_nmi_disable(cpu);
 408 }
 409
 410 static void watchdog_cleanup(unsigned int cpu, bool online)
 411 {
 412         watchdog_disable(cpu);
 413 }
 414
 415 static int watchdog_should_run(unsigned int cpu)
 416 {
 417         return __this_cpu_read(hrtimer_interrupts) !=
 418                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 419 }
 420
 421 /*
 422  * The watchdog thread function - touches the timestamp.
 423  *
 424  * It only runs once every sample_period seconds (4 seconds by
 425  * default) to reset the softlockup timestamp. If this gets delayed
 426  * for more than 2*watchdog_thresh seconds then the debug-printout
 427  * triggers in watchdog_timer_fn().
 428  */
 429 static void watchdog(unsigned int cpu)
 430 {
 431         __this_cpu_write(soft_lockup_hrtimer_cnt,
 432                          __this_cpu_read(hrtimer_interrupts));
 433         __touch_watchdog();
 434
 435         /*
 436          * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
 437          * failure path. Check for failures that can occur asynchronously -
 438          * for example, when CPUs are on-lined - and shut down the hardware
 439          * perf event on each CPU accordingly.
 440          *
 441          * The only non-obvious place this bit can be cleared is through
 442          * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
 443          * pr_info here would be too noisy as it would result in a message
 444          * every few seconds if the hardlockup was disabled but the softlockup
 445          * enabled.
 446          */
 447         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 448                 watchdog_nmi_disable(cpu);
 449 }
 450
 451 static struct smp_hotplug_thread watchdog_threads = {
 452         .store                  = &softlockup_watchdog,
 453         .thread_should_run      = watchdog_should_run,
 454         .thread_fn              = watchdog,
 455         .thread_comm            = "watchdog/%u",
 456         .setup                  = watchdog_enable,
 457         .cleanup                = watchdog_cleanup,
 458         .park                   = watchdog_disable,
 459         .unpark                 = watchdog_enable,
 460 };
 461
 462 /*
 463  * park all watchdog threads that are specified in 'watchdog_cpumask'
 464  *
 465  * This function returns an error if kthread_park() of a watchdog thread
 466  * fails. In this situation, the watchdog threads of some CPUs can already
 467  * be parked and the watchdog threads of other CPUs can still be runnable.
 468  * Callers are expected to handle this special condition as appropriate in
 469  * their context.
 470  *
 471  * This function may only be called in a context that is protected against
 472  * races with CPU hotplug - for example, via get_online_cpus().
 473  */
 474 static int watchdog_park_threads(void)
 475 {
 476         int cpu, ret = 0;
 477
 478         atomic_set(&watchdog_park_in_progress, 1);
 479
 480         for_each_watchdog_cpu(cpu) {
 481                 ret = kthread_park(per_cpu(softlockup_watchdog, cpu));
 482                 if (ret)
 483                         break;
 484         }
 485
 486         atomic_set(&watchdog_park_in_progress, 0);
 487
 488         return ret;
 489 }
 490
 491 /*
 492  * unpark all watchdog threads that are specified in 'watchdog_cpumask'
 493  *
 494  * This function may only be called in a context that is protected against
 495  * races with CPU hotplug - for example, via get_online_cpus().
 496  */
 497 static void watchdog_unpark_threads(void)
 498 {
 499         int cpu;
 500
 501         for_each_watchdog_cpu(cpu)
 502                 kthread_unpark(per_cpu(softlockup_watchdog, cpu));
 503 }
 504
 505 /*
 506  * Suspend the hard and soft lockup detector by parking the watchdog threads.
 507  */
 508 int lockup_detector_suspend(void)
 509 {
 510         int ret = 0;
 511
 512         get_online_cpus();
 513         mutex_lock(&watchdog_proc_mutex);
 514         /*
 515          * Multiple suspend requests can be active in parallel (counted by
 516          * the 'watchdog_suspended' variable). If the watchdog threads are
 517          * running, the first caller takes care that they will be parked.
 518          * The state of 'watchdog_running' cannot change while a suspend
 519          * request is active (see related code in 'proc' handlers).
 520          */
 521         if (watchdog_running && !watchdog_suspended)
 522                 ret = watchdog_park_threads();
 523
 524         if (ret == 0)
 525                 watchdog_suspended++;
 526         else {
 527                 watchdog_disable_all_cpus();
 528                 pr_err("Failed to suspend lockup detectors, disabled\n");
 529                 watchdog_enabled = 0;
 530         }
 531
 532         mutex_unlock(&watchdog_proc_mutex);
 533
 534         return ret;
 535 }
 536
 537 /*
 538  * Resume the hard and soft lockup detector by unparking the watchdog threads.
 539  */
 540 void lockup_detector_resume(void)
 541 {
 542         mutex_lock(&watchdog_proc_mutex);
 543
 544         watchdog_suspended--;
 545         /*
 546          * The watchdog threads are unparked if they were previously running
 547          * and if there is no more active suspend request.
 548          */
 549         if (watchdog_running && !watchdog_suspended)
 550                 watchdog_unpark_threads();
 551
 552         mutex_unlock(&watchdog_proc_mutex);
 553         put_online_cpus();
 554 }
 555
 556 static int update_watchdog_all_cpus(void)
 557 {
 558         int ret;
 559
 560         ret = watchdog_park_threads();
 561         if (ret)
 562                 return ret;
 563
 564         watchdog_unpark_threads();
 565
 566         return 0;
 567 }
 568
 569 static int watchdog_enable_all_cpus(void)
 570 {
 571         int err = 0;
 572
 573         if (!watchdog_running) {
 574                 err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
 575                                                              &watchdog_cpumask);
 576                 if (err)
 577                         pr_err("Failed to create watchdog threads, disabled\n");
 578                 else
 579                         watchdog_running = 1;
 580         } else {
 581                 /*
 582                  * Enable/disable the lockup detectors or
 583                  * change the sample period 'on the fly'.
 584                  */
 585                 err = update_watchdog_all_cpus();
 586
 587                 if (err) {
 588                         watchdog_disable_all_cpus();
 589                         pr_err("Failed to update lockup detectors, disabled\n");
 590                 }
 591         }
 592
 593         if (err)
 594                 watchdog_enabled = 0;
 595
 596         return err;
 597 }
 598
 599 static void watchdog_disable_all_cpus(void)
 600 {
 601         if (watchdog_running) {
 602                 watchdog_running = 0;
 603                 smpboot_unregister_percpu_thread(&watchdog_threads);
 604         }
 605 }
 606
 607 #ifdef CONFIG_SYSCTL
 608
 609 /*
 610  * Update the run state of the lockup detectors.
 611  */
 612 static int proc_watchdog_update(void)
 613 {
 614         int err = 0;
 615
 616         /*
 617          * Watchdog threads won't be started if they are already active.
 618          * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
 619          * care of this. If those threads are already active, the sample
 620          * period will be updated and the lockup detectors will be enabled
 621          * or disabled 'on the fly'.
 622          */
 623         if (watchdog_enabled && watchdog_thresh)
 624                 err = watchdog_enable_all_cpus();
 625         else
 626                 watchdog_disable_all_cpus();
 627
 628         return err;
 629
 630 }
 631
 632 /*
 633  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 634  *
 635  * caller             | table->data points to | 'which' contains the flag(s)
 636  * -------------------|-----------------------|-----------------------------
 637  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 638  *                    |                       | with SOFT_WATCHDOG_ENABLED
 639  * -------------------|-----------------------|-----------------------------
 640  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 641  * -------------------|-----------------------|-----------------------------
 642  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 643  */
 644 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 645                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 646 {
 647         int err, old, new;
 648         int *watchdog_param = (int *)table->data;
 649
 650         get_online_cpus();
 651         mutex_lock(&watchdog_proc_mutex);
 652
 653         if (watchdog_suspended) {
 654                 /* no parameter changes allowed while watchdog is suspended */
 655                 err = -EAGAIN;
 656                 goto out;
 657         }
 658
 659         /*
 660          * If the parameter is being read return the state of the corresponding
 661          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
 662          * run state of the lockup detectors.
 663          */
 664         if (!write) {
 665                 *watchdog_param = (watchdog_enabled & which) != 0;
 666                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 667         } else {
 668                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 669                 if (err)
 670                         goto out;
 671
 672                 /*
 673                  * There is a race window between fetching the current value
 674                  * from 'watchdog_enabled' and storing the new value. During
 675                  * this race window, watchdog_nmi_enable() can sneak in and
 676                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
 677                  * The 'cmpxchg' detects this race and the loop retries.
 678                  */
 679                 do {
 680                         old = watchdog_enabled;
 681                         /*
 682                          * If the parameter value is not zero set the
 683                          * corresponding bit(s), else clear it(them).
 684                          */
 685                         if (*watchdog_param)
 686                                 new = old | which;
 687                         else
 688                                 new = old & ~which;
 689                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
 690
 691                 /*
 692                  * Update the run state of the lockup detectors. There is _no_
 693                  * need to check the value returned by proc_watchdog_update()
 694                  * and to restore the previous value of 'watchdog_enabled' as
 695                  * both lockup detectors are disabled if proc_watchdog_update()
 696                  * returns an error.
 697                  */
 698                 if (old == new)
 699                         goto out;
 700
 701                 err = proc_watchdog_update();
 702         }
 703 out:
 704         mutex_unlock(&watchdog_proc_mutex);
 705         put_online_cpus();
 706         return err;
 707 }
 708
 709 /*
 710  * /proc/sys/kernel/watchdog
 711  */
 712 int proc_watchdog(struct ctl_table *table, int write,
 713                   void __user *buffer, size_t *lenp, loff_t *ppos)
 714 {
 715         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 716                                     table, write, buffer, lenp, ppos);
 717 }
 718
 719 /*
 720  * /proc/sys/kernel/nmi_watchdog
 721  */
 722 int proc_nmi_watchdog(struct ctl_table *table, int write,
 723                       void __user *buffer, size_t *lenp, loff_t *ppos)
 724 {
 725         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 726                                     table, write, buffer, lenp, ppos);
 727 }
 728
 729 /*
 730  * /proc/sys/kernel/soft_watchdog
 731  */
 732 int proc_soft_watchdog(struct ctl_table *table, int write,
 733                         void __user *buffer, size_t *lenp, loff_t *ppos)
 734 {
 735         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 736                                     table, write, buffer, lenp, ppos);
 737 }
 738
 739 /*
 740  * /proc/sys/kernel/watchdog_thresh
 741  */
 742 int proc_watchdog_thresh(struct ctl_table *table, int write,
 743                          void __user *buffer, size_t *lenp, loff_t *ppos)
 744 {
 745         int err, old, new;
 746
 747         get_online_cpus();
 748         mutex_lock(&watchdog_proc_mutex);
 749
 750         if (watchdog_suspended) {
 751                 /* no parameter changes allowed while watchdog is suspended */
 752                 err = -EAGAIN;
 753                 goto out;
 754         }
 755
 756         old = ACCESS_ONCE(watchdog_thresh);
 757         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 758
 759         if (err || !write)
 760                 goto out;
 761
 762         /*
 763          * Update the sample period. Restore on failure.
 764          */
 765         new = ACCESS_ONCE(watchdog_thresh);
 766         if (old == new)
 767                 goto out;
 768
 769         set_sample_period();
 770         err = proc_watchdog_update();
 771         if (err) {
 772                 watchdog_thresh = old;
 773                 set_sample_period();
 774         }
 775 out:
 776         mutex_unlock(&watchdog_proc_mutex);
 777         put_online_cpus();
 778         return err;
 779 }
 780
 781 /*
 782  * The cpumask is the mask of possible cpus that the watchdog can run
 783  * on, not the mask of cpus it is actually running on.  This allows the
 784  * user to specify a mask that will include cpus that have not yet
 785  * been brought online, if desired.
 786  */
 787 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 788                           void __user *buffer, size_t *lenp, loff_t *ppos)
 789 {
 790         int err;
 791
 792         get_online_cpus();
 793         mutex_lock(&watchdog_proc_mutex);
 794
 795         if (watchdog_suspended) {
 796                 /* no parameter changes allowed while watchdog is suspended */
 797                 err = -EAGAIN;
 798                 goto out;
 799         }
 800
 801         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 802         if (!err && write) {
 803                 /* Remove impossible cpus to keep sysctl output cleaner. */
 804                 cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
 805                             cpu_possible_mask);
 806
 807                 if (watchdog_running) {
 808                         /*
 809                          * Failure would be due to being unable to allocate
 810                          * a temporary cpumask, so we are likely not in a
 811                          * position to do much else to make things better.
 812                          */
 813                         if (smpboot_update_cpumask_percpu_thread(
 814                                     &watchdog_threads, &watchdog_cpumask) != 0)
 815                                 pr_err("cpumask update failed\n");
 816                 }
 817         }
 818 out:
 819         mutex_unlock(&watchdog_proc_mutex);
 820         put_online_cpus();
 821         return err;
 822 }
 823
 824 #endif /* CONFIG_SYSCTL */
 825
 826 void __init lockup_detector_init(void)
 827 {
 828         set_sample_period();
 829
 830 #ifdef CONFIG_NO_HZ_FULL
 831         if (tick_nohz_full_enabled()) {
 832                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 833                 cpumask_copy(&watchdog_cpumask, housekeeping_mask);
 834         } else
 835                 cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 836 #else
 837         cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 838 #endif
 839
 840         if (watchdog_enabled)
 841                 watchdog_enable_all_cpus();
 842 }