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
26 #include <asm/irq_regs.h>
27 #include <linux/perf_event.h>
28
29 int watchdog_enabled = 1;
30 int __read_mostly watchdog_thresh = 10;
31
32 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
33 static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
34 static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
35 static DEFINE_PER_CPU(bool, softlockup_touch_sync);
36 static DEFINE_PER_CPU(bool, soft_watchdog_warn);
37 #ifdef CONFIG_HARDLOCKUP_DETECTOR
38 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
39 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
40 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
41 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
42 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
43 #endif
44
45 /* boot commands */
46 /*
47 * Should we panic when a soft-lockup or hard-lockup occurs:
48 */
49 #ifdef CONFIG_HARDLOCKUP_DETECTOR
50 static int hardlockup_panic =
51 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
52
hardlockup_panic_setup(char * str)53 static int __init hardlockup_panic_setup(char *str)
54 {
55 if (!strncmp(str, "panic", 5))
56 hardlockup_panic = 1;
57 else if (!strncmp(str, "nopanic", 7))
58 hardlockup_panic = 0;
59 else if (!strncmp(str, "0", 1))
60 watchdog_enabled = 0;
61 return 1;
62 }
63 __setup("nmi_watchdog=", hardlockup_panic_setup);
64 #endif
65
66 unsigned int __read_mostly softlockup_panic =
67 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
68
softlockup_panic_setup(char * str)69 static int __init softlockup_panic_setup(char *str)
70 {
71 softlockup_panic = simple_strtoul(str, NULL, 0);
72
73 return 1;
74 }
75 __setup("softlockup_panic=", softlockup_panic_setup);
76
nowatchdog_setup(char * str)77 static int __init nowatchdog_setup(char *str)
78 {
79 watchdog_enabled = 0;
80 return 1;
81 }
82 __setup("nowatchdog", nowatchdog_setup);
83
84 /* deprecated */
nosoftlockup_setup(char * str)85 static int __init nosoftlockup_setup(char *str)
86 {
87 watchdog_enabled = 0;
88 return 1;
89 }
90 __setup("nosoftlockup", nosoftlockup_setup);
91 /* */
92
93 /*
94 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
95 * lockups can have false positives under extreme conditions. So we generally
96 * want a higher threshold for soft lockups than for hard lockups. So we couple
97 * the thresholds with a factor: we make the soft threshold twice the amount of
98 * time the hard threshold is.
99 */
get_softlockup_thresh(void)100 static int get_softlockup_thresh(void)
101 {
102 return watchdog_thresh * 2;
103 }
104
105 /*
106 * Returns seconds, approximately. We don't need nanosecond
107 * resolution, and we don't need to waste time with a big divide when
108 * 2^30ns == 1.074s.
109 */
get_timestamp(int this_cpu)110 static unsigned long get_timestamp(int this_cpu)
111 {
112 return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
113 }
114
get_sample_period(void)115 static u64 get_sample_period(void)
116 {
117 /*
118 * convert watchdog_thresh from seconds to ns
119 * the divide by 5 is to give hrtimer several chances (two
120 * or three with the current relation between the soft
121 * and hard thresholds) to increment before the
122 * hardlockup detector generates a warning
123 */
124 return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
125 }
126
127 /* Commands for resetting the watchdog */
__touch_watchdog(void)128 static void __touch_watchdog(void)
129 {
130 int this_cpu = smp_processor_id();
131
132 __this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));
133 }
134
touch_softlockup_watchdog(void)135 void touch_softlockup_watchdog(void)
136 {
137 __this_cpu_write(watchdog_touch_ts, 0);
138 }
139 EXPORT_SYMBOL(touch_softlockup_watchdog);
140
touch_all_softlockup_watchdogs(void)141 void touch_all_softlockup_watchdogs(void)
142 {
143 int cpu;
144
145 /*
146 * this is done lockless
147 * do we care if a 0 races with a timestamp?
148 * all it means is the softlock check starts one cycle later
149 */
150 for_each_online_cpu(cpu)
151 per_cpu(watchdog_touch_ts, cpu) = 0;
152 }
153
154 #ifdef CONFIG_HARDLOCKUP_DETECTOR
touch_nmi_watchdog(void)155 void touch_nmi_watchdog(void)
156 {
157 if (watchdog_enabled) {
158 unsigned cpu;
159
160 for_each_present_cpu(cpu) {
161 if (per_cpu(watchdog_nmi_touch, cpu) != true)
162 per_cpu(watchdog_nmi_touch, cpu) = true;
163 }
164 }
165 touch_softlockup_watchdog();
166 }
167 EXPORT_SYMBOL(touch_nmi_watchdog);
168
169 #endif
170
touch_softlockup_watchdog_sync(void)171 void touch_softlockup_watchdog_sync(void)
172 {
173 __raw_get_cpu_var(softlockup_touch_sync) = true;
174 __raw_get_cpu_var(watchdog_touch_ts) = 0;
175 }
176
177 #ifdef CONFIG_HARDLOCKUP_DETECTOR
178 /* watchdog detector functions */
is_hardlockup(void)179 static int is_hardlockup(void)
180 {
181 unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
182
183 if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
184 return 1;
185
186 __this_cpu_write(hrtimer_interrupts_saved, hrint);
187 return 0;
188 }
189 #endif
190
is_softlockup(unsigned long touch_ts)191 static int is_softlockup(unsigned long touch_ts)
192 {
193 unsigned long now = get_timestamp(smp_processor_id());
194
195 /* Warn about unreasonable delays: */
196 if (time_after(now, touch_ts + get_softlockup_thresh()))
197 return now - touch_ts;
198
199 return 0;
200 }
201
202 #ifdef CONFIG_HARDLOCKUP_DETECTOR
203
204 static struct perf_event_attr wd_hw_attr = {
205 .type = PERF_TYPE_HARDWARE,
206 .config = PERF_COUNT_HW_CPU_CYCLES,
207 .size = sizeof(struct perf_event_attr),
208 .pinned = 1,
209 .disabled = 1,
210 };
211
212 /* Callback function for perf event subsystem */
watchdog_overflow_callback(struct perf_event * event,struct perf_sample_data * data,struct pt_regs * regs)213 static void watchdog_overflow_callback(struct perf_event *event,
214 struct perf_sample_data *data,
215 struct pt_regs *regs)
216 {
217 /* Ensure the watchdog never gets throttled */
218 event->hw.interrupts = 0;
219
220 if (__this_cpu_read(watchdog_nmi_touch) == true) {
221 __this_cpu_write(watchdog_nmi_touch, false);
222 return;
223 }
224
225 /* check for a hardlockup
226 * This is done by making sure our timer interrupt
227 * is incrementing. The timer interrupt should have
228 * fired multiple times before we overflow'd. If it hasn't
229 * then this is a good indication the cpu is stuck
230 */
231 if (is_hardlockup()) {
232 int this_cpu = smp_processor_id();
233
234 /* only print hardlockups once */
235 if (__this_cpu_read(hard_watchdog_warn) == true)
236 return;
237
238 if (hardlockup_panic)
239 panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
240 else
241 WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
242
243 __this_cpu_write(hard_watchdog_warn, true);
244 return;
245 }
246
247 __this_cpu_write(hard_watchdog_warn, false);
248 return;
249 }
watchdog_interrupt_count(void)250 static void watchdog_interrupt_count(void)
251 {
252 __this_cpu_inc(hrtimer_interrupts);
253 }
254 #else
watchdog_interrupt_count(void)255 static inline void watchdog_interrupt_count(void) { return; }
256 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
257
258 /* watchdog kicker functions */
watchdog_timer_fn(struct hrtimer * hrtimer)259 static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
260 {
261 unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
262 struct pt_regs *regs = get_irq_regs();
263 int duration;
264
265 /* kick the hardlockup detector */
266 watchdog_interrupt_count();
267
268 /* kick the softlockup detector */
269 wake_up_process(__this_cpu_read(softlockup_watchdog));
270
271 /* .. and repeat */
272 hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
273
274 if (touch_ts == 0) {
275 if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
276 /*
277 * If the time stamp was touched atomically
278 * make sure the scheduler tick is up to date.
279 */
280 __this_cpu_write(softlockup_touch_sync, false);
281 sched_clock_tick();
282 }
283 __touch_watchdog();
284 return HRTIMER_RESTART;
285 }
286
287 /* check for a softlockup
288 * This is done by making sure a high priority task is
289 * being scheduled. The task touches the watchdog to
290 * indicate it is getting cpu time. If it hasn't then
291 * this is a good indication some task is hogging the cpu
292 */
293 duration = is_softlockup(touch_ts);
294 if (unlikely(duration)) {
295 /* only warn once */
296 if (__this_cpu_read(soft_watchdog_warn) == true)
297 return HRTIMER_RESTART;
298
299 printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
300 smp_processor_id(), duration,
301 current->comm, task_pid_nr(current));
302 print_modules();
303 print_irqtrace_events(current);
304 if (regs)
305 show_regs(regs);
306 else
307 dump_stack();
308
309 if (softlockup_panic)
310 panic("softlockup: hung tasks");
311 __this_cpu_write(soft_watchdog_warn, true);
312 } else
313 __this_cpu_write(soft_watchdog_warn, false);
314
315 return HRTIMER_RESTART;
316 }
317
318
319 /*
320 * The watchdog thread - touches the timestamp.
321 */
watchdog(void * unused)322 static int watchdog(void *unused)
323 {
324 struct sched_param param = { .sched_priority = 0 };
325 struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
326
327 /* initialize timestamp */
328 __touch_watchdog();
329
330 /* kick off the timer for the hardlockup detector */
331 /* done here because hrtimer_start can only pin to smp_processor_id() */
332 hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
333 HRTIMER_MODE_REL_PINNED);
334
335 set_current_state(TASK_INTERRUPTIBLE);
336 /*
337 * Run briefly (kicked by the hrtimer callback function) once every
338 * get_sample_period() seconds (4 seconds by default) to reset the
339 * softlockup timestamp. If this gets delayed for more than
340 * 2*watchdog_thresh seconds then the debug-printout triggers in
341 * watchdog_timer_fn().
342 */
343 while (!kthread_should_stop()) {
344 __touch_watchdog();
345 schedule();
346
347 if (kthread_should_stop())
348 break;
349
350 set_current_state(TASK_INTERRUPTIBLE);
351 }
352 /*
353 * Drop the policy/priority elevation during thread exit to avoid a
354 * scheduling latency spike.
355 */
356 __set_current_state(TASK_RUNNING);
357 sched_setscheduler(current, SCHED_NORMAL, ¶m);
358 return 0;
359 }
360
361
362 #ifdef CONFIG_HARDLOCKUP_DETECTOR
watchdog_nmi_enable(int cpu)363 static int watchdog_nmi_enable(int cpu)
364 {
365 struct perf_event_attr *wd_attr;
366 struct perf_event *event = per_cpu(watchdog_ev, cpu);
367
368 /* is it already setup and enabled? */
369 if (event && event->state > PERF_EVENT_STATE_OFF)
370 goto out;
371
372 /* it is setup but not enabled */
373 if (event != NULL)
374 goto out_enable;
375
376 wd_attr = &wd_hw_attr;
377 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
378
379 /* Try to register using hardware perf events */
380 event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
381 if (!IS_ERR(event)) {
382 pr_info("enabled, takes one hw-pmu counter.\n");
383 goto out_save;
384 }
385
386
387 /* vary the KERN level based on the returned errno */
388 if (PTR_ERR(event) == -EOPNOTSUPP)
389 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
390 else if (PTR_ERR(event) == -ENOENT)
391 pr_warning("disabled (cpu%i): hardware events not enabled\n",
392 cpu);
393 else
394 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
395 cpu, PTR_ERR(event));
396 return PTR_ERR(event);
397
398 /* success path */
399 out_save:
400 per_cpu(watchdog_ev, cpu) = event;
401 out_enable:
402 perf_event_enable(per_cpu(watchdog_ev, cpu));
403 out:
404 return 0;
405 }
406
watchdog_nmi_disable(int cpu)407 static void watchdog_nmi_disable(int cpu)
408 {
409 struct perf_event *event = per_cpu(watchdog_ev, cpu);
410
411 if (event) {
412 perf_event_disable(event);
413 per_cpu(watchdog_ev, cpu) = NULL;
414
415 /* should be in cleanup, but blocks oprofile */
416 perf_event_release_kernel(event);
417 }
418 return;
419 }
420 #else
watchdog_nmi_enable(int cpu)421 static int watchdog_nmi_enable(int cpu) { return 0; }
watchdog_nmi_disable(int cpu)422 static void watchdog_nmi_disable(int cpu) { return; }
423 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
424
425 /* prepare/enable/disable routines */
watchdog_prepare_cpu(int cpu)426 static void watchdog_prepare_cpu(int cpu)
427 {
428 struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
429
430 WARN_ON(per_cpu(softlockup_watchdog, cpu));
431 hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
432 hrtimer->function = watchdog_timer_fn;
433 }
434
watchdog_enable(int cpu)435 static int watchdog_enable(int cpu)
436 {
437 struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
438 int err = 0;
439
440 /* enable the perf event */
441 err = watchdog_nmi_enable(cpu);
442
443 /* Regardless of err above, fall through and start softlockup */
444
445 /* create the watchdog thread */
446 if (!p) {
447 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
448 p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu);
449 if (IS_ERR(p)) {
450 pr_err("softlockup watchdog for %i failed\n", cpu);
451 if (!err) {
452 /* if hardlockup hasn't already set this */
453 err = PTR_ERR(p);
454 /* and disable the perf event */
455 watchdog_nmi_disable(cpu);
456 }
457 goto out;
458 }
459 sched_setscheduler(p, SCHED_FIFO, ¶m);
460 kthread_bind(p, cpu);
461 per_cpu(watchdog_touch_ts, cpu) = 0;
462 per_cpu(softlockup_watchdog, cpu) = p;
463 wake_up_process(p);
464 }
465
466 out:
467 return err;
468 }
469
watchdog_disable(int cpu)470 static void watchdog_disable(int cpu)
471 {
472 struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
473 struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
474
475 /*
476 * cancel the timer first to stop incrementing the stats
477 * and waking up the kthread
478 */
479 hrtimer_cancel(hrtimer);
480
481 /* disable the perf event */
482 watchdog_nmi_disable(cpu);
483
484 /* stop the watchdog thread */
485 if (p) {
486 per_cpu(softlockup_watchdog, cpu) = NULL;
487 kthread_stop(p);
488 }
489 }
490
491 /* sysctl functions */
492 #ifdef CONFIG_SYSCTL
watchdog_enable_all_cpus(void)493 static void watchdog_enable_all_cpus(void)
494 {
495 int cpu;
496
497 watchdog_enabled = 0;
498
499 for_each_online_cpu(cpu)
500 if (!watchdog_enable(cpu))
501 /* if any cpu succeeds, watchdog is considered
502 enabled for the system */
503 watchdog_enabled = 1;
504
505 if (!watchdog_enabled)
506 pr_err("failed to be enabled on some cpus\n");
507
508 }
509
watchdog_disable_all_cpus(void)510 static void watchdog_disable_all_cpus(void)
511 {
512 int cpu;
513
514 for_each_online_cpu(cpu)
515 watchdog_disable(cpu);
516
517 /* if all watchdogs are disabled, then they are disabled for the system */
518 watchdog_enabled = 0;
519 }
520
521
522 /*
523 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
524 */
525
proc_dowatchdog(struct ctl_table * table,int write,void __user * buffer,size_t * lenp,loff_t * ppos)526 int proc_dowatchdog(struct ctl_table *table, int write,
527 void __user *buffer, size_t *lenp, loff_t *ppos)
528 {
529 int ret;
530
531 ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
532 if (ret || !write)
533 goto out;
534
535 if (watchdog_enabled && watchdog_thresh)
536 watchdog_enable_all_cpus();
537 else
538 watchdog_disable_all_cpus();
539
540 out:
541 return ret;
542 }
543 #endif /* CONFIG_SYSCTL */
544
545
546 /*
547 * Create/destroy watchdog threads as CPUs come and go:
548 */
549 static int __cpuinit
cpu_callback(struct notifier_block * nfb,unsigned long action,void * hcpu)550 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
551 {
552 int hotcpu = (unsigned long)hcpu;
553
554 switch (action) {
555 case CPU_UP_PREPARE:
556 case CPU_UP_PREPARE_FROZEN:
557 watchdog_prepare_cpu(hotcpu);
558 break;
559 case CPU_ONLINE:
560 case CPU_ONLINE_FROZEN:
561 if (watchdog_enabled)
562 watchdog_enable(hotcpu);
563 break;
564 #ifdef CONFIG_HOTPLUG_CPU
565 case CPU_UP_CANCELED:
566 case CPU_UP_CANCELED_FROZEN:
567 watchdog_disable(hotcpu);
568 break;
569 case CPU_DEAD:
570 case CPU_DEAD_FROZEN:
571 watchdog_disable(hotcpu);
572 break;
573 #endif /* CONFIG_HOTPLUG_CPU */
574 }
575
576 /*
577 * hardlockup and softlockup are not important enough
578 * to block cpu bring up. Just always succeed and
579 * rely on printk output to flag problems.
580 */
581 return NOTIFY_OK;
582 }
583
584 static struct notifier_block __cpuinitdata cpu_nfb = {
585 .notifier_call = cpu_callback
586 };
587
lockup_detector_init(void)588 void __init lockup_detector_init(void)
589 {
590 void *cpu = (void *)(long)smp_processor_id();
591 int err;
592
593 err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
594 WARN_ON(notifier_to_errno(err));
595
596 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
597 register_cpu_notifier(&cpu_nfb);
598
599 return;
600 }
601