projects/linux·blob v3.16 · refs

648 lines · 16.9 KiB

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/delay.h>
19#include <linux/freezer.h>
20#include <linux/kthread.h>
21#include <linux/lockdep.h>
22#include <linux/notifier.h>
23#include <linux/module.h>
24#include <linux/sysctl.h>
25#include <linux/smpboot.h>
26#include <linux/sched/rt.h>
27
28#include <asm/irq_regs.h>
29#include <linux/kvm_para.h>
30#include <linux/perf_event.h>
31
32int watchdog_user_enabled = 1;
33int __read_mostly watchdog_thresh = 10;
34#ifdef CONFIG_SMP
35int __read_mostly sysctl_softlockup_all_cpu_backtrace;
36#else
37#define sysctl_softlockup_all_cpu_backtrace 0
38#endif
39
40static int __read_mostly watchdog_running;
41static u64 __read_mostly sample_period;
42
43static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
44static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
45static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
46static DEFINE_PER_CPU(bool, softlockup_touch_sync);
47static DEFINE_PER_CPU(bool, soft_watchdog_warn);
48static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
49static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
50#ifdef CONFIG_HARDLOCKUP_DETECTOR
51static DEFINE_PER_CPU(bool, hard_watchdog_warn);
52static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
53static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
54static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
55#endif
56static unsigned long soft_lockup_nmi_warn;
57
58/* boot commands */
59/*
60 * Should we panic when a soft-lockup or hard-lockup occurs:
61 */
62#ifdef CONFIG_HARDLOCKUP_DETECTOR
63static int hardlockup_panic =
64 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
65
66static int __init hardlockup_panic_setup(char *str)
67{
68 if (!strncmp(str, "panic", 5))
69 hardlockup_panic = 1;
70 else if (!strncmp(str, "nopanic", 7))
71 hardlockup_panic = 0;
72 else if (!strncmp(str, "0", 1))
73 watchdog_user_enabled = 0;
74 return 1;
75}
76__setup("nmi_watchdog=", hardlockup_panic_setup);
77#endif
78
79unsigned int __read_mostly softlockup_panic =
80 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
81
82static int __init softlockup_panic_setup(char *str)
83{
84 softlockup_panic = simple_strtoul(str, NULL, 0);
85
86 return 1;
87}
88__setup("softlockup_panic=", softlockup_panic_setup);
89
90static int __init nowatchdog_setup(char *str)
91{
92 watchdog_user_enabled = 0;
93 return 1;
94}
95__setup("nowatchdog", nowatchdog_setup);
96
97/* deprecated */
98static int __init nosoftlockup_setup(char *str)
99{
100 watchdog_user_enabled = 0;
101 return 1;
102}
103__setup("nosoftlockup", nosoftlockup_setup);
104/* */
105#ifdef CONFIG_SMP
106static int __init softlockup_all_cpu_backtrace_setup(char *str)
107{
108 sysctl_softlockup_all_cpu_backtrace =
109 !!simple_strtol(str, NULL, 0);
110 return 1;
111}
112__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup);
113#endif
114
115/*
116 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
117 * lockups can have false positives under extreme conditions. So we generally
118 * want a higher threshold for soft lockups than for hard lockups. So we couple
119 * the thresholds with a factor: we make the soft threshold twice the amount of
120 * time the hard threshold is.
121 */
122static int get_softlockup_thresh(void)
123{
124 return watchdog_thresh * 2;
125}
126
127/*
128 * Returns seconds, approximately. We don't need nanosecond
129 * resolution, and we don't need to waste time with a big divide when
130 * 2^30ns == 1.074s.
131 */
132static unsigned long get_timestamp(void)
133{
134 return local_clock() >> 30LL; /* 2^30 ~= 10^9 */
135}
136
137static void set_sample_period(void)
138{
139 /*
140 * convert watchdog_thresh from seconds to ns
141 * the divide by 5 is to give hrtimer several chances (two
142 * or three with the current relation between the soft
143 * and hard thresholds) to increment before the
144 * hardlockup detector generates a warning
145 */
146 sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
147}
148
149/* Commands for resetting the watchdog */
150static void __touch_watchdog(void)
151{
152 __this_cpu_write(watchdog_touch_ts, get_timestamp());
153}
154
155void touch_softlockup_watchdog(void)
156{
157 /*
158 * Preemption can be enabled. It doesn't matter which CPU's timestamp
159 * gets zeroed here, so use the raw_ operation.
160 */
161 raw_cpu_write(watchdog_touch_ts, 0);
162}
163EXPORT_SYMBOL(touch_softlockup_watchdog);
164
165void touch_all_softlockup_watchdogs(void)
166{
167 int cpu;
168
169 /*
170 * this is done lockless
171 * do we care if a 0 races with a timestamp?
172 * all it means is the softlock check starts one cycle later
173 */
174 for_each_online_cpu(cpu)
175 per_cpu(watchdog_touch_ts, cpu) = 0;
176}
177
178#ifdef CONFIG_HARDLOCKUP_DETECTOR
179void touch_nmi_watchdog(void)
180{
181 /*
182 * Using __raw here because some code paths have
183 * preemption enabled. If preemption is enabled
184 * then interrupts should be enabled too, in which
185 * case we shouldn't have to worry about the watchdog
186 * going off.
187 */
188 __raw_get_cpu_var(watchdog_nmi_touch) = true;
189 touch_softlockup_watchdog();
190}
191EXPORT_SYMBOL(touch_nmi_watchdog);
192
193#endif
194
195void touch_softlockup_watchdog_sync(void)
196{
197 __raw_get_cpu_var(softlockup_touch_sync) = true;
198 __raw_get_cpu_var(watchdog_touch_ts) = 0;
199}
200
201#ifdef CONFIG_HARDLOCKUP_DETECTOR
202/* watchdog detector functions */
203static int is_hardlockup(void)
204{
205 unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
206
207 if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
208 return 1;
209
210 __this_cpu_write(hrtimer_interrupts_saved, hrint);
211 return 0;
212}
213#endif
214
215static int is_softlockup(unsigned long touch_ts)
216{
217 unsigned long now = get_timestamp();
218
219 /* Warn about unreasonable delays: */
220 if (time_after(now, touch_ts + get_softlockup_thresh()))
221 return now - touch_ts;
222
223 return 0;
224}
225
226#ifdef CONFIG_HARDLOCKUP_DETECTOR
227
228static struct perf_event_attr wd_hw_attr = {
229 .type = PERF_TYPE_HARDWARE,
230 .config = PERF_COUNT_HW_CPU_CYCLES,
231 .size = sizeof(struct perf_event_attr),
232 .pinned = 1,
233 .disabled = 1,
234};
235
236/* Callback function for perf event subsystem */
237static void watchdog_overflow_callback(struct perf_event *event,
238 struct perf_sample_data *data,
239 struct pt_regs *regs)
240{
241 /* Ensure the watchdog never gets throttled */
242 event->hw.interrupts = 0;
243
244 if (__this_cpu_read(watchdog_nmi_touch) == true) {
245 __this_cpu_write(watchdog_nmi_touch, false);
246 return;
247 }
248
249 /* check for a hardlockup
250 * This is done by making sure our timer interrupt
251 * is incrementing. The timer interrupt should have
252 * fired multiple times before we overflow'd. If it hasn't
253 * then this is a good indication the cpu is stuck
254 */
255 if (is_hardlockup()) {
256 int this_cpu = smp_processor_id();
257
258 /* only print hardlockups once */
259 if (__this_cpu_read(hard_watchdog_warn) == true)
260 return;
261
262 if (hardlockup_panic)
263 panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
264 else
265 WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
266
267 __this_cpu_write(hard_watchdog_warn, true);
268 return;
269 }
270
271 __this_cpu_write(hard_watchdog_warn, false);
272 return;
273}
274#endif /* CONFIG_HARDLOCKUP_DETECTOR */
275
276static void watchdog_interrupt_count(void)
277{
278 __this_cpu_inc(hrtimer_interrupts);
279}
280
281static int watchdog_nmi_enable(unsigned int cpu);
282static void watchdog_nmi_disable(unsigned int cpu);
283
284/* watchdog kicker functions */
285static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
286{
287 unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
288 struct pt_regs *regs = get_irq_regs();
289 int duration;
290 int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
291
292 /* kick the hardlockup detector */
293 watchdog_interrupt_count();
294
295 /* kick the softlockup detector */
296 wake_up_process(__this_cpu_read(softlockup_watchdog));
297
298 /* .. and repeat */
299 hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
300
301 if (touch_ts == 0) {
302 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
303 /*
304 * If the time stamp was touched atomically
305 * make sure the scheduler tick is up to date.
306 */
307 __this_cpu_write(softlockup_touch_sync, false);
308 sched_clock_tick();
309 }
310
311 /* Clear the guest paused flag on watchdog reset */
312 kvm_check_and_clear_guest_paused();
313 __touch_watchdog();
314 return HRTIMER_RESTART;
315 }
316
317 /* check for a softlockup
318 * This is done by making sure a high priority task is
319 * being scheduled. The task touches the watchdog to
320 * indicate it is getting cpu time. If it hasn't then
321 * this is a good indication some task is hogging the cpu
322 */
323 duration = is_softlockup(touch_ts);
324 if (unlikely(duration)) {
325 /*
326 * If a virtual machine is stopped by the host it can look to
327 * the watchdog like a soft lockup, check to see if the host
328 * stopped the vm before we issue the warning
329 */
330 if (kvm_check_and_clear_guest_paused())
331 return HRTIMER_RESTART;
332
333 /* only warn once */
334 if (__this_cpu_read(soft_watchdog_warn) == true)
335 return HRTIMER_RESTART;
336
337 if (softlockup_all_cpu_backtrace) {
338 /* Prevent multiple soft-lockup reports if one cpu is already
339 * engaged in dumping cpu back traces
340 */
341 if (test_and_set_bit(0, &soft_lockup_nmi_warn)) {
342 /* Someone else will report us. Let's give up */
343 __this_cpu_write(soft_watchdog_warn, true);
344 return HRTIMER_RESTART;
345 }
346 }
347
348 printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
349 smp_processor_id(), duration,
350 current->comm, task_pid_nr(current));
351 print_modules();
352 print_irqtrace_events(current);
353 if (regs)
354 show_regs(regs);
355 else
356 dump_stack();
357
358 if (softlockup_all_cpu_backtrace) {
359 /* Avoid generating two back traces for current
360 * given that one is already made above
361 */
362 trigger_allbutself_cpu_backtrace();
363
364 clear_bit(0, &soft_lockup_nmi_warn);
365 /* Barrier to sync with other cpus */
366 smp_mb__after_atomic();
367 }
368
369 if (softlockup_panic)
370 panic("softlockup: hung tasks");
371 __this_cpu_write(soft_watchdog_warn, true);
372 } else
373 __this_cpu_write(soft_watchdog_warn, false);
374
375 return HRTIMER_RESTART;
376}
377
378static void watchdog_set_prio(unsigned int policy, unsigned int prio)
379{
380 struct sched_param param = { .sched_priority = prio };
381
382 sched_setscheduler(current, policy, &param);
383}
384
385static void watchdog_enable(unsigned int cpu)
386{
387 struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
388
389 /* kick off the timer for the hardlockup detector */
390 hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
391 hrtimer->function = watchdog_timer_fn;
392
393 /* Enable the perf event */
394 watchdog_nmi_enable(cpu);
395
396 /* done here because hrtimer_start can only pin to smp_processor_id() */
397 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
398 HRTIMER_MODE_REL_PINNED);
399
400 /* initialize timestamp */
401 watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1);
402 __touch_watchdog();
403}
404
405static void watchdog_disable(unsigned int cpu)
406{
407 struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
408
409 watchdog_set_prio(SCHED_NORMAL, 0);
410 hrtimer_cancel(hrtimer);
411 /* disable the perf event */
412 watchdog_nmi_disable(cpu);
413}
414
415static void watchdog_cleanup(unsigned int cpu, bool online)
416{
417 watchdog_disable(cpu);
418}
419
420static int watchdog_should_run(unsigned int cpu)
421{
422 return __this_cpu_read(hrtimer_interrupts) !=
423 __this_cpu_read(soft_lockup_hrtimer_cnt);
424}
425
426/*
427 * The watchdog thread function - touches the timestamp.
428 *
429 * It only runs once every sample_period seconds (4 seconds by
430 * default) to reset the softlockup timestamp. If this gets delayed
431 * for more than 2*watchdog_thresh seconds then the debug-printout
432 * triggers in watchdog_timer_fn().
433 */
434static void watchdog(unsigned int cpu)
435{
436 __this_cpu_write(soft_lockup_hrtimer_cnt,
437 __this_cpu_read(hrtimer_interrupts));
438 __touch_watchdog();
439}
440
441#ifdef CONFIG_HARDLOCKUP_DETECTOR
442/*
443 * People like the simple clean cpu node info on boot.
444 * Reduce the watchdog noise by only printing messages
445 * that are different from what cpu0 displayed.
446 */
447static unsigned long cpu0_err;
448
449static int watchdog_nmi_enable(unsigned int cpu)
450{
451 struct perf_event_attr *wd_attr;
452 struct perf_event *event = per_cpu(watchdog_ev, cpu);
453
454 /* is it already setup and enabled? */
455 if (event && event->state > PERF_EVENT_STATE_OFF)
456 goto out;
457
458 /* it is setup but not enabled */
459 if (event != NULL)
460 goto out_enable;
461
462 wd_attr = &wd_hw_attr;
463 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
464
465 /* Try to register using hardware perf events */
466 event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
467
468 /* save cpu0 error for future comparision */
469 if (cpu == 0 && IS_ERR(event))
470 cpu0_err = PTR_ERR(event);
471
472 if (!IS_ERR(event)) {
473 /* only print for cpu0 or different than cpu0 */
474 if (cpu == 0 || cpu0_err)
475 pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
476 goto out_save;
477 }
478
479 /* skip displaying the same error again */
480 if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
481 return PTR_ERR(event);
482
483 /* vary the KERN level based on the returned errno */
484 if (PTR_ERR(event) == -EOPNOTSUPP)
485 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
486 else if (PTR_ERR(event) == -ENOENT)
487 pr_warning("disabled (cpu%i): hardware events not enabled\n",
488 cpu);
489 else
490 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
491 cpu, PTR_ERR(event));
492 return PTR_ERR(event);
493
494 /* success path */
495out_save:
496 per_cpu(watchdog_ev, cpu) = event;
497out_enable:
498 perf_event_enable(per_cpu(watchdog_ev, cpu));
499out:
500 return 0;
501}
502
503static void watchdog_nmi_disable(unsigned int cpu)
504{
505 struct perf_event *event = per_cpu(watchdog_ev, cpu);
506
507 if (event) {
508 perf_event_disable(event);
509 per_cpu(watchdog_ev, cpu) = NULL;
510
511 /* should be in cleanup, but blocks oprofile */
512 perf_event_release_kernel(event);
513 }
514 return;
515}
516#else
517static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
518static void watchdog_nmi_disable(unsigned int cpu) { return; }
519#endif /* CONFIG_HARDLOCKUP_DETECTOR */
520
521static struct smp_hotplug_thread watchdog_threads = {
522 .store = &softlockup_watchdog,
523 .thread_should_run = watchdog_should_run,
524 .thread_fn = watchdog,
525 .thread_comm = "watchdog/%u",
526 .setup = watchdog_enable,
527 .cleanup = watchdog_cleanup,
528 .park = watchdog_disable,
529 .unpark = watchdog_enable,
530};
531
532static void restart_watchdog_hrtimer(void *info)
533{
534 struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
535 int ret;
536
537 /*
538 * No need to cancel and restart hrtimer if it is currently executing
539 * because it will reprogram itself with the new period now.
540 * We should never see it unqueued here because we are running per-cpu
541 * with interrupts disabled.
542 */
543 ret = hrtimer_try_to_cancel(hrtimer);
544 if (ret == 1)
545 hrtimer_start(hrtimer, ns_to_ktime(sample_period),
546 HRTIMER_MODE_REL_PINNED);
547}
548
549static void update_timers(int cpu)
550{
551 /*
552 * Make sure that perf event counter will adopt to a new
553 * sampling period. Updating the sampling period directly would
554 * be much nicer but we do not have an API for that now so
555 * let's use a big hammer.
556 * Hrtimer will adopt the new period on the next tick but this
557 * might be late already so we have to restart the timer as well.
558 */
559 watchdog_nmi_disable(cpu);
560 smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1);
561 watchdog_nmi_enable(cpu);
562}
563
564static void update_timers_all_cpus(void)
565{
566 int cpu;
567
568 get_online_cpus();
569 for_each_online_cpu(cpu)
570 update_timers(cpu);
571 put_online_cpus();
572}
573
574static int watchdog_enable_all_cpus(bool sample_period_changed)
575{
576 int err = 0;
577
578 if (!watchdog_running) {
579 err = smpboot_register_percpu_thread(&watchdog_threads);
580 if (err)
581 pr_err("Failed to create watchdog threads, disabled\n");
582 else
583 watchdog_running = 1;
584 } else if (sample_period_changed) {
585 update_timers_all_cpus();
586 }
587
588 return err;
589}
590
591/* prepare/enable/disable routines */
592/* sysctl functions */
593#ifdef CONFIG_SYSCTL
594static void watchdog_disable_all_cpus(void)
595{
596 if (watchdog_running) {
597 watchdog_running = 0;
598 smpboot_unregister_percpu_thread(&watchdog_threads);
599 }
600}
601
602/*
603 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
604 */
605
606int proc_dowatchdog(struct ctl_table *table, int write,
607 void __user *buffer, size_t *lenp, loff_t *ppos)
608{
609 int err, old_thresh, old_enabled;
610 static DEFINE_MUTEX(watchdog_proc_mutex);
611
612 mutex_lock(&watchdog_proc_mutex);
613 old_thresh = ACCESS_ONCE(watchdog_thresh);
614 old_enabled = ACCESS_ONCE(watchdog_user_enabled);
615
616 err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
617 if (err || !write)
618 goto out;
619
620 set_sample_period();
621 /*
622 * Watchdog threads shouldn't be enabled if they are
623 * disabled. The 'watchdog_running' variable check in
624 * watchdog_*_all_cpus() function takes care of this.
625 */
626 if (watchdog_user_enabled && watchdog_thresh)
627 err = watchdog_enable_all_cpus(old_thresh != watchdog_thresh);
628 else
629 watchdog_disable_all_cpus();
630
631 /* Restore old values on failure */
632 if (err) {
633 watchdog_thresh = old_thresh;
634 watchdog_user_enabled = old_enabled;
635 }
636out:
637 mutex_unlock(&watchdog_proc_mutex);
638 return err;
639}
640#endif /* CONFIG_SYSCTL */
641
642void __init lockup_detector_init(void)
643{
644 set_sample_period();
645
646 if (watchdog_user_enabled)
647 watchdog_enable_all_cpus(false);
648}