Root/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 * this code detects hard lockups: incidents in where on a CPU
7 * the kernel does not respond to anything except NMI.
8 *
9 * Note: Most of this code is borrowed heavily from softlockup.c,
10 * so thanks to Ingo for the initial implementation.
11 * Some chunks also taken from arch/x86/kernel/apic/nmi.c, thanks
12 * to those contributors as well.
13 */
14
15#include <linux/mm.h>
16#include <linux/cpu.h>
17#include <linux/nmi.h>
18#include <linux/init.h>
19#include <linux/delay.h>
20#include <linux/freezer.h>
21#include <linux/kthread.h>
22#include <linux/lockdep.h>
23#include <linux/notifier.h>
24#include <linux/module.h>
25#include <linux/sysctl.h>
26
27#include <asm/irq_regs.h>
28#include <linux/perf_event.h>
29
30int watchdog_enabled = 1;
31int __read_mostly watchdog_thresh = 10;
32
33static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
34static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
35static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
36static DEFINE_PER_CPU(bool, softlockup_touch_sync);
37static DEFINE_PER_CPU(bool, soft_watchdog_warn);
38#ifdef CONFIG_HARDLOCKUP_DETECTOR
39static DEFINE_PER_CPU(bool, hard_watchdog_warn);
40static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
41static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
42static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved);
43static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
44#endif
45
46/* boot commands */
47/*
48 * Should we panic when a soft-lockup or hard-lockup occurs:
49 */
50#ifdef CONFIG_HARDLOCKUP_DETECTOR
51static int hardlockup_panic =
52            CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
53
54static int __init hardlockup_panic_setup(char *str)
55{
56    if (!strncmp(str, "panic", 5))
57        hardlockup_panic = 1;
58    else if (!strncmp(str, "nopanic", 7))
59        hardlockup_panic = 0;
60    else if (!strncmp(str, "0", 1))
61        watchdog_enabled = 0;
62    return 1;
63}
64__setup("nmi_watchdog=", hardlockup_panic_setup);
65#endif
66
67unsigned int __read_mostly softlockup_panic =
68            CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
69
70static int __init softlockup_panic_setup(char *str)
71{
72    softlockup_panic = simple_strtoul(str, NULL, 0);
73
74    return 1;
75}
76__setup("softlockup_panic=", softlockup_panic_setup);
77
78static int __init nowatchdog_setup(char *str)
79{
80    watchdog_enabled = 0;
81    return 1;
82}
83__setup("nowatchdog", nowatchdog_setup);
84
85/* deprecated */
86static int __init nosoftlockup_setup(char *str)
87{
88    watchdog_enabled = 0;
89    return 1;
90}
91__setup("nosoftlockup", nosoftlockup_setup);
92/* */
93
94/*
95 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
96 * lockups can have false positives under extreme conditions. So we generally
97 * want a higher threshold for soft lockups than for hard lockups. So we couple
98 * the thresholds with a factor: we make the soft threshold twice the amount of
99 * time the hard threshold is.
100 */
101static int get_softlockup_thresh(void)
102{
103    return watchdog_thresh * 2;
104}
105
106/*
107 * Returns seconds, approximately. We don't need nanosecond
108 * resolution, and we don't need to waste time with a big divide when
109 * 2^30ns == 1.074s.
110 */
111static unsigned long get_timestamp(int this_cpu)
112{
113    return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
114}
115
116static unsigned long get_sample_period(void)
117{
118    /*
119     * convert watchdog_thresh from seconds to ns
120     * the divide by 5 is to give hrtimer 5 chances to
121     * increment before the hardlockup detector generates
122     * a warning
123     */
124    return get_softlockup_thresh() * (NSEC_PER_SEC / 5);
125}
126
127/* Commands for resetting the watchdog */
128static 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
135void touch_softlockup_watchdog(void)
136{
137    __this_cpu_write(watchdog_touch_ts, 0);
138}
139EXPORT_SYMBOL(touch_softlockup_watchdog);
140
141void 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
155void 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}
167EXPORT_SYMBOL(touch_nmi_watchdog);
168
169#endif
170
171void 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 */
179static 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
191static 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
203static struct perf_event_attr wd_hw_attr = {
204    .type = PERF_TYPE_HARDWARE,
205    .config = PERF_COUNT_HW_CPU_CYCLES,
206    .size = sizeof(struct perf_event_attr),
207    .pinned = 1,
208    .disabled = 1,
209};
210
211/* Callback function for perf event subsystem */
212static void watchdog_overflow_callback(struct perf_event *event, int nmi,
213         struct perf_sample_data *data,
214         struct pt_regs *regs)
215{
216    /* Ensure the watchdog never gets throttled */
217    event->hw.interrupts = 0;
218
219    if (__this_cpu_read(watchdog_nmi_touch) == true) {
220        __this_cpu_write(watchdog_nmi_touch, false);
221        return;
222    }
223
224    /* check for a hardlockup
225     * This is done by making sure our timer interrupt
226     * is incrementing. The timer interrupt should have
227     * fired multiple times before we overflow'd. If it hasn't
228     * then this is a good indication the cpu is stuck
229     */
230    if (is_hardlockup()) {
231        int this_cpu = smp_processor_id();
232
233        /* only print hardlockups once */
234        if (__this_cpu_read(hard_watchdog_warn) == true)
235            return;
236
237        if (hardlockup_panic)
238            panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
239        else
240            WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
241
242        __this_cpu_write(hard_watchdog_warn, true);
243        return;
244    }
245
246    __this_cpu_write(hard_watchdog_warn, false);
247    return;
248}
249static void watchdog_interrupt_count(void)
250{
251    __this_cpu_inc(hrtimer_interrupts);
252}
253#else
254static inline void watchdog_interrupt_count(void) { return; }
255#endif /* CONFIG_HARDLOCKUP_DETECTOR */
256
257/* watchdog kicker functions */
258static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
259{
260    unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
261    struct pt_regs *regs = get_irq_regs();
262    int duration;
263
264    /* kick the hardlockup detector */
265    watchdog_interrupt_count();
266
267    /* kick the softlockup detector */
268    wake_up_process(__this_cpu_read(softlockup_watchdog));
269
270    /* .. and repeat */
271    hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
272
273    if (touch_ts == 0) {
274        if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
275            /*
276             * If the time stamp was touched atomically
277             * make sure the scheduler tick is up to date.
278             */
279            __this_cpu_write(softlockup_touch_sync, false);
280            sched_clock_tick();
281        }
282        __touch_watchdog();
283        return HRTIMER_RESTART;
284    }
285
286    /* check for a softlockup
287     * This is done by making sure a high priority task is
288     * being scheduled. The task touches the watchdog to
289     * indicate it is getting cpu time. If it hasn't then
290     * this is a good indication some task is hogging the cpu
291     */
292    duration = is_softlockup(touch_ts);
293    if (unlikely(duration)) {
294        /* only warn once */
295        if (__this_cpu_read(soft_watchdog_warn) == true)
296            return HRTIMER_RESTART;
297
298        printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
299            smp_processor_id(), duration,
300            current->comm, task_pid_nr(current));
301        print_modules();
302        print_irqtrace_events(current);
303        if (regs)
304            show_regs(regs);
305        else
306            dump_stack();
307
308        if (softlockup_panic)
309            panic("softlockup: hung tasks");
310        __this_cpu_write(soft_watchdog_warn, true);
311    } else
312        __this_cpu_write(soft_watchdog_warn, false);
313
314    return HRTIMER_RESTART;
315}
316
317
318/*
319 * The watchdog thread - touches the timestamp.
320 */
321static int watchdog(void *unused)
322{
323    static struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
324    struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
325
326    sched_setscheduler(current, SCHED_FIFO, &param);
327
328    /* initialize timestamp */
329    __touch_watchdog();
330
331    /* kick off the timer for the hardlockup detector */
332    /* done here because hrtimer_start can only pin to smp_processor_id() */
333    hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
334              HRTIMER_MODE_REL_PINNED);
335
336    set_current_state(TASK_INTERRUPTIBLE);
337    /*
338     * Run briefly once per second to reset the softlockup timestamp.
339     * If this gets delayed for more than 60 seconds then the
340     * debug-printout triggers in watchdog_timer_fn().
341     */
342    while (!kthread_should_stop()) {
343        __touch_watchdog();
344        schedule();
345
346        if (kthread_should_stop())
347            break;
348
349        set_current_state(TASK_INTERRUPTIBLE);
350    }
351    __set_current_state(TASK_RUNNING);
352
353    return 0;
354}
355
356
357#ifdef CONFIG_HARDLOCKUP_DETECTOR
358static int watchdog_nmi_enable(int cpu)
359{
360    struct perf_event_attr *wd_attr;
361    struct perf_event *event = per_cpu(watchdog_ev, cpu);
362
363    /* is it already setup and enabled? */
364    if (event && event->state > PERF_EVENT_STATE_OFF)
365        goto out;
366
367    /* it is setup but not enabled */
368    if (event != NULL)
369        goto out_enable;
370
371    /* Try to register using hardware perf events */
372    wd_attr = &wd_hw_attr;
373    wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
374    event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback);
375    if (!IS_ERR(event)) {
376        printk(KERN_INFO "NMI watchdog enabled, takes one hw-pmu counter.\n");
377        goto out_save;
378    }
379
380
381    /* vary the KERN level based on the returned errno */
382    if (PTR_ERR(event) == -EOPNOTSUPP)
383        printk(KERN_INFO "NMI watchdog disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
384    else if (PTR_ERR(event) == -ENOENT)
385        printk(KERN_WARNING "NMI watchdog disabled (cpu%i): hardware events not enabled\n", cpu);
386    else
387        printk(KERN_ERR "NMI watchdog disabled (cpu%i): unable to create perf event: %ld\n", cpu, PTR_ERR(event));
388    return PTR_ERR(event);
389
390    /* success path */
391out_save:
392    per_cpu(watchdog_ev, cpu) = event;
393out_enable:
394    perf_event_enable(per_cpu(watchdog_ev, cpu));
395out:
396    return 0;
397}
398
399static void watchdog_nmi_disable(int cpu)
400{
401    struct perf_event *event = per_cpu(watchdog_ev, cpu);
402
403    if (event) {
404        perf_event_disable(event);
405        per_cpu(watchdog_ev, cpu) = NULL;
406
407        /* should be in cleanup, but blocks oprofile */
408        perf_event_release_kernel(event);
409    }
410    return;
411}
412#else
413static int watchdog_nmi_enable(int cpu) { return 0; }
414static void watchdog_nmi_disable(int cpu) { return; }
415#endif /* CONFIG_HARDLOCKUP_DETECTOR */
416
417/* prepare/enable/disable routines */
418static void watchdog_prepare_cpu(int cpu)
419{
420    struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
421
422    WARN_ON(per_cpu(softlockup_watchdog, cpu));
423    hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
424    hrtimer->function = watchdog_timer_fn;
425}
426
427static int watchdog_enable(int cpu)
428{
429    struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
430    int err = 0;
431
432    /* enable the perf event */
433    err = watchdog_nmi_enable(cpu);
434
435    /* Regardless of err above, fall through and start softlockup */
436
437    /* create the watchdog thread */
438    if (!p) {
439        p = kthread_create(watchdog, (void *)(unsigned long)cpu, "watchdog/%d", cpu);
440        if (IS_ERR(p)) {
441            printk(KERN_ERR "softlockup watchdog for %i failed\n", cpu);
442            if (!err) {
443                /* if hardlockup hasn't already set this */
444                err = PTR_ERR(p);
445                /* and disable the perf event */
446                watchdog_nmi_disable(cpu);
447            }
448            goto out;
449        }
450        kthread_bind(p, cpu);
451        per_cpu(watchdog_touch_ts, cpu) = 0;
452        per_cpu(softlockup_watchdog, cpu) = p;
453        wake_up_process(p);
454    }
455
456out:
457    return err;
458}
459
460static void watchdog_disable(int cpu)
461{
462    struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
463    struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
464
465    /*
466     * cancel the timer first to stop incrementing the stats
467     * and waking up the kthread
468     */
469    hrtimer_cancel(hrtimer);
470
471    /* disable the perf event */
472    watchdog_nmi_disable(cpu);
473
474    /* stop the watchdog thread */
475    if (p) {
476        per_cpu(softlockup_watchdog, cpu) = NULL;
477        kthread_stop(p);
478    }
479}
480
481static void watchdog_enable_all_cpus(void)
482{
483    int cpu;
484
485    watchdog_enabled = 0;
486
487    for_each_online_cpu(cpu)
488        if (!watchdog_enable(cpu))
489            /* if any cpu succeeds, watchdog is considered
490               enabled for the system */
491            watchdog_enabled = 1;
492
493    if (!watchdog_enabled)
494        printk(KERN_ERR "watchdog: failed to be enabled on some cpus\n");
495
496}
497
498static void watchdog_disable_all_cpus(void)
499{
500    int cpu;
501
502    for_each_online_cpu(cpu)
503        watchdog_disable(cpu);
504
505    /* if all watchdogs are disabled, then they are disabled for the system */
506    watchdog_enabled = 0;
507}
508
509
510/* sysctl functions */
511#ifdef CONFIG_SYSCTL
512/*
513 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
514 */
515
516int proc_dowatchdog(struct ctl_table *table, int write,
517            void __user *buffer, size_t *lenp, loff_t *ppos)
518{
519    int ret;
520
521    ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
522    if (ret || !write)
523        goto out;
524
525    if (watchdog_enabled && watchdog_thresh)
526        watchdog_enable_all_cpus();
527    else
528        watchdog_disable_all_cpus();
529
530out:
531    return ret;
532}
533#endif /* CONFIG_SYSCTL */
534
535
536/*
537 * Create/destroy watchdog threads as CPUs come and go:
538 */
539static int __cpuinit
540cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
541{
542    int hotcpu = (unsigned long)hcpu;
543
544    switch (action) {
545    case CPU_UP_PREPARE:
546    case CPU_UP_PREPARE_FROZEN:
547        watchdog_prepare_cpu(hotcpu);
548        break;
549    case CPU_ONLINE:
550    case CPU_ONLINE_FROZEN:
551        if (watchdog_enabled)
552            watchdog_enable(hotcpu);
553        break;
554#ifdef CONFIG_HOTPLUG_CPU
555    case CPU_UP_CANCELED:
556    case CPU_UP_CANCELED_FROZEN:
557        watchdog_disable(hotcpu);
558        break;
559    case CPU_DEAD:
560    case CPU_DEAD_FROZEN:
561        watchdog_disable(hotcpu);
562        break;
563#endif /* CONFIG_HOTPLUG_CPU */
564    }
565
566    /*
567     * hardlockup and softlockup are not important enough
568     * to block cpu bring up. Just always succeed and
569     * rely on printk output to flag problems.
570     */
571    return NOTIFY_OK;
572}
573
574static struct notifier_block __cpuinitdata cpu_nfb = {
575    .notifier_call = cpu_callback
576};
577
578void __init lockup_detector_init(void)
579{
580    void *cpu = (void *)(long)smp_processor_id();
581    int err;
582
583    err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
584    WARN_ON(notifier_to_errno(err));
585
586    cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
587    register_cpu_notifier(&cpu_nfb);
588
589    return;
590}
591

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