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
  23 #include <asm/irq_regs.h>
  24 #include <linux/kvm_para.h>
  25 #include <linux/perf_event.h>
  26
  27 /*
  28  * The run state of the lockup detectors is controlled by the content of the
  29  * 'watchdog_enabled' variable. Each lockup detector has its dedicated bit -
  30  * bit 0 for the hard lockup detector and bit 1 for the soft lockup detector.
  31  *
  32  * 'watchdog_user_enabled', 'nmi_watchdog_enabled' and 'soft_watchdog_enabled'
  33  * are variables that are only used as an 'interface' between the parameters
  34  * in /proc/sys/kernel and the internal state bits in 'watchdog_enabled'. The
  35  * 'watchdog_thresh' variable is handled differently because its value is not
  36  * boolean, and the lockup detectors are 'suspended' while 'watchdog_thresh'
  37  * is equal zero.
  38  */
  39 #define NMI_WATCHDOG_ENABLED_BIT   0
  40 #define SOFT_WATCHDOG_ENABLED_BIT  1
  41 #define NMI_WATCHDOG_ENABLED      (1 << NMI_WATCHDOG_ENABLED_BIT)
  42 #define SOFT_WATCHDOG_ENABLED     (1 << SOFT_WATCHDOG_ENABLED_BIT)
  43
  44 static DEFINE_MUTEX(watchdog_proc_mutex);
  45
  46 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  47 static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
  48 #else
  49 static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
  50 #endif
  51 int __read_mostly nmi_watchdog_enabled;
  52 int __read_mostly soft_watchdog_enabled;
  53 int __read_mostly watchdog_user_enabled;
  54 int __read_mostly watchdog_thresh = 10;
  55
  56 #ifdef CONFIG_SMP
  57 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
  58 #else
  59 #define sysctl_softlockup_all_cpu_backtrace 0
  60 #endif
  61
  62 static int __read_mostly watchdog_running;
  63 static u64 __read_mostly sample_period;
  64
  65 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
  66 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
  67 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
  68 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
  69 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
  70 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
  71 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
  72 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
  73 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  74 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  75 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  76 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
  77 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  78 #endif
  79 static unsigned long soft_lockup_nmi_warn;
  80
  81 /* boot commands */
  82 /*
  83  * Should we panic when a soft-lockup or hard-lockup occurs:
  84  */
  85 #ifdef CONFIG_HARDLOCKUP_DETECTOR
  86 static int hardlockup_panic =
  87                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
  88 /*
  89  * We may not want to enable hard lockup detection by default in all cases,
  90  * for example when running the kernel as a guest on a hypervisor. In these
  91  * cases this function can be called to disable hard lockup detection. This
  92  * function should only be executed once by the boot processor before the
  93  * kernel command line parameters are parsed, because otherwise it is not
  94  * possible to override this in hardlockup_panic_setup().
  95  */
  96 void hardlockup_detector_disable(void)
  97 {
  98         watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
  99 }
 100
 101 static int __init hardlockup_panic_setup(char *str)
 102 {
 103         if (!strncmp(str, "panic", 5))
 104                 hardlockup_panic = 1;
 105         else if (!strncmp(str, "nopanic", 7))
 106                 hardlockup_panic = 0;
 107         else if (!strncmp(str, "0", 1))
 108                 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
 109         else if (!strncmp(str, "1", 1))
 110                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
 111         return 1;
 112 }
 113 __setup("nmi_watchdog=", hardlockup_panic_setup);
 114 #endif
 115
 116 unsigned int __read_mostly softlockup_panic =
 117                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
 118
 119 static int __init softlockup_panic_setup(char *str)
 120 {
 121         softlockup_panic = simple_strtoul(str, NULL, 0);
 122
 123         return 1;
 124 }
 125 __setup("softlockup_panic=", softlockup_panic_setup);
 126
 127 static int __init nowatchdog_setup(char *str)
 128 {
 129         watchdog_enabled = 0;
 130         return 1;
 131 }
 132 __setup("nowatchdog", nowatchdog_setup);
 133
 134 static int __init nosoftlockup_setup(char *str)
 135 {
 136         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
 137         return 1;
 138 }
 139 __setup("nosoftlockup", nosoftlockup_setup);
 140
 141 #ifdef CONFIG_SMP
 142 static int __init softlockup_all_cpu_backtrace_setup(char *str)
 143 {
 144         sysctl_softlockup_all_cpu_backtrace =
 145                 !!simple_strtol(str, NULL, 0);
 146         return 1;
 147 }
 148 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
 149 #endif
 150
 151 /*
 152  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 153  * lockups can have false positives under extreme conditions. So we generally
 154  * want a higher threshold for soft lockups than for hard lockups. So we couple
 155  * the thresholds with a factor: we make the soft threshold twice the amount of
 156  * time the hard threshold is.
 157  */
 158 static int get_softlockup_thresh(void)
 159 {
 160         return watchdog_thresh * 2;
 161 }
 162
 163 /*
 164  * Returns seconds, approximately.  We don't need nanosecond
 165  * resolution, and we don't need to waste time with a big divide when
 166  * 2^30ns == 1.074s.
 167  */
 168 static unsigned long get_timestamp(void)
 169 {
 170         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
 171 }
 172
 173 static void set_sample_period(void)
 174 {
 175         /*
 176          * convert watchdog_thresh from seconds to ns
 177          * the divide by 5 is to give hrtimer several chances (two
 178          * or three with the current relation between the soft
 179          * and hard thresholds) to increment before the
 180          * hardlockup detector generates a warning
 181          */
 182         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
 183 }
 184
 185 /* Commands for resetting the watchdog */
 186 static void __touch_watchdog(void)
 187 {
 188         __this_cpu_write(watchdog_touch_ts, get_timestamp());
 189 }
 190
 191 void touch_softlockup_watchdog(void)
 192 {
 193         /*
 194          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
 195          * gets zeroed here, so use the raw_ operation.
 196          */
 197         raw_cpu_write(watchdog_touch_ts, 0);
 198 }
 199 EXPORT_SYMBOL(touch_softlockup_watchdog);
 200
 201 void touch_all_softlockup_watchdogs(void)
 202 {
 203         int cpu;
 204
 205         /*
 206          * this is done lockless
 207          * do we care if a 0 races with a timestamp?
 208          * all it means is the softlock check starts one cycle later
 209          */
 210         for_each_online_cpu(cpu)
 211                 per_cpu(watchdog_touch_ts, cpu) = 0;
 212 }
 213
 214 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 215 void touch_nmi_watchdog(void)
 216 {
 217         /*
 218          * Using __raw here because some code paths have
 219          * preemption enabled.  If preemption is enabled
 220          * then interrupts should be enabled too, in which
 221          * case we shouldn't have to worry about the watchdog
 222          * going off.
 223          */
 224         raw_cpu_write(watchdog_nmi_touch, true);
 225         touch_softlockup_watchdog();
 226 }
 227 EXPORT_SYMBOL(touch_nmi_watchdog);
 228
 229 #endif
 230
 231 void touch_softlockup_watchdog_sync(void)
 232 {
 233         __this_cpu_write(softlockup_touch_sync, true);
 234         __this_cpu_write(watchdog_touch_ts, 0);
 235 }
 236
 237 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 238 /* watchdog detector functions */
 239 static int is_hardlockup(void)
 240 {
 241         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
 242
 243         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
 244                 return 1;
 245
 246         __this_cpu_write(hrtimer_interrupts_saved, hrint);
 247         return 0;
 248 }
 249 #endif
 250
 251 static int is_softlockup(unsigned long touch_ts)
 252 {
 253         unsigned long now = get_timestamp();
 254
 255         if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) {
 256                 /* Warn about unreasonable delays. */
 257                 if (time_after(now, touch_ts + get_softlockup_thresh()))
 258                         return now - touch_ts;
 259         }
 260         return 0;
 261 }
 262
 263 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 264
 265 static struct perf_event_attr wd_hw_attr = {
 266         .type           = PERF_TYPE_HARDWARE,
 267         .config         = PERF_COUNT_HW_CPU_CYCLES,
 268         .size           = sizeof(struct perf_event_attr),
 269         .pinned         = 1,
 270         .disabled       = 1,
 271 };
 272
 273 /* Callback function for perf event subsystem */
 274 static void watchdog_overflow_callback(struct perf_event *event,
 275                  struct perf_sample_data *data,
 276                  struct pt_regs *regs)
 277 {
 278         /* Ensure the watchdog never gets throttled */
 279         event->hw.interrupts = 0;
 280
 281         if (__this_cpu_read(watchdog_nmi_touch) == true) {
 282                 __this_cpu_write(watchdog_nmi_touch, false);
 283                 return;
 284         }
 285
 286         /* check for a hardlockup
 287          * This is done by making sure our timer interrupt
 288          * is incrementing.  The timer interrupt should have
 289          * fired multiple times before we overflow'd.  If it hasn't
 290          * then this is a good indication the cpu is stuck
 291          */
 292         if (is_hardlockup()) {
 293                 int this_cpu = smp_processor_id();
 294
 295                 /* only print hardlockups once */
 296                 if (__this_cpu_read(hard_watchdog_warn) == true)
 297                         return;
 298
 299                 if (hardlockup_panic)
 300                         panic("Watchdog detected hard LOCKUP on cpu %d",
 301                               this_cpu);
 302                 else
 303                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
 304                              this_cpu);
 305
 306                 __this_cpu_write(hard_watchdog_warn, true);
 307                 return;
 308         }
 309
 310         __this_cpu_write(hard_watchdog_warn, false);
 311         return;
 312 }
 313 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 314
 315 static void watchdog_interrupt_count(void)
 316 {
 317         __this_cpu_inc(hrtimer_interrupts);
 318 }
 319
 320 static int watchdog_nmi_enable(unsigned int cpu);
 321 static void watchdog_nmi_disable(unsigned int cpu);
 322
 323 /* watchdog kicker functions */
 324 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 325 {
 326         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
 327         struct pt_regs *regs = get_irq_regs();
 328         int duration;
 329         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
 330
 331         /* kick the hardlockup detector */
 332         watchdog_interrupt_count();
 333
 334         /* kick the softlockup detector */
 335         wake_up_process(__this_cpu_read(softlockup_watchdog));
 336
 337         /* .. and repeat */
 338         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
 339
 340         if (touch_ts == 0) {
 341                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
 342                         /*
 343                          * If the time stamp was touched atomically
 344                          * make sure the scheduler tick is up to date.
 345                          */
 346                         __this_cpu_write(softlockup_touch_sync, false);
 347                         sched_clock_tick();
 348                 }
 349
 350                 /* Clear the guest paused flag on watchdog reset */
 351                 kvm_check_and_clear_guest_paused();
 352                 __touch_watchdog();
 353                 return HRTIMER_RESTART;
 354         }
 355
 356         /* check for a softlockup
 357          * This is done by making sure a high priority task is
 358          * being scheduled.  The task touches the watchdog to
 359          * indicate it is getting cpu time.  If it hasn't then
 360          * this is a good indication some task is hogging the cpu
 361          */
 362         duration = is_softlockup(touch_ts);
 363         if (unlikely(duration)) {
 364                 /*
 365                  * If a virtual machine is stopped by the host it can look to
 366                  * the watchdog like a soft lockup, check to see if the host
 367                  * stopped the vm before we issue the warning
 368                  */
 369                 if (kvm_check_and_clear_guest_paused())
 370                         return HRTIMER_RESTART;
 371
 372                 /* only warn once */
 373                 if (__this_cpu_read(soft_watchdog_warn) == true) {
 374                         /*
 375                          * When multiple processes are causing softlockups the
 376                          * softlockup detector only warns on the first one
 377                          * because the code relies on a full quiet cycle to
 378                          * re-arm.  The second process prevents the quiet cycle
 379                          * and never gets reported.  Use task pointers to detect
 380                          * this.
 381                          */
 382                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
 383                             current) {
 384                                 __this_cpu_write(soft_watchdog_warn, false);
 385                                 __touch_watchdog();
 386                         }
 387                         return HRTIMER_RESTART;
 388                 }
 389
 390                 if (softlockup_all_cpu_backtrace) {
 391                         /* Prevent multiple soft-lockup reports if one cpu is already
 392                          * engaged in dumping cpu back traces
 393                          */
 394                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
 395                                 /* Someone else will report us. Let's give up */
 396                                 __this_cpu_write(soft_watchdog_warn, true);
 397                                 return HRTIMER_RESTART;
 398                         }
 399                 }
 400
 401                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 402                         smp_processor_id(), duration,
 403                         current->comm, task_pid_nr(current));
 404                 __this_cpu_write(softlockup_task_ptr_saved, current);
 405                 print_modules();
 406                 print_irqtrace_events(current);
 407                 if (regs)
 408                         show_regs(regs);
 409                 else
 410                         dump_stack();
 411
 412                 if (softlockup_all_cpu_backtrace) {
 413                         /* Avoid generating two back traces for current
 414                          * given that one is already made above
 415                          */
 416                         trigger_allbutself_cpu_backtrace();
 417
 418                         clear_bit(0, &soft_lockup_nmi_warn);
 419                         /* Barrier to sync with other cpus */
 420                         smp_mb__after_atomic();
 421                 }
 422
 423                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 424                 if (softlockup_panic)
 425                         panic("softlockup: hung tasks");
 426                 __this_cpu_write(soft_watchdog_warn, true);
 427         } else
 428                 __this_cpu_write(soft_watchdog_warn, false);
 429
 430         return HRTIMER_RESTART;
 431 }
 432
 433 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
 434 {
 435         struct sched_param param = { .sched_priority = prio };
 436
 437         sched_setscheduler(current, policy, &param);
 438 }
 439
 440 static void watchdog_enable(unsigned int cpu)
 441 {
 442         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 443
 444         /* kick off the timer for the hardlockup detector */
 445         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 446         hrtimer->function = watchdog_timer_fn;
 447
 448         /* Enable the perf event */
 449         watchdog_nmi_enable(cpu);
 450
 451         /* done here because hrtimer_start can only pin to smp_processor_id() */
 452         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 453                       HRTIMER_MODE_REL_PINNED);
 454
 455         /* initialize timestamp */
 456         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
 457         __touch_watchdog();
 458 }
 459
 460 static void watchdog_disable(unsigned int cpu)
 461 {
 462         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 463
 464         watchdog_set_prio(SCHED_NORMAL, 0);
 465         hrtimer_cancel(hrtimer);
 466         /* disable the perf event */
 467         watchdog_nmi_disable(cpu);
 468 }
 469
 470 static void watchdog_cleanup(unsigned int cpu, bool online)
 471 {
 472         watchdog_disable(cpu);
 473 }
 474
 475 static int watchdog_should_run(unsigned int cpu)
 476 {
 477         return __this_cpu_read(hrtimer_interrupts) !=
 478                 __this_cpu_read(soft_lockup_hrtimer_cnt);
 479 }
 480
 481 /*
 482  * The watchdog thread function - touches the timestamp.
 483  *
 484  * It only runs once every sample_period seconds (4 seconds by
 485  * default) to reset the softlockup timestamp. If this gets delayed
 486  * for more than 2*watchdog_thresh seconds then the debug-printout
 487  * triggers in watchdog_timer_fn().
 488  */
 489 static void watchdog(unsigned int cpu)
 490 {
 491         __this_cpu_write(soft_lockup_hrtimer_cnt,
 492                          __this_cpu_read(hrtimer_interrupts));
 493         __touch_watchdog();
 494
 495         /*
 496          * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
 497          * failure path. Check for failures that can occur asynchronously -
 498          * for example, when CPUs are on-lined - and shut down the hardware
 499          * perf event on each CPU accordingly.
 500          *
 501          * The only non-obvious place this bit can be cleared is through
 502          * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
 503          * pr_info here would be too noisy as it would result in a message
 504          * every few seconds if the hardlockup was disabled but the softlockup
 505          * enabled.
 506          */
 507         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 508                 watchdog_nmi_disable(cpu);
 509 }
 510
 511 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 512 /*
 513  * People like the simple clean cpu node info on boot.
 514  * Reduce the watchdog noise by only printing messages
 515  * that are different from what cpu0 displayed.
 516  */
 517 static unsigned long cpu0_err;
 518
 519 static int watchdog_nmi_enable(unsigned int cpu)
 520 {
 521         struct perf_event_attr *wd_attr;
 522         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 523
 524         /* nothing to do if the hard lockup detector is disabled */
 525         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 526                 goto out;
 527
 528         /* is it already setup and enabled? */
 529         if (event && event->state > PERF_EVENT_STATE_OFF)
 530                 goto out;
 531
 532         /* it is setup but not enabled */
 533         if (event != NULL)
 534                 goto out_enable;
 535
 536         wd_attr = &wd_hw_attr;
 537         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 538
 539         /* Try to register using hardware perf events */
 540         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
 541
 542         /* save cpu0 error for future comparision */
 543         if (cpu == 0 && IS_ERR(event))
 544                 cpu0_err = PTR_ERR(event);
 545
 546         if (!IS_ERR(event)) {
 547                 /* only print for cpu0 or different than cpu0 */
 548                 if (cpu == 0 || cpu0_err)
 549                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
 550                 goto out_save;
 551         }
 552
 553         /*
 554          * Disable the hard lockup detector if _any_ CPU fails to set up
 555          * set up the hardware perf event. The watchdog() function checks
 556          * the NMI_WATCHDOG_ENABLED bit periodically.
 557          *
 558          * The barriers are for syncing up watchdog_enabled across all the
 559          * cpus, as clear_bit() does not use barriers.
 560          */
 561         smp_mb__before_atomic();
 562         clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
 563         smp_mb__after_atomic();
 564
 565         /* skip displaying the same error again */
 566         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
 567                 return PTR_ERR(event);
 568
 569         /* vary the KERN level based on the returned errno */
 570         if (PTR_ERR(event) == -EOPNOTSUPP)
 571                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
 572         else if (PTR_ERR(event) == -ENOENT)
 573                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
 574                          cpu);
 575         else
 576                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
 577                         cpu, PTR_ERR(event));
 578
 579         pr_info("Shutting down hard lockup detector on all cpus\n");
 580
 581         return PTR_ERR(event);
 582
 583         /* success path */
 584 out_save:
 585         per_cpu(watchdog_ev, cpu) = event;
 586 out_enable:
 587         perf_event_enable(per_cpu(watchdog_ev, cpu));
 588 out:
 589         return 0;
 590 }
 591
 592 static void watchdog_nmi_disable(unsigned int cpu)
 593 {
 594         struct perf_event *event = per_cpu(watchdog_ev, cpu);
 595
 596         if (event) {
 597                 perf_event_disable(event);
 598                 per_cpu(watchdog_ev, cpu) = NULL;
 599
 600                 /* should be in cleanup, but blocks oprofile */
 601                 perf_event_release_kernel(event);
 602         }
 603         if (cpu == 0) {
 604                 /* watchdog_nmi_enable() expects this to be zero initially. */
 605                 cpu0_err = 0;
 606         }
 607 }
 608
 609 void watchdog_nmi_enable_all(void)
 610 {
 611         int cpu;
 612
 613         mutex_lock(&watchdog_proc_mutex);
 614
 615         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 616                 goto unlock;
 617
 618         get_online_cpus();
 619         for_each_online_cpu(cpu)
 620                 watchdog_nmi_enable(cpu);
 621         put_online_cpus();
 622
 623 unlock:
 624         mutex_unlock(&watchdog_proc_mutex);
 625 }
 626
 627 void watchdog_nmi_disable_all(void)
 628 {
 629         int cpu;
 630
 631         mutex_lock(&watchdog_proc_mutex);
 632
 633         if (!watchdog_running)
 634                 goto unlock;
 635
 636         get_online_cpus();
 637         for_each_online_cpu(cpu)
 638                 watchdog_nmi_disable(cpu);
 639         put_online_cpus();
 640
 641 unlock:
 642         mutex_unlock(&watchdog_proc_mutex);
 643 }
 644 #else
 645 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
 646 static void watchdog_nmi_disable(unsigned int cpu) { return; }
 647 void watchdog_nmi_enable_all(void) {}
 648 void watchdog_nmi_disable_all(void) {}
 649 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
 650
 651 static struct smp_hotplug_thread watchdog_threads = {
 652         .store                  = &softlockup_watchdog,
 653         .thread_should_run      = watchdog_should_run,
 654         .thread_fn              = watchdog,
 655         .thread_comm            = "watchdog/%u",
 656         .setup                  = watchdog_enable,
 657         .cleanup                = watchdog_cleanup,
 658         .park                   = watchdog_disable,
 659         .unpark                 = watchdog_enable,
 660 };
 661
 662 static void restart_watchdog_hrtimer(void *info)
 663 {
 664         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
 665         int ret;
 666
 667         /*
 668          * No need to cancel and restart hrtimer if it is currently executing
 669          * because it will reprogram itself with the new period now.
 670          * We should never see it unqueued here because we are running per-cpu
 671          * with interrupts disabled.
 672          */
 673         ret = hrtimer_try_to_cancel(hrtimer);
 674         if (ret == 1)
 675                 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
 676                                 HRTIMER_MODE_REL_PINNED);
 677 }
 678
 679 static void update_watchdog(int cpu)
 680 {
 681         /*
 682          * Make sure that perf event counter will adopt to a new
 683          * sampling period. Updating the sampling period directly would
 684          * be much nicer but we do not have an API for that now so
 685          * let's use a big hammer.
 686          * Hrtimer will adopt the new period on the next tick but this
 687          * might be late already so we have to restart the timer as well.
 688          */
 689         watchdog_nmi_disable(cpu);
 690         smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
 691         watchdog_nmi_enable(cpu);
 692 }
 693
 694 static void update_watchdog_all_cpus(void)
 695 {
 696         int cpu;
 697
 698         get_online_cpus();
 699         for_each_online_cpu(cpu)
 700                 update_watchdog(cpu);
 701         put_online_cpus();
 702 }
 703
 704 static int watchdog_enable_all_cpus(void)
 705 {
 706         int err = 0;
 707
 708         if (!watchdog_running) {
 709                 err = smpboot_register_percpu_thread(&watchdog_threads);
 710                 if (err)
 711                         pr_err("Failed to create watchdog threads, disabled\n");
 712                 else
 713                         watchdog_running = 1;
 714         } else {
 715                 /*
 716                  * Enable/disable the lockup detectors or
 717                  * change the sample period 'on the fly'.
 718                  */
 719                 update_watchdog_all_cpus();
 720         }
 721
 722         return err;
 723 }
 724
 725 /* prepare/enable/disable routines */
 726 /* sysctl functions */
 727 #ifdef CONFIG_SYSCTL
 728 static void watchdog_disable_all_cpus(void)
 729 {
 730         if (watchdog_running) {
 731                 watchdog_running = 0;
 732                 smpboot_unregister_percpu_thread(&watchdog_threads);
 733         }
 734 }
 735
 736 /*
 737  * Update the run state of the lockup detectors.
 738  */
 739 static int proc_watchdog_update(void)
 740 {
 741         int err = 0;
 742
 743         /*
 744          * Watchdog threads won't be started if they are already active.
 745          * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
 746          * care of this. If those threads are already active, the sample
 747          * period will be updated and the lockup detectors will be enabled
 748          * or disabled 'on the fly'.
 749          */
 750         if (watchdog_enabled && watchdog_thresh)
 751                 err = watchdog_enable_all_cpus();
 752         else
 753                 watchdog_disable_all_cpus();
 754
 755         return err;
 756
 757 }
 758
 759 /*
 760  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 761  *
 762  * caller             | table->data points to | 'which' contains the flag(s)
 763  * -------------------|-----------------------|-----------------------------
 764  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 765  *                    |                       | with SOFT_WATCHDOG_ENABLED
 766  * -------------------|-----------------------|-----------------------------
 767  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 768  * -------------------|-----------------------|-----------------------------
 769  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 770  */
 771 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
 772                                 void __user *buffer, size_t *lenp, loff_t *ppos)
 773 {
 774         int err, old, new;
 775         int *watchdog_param = (int *)table->data;
 776
 777         mutex_lock(&watchdog_proc_mutex);
 778
 779         /*
 780          * If the parameter is being read return the state of the corresponding
 781          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
 782          * run state of the lockup detectors.
 783          */
 784         if (!write) {
 785                 *watchdog_param = (watchdog_enabled & which) != 0;
 786                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 787         } else {
 788                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 789                 if (err)
 790                         goto out;
 791
 792                 /*
 793                  * There is a race window between fetching the current value
 794                  * from 'watchdog_enabled' and storing the new value. During
 795                  * this race window, watchdog_nmi_enable() can sneak in and
 796                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
 797                  * The 'cmpxchg' detects this race and the loop retries.
 798                  */
 799                 do {
 800                         old = watchdog_enabled;
 801                         /*
 802                          * If the parameter value is not zero set the
 803                          * corresponding bit(s), else clear it(them).
 804                          */
 805                         if (*watchdog_param)
 806                                 new = old | which;
 807                         else
 808                                 new = old & ~which;
 809                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
 810
 811                 /*
 812                  * Update the run state of the lockup detectors.
 813                  * Restore 'watchdog_enabled' on failure.
 814                  */
 815                 err = proc_watchdog_update();
 816                 if (err)
 817                         watchdog_enabled = old;
 818         }
 819 out:
 820         mutex_unlock(&watchdog_proc_mutex);
 821         return err;
 822 }
 823
 824 /*
 825  * /proc/sys/kernel/watchdog
 826  */
 827 int proc_watchdog(struct ctl_table *table, int write,
 828                   void __user *buffer, size_t *lenp, loff_t *ppos)
 829 {
 830         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
 831                                     table, write, buffer, lenp, ppos);
 832 }
 833
 834 /*
 835  * /proc/sys/kernel/nmi_watchdog
 836  */
 837 int proc_nmi_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,
 841                                     table, write, buffer, lenp, ppos);
 842 }
 843
 844 /*
 845  * /proc/sys/kernel/soft_watchdog
 846  */
 847 int proc_soft_watchdog(struct ctl_table *table, int write,
 848                         void __user *buffer, size_t *lenp, loff_t *ppos)
 849 {
 850         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
 851                                     table, write, buffer, lenp, ppos);
 852 }
 853
 854 /*
 855  * /proc/sys/kernel/watchdog_thresh
 856  */
 857 int proc_watchdog_thresh(struct ctl_table *table, int write,
 858                          void __user *buffer, size_t *lenp, loff_t *ppos)
 859 {
 860         int err, old;
 861
 862         mutex_lock(&watchdog_proc_mutex);
 863
 864         old = ACCESS_ONCE(watchdog_thresh);
 865         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 866
 867         if (err || !write)
 868                 goto out;
 869
 870         /*
 871          * Update the sample period.
 872          * Restore 'watchdog_thresh' on failure.
 873          */
 874         set_sample_period();
 875         err = proc_watchdog_update();
 876         if (err)
 877                 watchdog_thresh = old;
 878 out:
 879         mutex_unlock(&watchdog_proc_mutex);
 880         return err;
 881 }
 882 #endif /* CONFIG_SYSCTL */
 883
 884 void __init lockup_detector_init(void)
 885 {
 886         set_sample_period();
 887
 888         if (watchdog_enabled)
 889                 watchdog_enable_all_cpus();
 890 }