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Linux/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 int watchdog_user_enabled = 1;
 28 int __read_mostly watchdog_thresh = 10;
 29 #ifdef CONFIG_SMP
 30 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 31 #else
 32 #define sysctl_softlockup_all_cpu_backtrace 0
 33 #endif
 34 
 35 static int __read_mostly watchdog_running;
 36 static u64 __read_mostly sample_period;
 37 
 38 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 39 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
 40 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 41 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 42 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 43 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 44 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
 45 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
 46 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 47 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 48 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 49 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
 50 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 51 #endif
 52 static unsigned long soft_lockup_nmi_warn;
 53 
 54 /* boot commands */
 55 /*
 56  * Should we panic when a soft-lockup or hard-lockup occurs:
 57  */
 58 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 59 static int hardlockup_panic =
 60                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
 61 
 62 static bool hardlockup_detector_enabled = true;
 63 /*
 64  * We may not want to enable hard lockup detection by default in all cases,
 65  * for example when running the kernel as a guest on a hypervisor. In these
 66  * cases this function can be called to disable hard lockup detection. This
 67  * function should only be executed once by the boot processor before the
 68  * kernel command line parameters are parsed, because otherwise it is not
 69  * possible to override this in hardlockup_panic_setup().
 70  */
 71 void watchdog_enable_hardlockup_detector(bool val)
 72 {
 73         hardlockup_detector_enabled = val;
 74 }
 75 
 76 bool watchdog_hardlockup_detector_is_enabled(void)
 77 {
 78         return hardlockup_detector_enabled;
 79 }
 80 
 81 static int __init hardlockup_panic_setup(char *str)
 82 {
 83         if (!strncmp(str, "panic", 5))
 84                 hardlockup_panic = 1;
 85         else if (!strncmp(str, "nopanic", 7))
 86                 hardlockup_panic = 0;
 87         else if (!strncmp(str, "", 1))
 88                 watchdog_user_enabled = 0;
 89         else if (!strncmp(str, "1", 1) || !strncmp(str, "2", 1)) {
 90                 /*
 91                  * Setting 'nmi_watchdog=1' or 'nmi_watchdog=2' (legacy option)
 92                  * has the same effect.
 93                  */
 94                 watchdog_user_enabled = 1;
 95                 watchdog_enable_hardlockup_detector(true);
 96         }
 97         return 1;
 98 }
 99 __setup("nmi_watchdog=", hardlockup_panic_setup);
100 #endif
101 
102 unsigned int __read_mostly softlockup_panic =
103                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
104 
105 static int __init softlockup_panic_setup(char *str)
106 {
107         softlockup_panic = simple_strtoul(str, NULL, 0);
108 
109         return 1;
110 }
111 __setup("softlockup_panic=", softlockup_panic_setup);
112 
113 static int __init nowatchdog_setup(char *str)
114 {
115         watchdog_user_enabled = 0;
116         return 1;
117 }
118 __setup("nowatchdog", nowatchdog_setup);
119 
120 /* deprecated */
121 static int __init nosoftlockup_setup(char *str)
122 {
123         watchdog_user_enabled = 0;
124         return 1;
125 }
126 __setup("nosoftlockup", nosoftlockup_setup);
127 /*  */
128 #ifdef CONFIG_SMP
129 static int __init softlockup_all_cpu_backtrace_setup(char *str)
130 {
131         sysctl_softlockup_all_cpu_backtrace =
132                 !!simple_strtol(str, NULL, 0);
133         return 1;
134 }
135 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
136 #endif
137 
138 /*
139  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
140  * lockups can have false positives under extreme conditions. So we generally
141  * want a higher threshold for soft lockups than for hard lockups. So we couple
142  * the thresholds with a factor: we make the soft threshold twice the amount of
143  * time the hard threshold is.
144  */
145 static int get_softlockup_thresh(void)
146 {
147         return watchdog_thresh * 2;
148 }
149 
150 /*
151  * Returns seconds, approximately.  We don't need nanosecond
152  * resolution, and we don't need to waste time with a big divide when
153  * 2^30ns == 1.074s.
154  */
155 static unsigned long get_timestamp(void)
156 {
157         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
158 }
159 
160 static void set_sample_period(void)
161 {
162         /*
163          * convert watchdog_thresh from seconds to ns
164          * the divide by 5 is to give hrtimer several chances (two
165          * or three with the current relation between the soft
166          * and hard thresholds) to increment before the
167          * hardlockup detector generates a warning
168          */
169         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
170 }
171 
172 /* Commands for resetting the watchdog */
173 static void __touch_watchdog(void)
174 {
175         __this_cpu_write(watchdog_touch_ts, get_timestamp());
176 }
177 
178 void touch_softlockup_watchdog(void)
179 {
180         /*
181          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
182          * gets zeroed here, so use the raw_ operation.
183          */
184         raw_cpu_write(watchdog_touch_ts, 0);
185 }
186 EXPORT_SYMBOL(touch_softlockup_watchdog);
187 
188 void touch_all_softlockup_watchdogs(void)
189 {
190         int cpu;
191 
192         /*
193          * this is done lockless
194          * do we care if a 0 races with a timestamp?
195          * all it means is the softlock check starts one cycle later
196          */
197         for_each_online_cpu(cpu)
198                 per_cpu(watchdog_touch_ts, cpu) = 0;
199 }
200 
201 #ifdef CONFIG_HARDLOCKUP_DETECTOR
202 void touch_nmi_watchdog(void)
203 {
204         /*
205          * Using __raw here because some code paths have
206          * preemption enabled.  If preemption is enabled
207          * then interrupts should be enabled too, in which
208          * case we shouldn't have to worry about the watchdog
209          * going off.
210          */
211         raw_cpu_write(watchdog_nmi_touch, true);
212         touch_softlockup_watchdog();
213 }
214 EXPORT_SYMBOL(touch_nmi_watchdog);
215 
216 #endif
217 
218 void touch_softlockup_watchdog_sync(void)
219 {
220         __this_cpu_write(softlockup_touch_sync, true);
221         __this_cpu_write(watchdog_touch_ts, 0);
222 }
223 
224 #ifdef CONFIG_HARDLOCKUP_DETECTOR
225 /* watchdog detector functions */
226 static int is_hardlockup(void)
227 {
228         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
229 
230         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
231                 return 1;
232 
233         __this_cpu_write(hrtimer_interrupts_saved, hrint);
234         return 0;
235 }
236 #endif
237 
238 static int is_softlockup(unsigned long touch_ts)
239 {
240         unsigned long now = get_timestamp();
241 
242         /* Warn about unreasonable delays: */
243         if (time_after(now, touch_ts + get_softlockup_thresh()))
244                 return now - touch_ts;
245 
246         return 0;
247 }
248 
249 #ifdef CONFIG_HARDLOCKUP_DETECTOR
250 
251 static struct perf_event_attr wd_hw_attr = {
252         .type           = PERF_TYPE_HARDWARE,
253         .config         = PERF_COUNT_HW_CPU_CYCLES,
254         .size           = sizeof(struct perf_event_attr),
255         .pinned         = 1,
256         .disabled       = 1,
257 };
258 
259 /* Callback function for perf event subsystem */
260 static void watchdog_overflow_callback(struct perf_event *event,
261                  struct perf_sample_data *data,
262                  struct pt_regs *regs)
263 {
264         /* Ensure the watchdog never gets throttled */
265         event->hw.interrupts = 0;
266 
267         if (__this_cpu_read(watchdog_nmi_touch) == true) {
268                 __this_cpu_write(watchdog_nmi_touch, false);
269                 return;
270         }
271 
272         /* check for a hardlockup
273          * This is done by making sure our timer interrupt
274          * is incrementing.  The timer interrupt should have
275          * fired multiple times before we overflow'd.  If it hasn't
276          * then this is a good indication the cpu is stuck
277          */
278         if (is_hardlockup()) {
279                 int this_cpu = smp_processor_id();
280 
281                 /* only print hardlockups once */
282                 if (__this_cpu_read(hard_watchdog_warn) == true)
283                         return;
284 
285                 if (hardlockup_panic)
286                         panic("Watchdog detected hard LOCKUP on cpu %d",
287                               this_cpu);
288                 else
289                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
290                              this_cpu);
291 
292                 __this_cpu_write(hard_watchdog_warn, true);
293                 return;
294         }
295 
296         __this_cpu_write(hard_watchdog_warn, false);
297         return;
298 }
299 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
300 
301 static void watchdog_interrupt_count(void)
302 {
303         __this_cpu_inc(hrtimer_interrupts);
304 }
305 
306 static int watchdog_nmi_enable(unsigned int cpu);
307 static void watchdog_nmi_disable(unsigned int cpu);
308 
309 /* watchdog kicker functions */
310 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
311 {
312         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
313         struct pt_regs *regs = get_irq_regs();
314         int duration;
315         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
316 
317         /* kick the hardlockup detector */
318         watchdog_interrupt_count();
319 
320         /* 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                          * If the time stamp was touched atomically
330                          * make sure the scheduler tick is up to date.
331                          */
332                         __this_cpu_write(softlockup_touch_sync, false);
333                         sched_clock_tick();
334                 }
335 
336                 /* Clear the guest paused flag on watchdog reset */
337                 kvm_check_and_clear_guest_paused();
338                 __touch_watchdog();
339                 return HRTIMER_RESTART;
340         }
341 
342         /* check for a softlockup
343          * This is done by making sure a high priority task is
344          * being scheduled.  The task touches the watchdog to
345          * indicate it is getting cpu time.  If it hasn't then
346          * this is a good indication some task is hogging the cpu
347          */
348         duration = is_softlockup(touch_ts);
349         if (unlikely(duration)) {
350                 /*
351                  * If a virtual machine is stopped by the host it can look to
352                  * the watchdog like a soft lockup, check to see if the host
353                  * stopped the vm before we issue the warning
354                  */
355                 if (kvm_check_and_clear_guest_paused())
356                         return HRTIMER_RESTART;
357 
358                 /* only warn once */
359                 if (__this_cpu_read(soft_watchdog_warn) == true) {
360                         /*
361                          * When multiple processes are causing softlockups the
362                          * softlockup detector only warns on the first one
363                          * because the code relies on a full quiet cycle to
364                          * re-arm.  The second process prevents the quiet cycle
365                          * and never gets reported.  Use task pointers to detect
366                          * this.
367                          */
368                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
369                             current) {
370                                 __this_cpu_write(soft_watchdog_warn, false);
371                                 __touch_watchdog();
372                         }
373                         return HRTIMER_RESTART;
374                 }
375 
376                 if (softlockup_all_cpu_backtrace) {
377                         /* Prevent multiple soft-lockup reports if one cpu is already
378                          * engaged in dumping cpu back traces
379                          */
380                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
381                                 /* Someone else will report us. Let's give up */
382                                 __this_cpu_write(soft_watchdog_warn, true);
383                                 return HRTIMER_RESTART;
384                         }
385                 }
386 
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                 print_modules();
392                 print_irqtrace_events(current);
393                 if (regs)
394                         show_regs(regs);
395                 else
396                         dump_stack();
397 
398                 if (softlockup_all_cpu_backtrace) {
399                         /* Avoid generating two back traces for current
400                          * given that one is already made above
401                          */
402                         trigger_allbutself_cpu_backtrace();
403 
404                         clear_bit(0, &soft_lockup_nmi_warn);
405                         /* Barrier to sync with other cpus */
406                         smp_mb__after_atomic();
407                 }
408 
409                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
410                 if (softlockup_panic)
411                         panic("softlockup: hung tasks");
412                 __this_cpu_write(soft_watchdog_warn, true);
413         } else
414                 __this_cpu_write(soft_watchdog_warn, false);
415 
416         return HRTIMER_RESTART;
417 }
418 
419 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
420 {
421         struct sched_param param = { .sched_priority = prio };
422 
423         sched_setscheduler(current, policy, &param);
424 }
425 
426 static void watchdog_enable(unsigned int cpu)
427 {
428         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
429 
430         /* kick off the timer for the hardlockup detector */
431         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
432         hrtimer->function = watchdog_timer_fn;
433 
434         /* Enable the perf event */
435         watchdog_nmi_enable(cpu);
436 
437         /* done here because hrtimer_start can only pin to smp_processor_id() */
438         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
439                       HRTIMER_MODE_REL_PINNED);
440 
441         /* initialize timestamp */
442         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
443         __touch_watchdog();
444 }
445 
446 static void watchdog_disable(unsigned int cpu)
447 {
448         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
449 
450         watchdog_set_prio(SCHED_NORMAL, 0);
451         hrtimer_cancel(hrtimer);
452         /* disable the perf event */
453         watchdog_nmi_disable(cpu);
454 }
455 
456 static void watchdog_cleanup(unsigned int cpu, bool online)
457 {
458         watchdog_disable(cpu);
459 }
460 
461 static int watchdog_should_run(unsigned int cpu)
462 {
463         return __this_cpu_read(hrtimer_interrupts) !=
464                 __this_cpu_read(soft_lockup_hrtimer_cnt);
465 }
466 
467 /*
468  * The watchdog thread function - touches the timestamp.
469  *
470  * It only runs once every sample_period seconds (4 seconds by
471  * default) to reset the softlockup timestamp. If this gets delayed
472  * for more than 2*watchdog_thresh seconds then the debug-printout
473  * triggers in watchdog_timer_fn().
474  */
475 static void watchdog(unsigned int cpu)
476 {
477         __this_cpu_write(soft_lockup_hrtimer_cnt,
478                          __this_cpu_read(hrtimer_interrupts));
479         __touch_watchdog();
480 }
481 
482 #ifdef CONFIG_HARDLOCKUP_DETECTOR
483 /*
484  * People like the simple clean cpu node info on boot.
485  * Reduce the watchdog noise by only printing messages
486  * that are different from what cpu0 displayed.
487  */
488 static unsigned long cpu0_err;
489 
490 static int watchdog_nmi_enable(unsigned int cpu)
491 {
492         struct perf_event_attr *wd_attr;
493         struct perf_event *event = per_cpu(watchdog_ev, cpu);
494 
495         /*
496          * Some kernels need to default hard lockup detection to
497          * 'disabled', for example a guest on a hypervisor.
498          */
499         if (!watchdog_hardlockup_detector_is_enabled()) {
500                 event = ERR_PTR(-ENOENT);
501                 goto handle_err;
502         }
503 
504         /* is it already setup and enabled? */
505         if (event && event->state > PERF_EVENT_STATE_OFF)
506                 goto out;
507 
508         /* it is setup but not enabled */
509         if (event != NULL)
510                 goto out_enable;
511 
512         wd_attr = &wd_hw_attr;
513         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
514 
515         /* Try to register using hardware perf events */
516         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
517 
518 handle_err:
519         /* save cpu0 error for future comparision */
520         if (cpu == 0 && IS_ERR(event))
521                 cpu0_err = PTR_ERR(event);
522 
523         if (!IS_ERR(event)) {
524                 /* only print for cpu0 or different than cpu0 */
525                 if (cpu == 0 || cpu0_err)
526                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
527                 goto out_save;
528         }
529 
530         /* skip displaying the same error again */
531         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
532                 return PTR_ERR(event);
533 
534         /* vary the KERN level based on the returned errno */
535         if (PTR_ERR(event) == -EOPNOTSUPP)
536                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
537         else if (PTR_ERR(event) == -ENOENT)
538                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
539                          cpu);
540         else
541                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
542                         cpu, PTR_ERR(event));
543         return PTR_ERR(event);
544 
545         /* success path */
546 out_save:
547         per_cpu(watchdog_ev, cpu) = event;
548 out_enable:
549         perf_event_enable(per_cpu(watchdog_ev, cpu));
550 out:
551         return 0;
552 }
553 
554 static void watchdog_nmi_disable(unsigned int cpu)
555 {
556         struct perf_event *event = per_cpu(watchdog_ev, cpu);
557 
558         if (event) {
559                 perf_event_disable(event);
560                 per_cpu(watchdog_ev, cpu) = NULL;
561 
562                 /* should be in cleanup, but blocks oprofile */
563                 perf_event_release_kernel(event);
564         }
565         if (cpu == 0) {
566                 /* watchdog_nmi_enable() expects this to be zero initially. */
567                 cpu0_err = 0;
568         }
569 }
570 #else
571 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
572 static void watchdog_nmi_disable(unsigned int cpu) { return; }
573 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
574 
575 static struct smp_hotplug_thread watchdog_threads = {
576         .store                  = &softlockup_watchdog,
577         .thread_should_run      = watchdog_should_run,
578         .thread_fn              = watchdog,
579         .thread_comm            = "watchdog/%u",
580         .setup                  = watchdog_enable,
581         .cleanup                = watchdog_cleanup,
582         .park                   = watchdog_disable,
583         .unpark                 = watchdog_enable,
584 };
585 
586 static void restart_watchdog_hrtimer(void *info)
587 {
588         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
589         int ret;
590 
591         /*
592          * No need to cancel and restart hrtimer if it is currently executing
593          * because it will reprogram itself with the new period now.
594          * We should never see it unqueued here because we are running per-cpu
595          * with interrupts disabled.
596          */
597         ret = hrtimer_try_to_cancel(hrtimer);
598         if (ret == 1)
599                 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
600                                 HRTIMER_MODE_REL_PINNED);
601 }
602 
603 static void update_timers(int cpu)
604 {
605         /*
606          * Make sure that perf event counter will adopt to a new
607          * sampling period. Updating the sampling period directly would
608          * be much nicer but we do not have an API for that now so
609          * let's use a big hammer.
610          * Hrtimer will adopt the new period on the next tick but this
611          * might be late already so we have to restart the timer as well.
612          */
613         watchdog_nmi_disable(cpu);
614         smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
615         watchdog_nmi_enable(cpu);
616 }
617 
618 static void update_timers_all_cpus(void)
619 {
620         int cpu;
621 
622         get_online_cpus();
623         for_each_online_cpu(cpu)
624                 update_timers(cpu);
625         put_online_cpus();
626 }
627 
628 static int watchdog_enable_all_cpus(bool sample_period_changed)
629 {
630         int err = 0;
631 
632         if (!watchdog_running) {
633                 err = smpboot_register_percpu_thread(&watchdog_threads);
634                 if (err)
635                         pr_err("Failed to create watchdog threads, disabled\n");
636                 else
637                         watchdog_running = 1;
638         } else if (sample_period_changed) {
639                 update_timers_all_cpus();
640         }
641 
642         return err;
643 }
644 
645 /* prepare/enable/disable routines */
646 /* sysctl functions */
647 #ifdef CONFIG_SYSCTL
648 static void watchdog_disable_all_cpus(void)
649 {
650         if (watchdog_running) {
651                 watchdog_running = 0;
652                 smpboot_unregister_percpu_thread(&watchdog_threads);
653         }
654 }
655 
656 /*
657  * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
658  */
659 
660 int proc_dowatchdog(struct ctl_table *table, int write,
661                     void __user *buffer, size_t *lenp, loff_t *ppos)
662 {
663         int err, old_thresh, old_enabled;
664         bool old_hardlockup;
665         static DEFINE_MUTEX(watchdog_proc_mutex);
666 
667         mutex_lock(&watchdog_proc_mutex);
668         old_thresh = ACCESS_ONCE(watchdog_thresh);
669         old_enabled = ACCESS_ONCE(watchdog_user_enabled);
670         old_hardlockup = watchdog_hardlockup_detector_is_enabled();
671 
672         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
673         if (err || !write)
674                 goto out;
675 
676         set_sample_period();
677         /*
678          * Watchdog threads shouldn't be enabled if they are
679          * disabled. The 'watchdog_running' variable check in
680          * watchdog_*_all_cpus() function takes care of this.
681          */
682         if (watchdog_user_enabled && watchdog_thresh) {
683                 /*
684                  * Prevent a change in watchdog_thresh accidentally overriding
685                  * the enablement of the hardlockup detector.
686                  */
687                 if (watchdog_user_enabled != old_enabled)
688                         watchdog_enable_hardlockup_detector(true);
689                 err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
690         } else
691                 watchdog_disable_all_cpus();
692 
693         /* Restore old values on failure */
694         if (err) {
695                 watchdog_thresh = old_thresh;
696                 watchdog_user_enabled = old_enabled;
697                 watchdog_enable_hardlockup_detector(old_hardlockup);
698         }
699 out:
700         mutex_unlock(&watchdog_proc_mutex);
701         return err;
702 }
703 #endif /* CONFIG_SYSCTL */
704 
705 void __init lockup_detector_init(void)
706 {
707         set_sample_period();
708 
709         if (watchdog_user_enabled)
710                 watchdog_enable_all_cpus(false);
711 }
712 

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