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TOMOYO Linux Cross Reference
Linux/kernel/watchdog.c

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  1 /*
  2  * Detect hard and soft lockups on a system
  3  *
  4  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  5  *
  6  * Note: Most of this code is borrowed heavily from the original softlockup
  7  * detector, so thanks to Ingo for the initial implementation.
  8  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
  9  * to those contributors as well.
 10  */
 11 
 12 #define pr_fmt(fmt) "NMI watchdog: " fmt
 13 
 14 #include <linux/mm.h>
 15 #include <linux/cpu.h>
 16 #include <linux/nmi.h>
 17 #include <linux/init.h>
 18 #include <linux/module.h>
 19 #include <linux/sysctl.h>
 20 #include <linux/smpboot.h>
 21 #include <linux/sched/rt.h>
 22 #include <linux/tick.h>
 23 
 24 #include <asm/irq_regs.h>
 25 #include <linux/kvm_para.h>
 26 #include <linux/perf_event.h>
 27 #include <linux/kthread.h>
 28 
 29 /*
 30  * The run state of the lockup detectors is controlled by the content of the
 31  * 'watchdog_enabled' variable. Each lockup detector has its dedicated bit -
 32  * bit 0 for the hard lockup detector and bit 1 for the soft lockup detector.
 33  *
 34  * 'watchdog_user_enabled', 'nmi_watchdog_enabled' and 'soft_watchdog_enabled'
 35  * are variables that are only used as an 'interface' between the parameters
 36  * in /proc/sys/kernel and the internal state bits in 'watchdog_enabled'. The
 37  * 'watchdog_thresh' variable is handled differently because its value is not
 38  * boolean, and the lockup detectors are 'suspended' while 'watchdog_thresh'
 39  * is equal zero.
 40  */
 41 #define NMI_WATCHDOG_ENABLED_BIT   0
 42 #define SOFT_WATCHDOG_ENABLED_BIT  1
 43 #define NMI_WATCHDOG_ENABLED      (1 << NMI_WATCHDOG_ENABLED_BIT)
 44 #define SOFT_WATCHDOG_ENABLED     (1 << SOFT_WATCHDOG_ENABLED_BIT)
 45 
 46 static DEFINE_MUTEX(watchdog_proc_mutex);
 47 
 48 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 49 static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED;
 50 #else
 51 static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED;
 52 #endif
 53 int __read_mostly nmi_watchdog_enabled;
 54 int __read_mostly soft_watchdog_enabled;
 55 int __read_mostly watchdog_user_enabled;
 56 int __read_mostly watchdog_thresh = 10;
 57 
 58 #ifdef CONFIG_SMP
 59 int __read_mostly sysctl_softlockup_all_cpu_backtrace;
 60 #else
 61 #define sysctl_softlockup_all_cpu_backtrace 0
 62 #endif
 63 static struct cpumask watchdog_cpumask __read_mostly;
 64 unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
 65 
 66 /* Helper for online, unparked cpus. */
 67 #define for_each_watchdog_cpu(cpu) \
 68         for_each_cpu_and((cpu), cpu_online_mask, &watchdog_cpumask)
 69 
 70 /*
 71  * The 'watchdog_running' variable is set to 1 when the watchdog threads
 72  * are registered/started and is set to 0 when the watchdog threads are
 73  * unregistered/stopped, so it is an indicator whether the threads exist.
 74  */
 75 static int __read_mostly watchdog_running;
 76 /*
 77  * If a subsystem has a need to deactivate the watchdog temporarily, it
 78  * can use the suspend/resume interface to achieve this. The content of
 79  * the 'watchdog_suspended' variable reflects this state. Existing threads
 80  * are parked/unparked by the lockup_detector_{suspend|resume} functions
 81  * (see comment blocks pertaining to those functions for further details).
 82  *
 83  * 'watchdog_suspended' also prevents threads from being registered/started
 84  * or unregistered/stopped via parameters in /proc/sys/kernel, so the state
 85  * of 'watchdog_running' cannot change while the watchdog is deactivated
 86  * temporarily (see related code in 'proc' handlers).
 87  */
 88 static int __read_mostly watchdog_suspended;
 89 
 90 static u64 __read_mostly sample_period;
 91 
 92 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
 93 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
 94 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
 95 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
 96 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
 97 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
 98 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
 99 static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
100 #ifdef CONFIG_HARDLOCKUP_DETECTOR
101 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
102 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
103 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
104 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
105 #endif
106 static unsigned long soft_lockup_nmi_warn;
107 
108 /* boot commands */
109 /*
110  * Should we panic when a soft-lockup or hard-lockup occurs:
111  */
112 #ifdef CONFIG_HARDLOCKUP_DETECTOR
113 static int hardlockup_panic =
114                         CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
115 /*
116  * We may not want to enable hard lockup detection by default in all cases,
117  * for example when running the kernel as a guest on a hypervisor. In these
118  * cases this function can be called to disable hard lockup detection. This
119  * function should only be executed once by the boot processor before the
120  * kernel command line parameters are parsed, because otherwise it is not
121  * possible to override this in hardlockup_panic_setup().
122  */
123 void hardlockup_detector_disable(void)
124 {
125         watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
126 }
127 
128 static int __init hardlockup_panic_setup(char *str)
129 {
130         if (!strncmp(str, "panic", 5))
131                 hardlockup_panic = 1;
132         else if (!strncmp(str, "nopanic", 7))
133                 hardlockup_panic = 0;
134         else if (!strncmp(str, "", 1))
135                 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
136         else if (!strncmp(str, "1", 1))
137                 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
138         return 1;
139 }
140 __setup("nmi_watchdog=", hardlockup_panic_setup);
141 #endif
142 
143 unsigned int __read_mostly softlockup_panic =
144                         CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
145 
146 static int __init softlockup_panic_setup(char *str)
147 {
148         softlockup_panic = simple_strtoul(str, NULL, 0);
149 
150         return 1;
151 }
152 __setup("softlockup_panic=", softlockup_panic_setup);
153 
154 static int __init nowatchdog_setup(char *str)
155 {
156         watchdog_enabled = 0;
157         return 1;
158 }
159 __setup("nowatchdog", nowatchdog_setup);
160 
161 static int __init nosoftlockup_setup(char *str)
162 {
163         watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED;
164         return 1;
165 }
166 __setup("nosoftlockup", nosoftlockup_setup);
167 
168 #ifdef CONFIG_SMP
169 static int __init softlockup_all_cpu_backtrace_setup(char *str)
170 {
171         sysctl_softlockup_all_cpu_backtrace =
172                 !!simple_strtol(str, NULL, 0);
173         return 1;
174 }
175 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
176 #endif
177 
178 /*
179  * Hard-lockup warnings should be triggered after just a few seconds. Soft-
180  * lockups can have false positives under extreme conditions. So we generally
181  * want a higher threshold for soft lockups than for hard lockups. So we couple
182  * the thresholds with a factor: we make the soft threshold twice the amount of
183  * time the hard threshold is.
184  */
185 static int get_softlockup_thresh(void)
186 {
187         return watchdog_thresh * 2;
188 }
189 
190 /*
191  * Returns seconds, approximately.  We don't need nanosecond
192  * resolution, and we don't need to waste time with a big divide when
193  * 2^30ns == 1.074s.
194  */
195 static unsigned long get_timestamp(void)
196 {
197         return running_clock() >> 30LL;  /* 2^30 ~= 10^9 */
198 }
199 
200 static void set_sample_period(void)
201 {
202         /*
203          * convert watchdog_thresh from seconds to ns
204          * the divide by 5 is to give hrtimer several chances (two
205          * or three with the current relation between the soft
206          * and hard thresholds) to increment before the
207          * hardlockup detector generates a warning
208          */
209         sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
210 }
211 
212 /* Commands for resetting the watchdog */
213 static void __touch_watchdog(void)
214 {
215         __this_cpu_write(watchdog_touch_ts, get_timestamp());
216 }
217 
218 void touch_softlockup_watchdog(void)
219 {
220         /*
221          * Preemption can be enabled.  It doesn't matter which CPU's timestamp
222          * gets zeroed here, so use the raw_ operation.
223          */
224         raw_cpu_write(watchdog_touch_ts, 0);
225 }
226 EXPORT_SYMBOL(touch_softlockup_watchdog);
227 
228 void touch_all_softlockup_watchdogs(void)
229 {
230         int cpu;
231 
232         /*
233          * this is done lockless
234          * do we care if a 0 races with a timestamp?
235          * all it means is the softlock check starts one cycle later
236          */
237         for_each_watchdog_cpu(cpu)
238                 per_cpu(watchdog_touch_ts, cpu) = 0;
239 }
240 
241 #ifdef CONFIG_HARDLOCKUP_DETECTOR
242 void touch_nmi_watchdog(void)
243 {
244         /*
245          * Using __raw here because some code paths have
246          * preemption enabled.  If preemption is enabled
247          * then interrupts should be enabled too, in which
248          * case we shouldn't have to worry about the watchdog
249          * going off.
250          */
251         raw_cpu_write(watchdog_nmi_touch, true);
252         touch_softlockup_watchdog();
253 }
254 EXPORT_SYMBOL(touch_nmi_watchdog);
255 
256 #endif
257 
258 void touch_softlockup_watchdog_sync(void)
259 {
260         __this_cpu_write(softlockup_touch_sync, true);
261         __this_cpu_write(watchdog_touch_ts, 0);
262 }
263 
264 #ifdef CONFIG_HARDLOCKUP_DETECTOR
265 /* watchdog detector functions */
266 static int is_hardlockup(void)
267 {
268         unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
269 
270         if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
271                 return 1;
272 
273         __this_cpu_write(hrtimer_interrupts_saved, hrint);
274         return 0;
275 }
276 #endif
277 
278 static int is_softlockup(unsigned long touch_ts)
279 {
280         unsigned long now = get_timestamp();
281 
282         if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) {
283                 /* Warn about unreasonable delays. */
284                 if (time_after(now, touch_ts + get_softlockup_thresh()))
285                         return now - touch_ts;
286         }
287         return 0;
288 }
289 
290 #ifdef CONFIG_HARDLOCKUP_DETECTOR
291 
292 static struct perf_event_attr wd_hw_attr = {
293         .type           = PERF_TYPE_HARDWARE,
294         .config         = PERF_COUNT_HW_CPU_CYCLES,
295         .size           = sizeof(struct perf_event_attr),
296         .pinned         = 1,
297         .disabled       = 1,
298 };
299 
300 /* Callback function for perf event subsystem */
301 static void watchdog_overflow_callback(struct perf_event *event,
302                  struct perf_sample_data *data,
303                  struct pt_regs *regs)
304 {
305         /* Ensure the watchdog never gets throttled */
306         event->hw.interrupts = 0;
307 
308         if (__this_cpu_read(watchdog_nmi_touch) == true) {
309                 __this_cpu_write(watchdog_nmi_touch, false);
310                 return;
311         }
312 
313         /* check for a hardlockup
314          * This is done by making sure our timer interrupt
315          * is incrementing.  The timer interrupt should have
316          * fired multiple times before we overflow'd.  If it hasn't
317          * then this is a good indication the cpu is stuck
318          */
319         if (is_hardlockup()) {
320                 int this_cpu = smp_processor_id();
321 
322                 /* only print hardlockups once */
323                 if (__this_cpu_read(hard_watchdog_warn) == true)
324                         return;
325 
326                 if (hardlockup_panic)
327                         panic("Watchdog detected hard LOCKUP on cpu %d",
328                               this_cpu);
329                 else
330                         WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
331                              this_cpu);
332 
333                 __this_cpu_write(hard_watchdog_warn, true);
334                 return;
335         }
336 
337         __this_cpu_write(hard_watchdog_warn, false);
338         return;
339 }
340 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
341 
342 static void watchdog_interrupt_count(void)
343 {
344         __this_cpu_inc(hrtimer_interrupts);
345 }
346 
347 static int watchdog_nmi_enable(unsigned int cpu);
348 static void watchdog_nmi_disable(unsigned int cpu);
349 
350 /* watchdog kicker functions */
351 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
352 {
353         unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
354         struct pt_regs *regs = get_irq_regs();
355         int duration;
356         int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
357 
358         /* kick the hardlockup detector */
359         watchdog_interrupt_count();
360 
361         /* kick the softlockup detector */
362         wake_up_process(__this_cpu_read(softlockup_watchdog));
363 
364         /* .. and repeat */
365         hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
366 
367         if (touch_ts == 0) {
368                 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
369                         /*
370                          * If the time stamp was touched atomically
371                          * make sure the scheduler tick is up to date.
372                          */
373                         __this_cpu_write(softlockup_touch_sync, false);
374                         sched_clock_tick();
375                 }
376 
377                 /* Clear the guest paused flag on watchdog reset */
378                 kvm_check_and_clear_guest_paused();
379                 __touch_watchdog();
380                 return HRTIMER_RESTART;
381         }
382 
383         /* check for a softlockup
384          * This is done by making sure a high priority task is
385          * being scheduled.  The task touches the watchdog to
386          * indicate it is getting cpu time.  If it hasn't then
387          * this is a good indication some task is hogging the cpu
388          */
389         duration = is_softlockup(touch_ts);
390         if (unlikely(duration)) {
391                 /*
392                  * If a virtual machine is stopped by the host it can look to
393                  * the watchdog like a soft lockup, check to see if the host
394                  * stopped the vm before we issue the warning
395                  */
396                 if (kvm_check_and_clear_guest_paused())
397                         return HRTIMER_RESTART;
398 
399                 /* only warn once */
400                 if (__this_cpu_read(soft_watchdog_warn) == true) {
401                         /*
402                          * When multiple processes are causing softlockups the
403                          * softlockup detector only warns on the first one
404                          * because the code relies on a full quiet cycle to
405                          * re-arm.  The second process prevents the quiet cycle
406                          * and never gets reported.  Use task pointers to detect
407                          * this.
408                          */
409                         if (__this_cpu_read(softlockup_task_ptr_saved) !=
410                             current) {
411                                 __this_cpu_write(soft_watchdog_warn, false);
412                                 __touch_watchdog();
413                         }
414                         return HRTIMER_RESTART;
415                 }
416 
417                 if (softlockup_all_cpu_backtrace) {
418                         /* Prevent multiple soft-lockup reports if one cpu is already
419                          * engaged in dumping cpu back traces
420                          */
421                         if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
422                                 /* Someone else will report us. Let's give up */
423                                 __this_cpu_write(soft_watchdog_warn, true);
424                                 return HRTIMER_RESTART;
425                         }
426                 }
427 
428                 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
429                         smp_processor_id(), duration,
430                         current->comm, task_pid_nr(current));
431                 __this_cpu_write(softlockup_task_ptr_saved, current);
432                 print_modules();
433                 print_irqtrace_events(current);
434                 if (regs)
435                         show_regs(regs);
436                 else
437                         dump_stack();
438 
439                 if (softlockup_all_cpu_backtrace) {
440                         /* Avoid generating two back traces for current
441                          * given that one is already made above
442                          */
443                         trigger_allbutself_cpu_backtrace();
444 
445                         clear_bit(0, &soft_lockup_nmi_warn);
446                         /* Barrier to sync with other cpus */
447                         smp_mb__after_atomic();
448                 }
449 
450                 add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
451                 if (softlockup_panic)
452                         panic("softlockup: hung tasks");
453                 __this_cpu_write(soft_watchdog_warn, true);
454         } else
455                 __this_cpu_write(soft_watchdog_warn, false);
456 
457         return HRTIMER_RESTART;
458 }
459 
460 static void watchdog_set_prio(unsigned int policy, unsigned int prio)
461 {
462         struct sched_param param = { .sched_priority = prio };
463 
464         sched_setscheduler(current, policy, &param);
465 }
466 
467 static void watchdog_enable(unsigned int cpu)
468 {
469         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
470 
471         /* kick off the timer for the hardlockup detector */
472         hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
473         hrtimer->function = watchdog_timer_fn;
474 
475         /* Enable the perf event */
476         watchdog_nmi_enable(cpu);
477 
478         /* done here because hrtimer_start can only pin to smp_processor_id() */
479         hrtimer_start(hrtimer, ns_to_ktime(sample_period),
480                       HRTIMER_MODE_REL_PINNED);
481 
482         /* initialize timestamp */
483         watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
484         __touch_watchdog();
485 }
486 
487 static void watchdog_disable(unsigned int cpu)
488 {
489         struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer);
490 
491         watchdog_set_prio(SCHED_NORMAL, 0);
492         hrtimer_cancel(hrtimer);
493         /* disable the perf event */
494         watchdog_nmi_disable(cpu);
495 }
496 
497 static void watchdog_cleanup(unsigned int cpu, bool online)
498 {
499         watchdog_disable(cpu);
500 }
501 
502 static int watchdog_should_run(unsigned int cpu)
503 {
504         return __this_cpu_read(hrtimer_interrupts) !=
505                 __this_cpu_read(soft_lockup_hrtimer_cnt);
506 }
507 
508 /*
509  * The watchdog thread function - touches the timestamp.
510  *
511  * It only runs once every sample_period seconds (4 seconds by
512  * default) to reset the softlockup timestamp. If this gets delayed
513  * for more than 2*watchdog_thresh seconds then the debug-printout
514  * triggers in watchdog_timer_fn().
515  */
516 static void watchdog(unsigned int cpu)
517 {
518         __this_cpu_write(soft_lockup_hrtimer_cnt,
519                          __this_cpu_read(hrtimer_interrupts));
520         __touch_watchdog();
521 
522         /*
523          * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the
524          * failure path. Check for failures that can occur asynchronously -
525          * for example, when CPUs are on-lined - and shut down the hardware
526          * perf event on each CPU accordingly.
527          *
528          * The only non-obvious place this bit can be cleared is through
529          * watchdog_nmi_enable(), so a pr_info() is placed there.  Placing a
530          * pr_info here would be too noisy as it would result in a message
531          * every few seconds if the hardlockup was disabled but the softlockup
532          * enabled.
533          */
534         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
535                 watchdog_nmi_disable(cpu);
536 }
537 
538 #ifdef CONFIG_HARDLOCKUP_DETECTOR
539 /*
540  * People like the simple clean cpu node info on boot.
541  * Reduce the watchdog noise by only printing messages
542  * that are different from what cpu0 displayed.
543  */
544 static unsigned long cpu0_err;
545 
546 static int watchdog_nmi_enable(unsigned int cpu)
547 {
548         struct perf_event_attr *wd_attr;
549         struct perf_event *event = per_cpu(watchdog_ev, cpu);
550 
551         /* nothing to do if the hard lockup detector is disabled */
552         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
553                 goto out;
554 
555         /* is it already setup and enabled? */
556         if (event && event->state > PERF_EVENT_STATE_OFF)
557                 goto out;
558 
559         /* it is setup but not enabled */
560         if (event != NULL)
561                 goto out_enable;
562 
563         wd_attr = &wd_hw_attr;
564         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
565 
566         /* Try to register using hardware perf events */
567         event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
568 
569         /* save cpu0 error for future comparision */
570         if (cpu == 0 && IS_ERR(event))
571                 cpu0_err = PTR_ERR(event);
572 
573         if (!IS_ERR(event)) {
574                 /* only print for cpu0 or different than cpu0 */
575                 if (cpu == 0 || cpu0_err)
576                         pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
577                 goto out_save;
578         }
579 
580         /*
581          * Disable the hard lockup detector if _any_ CPU fails to set up
582          * set up the hardware perf event. The watchdog() function checks
583          * the NMI_WATCHDOG_ENABLED bit periodically.
584          *
585          * The barriers are for syncing up watchdog_enabled across all the
586          * cpus, as clear_bit() does not use barriers.
587          */
588         smp_mb__before_atomic();
589         clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
590         smp_mb__after_atomic();
591 
592         /* skip displaying the same error again */
593         if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
594                 return PTR_ERR(event);
595 
596         /* vary the KERN level based on the returned errno */
597         if (PTR_ERR(event) == -EOPNOTSUPP)
598                 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
599         else if (PTR_ERR(event) == -ENOENT)
600                 pr_warn("disabled (cpu%i): hardware events not enabled\n",
601                          cpu);
602         else
603                 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
604                         cpu, PTR_ERR(event));
605 
606         pr_info("Shutting down hard lockup detector on all cpus\n");
607 
608         return PTR_ERR(event);
609 
610         /* success path */
611 out_save:
612         per_cpu(watchdog_ev, cpu) = event;
613 out_enable:
614         perf_event_enable(per_cpu(watchdog_ev, cpu));
615 out:
616         return 0;
617 }
618 
619 static void watchdog_nmi_disable(unsigned int cpu)
620 {
621         struct perf_event *event = per_cpu(watchdog_ev, cpu);
622 
623         if (event) {
624                 perf_event_disable(event);
625                 per_cpu(watchdog_ev, cpu) = NULL;
626 
627                 /* should be in cleanup, but blocks oprofile */
628                 perf_event_release_kernel(event);
629         }
630         if (cpu == 0) {
631                 /* watchdog_nmi_enable() expects this to be zero initially. */
632                 cpu0_err = 0;
633         }
634 }
635 
636 #else
637 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
638 static void watchdog_nmi_disable(unsigned int cpu) { return; }
639 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
640 
641 static struct smp_hotplug_thread watchdog_threads = {
642         .store                  = &softlockup_watchdog,
643         .thread_should_run      = watchdog_should_run,
644         .thread_fn              = watchdog,
645         .thread_comm            = "watchdog/%u",
646         .setup                  = watchdog_enable,
647         .cleanup                = watchdog_cleanup,
648         .park                   = watchdog_disable,
649         .unpark                 = watchdog_enable,
650 };
651 
652 /*
653  * park all watchdog threads that are specified in 'watchdog_cpumask'
654  */
655 static int watchdog_park_threads(void)
656 {
657         int cpu, ret = 0;
658 
659         get_online_cpus();
660         for_each_watchdog_cpu(cpu) {
661                 ret = kthread_park(per_cpu(softlockup_watchdog, cpu));
662                 if (ret)
663                         break;
664         }
665         if (ret) {
666                 for_each_watchdog_cpu(cpu)
667                         kthread_unpark(per_cpu(softlockup_watchdog, cpu));
668         }
669         put_online_cpus();
670 
671         return ret;
672 }
673 
674 /*
675  * unpark all watchdog threads that are specified in 'watchdog_cpumask'
676  */
677 static void watchdog_unpark_threads(void)
678 {
679         int cpu;
680 
681         get_online_cpus();
682         for_each_watchdog_cpu(cpu)
683                 kthread_unpark(per_cpu(softlockup_watchdog, cpu));
684         put_online_cpus();
685 }
686 
687 /*
688  * Suspend the hard and soft lockup detector by parking the watchdog threads.
689  */
690 int lockup_detector_suspend(void)
691 {
692         int ret = 0;
693 
694         mutex_lock(&watchdog_proc_mutex);
695         /*
696          * Multiple suspend requests can be active in parallel (counted by
697          * the 'watchdog_suspended' variable). If the watchdog threads are
698          * running, the first caller takes care that they will be parked.
699          * The state of 'watchdog_running' cannot change while a suspend
700          * request is active (see related code in 'proc' handlers).
701          */
702         if (watchdog_running && !watchdog_suspended)
703                 ret = watchdog_park_threads();
704 
705         if (ret == 0)
706                 watchdog_suspended++;
707 
708         mutex_unlock(&watchdog_proc_mutex);
709 
710         return ret;
711 }
712 
713 /*
714  * Resume the hard and soft lockup detector by unparking the watchdog threads.
715  */
716 void lockup_detector_resume(void)
717 {
718         mutex_lock(&watchdog_proc_mutex);
719 
720         watchdog_suspended--;
721         /*
722          * The watchdog threads are unparked if they were previously running
723          * and if there is no more active suspend request.
724          */
725         if (watchdog_running && !watchdog_suspended)
726                 watchdog_unpark_threads();
727 
728         mutex_unlock(&watchdog_proc_mutex);
729 }
730 
731 static void update_watchdog_all_cpus(void)
732 {
733         watchdog_park_threads();
734         watchdog_unpark_threads();
735 }
736 
737 static int watchdog_enable_all_cpus(void)
738 {
739         int err = 0;
740 
741         if (!watchdog_running) {
742                 err = smpboot_register_percpu_thread_cpumask(&watchdog_threads,
743                                                              &watchdog_cpumask);
744                 if (err)
745                         pr_err("Failed to create watchdog threads, disabled\n");
746                 else
747                         watchdog_running = 1;
748         } else {
749                 /*
750                  * Enable/disable the lockup detectors or
751                  * change the sample period 'on the fly'.
752                  */
753                 update_watchdog_all_cpus();
754         }
755 
756         return err;
757 }
758 
759 /* prepare/enable/disable routines */
760 /* sysctl functions */
761 #ifdef CONFIG_SYSCTL
762 static void watchdog_disable_all_cpus(void)
763 {
764         if (watchdog_running) {
765                 watchdog_running = 0;
766                 smpboot_unregister_percpu_thread(&watchdog_threads);
767         }
768 }
769 
770 /*
771  * Update the run state of the lockup detectors.
772  */
773 static int proc_watchdog_update(void)
774 {
775         int err = 0;
776 
777         /*
778          * Watchdog threads won't be started if they are already active.
779          * The 'watchdog_running' variable in watchdog_*_all_cpus() takes
780          * care of this. If those threads are already active, the sample
781          * period will be updated and the lockup detectors will be enabled
782          * or disabled 'on the fly'.
783          */
784         if (watchdog_enabled && watchdog_thresh)
785                 err = watchdog_enable_all_cpus();
786         else
787                 watchdog_disable_all_cpus();
788 
789         return err;
790 
791 }
792 
793 /*
794  * common function for watchdog, nmi_watchdog and soft_watchdog parameter
795  *
796  * caller             | table->data points to | 'which' contains the flag(s)
797  * -------------------|-----------------------|-----------------------------
798  * proc_watchdog      | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed
799  *                    |                       | with SOFT_WATCHDOG_ENABLED
800  * -------------------|-----------------------|-----------------------------
801  * proc_nmi_watchdog  | nmi_watchdog_enabled  | NMI_WATCHDOG_ENABLED
802  * -------------------|-----------------------|-----------------------------
803  * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED
804  */
805 static int proc_watchdog_common(int which, struct ctl_table *table, int write,
806                                 void __user *buffer, size_t *lenp, loff_t *ppos)
807 {
808         int err, old, new;
809         int *watchdog_param = (int *)table->data;
810 
811         mutex_lock(&watchdog_proc_mutex);
812 
813         if (watchdog_suspended) {
814                 /* no parameter changes allowed while watchdog is suspended */
815                 err = -EAGAIN;
816                 goto out;
817         }
818 
819         /*
820          * If the parameter is being read return the state of the corresponding
821          * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the
822          * run state of the lockup detectors.
823          */
824         if (!write) {
825                 *watchdog_param = (watchdog_enabled & which) != 0;
826                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
827         } else {
828                 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
829                 if (err)
830                         goto out;
831 
832                 /*
833                  * There is a race window between fetching the current value
834                  * from 'watchdog_enabled' and storing the new value. During
835                  * this race window, watchdog_nmi_enable() can sneak in and
836                  * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'.
837                  * The 'cmpxchg' detects this race and the loop retries.
838                  */
839                 do {
840                         old = watchdog_enabled;
841                         /*
842                          * If the parameter value is not zero set the
843                          * corresponding bit(s), else clear it(them).
844                          */
845                         if (*watchdog_param)
846                                 new = old | which;
847                         else
848                                 new = old & ~which;
849                 } while (cmpxchg(&watchdog_enabled, old, new) != old);
850 
851                 /*
852                  * Update the run state of the lockup detectors.
853                  * Restore 'watchdog_enabled' on failure.
854                  */
855                 err = proc_watchdog_update();
856                 if (err)
857                         watchdog_enabled = old;
858         }
859 out:
860         mutex_unlock(&watchdog_proc_mutex);
861         return err;
862 }
863 
864 /*
865  * /proc/sys/kernel/watchdog
866  */
867 int proc_watchdog(struct ctl_table *table, int write,
868                   void __user *buffer, size_t *lenp, loff_t *ppos)
869 {
870         return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED,
871                                     table, write, buffer, lenp, ppos);
872 }
873 
874 /*
875  * /proc/sys/kernel/nmi_watchdog
876  */
877 int proc_nmi_watchdog(struct ctl_table *table, int write,
878                       void __user *buffer, size_t *lenp, loff_t *ppos)
879 {
880         return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
881                                     table, write, buffer, lenp, ppos);
882 }
883 
884 /*
885  * /proc/sys/kernel/soft_watchdog
886  */
887 int proc_soft_watchdog(struct ctl_table *table, int write,
888                         void __user *buffer, size_t *lenp, loff_t *ppos)
889 {
890         return proc_watchdog_common(SOFT_WATCHDOG_ENABLED,
891                                     table, write, buffer, lenp, ppos);
892 }
893 
894 /*
895  * /proc/sys/kernel/watchdog_thresh
896  */
897 int proc_watchdog_thresh(struct ctl_table *table, int write,
898                          void __user *buffer, size_t *lenp, loff_t *ppos)
899 {
900         int err, old;
901 
902         mutex_lock(&watchdog_proc_mutex);
903 
904         if (watchdog_suspended) {
905                 /* no parameter changes allowed while watchdog is suspended */
906                 err = -EAGAIN;
907                 goto out;
908         }
909 
910         old = ACCESS_ONCE(watchdog_thresh);
911         err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
912 
913         if (err || !write)
914                 goto out;
915 
916         /*
917          * Update the sample period.
918          * Restore 'watchdog_thresh' on failure.
919          */
920         set_sample_period();
921         err = proc_watchdog_update();
922         if (err)
923                 watchdog_thresh = old;
924 out:
925         mutex_unlock(&watchdog_proc_mutex);
926         return err;
927 }
928 
929 /*
930  * The cpumask is the mask of possible cpus that the watchdog can run
931  * on, not the mask of cpus it is actually running on.  This allows the
932  * user to specify a mask that will include cpus that have not yet
933  * been brought online, if desired.
934  */
935 int proc_watchdog_cpumask(struct ctl_table *table, int write,
936                           void __user *buffer, size_t *lenp, loff_t *ppos)
937 {
938         int err;
939 
940         mutex_lock(&watchdog_proc_mutex);
941 
942         if (watchdog_suspended) {
943                 /* no parameter changes allowed while watchdog is suspended */
944                 err = -EAGAIN;
945                 goto out;
946         }
947 
948         err = proc_do_large_bitmap(table, write, buffer, lenp, ppos);
949         if (!err && write) {
950                 /* Remove impossible cpus to keep sysctl output cleaner. */
951                 cpumask_and(&watchdog_cpumask, &watchdog_cpumask,
952                             cpu_possible_mask);
953 
954                 if (watchdog_running) {
955                         /*
956                          * Failure would be due to being unable to allocate
957                          * a temporary cpumask, so we are likely not in a
958                          * position to do much else to make things better.
959                          */
960                         if (smpboot_update_cpumask_percpu_thread(
961                                     &watchdog_threads, &watchdog_cpumask) != 0)
962                                 pr_err("cpumask update failed\n");
963                 }
964         }
965 out:
966         mutex_unlock(&watchdog_proc_mutex);
967         return err;
968 }
969 
970 #endif /* CONFIG_SYSCTL */
971 
972 void __init lockup_detector_init(void)
973 {
974         set_sample_period();
975 
976 #ifdef CONFIG_NO_HZ_FULL
977         if (tick_nohz_full_enabled()) {
978                 pr_info("Disabling watchdog on nohz_full cores by default\n");
979                 cpumask_copy(&watchdog_cpumask, housekeeping_mask);
980         } else
981                 cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
982 #else
983         cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
984 #endif
985 
986         if (watchdog_enabled)
987                 watchdog_enable_all_cpus();
988 }
989 

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