kernel/watchdog.c

   1 /*
   2  * Detect hard and soft lockups on a system
   3  *
   4  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   5  *
   6  * Note: Most of this code is borrowed heavily from the original softlockup
   7  * detector, so thanks to Ingo for the initial implementation.
   8  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
   9  * to those contributors as well.
  10  */
  11
  12 #define pr_fmt(fmt) "watchdog: " fmt
  13
  14 #include <linux/mm.h>
  15 #include <linux/cpu.h>
  16 #include <linux/nmi.h>
  17 #include <linux/init.h>
  18 #include <linux/module.h>
  19 #include <linux/sysctl.h>
  20 #include <linux/smpboot.h>
  21 #include <linux/sched/rt.h>
  22 #include <uapi/linux/sched/types.h>
  23 #include <linux/tick.h>
  24 #include <linux/workqueue.h>
  25 #include <linux/sched/clock.h>
  26 #include <linux/sched/debug.h>
  27
  28 #include <asm/irq_regs.h>
  29 #include <linux/kvm_para.h>
  30 #include <linux/kthread.h>
  31
  32 /* Watchdog configuration */
  33 static DEFINE_MUTEX(watchdog_proc_mutex);
  34
  35 int __read_mostly nmi_watchdog_enabled;
  36
  37 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
  38 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED |
  39                                                 NMI_WATCHDOG_ENABLED;
  40 #else
  41 unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  42 #endif
  43
  44 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  45 /* boot commands */
  46 /*
  47  * Should we panic when a soft-lockup or hard-lockup occurs:
  48  */
  49 unsigned int __read_mostly hardlockup_panic =
  50                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  51 /*
  52  * We may not want to enable hard lockup detection by default in all cases,
  53  * for example when running the kernel as a guest on a hypervisor. In these
  54  * cases this function can be called to disable hard lockup detection. This
  55  * function should only be executed once by the boot processor before the
  56  * kernel command line parameters are parsed, because otherwise it is not
  57  * possible to override this in hardlockup_panic_setup().
  58  */
  59 void hardlockup_detector_disable(void)
  60 {
  61         watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  62 }
  63
  64 static int __init hardlockup_panic_setup(char *str)
  65 {
  66         if (!strncmp(str, "panic", 5))
  67                 hardlockup_panic = 1;
  68         else if (!strncmp(str, "nopanic", 7))
  69                 hardlockup_panic = 0;
  70         else if (!strncmp(str, "0", 1))
  71                 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  72         else if (!strncmp(str, "1", 1))
  73                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
  74         return 1;
  75 }
  76 __setup("nmi_watchdog=", hardlockup_panic_setup);
  77
  78 #endif
  79
  80 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
  81 int __read_mostly soft_watchdog_enabled;
  82 #endif
  83
  84 int __read_mostly watchdog_user_enabled;
  85 int __read_mostly watchdog_thresh = 10;
  86
  87 #ifdef CONFIG_SMP
  88 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  89 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
  90 #endif
  91 struct cpumask watchdog_cpumask __read_mostly;
  92 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
  93
  94 /*
  95  * The 'watchdog_running' variable is set to 1 when the watchdog threads
  96  * are registered/started and is set to 0 when the watchdog threads are
  97  * unregistered/stopped, so it is an indicator whether the threads exist.
  98  */
  99 static int __read_mostly watchdog_running;
 100 /*
 101  * If a subsystem has a need to deactivate the watchdog temporarily, it
 102  * can use the suspend/resume interface to achieve this. The content of
 103  * the 'watchdog_suspended' variable reflects this state. Existing threads
 104  * are parked/unparked by the lockup_detector_{suspend|resume} functions
 105  * (see comment blocks pertaining to those functions for further details).
 106  *
 107  * 'watchdog_suspended' also prevents threads from being registered/started
 108  * or unregistered/stopped via parameters in /proc/sys/kernel, so the state
 109  * of 'watchdog_running' cannot change while the watchdog is deactivated
 110  * temporarily (see related code in 'proc' handlers).
 111  */
 112 int __read_mostly watchdog_suspended;
 113
 114 /*
 115  * These functions can be overridden if an architecture implements its
 116  * own hardlockup detector.
 117  *
 118  * watchdog_nmi_enable/disable can be implemented to start and stop when
 119  * softlockup watchdog threads start and stop. The arch must select the
 120  * SOFTLOCKUP_DETECTOR Kconfig.
 121  */
 122 int __weak watchdog_nmi_enable(unsigned int cpu)
 123 {
 124         return 0;
 125 }
 126 void __weak watchdog_nmi_disable(unsigned int cpu)
 127 {
 128 }
 129
 130 /*
 131  * watchdog_nmi_reconfigure can be implemented to be notified after any
 132  * watchdog configuration change. The arch hardlockup watchdog should
 133  * respond to the following variables:
 134  * - nmi_watchdog_enabled
 135  * - watchdog_thresh
 136  * - watchdog_cpumask
 137  * - sysctl_hardlockup_all_cpu_backtrace
 138  * - hardlockup_panic
 139  * - watchdog_suspended
 140  */
 141 void __weak watchdog_nmi_reconfigure(void)
 142 {
 143 }
 144
 145
 146 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
 147
 148 /* Helper for online, unparked cpus. */
 149 #define for_each_watchdog_cpu(cpu) \
 150         for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
 151
 152 atomic_t watchdog_park_in_progress = ATOMIC_INIT(0);
 153
 154 static u64 __read_mostly sample_period;
 155
 156 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 157 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
 158 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 159 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 160 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 161 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 162 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
 163 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
 164 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 165 static unsigned long soft_lockup_nmi_warn;
 166
 167 unsigned int __read_mostly softlockup_panic =
 168                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 169
 170 static int __init softlockup_panic_setup(char *str)
 171 {
 172         softlockup_panic = simple_strtoul(str, NULL, 0);
 173
 174         return 1;
 175 }
 176 __setup("softlockup_panic=", softlockup_panic_setup);
 177
 178 static int __init nowatchdog_setup(char *str)
 179 {
 180         watchdog_enabled = 0;
 181         return 1;
 182 }
 183 __setup("nowatchdog", nowatchdog_setup);
 184
 185 static int __init nosoftlockup_setup(char *str)
 186 {
 187         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
 188         return 1;
 189 }
 190 __setup("nosoftlockup", nosoftlockup_setup);
 191
 192 #ifdef CONFIG_SMP
 193 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 194 {
 195         sysctl_softlockup_all_cpu_backtrace =
 196                 !!simple_strtol(str, NULL, 0);
 197         return 1;
 198 }
 199 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 200 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 201 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
 202 {
 203         sysctl_hardlockup_all_cpu_backtrace =
 204                 !!simple_strtol(str, NULL, 0);
 205         return 1;
 206 }
 207 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
 208 #endif
 209 #endif
 210
 211 /*
 212  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 213  * lockups can have false positives under extreme conditions. So we generally
 214  * want a higher threshold for soft lockups than for hard lockups. So we couple
 215  * the thresholds with a factor: we make the soft threshold twice the amount of
 216  * time the hard threshold is.
 217  */
 218 static int get_softlockup_thresh(void)
 219 {
 220         return watchdog_thresh * 2;
 221 }
 222
 223 /*
 224  * Returns seconds, approximately.  We don't need nanosecond
 225  * resolution, and we don't need to waste time with a big divide when
 226  * 2^30ns == 1.074s.
 227  */
 228 static unsigned long get_timestamp(void)
 229 {
 230         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 231 }
 232
 233 static void set_sample_period(void)
 234 {
 235         /*
 236          * convert watchdog_thresh from seconds to ns
 237          * the divide by 5 is to give hrtimer several chances (two
 238          * or three with the current relation between the soft
 239          * and hard thresholds) to increment before the
 240          * hardlockup detector generates a warning
 241          */
 242         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 243         watchdog_update_hrtimer_threshold(sample_period);
 244 }
 245
 246 /* Commands for resetting the watchdog */
 247 static void __touch_watchdog(void)
 248 {
 249         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 250 }
 251
 252 /**
 253  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 254  *
 255  * Call when the scheduler may have stalled for legitimate reasons
 256  * preventing the watchdog task from executing - e.g. the scheduler
 257  * entering idle state.  This should only be used for scheduler events.
 258  * Use touch_softlockup_watchdog() for everything else.
 259  */
 260 void touch_softlockup_watchdog_sched(void)
 261 {
 262         /*
 263          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 264          * gets zeroed here, so use the raw_ operation.
 265          */
 266         raw_cpu_write(watchdog_touch_ts, 0);
 267 }
 268
 269 void touch_softlockup_watchdog(void)
 270 {
 271         touch_softlockup_watchdog_sched();
 272         wq_watchdog_touch(raw_smp_processor_id());
 273 }
 274 EXPORT_SYMBOL(touch_softlockup_watchdog);
 275
 276 void touch_all_softlockup_watchdogs(void)
 277 {
 278         int cpu;
 279
 280         /*
 281          * this is done lockless
 282          * do we care if a 0 races with a timestamp?
 283          * all it means is the softlock check starts one cycle later
 284          */
 285         for_each_watchdog_cpu(cpu)
 286                 per_cpu(watchdog_touch_ts, cpu) = 0;
 287         wq_watchdog_touch(-1);
 288 }
 289
 290 void touch_softlockup_watchdog_sync(void)
 291 {
 292         __this_cpu_write(softlockup_touch_sync, true);
 293         __this_cpu_write(watchdog_touch_ts, 0);
 294 }
 295
 296 static int is_softlockup(unsigned long touch_ts)
 297 {
 298         unsigned long now = get_timestamp();
 299
 300         if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
 301                 /* Warn about unreasonable delays. */
 302                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 303                         return now - touch_ts;
 304         }
 305         return 0;
 306 }
 307
 308 /* watchdog detector functions */
 309 bool is_hardlockup(void)
 310 {
 311         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 312
 313         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 314                 return true;
 315
 316         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 317         return false;
 318 }
 319
 320 static void watchdog_interrupt_count(void)
 321 {
 322         __this_cpu_inc(hrtimer_interrupts);
 323 }
 324
 325 static int watchdog_enable_all_cpus(void);
 326 static void watchdog_disable_all_cpus(void);
 327
 328 /* watchdog kicker functions */
 329 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 330 {
 331         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 332         struct pt_regs *regs = get_irq_regs();
 333         int duration;
 334         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 335
 336         if (!watchdog_enabled ||
 337             atomic_read(&watchdog_park_in_progress) != 0)
 338                 return HRTIMER_NORESTART;
 339
 340         /* kick the hardlockup detector */
 341         watchdog_interrupt_count();
 342
 343         /* kick the softlockup detector */
 344         wake_up_process(__this_cpu_read(softlockup_watchdog));
 345
 346         /* .. and repeat */
 347         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 348
 349         if (touch_ts == 0) {
 350                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 351                         /*
 352                          * If the time stamp was touched atomically
 353                          * make sure the scheduler tick is up to date.
 354                          */
 355                         __this_cpu_write(softlockup_touch_sync, false);
 356                         sched_clock_tick();
 357                 }
 358
 359                 /* Clear the guest paused flag on watchdog reset */
 360                 kvm_check_and_clear_guest_paused();
 361                 __touch_watchdog();
 362                 return HRTIMER_RESTART;
 363         }
 364
 365         /* check for a softlockup
 366          * This is done by making sure a high priority task is
 367          * being scheduled.  The task touches the watchdog to
 368          * indicate it is getting cpu time.  If it hasn't then
 369          * this is a good indication some task is hogging the cpu
 370          */
 371         duration = is_softlockup(touch_ts);
 372         if (unlikely(duration)) {
 373                 /*
 374                  * If a virtual machine is stopped by the host it can look to
 375                  * the watchdog like a soft lockup, check to see if the host
 376                  * stopped the vm before we issue the warning
 377                  */
 378                 if (kvm_check_and_clear_guest_paused())
 379                         return HRTIMER_RESTART;
 380
 381                 /* only warn once */
 382                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 383                         /*
 384                          * When multiple processes are causing softlockups the
 385                          * softlockup detector only warns on the first one
 386                          * because the code relies on a full quiet cycle to
 387                          * re-arm.  The second process prevents the quiet cycle
 388                          * and never gets reported.  Use task pointers to detect
 389                          * this.
 390                          */
 391                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 392                             current) {
 393                                 __this_cpu_write(soft_watchdog_warn, false);
 394                                 __touch_watchdog();
 395                         }
 396                         return HRTIMER_RESTART;
 397                 }
 398
 399                 if (softlockup_all_cpu_backtrace) {
 400                         /* Prevent multiple soft-lockup reports if one cpu is already
 401                          * engaged in dumping cpu back traces
 402                          */
 403                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 404                                 /* Someone else will report us. Let's give up */
 405                                 __this_cpu_write(soft_watchdog_warn, true);
 406                                 return HRTIMER_RESTART;
 407                         }
 408                 }
 409
 410                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 411                         smp_processor_id(), duration,
 412                         current->comm, task_pid_nr(current));
 413                 __this_cpu_write(softlockup_task_ptr_saved, current);
 414                 print_modules();
 415                 print_irqtrace_events(current);
 416                 if (regs)
 417                         show_regs(regs);
 418                 else
 419                         dump_stack();
 420
 421                 if (softlockup_all_cpu_backtrace) {
 422                         /* Avoid generating two back traces for current
 423                          * given that one is already made above
 424                          */
 425                         trigger_allbutself_cpu_backtrace();
 426
 427                         clear_bit(0, &soft_lockup_nmi_warn);
 428                         /* Barrier to sync with other cpus */
 429                         smp_mb__after_atomic();
 430                 }
 431
 432                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 433                 if (softlockup_panic)
 434                         panic("softlockup: hung tasks");
 435                 __this_cpu_write(soft_watchdog_warn, true);
 436         } else
 437                 __this_cpu_write(soft_watchdog_warn, false);
 438
 439         return HRTIMER_RESTART;
 440 }
 441
 442 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 443 {
 444         struct sched_param param = { .sched_priority = prio };
 445
 446         sched_setscheduler(current, policy, &param);
 447 }
 448
 449 static void watchdog_enable(unsigned int cpu)
 450 {
 451         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 452
 453         /* kick off the timer for the hardlockup detector */
 454         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 455         hrtimer->function = watchdog_timer_fn;
 456
 457         /* Enable the perf event */
 458         watchdog_nmi_enable(cpu);
 459
 460         /* done here because hrtimer_start can only pin to smp_processor_id() */
 461         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 462                       HRTIMER_MODE_REL_PINNED);
 463
 464         /* initialize timestamp */
 465         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 466         __touch_watchdog();
 467 }
 468
 469 static void watchdog_disable(unsigned int cpu)
 470 {
 471         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 472
 473         watchdog_set_prio(SCHED_NORMAL, 0);
 474         hrtimer_cancel(hrtimer);
 475         /* disable the perf event */
 476         watchdog_nmi_disable(cpu);
 477 }
 478
 479 static void watchdog_cleanup(unsigned int cpu, bool online)
 480 {
 481         watchdog_disable(cpu);
 482 }
 483
 484 static int watchdog_should_run(unsigned int cpu)
 485 {
 486         return __this_cpu_read(hrtimer_interrupts) !=
 487                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 488 }
 489
 490 /*
 491  * The watchdog thread function - touches the timestamp.
 492  *
 493  * It only runs once every sample_period seconds (4 seconds by
 494  * default) to reset the softlockup timestamp. If this gets delayed
 495  * for more than 2*watchdog_thresh seconds then the debug-printout
 496  * triggers in watchdog_timer_fn().
 497  */
 498 static void watchdog(unsigned int cpu)
 499 {
 500         __this_cpu_write(soft_lockup_hrtimer_cnt,
 501                          __this_cpu_read(hrtimer_interrupts));
 502         __touch_watchdog();
 503
 504         /*
 505          * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
 506          * failure path. Check for failures that can occur asynchronously -
 507          * for example, when CPUs are on-lined - and shut down the hardware
 508          * perf event on each CPU accordingly.
 509          *
 510          * The only non-obvious place this bit can be cleared is through
 511          * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
 512          * pr_info here would be too noisy as it would result in a message
 513          * every few seconds if the hardlockup was disabled but the softlockup
 514          * enabled.
 515          */
 516         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 517                 watchdog_nmi_disable(cpu);
 518 }
 519
 520 static struct smp_hotplug_thread watchdog_threads = {
 521         .store                  = &softlockup_watchdog,
 522         .thread_should_run      = watchdog_should_run,
 523         .thread_fn              = watchdog,
 524         .thread_comm            = "watchdog/%u",
 525         .setup                  = watchdog_enable,
 526         .cleanup                = watchdog_cleanup,
 527         .park                   = watchdog_disable,
 528         .unpark                 = watchdog_enable,
 529 };
 530
 531 /*
 532  * park all watchdog threads that are specified in 'watchdog_cpumask'
 533  *
 534  * This function returns an error if kthread_park() of a watchdog thread
 535  * fails. In this situation, the watchdog threads of some CPUs can already
 536  * be parked and the watchdog threads of other CPUs can still be runnable.
 537  * Callers are expected to handle this special condition as appropriate in
 538  * their context.
 539  *
 540  * This function may only be called in a context that is protected against
 541  * races with CPU hotplug - for example, via get_online_cpus().
 542  */
 543 static int watchdog_park_threads(void)
 544 {
 545         int cpu, ret = 0;
 546
 547         atomic_set(&watchdog_park_in_progress, 1);
 548
 549         for_each_watchdog_cpu(cpu) {
 550                 ret = kthread_park(per_cpu(softlockup_watchdog, cpu));
 551                 if (ret)
 552                         break;
 553         }
 554
 555         atomic_set(&watchdog_park_in_progress, 0);
 556
 557         return ret;
 558 }
 559
 560 /*
 561  * unpark all watchdog threads that are specified in 'watchdog_cpumask'
 562  *
 563  * This function may only be called in a context that is protected against
 564  * races with CPU hotplug - for example, via get_online_cpus().
 565  */
 566 static void watchdog_unpark_threads(void)
 567 {
 568         int cpu;
 569
 570         for_each_watchdog_cpu(cpu)
 571                 kthread_unpark(per_cpu(softlockup_watchdog, cpu));
 572 }
 573
 574 static int update_watchdog_all_cpus(void)
 575 {
 576         int ret;
 577
 578         ret = watchdog_park_threads();
 579         if (ret)
 580                 return ret;
 581
 582         watchdog_unpark_threads();
 583
 584         return 0;
 585 }
 586
 587 static int watchdog_enable_all_cpus(void)
 588 {
 589         int err = 0;
 590
 591         if (!watchdog_running) {
 592                 err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
 593                                                              &watchdog_cpumask);
 594                 if (err)
 595                         pr_err("Failed to create watchdog threads, disabled\n");
 596                 else
 597                         watchdog_running = 1;
 598         } else {
 599                 /*
 600                  * Enable/disable the lockup detectors or
 601                  * change the sample period 'on the fly'.
 602                  */
 603                 err = update_watchdog_all_cpus();
 604
 605                 if (err) {
 606                         watchdog_disable_all_cpus();
 607                         pr_err("Failed to update lockup detectors, disabled\n");
 608                 }
 609         }
 610
 611         if (err)
 612                 watchdog_enabled = 0;
 613
 614         return err;
 615 }
 616
 617 static void watchdog_disable_all_cpus(void)
 618 {
 619         if (watchdog_running) {
 620                 watchdog_running = 0;
 621                 smpboot_unregister_percpu_thread(&watchdog_threads);
 622         }
 623 }
 624
 625 #ifdef CONFIG_SYSCTL
 626 static int watchdog_update_cpus(void)
 627 {
 628         return smpboot_update_cpumask_percpu_thread(
 629                     &watchdog_threads, &watchdog_cpumask);
 630 }
 631 #endif
 632
 633 #else /* SOFTLOCKUP */
 634 static int watchdog_park_threads(void)
 635 {
 636         return 0;
 637 }
 638
 639 static void watchdog_unpark_threads(void)
 640 {
 641 }
 642
 643 static int watchdog_enable_all_cpus(void)
 644 {
 645         return 0;
 646 }
 647
 648 static void watchdog_disable_all_cpus(void)
 649 {
 650 }
 651
 652 #ifdef CONFIG_SYSCTL
 653 static int watchdog_update_cpus(void)
 654 {
 655         return 0;
 656 }
 657 #endif
 658
 659 static void set_sample_period(void)
 660 {
 661 }
 662 #endif /* SOFTLOCKUP */
 663
 664 /**
 665  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 666  *
 667  * Special interface for parisc. It prevents lockup detector warnings from
 668  * the default pm_poweroff() function which busy loops forever.
 669  */
 670 void lockup_detector_soft_poweroff(void)
 671 {
 672         watchdog_enabled = 0;
 673 }
 674
 675 /*
 676  * Suspend the hard and soft lockup detector by parking the watchdog threads.
 677  */
 678 int lockup_detector_suspend(void)
 679 {
 680         int ret = 0;
 681
 682         get_online_cpus();
 683         mutex_lock(&watchdog_proc_mutex);
 684         /*
 685          * Multiple suspend requests can be active in parallel (counted by
 686          * the 'watchdog_suspended' variable). If the watchdog threads are
 687          * running, the first caller takes care that they will be parked.
 688          * The state of 'watchdog_running' cannot change while a suspend
 689          * request is active (see related code in 'proc' handlers).
 690          */
 691         if (watchdog_running && !watchdog_suspended)
 692                 ret = watchdog_park_threads();
 693
 694         if (ret == 0)
 695                 watchdog_suspended++;
 696         else {
 697                 watchdog_disable_all_cpus();
 698                 pr_err("Failed to suspend lockup detectors, disabled\n");
 699                 watchdog_enabled = 0;
 700         }
 701
 702         watchdog_nmi_reconfigure();
 703
 704         mutex_unlock(&watchdog_proc_mutex);
 705
 706         return ret;
 707 }
 708
 709 /*
 710  * Resume the hard and soft lockup detector by unparking the watchdog threads.
 711  */
 712 void lockup_detector_resume(void)
 713 {
 714         mutex_lock(&watchdog_proc_mutex);
 715
 716         watchdog_suspended--;
 717         /*
 718          * The watchdog threads are unparked if they were previously running
 719          * and if there is no more active suspend request.
 720          */
 721         if (watchdog_running && !watchdog_suspended)
 722                 watchdog_unpark_threads();
 723
 724         watchdog_nmi_reconfigure();
 725
 726         mutex_unlock(&watchdog_proc_mutex);
 727         put_online_cpus();
 728 }
 729
 730 #ifdef CONFIG_SYSCTL
 731
 732 /*
 733  * Update the run state of the lockup detectors.
 734  */
 735 static int proc_watchdog_update(void)
 736 {
 737         int err = 0;
 738
 739         /*
 740          * Watchdog threads won't be started if they are already active.
 741          * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
 742          * care of this. If those threads are already active, the sample
 743          * period will be updated and the lockup detectors will be enabled
 744          * or disabled 'on the fly'.
 745          */
 746         if (watchdog_enabled && watchdog_thresh)
 747                 err = watchdog_enable_all_cpus();
 748         else
 749                 watchdog_disable_all_cpus();
 750
 751         watchdog_nmi_reconfigure();
 752
 753         return err;
 754
 755 }
 756
 757 /*
 758  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 759  *
 760  * caller             | table->data points to | 'which' contains the flag(s)
 761  * -------------------|-----------------------|-----------------------------
 762  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 763  *                    |                       | with SOFT_WATCHDOG_ENABLED
 764  * -------------------|-----------------------|-----------------------------
 765  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 766  * -------------------|-----------------------|-----------------------------
 767  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 768  */
 769 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 770                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 771 {
 772         int err, old, new;
 773         int *watchdog_param = (int *)table->data;
 774
 775         get_online_cpus();
 776         mutex_lock(&watchdog_proc_mutex);
 777
 778         if (watchdog_suspended) {
 779                 /* no parameter changes allowed while watchdog is suspended */
 780                 err = -EAGAIN;
 781                 goto out;
 782         }
 783
 784         /*
 785          * If the parameter is being read return the state of the corresponding
 786          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
 787          * run state of the lockup detectors.
 788          */
 789         if (!write) {
 790                 *watchdog_param = (watchdog_enabled & which) != 0;
 791                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 792         } else {
 793                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 794                 if (err)
 795                         goto out;
 796
 797                 /*
 798                  * There is a race window between fetching the current value
 799                  * from 'watchdog_enabled' and storing the new value. During
 800                  * this race window, watchdog_nmi_enable() can sneak in and
 801                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
 802                  * The 'cmpxchg' detects this race and the loop retries.
 803                  */
 804                 do {
 805                         old = watchdog_enabled;
 806                         /*
 807                          * If the parameter value is not zero set the
 808                          * corresponding bit(s), else clear it(them).
 809                          */
 810                         if (*watchdog_param)
 811                                 new = old | which;
 812                         else
 813                                 new = old & ~which;
 814                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
 815
 816                 /*
 817                  * Update the run state of the lockup detectors. There is _no_
 818                  * need to check the value returned by proc_watchdog_update()
 819                  * and to restore the previous value of 'watchdog_enabled' as
 820                  * both lockup detectors are disabled if proc_watchdog_update()
 821                  * returns an error.
 822                  */
 823                 if (old == new)
 824                         goto out;
 825
 826                 err = proc_watchdog_update();
 827         }
 828 out:
 829         mutex_unlock(&watchdog_proc_mutex);
 830         put_online_cpus();
 831         return err;
 832 }
 833
 834 /*
 835  * /proc/sys/kernel/watchdog
 836  */
 837 int proc_watchdog(struct ctl_table *table, int write,
 838                   void __user *buffer, size_t *lenp, loff_t *ppos)
 839 {
 840         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 841                                     table, write, buffer, lenp, ppos);
 842 }
 843
 844 /*
 845  * /proc/sys/kernel/nmi_watchdog
 846  */
 847 int proc_nmi_watchdog(struct ctl_table *table, int write,
 848                       void __user *buffer, size_t *lenp, loff_t *ppos)
 849 {
 850         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
 851                                     table, write, buffer, lenp, ppos);
 852 }
 853
 854 /*
 855  * /proc/sys/kernel/soft_watchdog
 856  */
 857 int proc_soft_watchdog(struct ctl_table *table, int write,
 858                         void __user *buffer, size_t *lenp, loff_t *ppos)
 859 {
 860         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 861                                     table, write, buffer, lenp, ppos);
 862 }
 863
 864 /*
 865  * /proc/sys/kernel/watchdog_thresh
 866  */
 867 int proc_watchdog_thresh(struct ctl_table *table, int write,
 868                          void __user *buffer, size_t *lenp, loff_t *ppos)
 869 {
 870         int err, old, new;
 871
 872         get_online_cpus();
 873         mutex_lock(&watchdog_proc_mutex);
 874
 875         if (watchdog_suspended) {
 876                 /* no parameter changes allowed while watchdog is suspended */
 877                 err = -EAGAIN;
 878                 goto out;
 879         }
 880
 881         old = ACCESS_ONCE(watchdog_thresh);
 882         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 883
 884         if (err || !write)
 885                 goto out;
 886
 887         /*
 888          * Update the sample period. Restore on failure.
 889          */
 890         new = ACCESS_ONCE(watchdog_thresh);
 891         if (old == new)
 892                 goto out;
 893
 894         set_sample_period();
 895         err = proc_watchdog_update();
 896         if (err) {
 897                 watchdog_thresh = old;
 898                 set_sample_period();
 899         }
 900 out:
 901         mutex_unlock(&watchdog_proc_mutex);
 902         put_online_cpus();
 903         return err;
 904 }
 905
 906 /*
 907  * The cpumask is the mask of possible cpus that the watchdog can run
 908  * on, not the mask of cpus it is actually running on.  This allows the
 909  * user to specify a mask that will include cpus that have not yet
 910  * been brought online, if desired.
 911  */
 912 int proc_watchdog_cpumask(struct ctl_table *table, int write,
 913                           void __user *buffer, size_t *lenp, loff_t *ppos)
 914 {
 915         int err;
 916
 917         get_online_cpus();
 918         mutex_lock(&watchdog_proc_mutex);
 919
 920         if (watchdog_suspended) {
 921                 /* no parameter changes allowed while watchdog is suspended */
 922                 err = -EAGAIN;
 923                 goto out;
 924         }
 925
 926         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
 927         if (!err && write) {
 928                 /* Remove impossible cpus to keep sysctl output cleaner. */
 929                 cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
 930                             cpu_possible_mask);
 931
 932                 if (watchdog_running) {
 933                         /*
 934                          * Failure would be due to being unable to allocate
 935                          * a temporary cpumask, so we are likely not in a
 936                          * position to do much else to make things better.
 937                          */
 938                         if (watchdog_update_cpus() != 0)
 939                                 pr_err("cpumask update failed\n");
 940                 }
 941
 942                 watchdog_nmi_reconfigure();
 943         }
 944 out:
 945         mutex_unlock(&watchdog_proc_mutex);
 946         put_online_cpus();
 947         return err;
 948 }
 949
 950 #endif /* CONFIG_SYSCTL */
 951
 952 void __init lockup_detector_init(void)
 953 {
 954         set_sample_period();
 955
 956 #ifdef CONFIG_NO_HZ_FULL
 957         if (tick_nohz_full_enabled()) {
 958                 pr_info("Disabling watchdog on nohz_full cores by default\n");
 959                 cpumask_copy(&watchdog_cpumask, housekeeping_mask);
 960         } else
 961                 cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 962 #else
 963         cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
 964 #endif
 965
 966         if (watchdog_enabled)
 967                 watchdog_enable_all_cpus();
 968 }