xref: /openbmc/linux/kernel/watchdog.c (revision d2574c33)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Detect hard and soft lockups on a system
4  *
5  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
6  *
7  * Note: Most of this code is borrowed heavily from the original softlockup
8  * detector, so thanks to Ingo for the initial implementation.
9  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
10  * to those contributors as well.
11  */
12 
13 #define pr_fmt(fmt) "watchdog: " fmt
14 
15 #include <linux/mm.h>
16 #include <linux/cpu.h>
17 #include <linux/nmi.h>
18 #include <linux/init.h>
19 #include <linux/module.h>
20 #include <linux/sysctl.h>
21 #include <linux/tick.h>
22 #include <linux/sched/clock.h>
23 #include <linux/sched/debug.h>
24 #include <linux/sched/isolation.h>
25 #include <linux/stop_machine.h>
26 
27 #include <asm/irq_regs.h>
28 #include <linux/kvm_para.h>
29 
30 static DEFINE_MUTEX(watchdog_mutex);
31 
32 #if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HAVE_NMI_WATCHDOG)
33 # define WATCHDOG_DEFAULT	(SOFT_WATCHDOG_ENABLED | NMI_WATCHDOG_ENABLED)
34 # define NMI_WATCHDOG_DEFAULT	1
35 #else
36 # define WATCHDOG_DEFAULT	(SOFT_WATCHDOG_ENABLED)
37 # define NMI_WATCHDOG_DEFAULT	0
38 #endif
39 
40 unsigned long __read_mostly watchdog_enabled;
41 int __read_mostly watchdog_user_enabled = 1;
42 int __read_mostly nmi_watchdog_user_enabled = NMI_WATCHDOG_DEFAULT;
43 int __read_mostly soft_watchdog_user_enabled = 1;
44 int __read_mostly watchdog_thresh = 10;
45 static int __read_mostly nmi_watchdog_available;
46 
47 static struct cpumask watchdog_allowed_mask __read_mostly;
48 
49 struct cpumask watchdog_cpumask __read_mostly;
50 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
51 
52 #ifdef CONFIG_HARDLOCKUP_DETECTOR
53 /*
54  * Should we panic when a soft-lockup or hard-lockup occurs:
55  */
56 unsigned int __read_mostly hardlockup_panic =
57 			CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
58 /*
59  * We may not want to enable hard lockup detection by default in all cases,
60  * for example when running the kernel as a guest on a hypervisor. In these
61  * cases this function can be called to disable hard lockup detection. This
62  * function should only be executed once by the boot processor before the
63  * kernel command line parameters are parsed, because otherwise it is not
64  * possible to override this in hardlockup_panic_setup().
65  */
66 void __init hardlockup_detector_disable(void)
67 {
68 	nmi_watchdog_user_enabled = 0;
69 }
70 
71 static int __init hardlockup_panic_setup(char *str)
72 {
73 	if (!strncmp(str, "panic", 5))
74 		hardlockup_panic = 1;
75 	else if (!strncmp(str, "nopanic", 7))
76 		hardlockup_panic = 0;
77 	else if (!strncmp(str, "0", 1))
78 		nmi_watchdog_user_enabled = 0;
79 	else if (!strncmp(str, "1", 1))
80 		nmi_watchdog_user_enabled = 1;
81 	return 1;
82 }
83 __setup("nmi_watchdog=", hardlockup_panic_setup);
84 
85 # ifdef CONFIG_SMP
86 int __read_mostly sysctl_hardlockup_all_cpu_backtrace;
87 
88 static int __init hardlockup_all_cpu_backtrace_setup(char *str)
89 {
90 	sysctl_hardlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
91 	return 1;
92 }
93 __setup("hardlockup_all_cpu_backtrace=", hardlockup_all_cpu_backtrace_setup);
94 # endif /* CONFIG_SMP */
95 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
96 
97 /*
98  * These functions can be overridden if an architecture implements its
99  * own hardlockup detector.
100  *
101  * watchdog_nmi_enable/disable can be implemented to start and stop when
102  * softlockup watchdog threads start and stop. The arch must select the
103  * SOFTLOCKUP_DETECTOR Kconfig.
104  */
105 int __weak watchdog_nmi_enable(unsigned int cpu)
106 {
107 	hardlockup_detector_perf_enable();
108 	return 0;
109 }
110 
111 void __weak watchdog_nmi_disable(unsigned int cpu)
112 {
113 	hardlockup_detector_perf_disable();
114 }
115 
116 /* Return 0, if a NMI watchdog is available. Error code otherwise */
117 int __weak __init watchdog_nmi_probe(void)
118 {
119 	return hardlockup_detector_perf_init();
120 }
121 
122 /**
123  * watchdog_nmi_stop - Stop the watchdog for reconfiguration
124  *
125  * The reconfiguration steps are:
126  * watchdog_nmi_stop();
127  * update_variables();
128  * watchdog_nmi_start();
129  */
130 void __weak watchdog_nmi_stop(void) { }
131 
132 /**
133  * watchdog_nmi_start - Start the watchdog after reconfiguration
134  *
135  * Counterpart to watchdog_nmi_stop().
136  *
137  * The following variables have been updated in update_variables() and
138  * contain the currently valid configuration:
139  * - watchdog_enabled
140  * - watchdog_thresh
141  * - watchdog_cpumask
142  */
143 void __weak watchdog_nmi_start(void) { }
144 
145 /**
146  * lockup_detector_update_enable - Update the sysctl enable bit
147  *
148  * Caller needs to make sure that the NMI/perf watchdogs are off, so this
149  * can't race with watchdog_nmi_disable().
150  */
151 static void lockup_detector_update_enable(void)
152 {
153 	watchdog_enabled = 0;
154 	if (!watchdog_user_enabled)
155 		return;
156 	if (nmi_watchdog_available && nmi_watchdog_user_enabled)
157 		watchdog_enabled |= NMI_WATCHDOG_ENABLED;
158 	if (soft_watchdog_user_enabled)
159 		watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
160 }
161 
162 #ifdef CONFIG_SOFTLOCKUP_DETECTOR
163 
164 /* Global variables, exported for sysctl */
165 unsigned int __read_mostly softlockup_panic =
166 			CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
167 
168 static bool softlockup_initialized __read_mostly;
169 static u64 __read_mostly sample_period;
170 
171 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
172 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
173 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
174 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
175 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
176 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
177 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
178 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
179 static unsigned long soft_lockup_nmi_warn;
180 
181 static int __init softlockup_panic_setup(char *str)
182 {
183 	softlockup_panic = simple_strtoul(str, NULL, 0);
184 	return 1;
185 }
186 __setup("softlockup_panic=", softlockup_panic_setup);
187 
188 static int __init nowatchdog_setup(char *str)
189 {
190 	watchdog_user_enabled = 0;
191 	return 1;
192 }
193 __setup("nowatchdog", nowatchdog_setup);
194 
195 static int __init nosoftlockup_setup(char *str)
196 {
197 	soft_watchdog_user_enabled = 0;
198 	return 1;
199 }
200 __setup("nosoftlockup", nosoftlockup_setup);
201 
202 static int __init watchdog_thresh_setup(char *str)
203 {
204 	get_option(&str, &watchdog_thresh);
205 	return 1;
206 }
207 __setup("watchdog_thresh=", watchdog_thresh_setup);
208 
209 #ifdef CONFIG_SMP
210 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
211 
212 static int __init softlockup_all_cpu_backtrace_setup(char *str)
213 {
214 	sysctl_softlockup_all_cpu_backtrace = !!simple_strtol(str, NULL, 0);
215 	return 1;
216 }
217 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
218 #endif
219 
220 static void __lockup_detector_cleanup(void);
221 
222 /*
223  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
224  * lockups can have false positives under extreme conditions. So we generally
225  * want a higher threshold for soft lockups than for hard lockups. So we couple
226  * the thresholds with a factor: we make the soft threshold twice the amount of
227  * time the hard threshold is.
228  */
229 static int get_softlockup_thresh(void)
230 {
231 	return watchdog_thresh * 2;
232 }
233 
234 /*
235  * Returns seconds, approximately.  We don't need nanosecond
236  * resolution, and we don't need to waste time with a big divide when
237  * 2^30ns == 1.074s.
238  */
239 static unsigned long get_timestamp(void)
240 {
241 	return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
242 }
243 
244 static void set_sample_period(void)
245 {
246 	/*
247 	 * convert watchdog_thresh from seconds to ns
248 	 * the divide by 5 is to give hrtimer several chances (two
249 	 * or three with the current relation between the soft
250 	 * and hard thresholds) to increment before the
251 	 * hardlockup detector generates a warning
252 	 */
253 	sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
254 	watchdog_update_hrtimer_threshold(sample_period);
255 }
256 
257 /* Commands for resetting the watchdog */
258 static void __touch_watchdog(void)
259 {
260 	__this_cpu_write(watchdog_touch_ts, get_timestamp());
261 }
262 
263 /**
264  * touch_softlockup_watchdog_sched - touch watchdog on scheduler stalls
265  *
266  * Call when the scheduler may have stalled for legitimate reasons
267  * preventing the watchdog task from executing - e.g. the scheduler
268  * entering idle state.  This should only be used for scheduler events.
269  * Use touch_softlockup_watchdog() for everything else.
270  */
271 notrace void touch_softlockup_watchdog_sched(void)
272 {
273 	/*
274 	 * Preemption can be enabled.  It doesn't matter which CPU's timestamp
275 	 * gets zeroed here, so use the raw_ operation.
276 	 */
277 	raw_cpu_write(watchdog_touch_ts, 0);
278 }
279 
280 notrace void touch_softlockup_watchdog(void)
281 {
282 	touch_softlockup_watchdog_sched();
283 	wq_watchdog_touch(raw_smp_processor_id());
284 }
285 EXPORT_SYMBOL(touch_softlockup_watchdog);
286 
287 void touch_all_softlockup_watchdogs(void)
288 {
289 	int cpu;
290 
291 	/*
292 	 * watchdog_mutex cannpt be taken here, as this might be called
293 	 * from (soft)interrupt context, so the access to
294 	 * watchdog_allowed_cpumask might race with a concurrent update.
295 	 *
296 	 * The watchdog time stamp can race against a concurrent real
297 	 * update as well, the only side effect might be a cycle delay for
298 	 * the softlockup check.
299 	 */
300 	for_each_cpu(cpu, &watchdog_allowed_mask)
301 		per_cpu(watchdog_touch_ts, cpu) = 0;
302 	wq_watchdog_touch(-1);
303 }
304 
305 void touch_softlockup_watchdog_sync(void)
306 {
307 	__this_cpu_write(softlockup_touch_sync, true);
308 	__this_cpu_write(watchdog_touch_ts, 0);
309 }
310 
311 static int is_softlockup(unsigned long touch_ts)
312 {
313 	unsigned long now = get_timestamp();
314 
315 	if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh){
316 		/* Warn about unreasonable delays. */
317 		if (time_after(now, touch_ts + get_softlockup_thresh()))
318 			return now - touch_ts;
319 	}
320 	return 0;
321 }
322 
323 /* watchdog detector functions */
324 bool is_hardlockup(void)
325 {
326 	unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
327 
328 	if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
329 		return true;
330 
331 	__this_cpu_write(hrtimer_interrupts_saved, hrint);
332 	return false;
333 }
334 
335 static void watchdog_interrupt_count(void)
336 {
337 	__this_cpu_inc(hrtimer_interrupts);
338 }
339 
340 static DEFINE_PER_CPU(struct completion, softlockup_completion);
341 static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
342 
343 /*
344  * The watchdog thread function - touches the timestamp.
345  *
346  * It only runs once every sample_period seconds (4 seconds by
347  * default) to reset the softlockup timestamp. If this gets delayed
348  * for more than 2*watchdog_thresh seconds then the debug-printout
349  * triggers in watchdog_timer_fn().
350  */
351 static int softlockup_fn(void *data)
352 {
353 	__this_cpu_write(soft_lockup_hrtimer_cnt,
354 			 __this_cpu_read(hrtimer_interrupts));
355 	__touch_watchdog();
356 	complete(this_cpu_ptr(&softlockup_completion));
357 
358 	return 0;
359 }
360 
361 /* watchdog kicker functions */
362 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
363 {
364 	unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
365 	struct pt_regs *regs = get_irq_regs();
366 	int duration;
367 	int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
368 
369 	if (!watchdog_enabled)
370 		return HRTIMER_NORESTART;
371 
372 	/* kick the hardlockup detector */
373 	watchdog_interrupt_count();
374 
375 	/* kick the softlockup detector */
376 	if (completion_done(this_cpu_ptr(&softlockup_completion))) {
377 		reinit_completion(this_cpu_ptr(&softlockup_completion));
378 		stop_one_cpu_nowait(smp_processor_id(),
379 				softlockup_fn, NULL,
380 				this_cpu_ptr(&softlockup_stop_work));
381 	}
382 
383 	/* .. and repeat */
384 	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
385 
386 	if (touch_ts == 0) {
387 		if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
388 			/*
389 			 * If the time stamp was touched atomically
390 			 * make sure the scheduler tick is up to date.
391 			 */
392 			__this_cpu_write(softlockup_touch_sync, false);
393 			sched_clock_tick();
394 		}
395 
396 		/* Clear the guest paused flag on watchdog reset */
397 		kvm_check_and_clear_guest_paused();
398 		__touch_watchdog();
399 		return HRTIMER_RESTART;
400 	}
401 
402 	/* check for a softlockup
403 	 * This is done by making sure a high priority task is
404 	 * being scheduled.  The task touches the watchdog to
405 	 * indicate it is getting cpu time.  If it hasn't then
406 	 * this is a good indication some task is hogging the cpu
407 	 */
408 	duration = is_softlockup(touch_ts);
409 	if (unlikely(duration)) {
410 		/*
411 		 * If a virtual machine is stopped by the host it can look to
412 		 * the watchdog like a soft lockup, check to see if the host
413 		 * stopped the vm before we issue the warning
414 		 */
415 		if (kvm_check_and_clear_guest_paused())
416 			return HRTIMER_RESTART;
417 
418 		/* only warn once */
419 		if (__this_cpu_read(soft_watchdog_warn) == true) {
420 			/*
421 			 * When multiple processes are causing softlockups the
422 			 * softlockup detector only warns on the first one
423 			 * because the code relies on a full quiet cycle to
424 			 * re-arm.  The second process prevents the quiet cycle
425 			 * and never gets reported.  Use task pointers to detect
426 			 * this.
427 			 */
428 			if (__this_cpu_read(softlockup_task_ptr_saved) !=
429 			    current) {
430 				__this_cpu_write(soft_watchdog_warn, false);
431 				__touch_watchdog();
432 			}
433 			return HRTIMER_RESTART;
434 		}
435 
436 		if (softlockup_all_cpu_backtrace) {
437 			/* Prevent multiple soft-lockup reports if one cpu is already
438 			 * engaged in dumping cpu back traces
439 			 */
440 			if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
441 				/* Someone else will report us. Let's give up */
442 				__this_cpu_write(soft_watchdog_warn, true);
443 				return HRTIMER_RESTART;
444 			}
445 		}
446 
447 		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
448 			smp_processor_id(), duration,
449 			current->comm, task_pid_nr(current));
450 		__this_cpu_write(softlockup_task_ptr_saved, current);
451 		print_modules();
452 		print_irqtrace_events(current);
453 		if (regs)
454 			show_regs(regs);
455 		else
456 			dump_stack();
457 
458 		if (softlockup_all_cpu_backtrace) {
459 			/* Avoid generating two back traces for current
460 			 * given that one is already made above
461 			 */
462 			trigger_allbutself_cpu_backtrace();
463 
464 			clear_bit(0, &soft_lockup_nmi_warn);
465 			/* Barrier to sync with other cpus */
466 			smp_mb__after_atomic();
467 		}
468 
469 		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
470 		if (softlockup_panic)
471 			panic("softlockup: hung tasks");
472 		__this_cpu_write(soft_watchdog_warn, true);
473 	} else
474 		__this_cpu_write(soft_watchdog_warn, false);
475 
476 	return HRTIMER_RESTART;
477 }
478 
479 static void watchdog_enable(unsigned int cpu)
480 {
481 	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
482 	struct completion *done = this_cpu_ptr(&softlockup_completion);
483 
484 	WARN_ON_ONCE(cpu != smp_processor_id());
485 
486 	init_completion(done);
487 	complete(done);
488 
489 	/*
490 	 * Start the timer first to prevent the NMI watchdog triggering
491 	 * before the timer has a chance to fire.
492 	 */
493 	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
494 	hrtimer->function = watchdog_timer_fn;
495 	hrtimer_start(hrtimer, ns_to_ktime(sample_period),
496 		      HRTIMER_MODE_REL_PINNED);
497 
498 	/* Initialize timestamp */
499 	__touch_watchdog();
500 	/* Enable the perf event */
501 	if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
502 		watchdog_nmi_enable(cpu);
503 }
504 
505 static void watchdog_disable(unsigned int cpu)
506 {
507 	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);
508 
509 	WARN_ON_ONCE(cpu != smp_processor_id());
510 
511 	/*
512 	 * Disable the perf event first. That prevents that a large delay
513 	 * between disabling the timer and disabling the perf event causes
514 	 * the perf NMI to detect a false positive.
515 	 */
516 	watchdog_nmi_disable(cpu);
517 	hrtimer_cancel(hrtimer);
518 	wait_for_completion(this_cpu_ptr(&softlockup_completion));
519 }
520 
521 static int softlockup_stop_fn(void *data)
522 {
523 	watchdog_disable(smp_processor_id());
524 	return 0;
525 }
526 
527 static void softlockup_stop_all(void)
528 {
529 	int cpu;
530 
531 	if (!softlockup_initialized)
532 		return;
533 
534 	for_each_cpu(cpu, &watchdog_allowed_mask)
535 		smp_call_on_cpu(cpu, softlockup_stop_fn, NULL, false);
536 
537 	cpumask_clear(&watchdog_allowed_mask);
538 }
539 
540 static int softlockup_start_fn(void *data)
541 {
542 	watchdog_enable(smp_processor_id());
543 	return 0;
544 }
545 
546 static void softlockup_start_all(void)
547 {
548 	int cpu;
549 
550 	cpumask_copy(&watchdog_allowed_mask, &watchdog_cpumask);
551 	for_each_cpu(cpu, &watchdog_allowed_mask)
552 		smp_call_on_cpu(cpu, softlockup_start_fn, NULL, false);
553 }
554 
555 int lockup_detector_online_cpu(unsigned int cpu)
556 {
557 	watchdog_enable(cpu);
558 	return 0;
559 }
560 
561 int lockup_detector_offline_cpu(unsigned int cpu)
562 {
563 	watchdog_disable(cpu);
564 	return 0;
565 }
566 
567 static void lockup_detector_reconfigure(void)
568 {
569 	cpus_read_lock();
570 	watchdog_nmi_stop();
571 
572 	softlockup_stop_all();
573 	set_sample_period();
574 	lockup_detector_update_enable();
575 	if (watchdog_enabled && watchdog_thresh)
576 		softlockup_start_all();
577 
578 	watchdog_nmi_start();
579 	cpus_read_unlock();
580 	/*
581 	 * Must be called outside the cpus locked section to prevent
582 	 * recursive locking in the perf code.
583 	 */
584 	__lockup_detector_cleanup();
585 }
586 
587 /*
588  * Create the watchdog thread infrastructure and configure the detector(s).
589  *
590  * The threads are not unparked as watchdog_allowed_mask is empty.  When
591  * the threads are sucessfully initialized, take the proper locks and
592  * unpark the threads in the watchdog_cpumask if the watchdog is enabled.
593  */
594 static __init void lockup_detector_setup(void)
595 {
596 	/*
597 	 * If sysctl is off and watchdog got disabled on the command line,
598 	 * nothing to do here.
599 	 */
600 	lockup_detector_update_enable();
601 
602 	if (!IS_ENABLED(CONFIG_SYSCTL) &&
603 	    !(watchdog_enabled && watchdog_thresh))
604 		return;
605 
606 	mutex_lock(&watchdog_mutex);
607 	lockup_detector_reconfigure();
608 	softlockup_initialized = true;
609 	mutex_unlock(&watchdog_mutex);
610 }
611 
612 #else /* CONFIG_SOFTLOCKUP_DETECTOR */
613 static void lockup_detector_reconfigure(void)
614 {
615 	cpus_read_lock();
616 	watchdog_nmi_stop();
617 	lockup_detector_update_enable();
618 	watchdog_nmi_start();
619 	cpus_read_unlock();
620 }
621 static inline void lockup_detector_setup(void)
622 {
623 	lockup_detector_reconfigure();
624 }
625 #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
626 
627 static void __lockup_detector_cleanup(void)
628 {
629 	lockdep_assert_held(&watchdog_mutex);
630 	hardlockup_detector_perf_cleanup();
631 }
632 
633 /**
634  * lockup_detector_cleanup - Cleanup after cpu hotplug or sysctl changes
635  *
636  * Caller must not hold the cpu hotplug rwsem.
637  */
638 void lockup_detector_cleanup(void)
639 {
640 	mutex_lock(&watchdog_mutex);
641 	__lockup_detector_cleanup();
642 	mutex_unlock(&watchdog_mutex);
643 }
644 
645 /**
646  * lockup_detector_soft_poweroff - Interface to stop lockup detector(s)
647  *
648  * Special interface for parisc. It prevents lockup detector warnings from
649  * the default pm_poweroff() function which busy loops forever.
650  */
651 void lockup_detector_soft_poweroff(void)
652 {
653 	watchdog_enabled = 0;
654 }
655 
656 #ifdef CONFIG_SYSCTL
657 
658 /* Propagate any changes to the watchdog threads */
659 static void proc_watchdog_update(void)
660 {
661 	/* Remove impossible cpus to keep sysctl output clean. */
662 	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
663 	lockup_detector_reconfigure();
664 }
665 
666 /*
667  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
668  *
669  * caller             | table->data points to      | 'which'
670  * -------------------|----------------------------|--------------------------
671  * proc_watchdog      | watchdog_user_enabled      | NMI_WATCHDOG_ENABLED |
672  *                    |                            | SOFT_WATCHDOG_ENABLED
673  * -------------------|----------------------------|--------------------------
674  * proc_nmi_watchdog  | nmi_watchdog_user_enabled  | NMI_WATCHDOG_ENABLED
675  * -------------------|----------------------------|--------------------------
676  * proc_soft_watchdog | soft_watchdog_user_enabled | SOFT_WATCHDOG_ENABLED
677  */
678 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
679 				void __user *buffer, size_t *lenp, loff_t *ppos)
680 {
681 	int err, old, *param = table->data;
682 
683 	mutex_lock(&watchdog_mutex);
684 
685 	if (!write) {
686 		/*
687 		 * On read synchronize the userspace interface. This is a
688 		 * racy snapshot.
689 		 */
690 		*param = (watchdog_enabled & which) != 0;
691 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
692 	} else {
693 		old = READ_ONCE(*param);
694 		err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
695 		if (!err && old != READ_ONCE(*param))
696 			proc_watchdog_update();
697 	}
698 	mutex_unlock(&watchdog_mutex);
699 	return err;
700 }
701 
702 /*
703  * /proc/sys/kernel/watchdog
704  */
705 int proc_watchdog(struct ctl_table *table, int write,
706 		  void __user *buffer, size_t *lenp, loff_t *ppos)
707 {
708 	return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
709 				    table, write, buffer, lenp, ppos);
710 }
711 
712 /*
713  * /proc/sys/kernel/nmi_watchdog
714  */
715 int proc_nmi_watchdog(struct ctl_table *table, int write,
716 		      void __user *buffer, size_t *lenp, loff_t *ppos)
717 {
718 	if (!nmi_watchdog_available && write)
719 		return -ENOTSUPP;
720 	return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
721 				    table, write, buffer, lenp, ppos);
722 }
723 
724 /*
725  * /proc/sys/kernel/soft_watchdog
726  */
727 int proc_soft_watchdog(struct ctl_table *table, int write,
728 			void __user *buffer, size_t *lenp, loff_t *ppos)
729 {
730 	return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
731 				    table, write, buffer, lenp, ppos);
732 }
733 
734 /*
735  * /proc/sys/kernel/watchdog_thresh
736  */
737 int proc_watchdog_thresh(struct ctl_table *table, int write,
738 			 void __user *buffer, size_t *lenp, loff_t *ppos)
739 {
740 	int err, old;
741 
742 	mutex_lock(&watchdog_mutex);
743 
744 	old = READ_ONCE(watchdog_thresh);
745 	err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
746 
747 	if (!err && write && old != READ_ONCE(watchdog_thresh))
748 		proc_watchdog_update();
749 
750 	mutex_unlock(&watchdog_mutex);
751 	return err;
752 }
753 
754 /*
755  * The cpumask is the mask of possible cpus that the watchdog can run
756  * on, not the mask of cpus it is actually running on.  This allows the
757  * user to specify a mask that will include cpus that have not yet
758  * been brought online, if desired.
759  */
760 int proc_watchdog_cpumask(struct ctl_table *table, int write,
761 			  void __user *buffer, size_t *lenp, loff_t *ppos)
762 {
763 	int err;
764 
765 	mutex_lock(&watchdog_mutex);
766 
767 	err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
768 	if (!err && write)
769 		proc_watchdog_update();
770 
771 	mutex_unlock(&watchdog_mutex);
772 	return err;
773 }
774 #endif /* CONFIG_SYSCTL */
775 
776 void __init lockup_detector_init(void)
777 {
778 	if (tick_nohz_full_enabled())
779 		pr_info("Disabling watchdog on nohz_full cores by default\n");
780 
781 	cpumask_copy(&watchdog_cpumask,
782 		     housekeeping_cpumask(HK_FLAG_TIMER));
783 
784 	if (!watchdog_nmi_probe())
785 		nmi_watchdog_available = true;
786 	lockup_detector_setup();
787 }
788