watchdog.c 22.9 KB
Newer Older
1 2 3 4 5
/*
 * Detect hard and soft lockups on a system
 *
 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
 *
6 7 8
 * Note: Most of this code is borrowed heavily from the original softlockup
 * detector, so thanks to Ingo for the initial implementation.
 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
9 10 11
 * to those contributors as well.
 */

12
#define pr_fmt(fmt) "watchdog: " fmt
13

14 15 16 17 18 19
#include <linux/mm.h>
#include <linux/cpu.h>
#include <linux/nmi.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sysctl.h>
20
#include <linux/smpboot.h>
21
#include <linux/sched/rt.h>
22
#include <uapi/linux/sched/types.h>
23
#include <linux/tick.h>
24
#include <linux/workqueue.h>
25
#include <linux/sched/clock.h>
26
#include <linux/sched/debug.h>
27 28

#include <asm/irq_regs.h>
29
#include <linux/kvm_para.h>
30
#include <linux/kthread.h>
31

32
static DEFINE_MUTEX(watchdog_mutex);
33

34 35 36 37 38
int __read_mostly nmi_watchdog_enabled;

#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED |
						NMI_WATCHDOG_ENABLED;
39
#else
40
unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
41
#endif
42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

#ifdef CONFIG_HARDLOCKUP_DETECTOR
/*
 * Should we panic when a soft-lockup or hard-lockup occurs:
 */
unsigned int __read_mostly hardlockup_panic =
			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
/*
 * We may not want to enable hard lockup detection by default in all cases,
 * for example when running the kernel as a guest on a hypervisor. In these
 * cases this function can be called to disable hard lockup detection. This
 * function should only be executed once by the boot processor before the
 * kernel command line parameters are parsed, because otherwise it is not
 * possible to override this in hardlockup_panic_setup().
 */
57
void __init hardlockup_detector_disable(void)
58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75
{
	watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
}

static int __init hardlockup_panic_setup(char *str)
{
	if (!strncmp(str, "panic", 5))
		hardlockup_panic = 1;
	else if (!strncmp(str, "nopanic", 7))
		hardlockup_panic = 0;
	else if (!strncmp(str, "0", 1))
		watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
	else if (!strncmp(str, "1", 1))
		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
	return 1;
}
__setup("nmi_watchdog=", hardlockup_panic_setup);

76 77
# ifdef CONFIG_SMP
int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
78

79 80 81 82 83 84 85 86
static int __init hardlockup_all_cpu_backtrace_setup(char *str)
{
	sysctl_hardlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
	return 1;
}
__setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
# endif /* CONFIG_SMP */
#endif /* CONFIG_HARDLOCKUP_DETECTOR */
87

88
int __read_mostly watchdog_user_enabled;
89
int __read_mostly watchdog_thresh = 10;
90

91
struct cpumask watchdog_cpumask __read_mostly;
92 93
unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);

94 95 96 97 98
/*
 * The 'watchdog_running' variable is set to 1 when the watchdog threads
 * are registered/started and is set to 0 when the watchdog threads are
 * unregistered/stopped, so it is an indicator whether the threads exist.
 */
99
static int __read_mostly watchdog_running;
100 101 102 103

/*
 * These functions can be overridden if an architecture implements its
 * own hardlockup detector.
104 105 106 107
 *
 * watchdog_nmi_enable/disable can be implemented to start and stop when
 * softlockup watchdog threads start and stop. The arch must select the
 * SOFTLOCKUP_DETECTOR Kconfig.
108 109 110 111 112
 */
int __weak watchdog_nmi_enable(unsigned int cpu)
{
	return 0;
}
113

114 115
void __weak watchdog_nmi_disable(unsigned int cpu)
{
116
	hardlockup_detector_perf_disable();
117 118
}

119 120 121 122 123 124 125 126 127 128
/*
 * watchdog_nmi_reconfigure can be implemented to be notified after any
 * watchdog configuration change. The arch hardlockup watchdog should
 * respond to the following variables:
 * - nmi_watchdog_enabled
 * - watchdog_thresh
 * - watchdog_cpumask
 * - sysctl_hardlockup_all_cpu_backtrace
 * - hardlockup_panic
 */
129
void __weak watchdog_nmi_reconfigure(void) { }
130

131 132 133 134 135 136
#ifdef CONFIG_SOFTLOCKUP_DETECTOR

/* Helper for online, unparked cpus. */
#define for_each_watchdog_cpu(cpu) \
	for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)

137 138 139 140 141
/* Global variables, exported for sysctl */
unsigned int __read_mostly softlockup_panic =
			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
int __read_mostly soft_watchdog_enabled;

142
static u64 __read_mostly sample_period;
143 144 145 146 147 148

static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
static DEFINE_PER_CPU(bool, softlockup_touch_sync);
static DEFINE_PER_CPU(bool, soft_watchdog_warn);
149 150
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
151
static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
152
static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
153
static unsigned long soft_lockup_nmi_warn;
154 155 156 157 158 159 160 161 162 163

static int __init softlockup_panic_setup(char *str)
{
	softlockup_panic = simple_strtoul(str, NULL, 0);
	return 1;
}
__setup("softlockup_panic=", softlockup_panic_setup);

static int __init nowatchdog_setup(char *str)
{
164
	watchdog_enabled = 0;
165 166 167 168 169 170
	return 1;
}
__setup("nowatchdog", nowatchdog_setup);

static int __init nosoftlockup_setup(char *str)
{
171
	watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
172 173 174
	return 1;
}
__setup("nosoftlockup", nosoftlockup_setup);
175

176
#ifdef CONFIG_SMP
177 178
int __read_mostly sysctl_softlockup_all_cpu_backtrace;

179 180
static int __init softlockup_all_cpu_backtrace_setup(char *str)
{
181
	sysctl_softlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
182 183 184
	return 1;
}
__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
185
#endif
186

187 188
static void __lockup_detector_cleanup(void);

189 190 191 192 193 194 195
/*
 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
 * lockups can have false positives under extreme conditions. So we generally
 * want a higher threshold for soft lockups than for hard lockups. So we couple
 * the thresholds with a factor: we make the soft threshold twice the amount of
 * time the hard threshold is.
 */
196
static int get_softlockup_thresh(void)
197 198 199
{
	return watchdog_thresh * 2;
}
200 201 202 203 204 205

/*
 * Returns seconds, approximately.  We don't need nanosecond
 * resolution, and we don't need to waste time with a big divide when
 * 2^30ns == 1.074s.
 */
206
static unsigned long get_timestamp(void)
207
{
208
	return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
209 210
}

211
static void set_sample_period(void)
212 213
{
	/*
214
	 * convert watchdog_thresh from seconds to ns
215 216 217 218
	 * the divide by 5 is to give hrtimer several chances (two
	 * or three with the current relation between the soft
	 * and hard thresholds) to increment before the
	 * hardlockup detector generates a warning
219
	 */
220
	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
221
	watchdog_update_hrtimer_threshold(sample_period);
222 223 224 225 226
}

/* Commands for resetting the watchdog */
static void __touch_watchdog(void)
{
227
	__this_cpu_write(watchdog_touch_ts, get_timestamp());
228 229
}

230 231 232 233 234 235 236 237 238
/**
 * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
 *
 * Call when the scheduler may have stalled for legitimate reasons
 * preventing the watchdog task from executing - e.g. the scheduler
 * entering idle state.  This should only be used for scheduler events.
 * Use touch_softlockup_watchdog() for everything else.
 */
void touch_softlockup_watchdog_sched(void)
239
{
240 241 242 243 244
	/*
	 * Preemption can be enabled.  It doesn't matter which CPU's timestamp
	 * gets zeroed here, so use the raw_ operation.
	 */
	raw_cpu_write(watchdog_touch_ts, 0);
245
}
246 247 248 249

void touch_softlockup_watchdog(void)
{
	touch_softlockup_watchdog_sched();
250
	wq_watchdog_touch(raw_smp_processor_id());
251
}
252
EXPORT_SYMBOL(touch_softlockup_watchdog);
253

254
void touch_all_softlockup_watchdogs(void)
255 256 257 258 259 260 261 262
{
	int cpu;

	/*
	 * this is done lockless
	 * do we care if a 0 races with a timestamp?
	 * all it means is the softlock check starts one cycle later
	 */
263
	for_each_watchdog_cpu(cpu)
264
		per_cpu(watchdog_touch_ts, cpu) = 0;
265
	wq_watchdog_touch(-1);
266 267 268 269
}

void touch_softlockup_watchdog_sync(void)
{
270 271
	__this_cpu_write(softlockup_touch_sync, true);
	__this_cpu_write(watchdog_touch_ts, 0);
272 273
}

274
static int is_softlockup(unsigned long touch_ts)
275
{
276
	unsigned long now = get_timestamp();
277

278
	if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
279 280 281 282
		/* Warn about unreasonable delays. */
		if (time_after(now, touch_ts + get_softlockup_thresh()))
			return now - touch_ts;
	}
283 284 285
	return 0;
}

286 287
/* watchdog detector functions */
bool is_hardlockup(void)
288
{
289
	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
290

291 292 293 294 295
	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
		return true;

	__this_cpu_write(hrtimer_interrupts_saved, hrint);
	return false;
296
}
297 298

static void watchdog_interrupt_count(void)
299
{
300
	__this_cpu_inc(hrtimer_interrupts);
301
}
302

303 304 305
static int watchdog_enable_all_cpus(void);
static void watchdog_disable_all_cpus(void);

306 307 308
/* watchdog kicker functions */
static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
{
309
	unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
310 311
	struct pt_regs *regs = get_irq_regs();
	int duration;
312
	int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
313

314
	if (!watchdog_enabled)
315 316
		return HRTIMER_NORESTART;

317 318 319 320
	/* kick the hardlockup detector */
	watchdog_interrupt_count();

	/* kick the softlockup detector */
321
	wake_up_process(__this_cpu_read(softlockup_watchdog));
322 323

	/* .. and repeat */
324
	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
325 326

	if (touch_ts == 0) {
327
		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
328 329 330 331
			/*
			 * If the time stamp was touched atomically
			 * make sure the scheduler tick is up to date.
			 */
332
			__this_cpu_write(softlockup_touch_sync, false);
333 334
			sched_clock_tick();
		}
335 336 337

		/* Clear the guest paused flag on watchdog reset */
		kvm_check_and_clear_guest_paused();
338 339 340 341 342 343 344 345 346 347
		__touch_watchdog();
		return HRTIMER_RESTART;
	}

	/* check for a softlockup
	 * This is done by making sure a high priority task is
	 * being scheduled.  The task touches the watchdog to
	 * indicate it is getting cpu time.  If it hasn't then
	 * this is a good indication some task is hogging the cpu
	 */
348
	duration = is_softlockup(touch_ts);
349
	if (unlikely(duration)) {
350 351 352 353 354 355 356 357
		/*
		 * If a virtual machine is stopped by the host it can look to
		 * the watchdog like a soft lockup, check to see if the host
		 * stopped the vm before we issue the warning
		 */
		if (kvm_check_and_clear_guest_paused())
			return HRTIMER_RESTART;

358
		/* only warn once */
359 360 361 362 363 364 365 366 367 368 369 370 371 372
		if (__this_cpu_read(soft_watchdog_warn) == true) {
			/*
			 * When multiple processes are causing softlockups the
			 * softlockup detector only warns on the first one
			 * because the code relies on a full quiet cycle to
			 * re-arm.  The second process prevents the quiet cycle
			 * and never gets reported.  Use task pointers to detect
			 * this.
			 */
			if (__this_cpu_read(softlockup_task_ptr_saved) !=
			    current) {
				__this_cpu_write(soft_watchdog_warn, false);
				__touch_watchdog();
			}
373
			return HRTIMER_RESTART;
374
		}
375

376 377 378 379 380 381 382 383 384 385 386
		if (softlockup_all_cpu_backtrace) {
			/* Prevent multiple soft-lockup reports if one cpu is already
			 * engaged in dumping cpu back traces
			 */
			if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
				/* Someone else will report us. Let's give up */
				__this_cpu_write(soft_watchdog_warn, true);
				return HRTIMER_RESTART;
			}
		}

387
		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
388
			smp_processor_id(), duration,
389
			current->comm, task_pid_nr(current));
390
		__this_cpu_write(softlockup_task_ptr_saved, current);
391 392 393 394 395 396 397
		print_modules();
		print_irqtrace_events(current);
		if (regs)
			show_regs(regs);
		else
			dump_stack();

398 399 400 401 402 403 404 405 406 407 408
		if (softlockup_all_cpu_backtrace) {
			/* Avoid generating two back traces for current
			 * given that one is already made above
			 */
			trigger_allbutself_cpu_backtrace();

			clear_bit(0, &soft_lockup_nmi_warn);
			/* Barrier to sync with other cpus */
			smp_mb__after_atomic();
		}

Josh Hunt's avatar
Josh Hunt committed
409
		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
410 411
		if (softlockup_panic)
			panic("softlockup: hung tasks");
412
		__this_cpu_write(soft_watchdog_warn, true);
413
	} else
414
		__this_cpu_write(soft_watchdog_warn, false);
415 416 417 418

	return HRTIMER_RESTART;
}

419 420 421
static void watchdog_set_prio(unsigned int policy, unsigned int prio)
{
	struct sched_param param = { .sched_priority = prio };
422

423 424 425 426
	sched_setscheduler(current, policy, &param);
}

static void watchdog_enable(unsigned int cpu)
427
{
428
	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
429

430 431 432 433
	/*
	 * Start the timer first to prevent the NMI watchdog triggering
	 * before the timer has a chance to fire.
	 */
434 435
	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	hrtimer->function = watchdog_timer_fn;
436 437
	hrtimer_start(hrtimer, ns_to_ktime(sample_period),
		      HRTIMER_MODE_REL_PINNED);
438

439 440
	/* Initialize timestamp */
	__touch_watchdog();
441 442
	/* Enable the perf event */
	watchdog_nmi_enable(cpu);
443

444 445
	watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
}
446

447 448
static void watchdog_disable(unsigned int cpu)
{
449
	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
450

451
	watchdog_set_prio(SCHED_NORMAL, 0);
452 453 454 455 456
	/*
	 * Disable the perf event first. That prevents that a large delay
	 * between disabling the timer and disabling the perf event causes
	 * the perf NMI to detect a false positive.
	 */
457
	watchdog_nmi_disable(cpu);
458
	hrtimer_cancel(hrtimer);
459 460
}

461 462 463 464 465
static void watchdog_cleanup(unsigned int cpu, bool online)
{
	watchdog_disable(cpu);
}

466 467 468 469 470 471 472 473 474
static int watchdog_should_run(unsigned int cpu)
{
	return __this_cpu_read(hrtimer_interrupts) !=
		__this_cpu_read(soft_lockup_hrtimer_cnt);
}

/*
 * The watchdog thread function - touches the timestamp.
 *
475
 * It only runs once every sample_period seconds (4 seconds by
476 477 478 479 480 481 482 483 484 485
 * default) to reset the softlockup timestamp. If this gets delayed
 * for more than 2*watchdog_thresh seconds then the debug-printout
 * triggers in watchdog_timer_fn().
 */
static void watchdog(unsigned int cpu)
{
	__this_cpu_write(soft_lockup_hrtimer_cnt,
			 __this_cpu_read(hrtimer_interrupts));
	__touch_watchdog();
}
486

487 488 489 490 491 492 493 494 495 496 497
static struct smp_hotplug_thread watchdog_threads = {
	.store			= &softlockup_watchdog,
	.thread_should_run	= watchdog_should_run,
	.thread_fn		= watchdog,
	.thread_comm		= "watchdog/%u",
	.setup			= watchdog_enable,
	.cleanup		= watchdog_cleanup,
	.park			= watchdog_disable,
	.unpark			= watchdog_enable,
};

498 499
/*
 * park all watchdog threads that are specified in 'watchdog_cpumask'
500 501 502 503 504 505
 *
 * This function returns an error if kthread_park() of a watchdog thread
 * fails. In this situation, the watchdog threads of some CPUs can already
 * be parked and the watchdog threads of other CPUs can still be runnable.
 * Callers are expected to handle this special condition as appropriate in
 * their context.
506 507 508
 *
 * This function may only be called in a context that is protected against
 * races with CPU hotplug - for example, via get_online_cpus().
509 510 511 512 513 514 515 516 517 518 519 520 521 522 523
 */
static int watchdog_park_threads(void)
{
	int cpu, ret = 0;

	for_each_watchdog_cpu(cpu) {
		ret = kthread_park(per_cpu(softlockup_watchdog, cpu));
		if (ret)
			break;
	}
	return ret;
}

/*
 * unpark all watchdog threads that are specified in 'watchdog_cpumask'
524 525 526
 *
 * This function may only be called in a context that is protected against
 * races with CPU hotplug - for example, via get_online_cpus().
527 528 529 530 531 532 533 534 535
 */
static void watchdog_unpark_threads(void)
{
	int cpu;

	for_each_watchdog_cpu(cpu)
		kthread_unpark(per_cpu(softlockup_watchdog, cpu));
}

536
static int update_watchdog_all_cpus(void)
537
{
538 539 540 541 542 543
	int ret;

	ret = watchdog_park_threads();
	if (ret)
		return ret;

544
	watchdog_unpark_threads();
545 546

	return 0;
547 548
}

549
static int watchdog_enable_all_cpus(void)
550
{
551
	int err = 0;
552

553
	if (!watchdog_running) {
554 555
		err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
							     &watchdog_cpumask);
556 557
		if (err)
			pr_err("Failed to create watchdog threads, disabled\n");
558
		else
559
			watchdog_running = 1;
560 561 562 563 564
	} else {
		/*
		 * Enable/disable the lockup detectors or
		 * change the sample period 'on the fly'.
		 */
565 566 567 568 569 570
		err = update_watchdog_all_cpus();

		if (err) {
			watchdog_disable_all_cpus();
			pr_err("Failed to update lockup detectors, disabled\n");
		}
571
	}
572

573 574 575
	if (err)
		watchdog_enabled = 0;

576
	return err;
577 578 579 580
}

static void watchdog_disable_all_cpus(void)
{
581 582
	if (watchdog_running) {
		watchdog_running = 0;
583
		smpboot_unregister_percpu_thread(&watchdog_threads);
584
	}
585 586
}

587 588 589 590 591 592 593
#else /* CONFIG_SOFTLOCKUP_DETECTOR */
static inline int watchdog_park_threads(void) { return 0; }
static inline void watchdog_unpark_threads(void) { }
static inline int watchdog_enable_all_cpus(void) { return 0; }
static inline void watchdog_disable_all_cpus(void) { }
static inline void set_sample_period(void) { }
#endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
594

595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612
static void __lockup_detector_cleanup(void)
{
	lockdep_assert_held(&watchdog_mutex);
	hardlockup_detector_perf_cleanup();
}

/**
 * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
 *
 * Caller must not hold the cpu hotplug rwsem.
 */
void lockup_detector_cleanup(void)
{
	mutex_lock(&watchdog_mutex);
	__lockup_detector_cleanup();
	mutex_unlock(&watchdog_mutex);
}

613 614 615 616 617 618 619 620 621 622 623
/**
 * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
 *
 * Special interface for parisc. It prevents lockup detector warnings from
 * the default pm_poweroff() function which busy loops forever.
 */
void lockup_detector_soft_poweroff(void)
{
	watchdog_enabled = 0;
}

624 625
#ifdef CONFIG_SYSCTL

626
/*
627 628 629 630 631 632 633 634 635 636 637 638 639 640
 * Update the run state of the lockup detectors.
 */
static int proc_watchdog_update(void)
{
	int err = 0;

	/*
	 * Watchdog threads won't be started if they are already active.
	 * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
	 * care of this. If those threads are already active, the sample
	 * period will be updated and the lockup detectors will be enabled
	 * or disabled 'on the fly'.
	 */
	if (watchdog_enabled && watchdog_thresh)
641
		err = watchdog_enable_all_cpus();
642 643 644
	else
		watchdog_disable_all_cpus();

645 646
	watchdog_nmi_reconfigure();

647 648
	__lockup_detector_cleanup();

649 650 651 652
	return err;

}

653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670
/*
 * common function for watchdog, nmi_watchdog and soft_watchdog parameter
 *
 * caller             | table->data points to | 'which' contains the flag(s)
 * -------------------|-----------------------|-----------------------------
 * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
 *                    |                       | with SOFT_WATCHDOG_ENABLED
 * -------------------|-----------------------|-----------------------------
 * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
 * -------------------|-----------------------|-----------------------------
 * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
 */
static int proc_watchdog_common(int which, struct ctl_table *table, int write,
				void __user *buffer, size_t *lenp, loff_t *ppos)
{
	int err, old, new;
	int *watchdog_param = (int *)table->data;

671
	cpu_hotplug_disable();
672
	mutex_lock(&watchdog_mutex);
673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706

	/*
	 * If the parameter is being read return the state of the corresponding
	 * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
	 * run state of the lockup detectors.
	 */
	if (!write) {
		*watchdog_param = (watchdog_enabled & which) != 0;
		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
	} else {
		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
		if (err)
			goto out;

		/*
		 * There is a race window between fetching the current value
		 * from 'watchdog_enabled' and storing the new value. During
		 * this race window, watchdog_nmi_enable() can sneak in and
		 * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
		 * The 'cmpxchg' detects this race and the loop retries.
		 */
		do {
			old = watchdog_enabled;
			/*
			 * If the parameter value is not zero set the
			 * corresponding bit(s), else clear it(them).
			 */
			if (*watchdog_param)
				new = old | which;
			else
				new = old & ~which;
		} while (cmpxchg(&watchdog_enabled, old, new) != old);

		/*
707 708 709 710 711
		 * Update the run state of the lockup detectors. There is _no_
		 * need to check the value returned by proc_watchdog_update()
		 * and to restore the previous value of 'watchdog_enabled' as
		 * both lockup detectors are disabled if proc_watchdog_update()
		 * returns an error.
712
		 */
713 714 715
		if (old == new)
			goto out;

716 717 718
		err = proc_watchdog_update();
	}
out:
719
	mutex_unlock(&watchdog_mutex);
720
	cpu_hotplug_enable();
721 722 723
	return err;
}

724 725 726 727 728 729 730 731 732 733 734 735
/*
 * /proc/sys/kernel/watchdog
 */
int proc_watchdog(struct ctl_table *table, int write,
		  void __user *buffer, size_t *lenp, loff_t *ppos)
{
	return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
				    table, write, buffer, lenp, ppos);
}

/*
 * /proc/sys/kernel/nmi_watchdog
736
 */
737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752
int proc_nmi_watchdog(struct ctl_table *table, int write,
		      void __user *buffer, size_t *lenp, loff_t *ppos)
{
	return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
				    table, write, buffer, lenp, ppos);
}

/*
 * /proc/sys/kernel/soft_watchdog
 */
int proc_soft_watchdog(struct ctl_table *table, int write,
			void __user *buffer, size_t *lenp, loff_t *ppos)
{
	return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
				    table, write, buffer, lenp, ppos);
}
753

754 755 756 757 758
/*
 * /proc/sys/kernel/watchdog_thresh
 */
int proc_watchdog_thresh(struct ctl_table *table, int write,
			 void __user *buffer, size_t *lenp, loff_t *ppos)
759
{
760
	int err, old, new;
761

762
	cpu_hotplug_disable();
763
	mutex_lock(&watchdog_mutex);
764

765
	old = ACCESS_ONCE(watchdog_thresh);
766
	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
767

768
	if (err || !write)
769
		goto out;
770

771
	/*
772
	 * Update the sample period. Restore on failure.
773
	 */
774 775 776 777
	new = ACCESS_ONCE(watchdog_thresh);
	if (old == new)
		goto out;

778 779
	set_sample_period();
	err = proc_watchdog_update();
780
	if (err) {
781
		watchdog_thresh = old;
782 783
		set_sample_period();
	}
784
out:
785
	mutex_unlock(&watchdog_mutex);
786
	cpu_hotplug_enable();
787
	return err;
788
}
789

790
static void watchdog_update_cpus(void)
791
{
792 793 794
	if (IS_ENABLED(CONFIG_SOFTLOCKUP_DETECTOR) && watchdog_running) {
		smpboot_update_cpumask_percpu_thread(&watchdog_threads,
						     &watchdog_cpumask);
795
		__lockup_detector_cleanup();
796 797 798
	}
}

799 800 801 802
static void proc_watchdog_cpumask_update(void)
{
	/* Remove impossible cpus to keep sysctl output clean. */
	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
803
	watchdog_update_cpus();
804 805 806
	watchdog_nmi_reconfigure();
}

807 808 809 810 811 812 813 814 815 816 817
/*
 * The cpumask is the mask of possible cpus that the watchdog can run
 * on, not the mask of cpus it is actually running on.  This allows the
 * user to specify a mask that will include cpus that have not yet
 * been brought online, if desired.
 */
int proc_watchdog_cpumask(struct ctl_table *table, int write,
			  void __user *buffer, size_t *lenp, loff_t *ppos)
{
	int err;

818
	cpu_hotplug_disable();
819
	mutex_lock(&watchdog_mutex);
820

821
	err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
822 823
	if (!err && write)
		proc_watchdog_cpumask_update();
824

825
	mutex_unlock(&watchdog_mutex);
826
	cpu_hotplug_enable();
827 828
	return err;
}
829 830
#endif /* CONFIG_SYSCTL */

831
void __init lockup_detector_init(void)
832
{
833
	set_sample_period();
834

835 836
#ifdef CONFIG_NO_HZ_FULL
	if (tick_nohz_full_enabled()) {
837 838
		pr_info("Disabling watchdog on nohz_full cores by default\n");
		cpumask_copy(&watchdog_cpumask, housekeeping_mask);
839 840 841 842 843 844
	} else
		cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
#else
	cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
#endif

845
	if (watchdog_enabled)
846
		watchdog_enable_all_cpus();
847
}