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 * 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/kvm_para.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 several chances (two
121     * or three with the current relation between the soft
122     * and hard thresholds) to increment before the
123     * hardlockup detector generates a warning
124     */
125    return get_softlockup_thresh() * (NSEC_PER_SEC / 5);
126}
127
128/* Commands for resetting the watchdog */
129static void __touch_watchdog(void)
130{
131    int this_cpu = smp_processor_id();
132
133    __this_cpu_write(watchdog_touch_ts, get_timestamp(this_cpu));
134}
135
136void touch_softlockup_watchdog(void)
137{
138    __this_cpu_write(watchdog_touch_ts, 0);
139}
140EXPORT_SYMBOL(touch_softlockup_watchdog);
141
142void touch_all_softlockup_watchdogs(void)
143{
144    int cpu;
145
146    /*
147     * this is done lockless
148     * do we care if a 0 races with a timestamp?
149     * all it means is the softlock check starts one cycle later
150     */
151    for_each_online_cpu(cpu)
152        per_cpu(watchdog_touch_ts, cpu) = 0;
153}
154
155#ifdef CONFIG_HARDLOCKUP_DETECTOR
156void touch_nmi_watchdog(void)
157{
158    if (watchdog_enabled) {
159        unsigned cpu;
160
161        for_each_present_cpu(cpu) {
162            if (per_cpu(watchdog_nmi_touch, cpu) != true)
163                per_cpu(watchdog_nmi_touch, cpu) = true;
164        }
165    }
166    touch_softlockup_watchdog();
167}
168EXPORT_SYMBOL(touch_nmi_watchdog);
169
170#endif
171
172void touch_softlockup_watchdog_sync(void)
173{
174    __raw_get_cpu_var(softlockup_touch_sync) = true;
175    __raw_get_cpu_var(watchdog_touch_ts) = 0;
176}
177
178#ifdef CONFIG_HARDLOCKUP_DETECTOR
179/* watchdog detector functions */
180static int is_hardlockup(void)
181{
182    unsigned long hrint = __this_cpu_read(hrtimer_interrupts);
183
184    if (__this_cpu_read(hrtimer_interrupts_saved) == hrint)
185        return 1;
186
187    __this_cpu_write(hrtimer_interrupts_saved, hrint);
188    return 0;
189}
190#endif
191
192static int is_softlockup(unsigned long touch_ts)
193{
194    unsigned long now = get_timestamp(smp_processor_id());
195
196    /* Warn about unreasonable delays: */
197    if (time_after(now, touch_ts + get_softlockup_thresh()))
198        return now - touch_ts;
199
200    return 0;
201}
202
203#ifdef CONFIG_HARDLOCKUP_DETECTOR
204
205static struct perf_event_attr wd_hw_attr = {
206    .type = PERF_TYPE_HARDWARE,
207    .config = PERF_COUNT_HW_CPU_CYCLES,
208    .size = sizeof(struct perf_event_attr),
209    .pinned = 1,
210    .disabled = 1,
211};
212
213/* Callback function for perf event subsystem */
214static void watchdog_overflow_callback(struct perf_event *event,
215         struct perf_sample_data *data,
216         struct pt_regs *regs)
217{
218    /* Ensure the watchdog never gets throttled */
219    event->hw.interrupts = 0;
220
221    if (__this_cpu_read(watchdog_nmi_touch) == true) {
222        __this_cpu_write(watchdog_nmi_touch, false);
223        return;
224    }
225
226    /* check for a hardlockup
227     * This is done by making sure our timer interrupt
228     * is incrementing. The timer interrupt should have
229     * fired multiple times before we overflow'd. If it hasn't
230     * then this is a good indication the cpu is stuck
231     */
232    if (is_hardlockup()) {
233        int this_cpu = smp_processor_id();
234
235        /* only print hardlockups once */
236        if (__this_cpu_read(hard_watchdog_warn) == true)
237            return;
238
239        if (hardlockup_panic)
240            panic("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
241        else
242            WARN(1, "Watchdog detected hard LOCKUP on cpu %d", this_cpu);
243
244        __this_cpu_write(hard_watchdog_warn, true);
245        return;
246    }
247
248    __this_cpu_write(hard_watchdog_warn, false);
249    return;
250}
251static void watchdog_interrupt_count(void)
252{
253    __this_cpu_inc(hrtimer_interrupts);
254}
255#else
256static inline void watchdog_interrupt_count(void) { return; }
257#endif /* CONFIG_HARDLOCKUP_DETECTOR */
258
259/* watchdog kicker functions */
260static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
261{
262    unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
263    struct pt_regs *regs = get_irq_regs();
264    int duration;
265
266    /* kick the hardlockup detector */
267    watchdog_interrupt_count();
268
269    /* kick the softlockup detector */
270    wake_up_process(__this_cpu_read(softlockup_watchdog));
271
272    /* .. and repeat */
273    hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
274
275    if (touch_ts == 0) {
276        if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
277            /*
278             * If the time stamp was touched atomically
279             * make sure the scheduler tick is up to date.
280             */
281            __this_cpu_write(softlockup_touch_sync, false);
282            sched_clock_tick();
283        }
284
285        /* Clear the guest paused flag on watchdog reset */
286        kvm_check_and_clear_guest_paused();
287        __touch_watchdog();
288        return HRTIMER_RESTART;
289    }
290
291    /* check for a softlockup
292     * This is done by making sure a high priority task is
293     * being scheduled. The task touches the watchdog to
294     * indicate it is getting cpu time. If it hasn't then
295     * this is a good indication some task is hogging the cpu
296     */
297    duration = is_softlockup(touch_ts);
298    if (unlikely(duration)) {
299        /*
300         * If a virtual machine is stopped by the host it can look to
301         * the watchdog like a soft lockup, check to see if the host
302         * stopped the vm before we issue the warning
303         */
304        if (kvm_check_and_clear_guest_paused())
305            return HRTIMER_RESTART;
306
307        /* only warn once */
308        if (__this_cpu_read(soft_watchdog_warn) == true)
309            return HRTIMER_RESTART;
310
311        printk(KERN_EMERG "BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
312            smp_processor_id(), duration,
313            current->comm, task_pid_nr(current));
314        print_modules();
315        print_irqtrace_events(current);
316        if (regs)
317            show_regs(regs);
318        else
319            dump_stack();
320
321        if (softlockup_panic)
322            panic("softlockup: hung tasks");
323        __this_cpu_write(soft_watchdog_warn, true);
324    } else
325        __this_cpu_write(soft_watchdog_warn, false);
326
327    return HRTIMER_RESTART;
328}
329
330
331/*
332 * The watchdog thread - touches the timestamp.
333 */
334static int watchdog(void *unused)
335{
336    struct sched_param param = { .sched_priority = 0 };
337    struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
338
339    /* initialize timestamp */
340    __touch_watchdog();
341
342    /* kick off the timer for the hardlockup detector */
343    /* done here because hrtimer_start can only pin to smp_processor_id() */
344    hrtimer_start(hrtimer, ns_to_ktime(get_sample_period()),
345              HRTIMER_MODE_REL_PINNED);
346
347    set_current_state(TASK_INTERRUPTIBLE);
348    /*
349     * Run briefly (kicked by the hrtimer callback function) once every
350     * get_sample_period() seconds (4 seconds by default) to reset the
351     * softlockup timestamp. If this gets delayed for more than
352     * 2*watchdog_thresh seconds then the debug-printout triggers in
353     * watchdog_timer_fn().
354     */
355    while (!kthread_should_stop()) {
356        __touch_watchdog();
357        schedule();
358
359        if (kthread_should_stop())
360            break;
361
362        set_current_state(TASK_INTERRUPTIBLE);
363    }
364    /*
365     * Drop the policy/priority elevation during thread exit to avoid a
366     * scheduling latency spike.
367     */
368    __set_current_state(TASK_RUNNING);
369    sched_setscheduler(current, SCHED_NORMAL, &param);
370    return 0;
371}
372
373
374#ifdef CONFIG_HARDLOCKUP_DETECTOR
375/*
376 * People like the simple clean cpu node info on boot.
377 * Reduce the watchdog noise by only printing messages
378 * that are different from what cpu0 displayed.
379 */
380static unsigned long cpu0_err;
381
382static int watchdog_nmi_enable(int cpu)
383{
384    struct perf_event_attr *wd_attr;
385    struct perf_event *event = per_cpu(watchdog_ev, cpu);
386
387    /* is it already setup and enabled? */
388    if (event && event->state > PERF_EVENT_STATE_OFF)
389        goto out;
390
391    /* it is setup but not enabled */
392    if (event != NULL)
393        goto out_enable;
394
395    wd_attr = &wd_hw_attr;
396    wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
397
398    /* Try to register using hardware perf events */
399    event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
400
401    /* save cpu0 error for future comparision */
402    if (cpu == 0 && IS_ERR(event))
403        cpu0_err = PTR_ERR(event);
404
405    if (!IS_ERR(event)) {
406        /* only print for cpu0 or different than cpu0 */
407        if (cpu == 0 || cpu0_err)
408            pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
409        goto out_save;
410    }
411
412    /* skip displaying the same error again */
413    if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
414        return PTR_ERR(event);
415
416    /* vary the KERN level based on the returned errno */
417    if (PTR_ERR(event) == -EOPNOTSUPP)
418        pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
419    else if (PTR_ERR(event) == -ENOENT)
420        pr_warning("disabled (cpu%i): hardware events not enabled\n",
421             cpu);
422    else
423        pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
424            cpu, PTR_ERR(event));
425    return PTR_ERR(event);
426
427    /* success path */
428out_save:
429    per_cpu(watchdog_ev, cpu) = event;
430out_enable:
431    perf_event_enable(per_cpu(watchdog_ev, cpu));
432out:
433    return 0;
434}
435
436static void watchdog_nmi_disable(int cpu)
437{
438    struct perf_event *event = per_cpu(watchdog_ev, cpu);
439
440    if (event) {
441        perf_event_disable(event);
442        per_cpu(watchdog_ev, cpu) = NULL;
443
444        /* should be in cleanup, but blocks oprofile */
445        perf_event_release_kernel(event);
446    }
447    return;
448}
449#else
450static int watchdog_nmi_enable(int cpu) { return 0; }
451static void watchdog_nmi_disable(int cpu) { return; }
452#endif /* CONFIG_HARDLOCKUP_DETECTOR */
453
454/* prepare/enable/disable routines */
455static void watchdog_prepare_cpu(int cpu)
456{
457    struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
458
459    WARN_ON(per_cpu(softlockup_watchdog, cpu));
460    hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
461    hrtimer->function = watchdog_timer_fn;
462}
463
464static int watchdog_enable(int cpu)
465{
466    struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
467    int err = 0;
468
469    /* enable the perf event */
470    err = watchdog_nmi_enable(cpu);
471
472    /* Regardless of err above, fall through and start softlockup */
473
474    /* create the watchdog thread */
475    if (!p) {
476        struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
477        p = kthread_create_on_node(watchdog, NULL, cpu_to_node(cpu), "watchdog/%d", cpu);
478        if (IS_ERR(p)) {
479            pr_err("softlockup watchdog for %i failed\n", cpu);
480            if (!err) {
481                /* if hardlockup hasn't already set this */
482                err = PTR_ERR(p);
483                /* and disable the perf event */
484                watchdog_nmi_disable(cpu);
485            }
486            goto out;
487        }
488        sched_setscheduler(p, SCHED_FIFO, &param);
489        kthread_bind(p, cpu);
490        per_cpu(watchdog_touch_ts, cpu) = 0;
491        per_cpu(softlockup_watchdog, cpu) = p;
492        wake_up_process(p);
493    }
494
495out:
496    return err;
497}
498
499static void watchdog_disable(int cpu)
500{
501    struct task_struct *p = per_cpu(softlockup_watchdog, cpu);
502    struct hrtimer *hrtimer = &per_cpu(watchdog_hrtimer, cpu);
503
504    /*
505     * cancel the timer first to stop incrementing the stats
506     * and waking up the kthread
507     */
508    hrtimer_cancel(hrtimer);
509
510    /* disable the perf event */
511    watchdog_nmi_disable(cpu);
512
513    /* stop the watchdog thread */
514    if (p) {
515        per_cpu(softlockup_watchdog, cpu) = NULL;
516        kthread_stop(p);
517    }
518}
519
520/* sysctl functions */
521#ifdef CONFIG_SYSCTL
522static void watchdog_enable_all_cpus(void)
523{
524    int cpu;
525
526    watchdog_enabled = 0;
527
528    for_each_online_cpu(cpu)
529        if (!watchdog_enable(cpu))
530            /* if any cpu succeeds, watchdog is considered
531               enabled for the system */
532            watchdog_enabled = 1;
533
534    if (!watchdog_enabled)
535        pr_err("failed to be enabled on some cpus\n");
536
537}
538
539static void watchdog_disable_all_cpus(void)
540{
541    int cpu;
542
543    for_each_online_cpu(cpu)
544        watchdog_disable(cpu);
545
546    /* if all watchdogs are disabled, then they are disabled for the system */
547    watchdog_enabled = 0;
548}
549
550
551/*
552 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
553 */
554
555int proc_dowatchdog(struct ctl_table *table, int write,
556            void __user *buffer, size_t *lenp, loff_t *ppos)
557{
558    int ret;
559
560    ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
561    if (ret || !write)
562        goto out;
563
564    if (watchdog_enabled && watchdog_thresh)
565        watchdog_enable_all_cpus();
566    else
567        watchdog_disable_all_cpus();
568
569out:
570    return ret;
571}
572#endif /* CONFIG_SYSCTL */
573
574
575/*
576 * Create/destroy watchdog threads as CPUs come and go:
577 */
578static int __cpuinit
579cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
580{
581    int hotcpu = (unsigned long)hcpu;
582
583    switch (action) {
584    case CPU_UP_PREPARE:
585    case CPU_UP_PREPARE_FROZEN:
586        watchdog_prepare_cpu(hotcpu);
587        break;
588    case CPU_ONLINE:
589    case CPU_ONLINE_FROZEN:
590        if (watchdog_enabled)
591            watchdog_enable(hotcpu);
592        break;
593#ifdef CONFIG_HOTPLUG_CPU
594    case CPU_UP_CANCELED:
595    case CPU_UP_CANCELED_FROZEN:
596        watchdog_disable(hotcpu);
597        break;
598    case CPU_DEAD:
599    case CPU_DEAD_FROZEN:
600        watchdog_disable(hotcpu);
601        break;
602#endif /* CONFIG_HOTPLUG_CPU */
603    }
604
605    /*
606     * hardlockup and softlockup are not important enough
607     * to block cpu bring up. Just always succeed and
608     * rely on printk output to flag problems.
609     */
610    return NOTIFY_OK;
611}
612
613static struct notifier_block __cpuinitdata cpu_nfb = {
614    .notifier_call = cpu_callback
615};
616
617void __init lockup_detector_init(void)
618{
619    void *cpu = (void *)(long)smp_processor_id();
620    int err;
621
622    err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
623    WARN_ON(notifier_to_errno(err));
624
625    cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
626    register_cpu_notifier(&cpu_nfb);
627
628    return;
629}
630

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