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

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