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