2 * Detect hard and soft lockups on a system
4 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
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.
12 #define pr_fmt(fmt) "NMI watchdog: " fmt
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>
28 #include <asm/irq_regs.h>
29 #include <linux/kvm_para.h>
30 #include <linux/perf_event.h>
32 int watchdog_user_enabled
= 1;
33 int __read_mostly watchdog_thresh
= 10;
35 int __read_mostly sysctl_softlockup_all_cpu_backtrace
;
37 #define sysctl_softlockup_all_cpu_backtrace 0
40 static int __read_mostly watchdog_running
;
41 static u64 __read_mostly sample_period
;
43 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts
);
44 static DEFINE_PER_CPU(struct task_struct
*, softlockup_watchdog
);
45 static DEFINE_PER_CPU(struct hrtimer
, watchdog_hrtimer
);
46 static DEFINE_PER_CPU(bool, softlockup_touch_sync
);
47 static DEFINE_PER_CPU(bool, soft_watchdog_warn
);
48 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts
);
49 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt
);
50 static DEFINE_PER_CPU(struct task_struct
*, softlockup_task_ptr_saved
);
51 #ifdef CONFIG_HARDLOCKUP_DETECTOR
52 static DEFINE_PER_CPU(bool, hard_watchdog_warn
);
53 static DEFINE_PER_CPU(bool, watchdog_nmi_touch
);
54 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved
);
55 static DEFINE_PER_CPU(struct perf_event
*, watchdog_ev
);
57 static unsigned long soft_lockup_nmi_warn
;
61 * Should we panic when a soft-lockup or hard-lockup occurs:
63 #ifdef CONFIG_HARDLOCKUP_DETECTOR
64 static int hardlockup_panic
=
65 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE
;
67 static int __init
hardlockup_panic_setup(char *str
)
69 if (!strncmp(str
, "panic", 5))
71 else if (!strncmp(str
, "nopanic", 7))
73 else if (!strncmp(str
, "0", 1))
74 watchdog_user_enabled
= 0;
77 __setup("nmi_watchdog=", hardlockup_panic_setup
);
80 unsigned int __read_mostly softlockup_panic
=
81 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
;
83 static int __init
softlockup_panic_setup(char *str
)
85 softlockup_panic
= simple_strtoul(str
, NULL
, 0);
89 __setup("softlockup_panic=", softlockup_panic_setup
);
91 static int __init
nowatchdog_setup(char *str
)
93 watchdog_user_enabled
= 0;
96 __setup("nowatchdog", nowatchdog_setup
);
99 static int __init
nosoftlockup_setup(char *str
)
101 watchdog_user_enabled
= 0;
104 __setup("nosoftlockup", nosoftlockup_setup
);
107 static int __init
softlockup_all_cpu_backtrace_setup(char *str
)
109 sysctl_softlockup_all_cpu_backtrace
=
110 !!simple_strtol(str
, NULL
, 0);
113 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup
);
117 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
118 * lockups can have false positives under extreme conditions. So we generally
119 * want a higher threshold for soft lockups than for hard lockups. So we couple
120 * the thresholds with a factor: we make the soft threshold twice the amount of
121 * time the hard threshold is.
123 static int get_softlockup_thresh(void)
125 return watchdog_thresh
* 2;
129 * Returns seconds, approximately. We don't need nanosecond
130 * resolution, and we don't need to waste time with a big divide when
133 static unsigned long get_timestamp(void)
135 return local_clock() >> 30LL; /* 2^30 ~= 10^9 */
138 static void set_sample_period(void)
141 * convert watchdog_thresh from seconds to ns
142 * the divide by 5 is to give hrtimer several chances (two
143 * or three with the current relation between the soft
144 * and hard thresholds) to increment before the
145 * hardlockup detector generates a warning
147 sample_period
= get_softlockup_thresh() * ((u64
)NSEC_PER_SEC
/ 5);
150 /* Commands for resetting the watchdog */
151 static void __touch_watchdog(void)
153 __this_cpu_write(watchdog_touch_ts
, get_timestamp());
156 void touch_softlockup_watchdog(void)
159 * Preemption can be enabled. It doesn't matter which CPU's timestamp
160 * gets zeroed here, so use the raw_ operation.
162 raw_cpu_write(watchdog_touch_ts
, 0);
164 EXPORT_SYMBOL(touch_softlockup_watchdog
);
166 void touch_all_softlockup_watchdogs(void)
171 * this is done lockless
172 * do we care if a 0 races with a timestamp?
173 * all it means is the softlock check starts one cycle later
175 for_each_online_cpu(cpu
)
176 per_cpu(watchdog_touch_ts
, cpu
) = 0;
179 #ifdef CONFIG_HARDLOCKUP_DETECTOR
180 void touch_nmi_watchdog(void)
183 * Using __raw here because some code paths have
184 * preemption enabled. If preemption is enabled
185 * then interrupts should be enabled too, in which
186 * case we shouldn't have to worry about the watchdog
189 __raw_get_cpu_var(watchdog_nmi_touch
) = true;
190 touch_softlockup_watchdog();
192 EXPORT_SYMBOL(touch_nmi_watchdog
);
196 void touch_softlockup_watchdog_sync(void)
198 __raw_get_cpu_var(softlockup_touch_sync
) = true;
199 __raw_get_cpu_var(watchdog_touch_ts
) = 0;
202 #ifdef CONFIG_HARDLOCKUP_DETECTOR
203 /* watchdog detector functions */
204 static int is_hardlockup(void)
206 unsigned long hrint
= __this_cpu_read(hrtimer_interrupts
);
208 if (__this_cpu_read(hrtimer_interrupts_saved
) == hrint
)
211 __this_cpu_write(hrtimer_interrupts_saved
, hrint
);
216 static int is_softlockup(unsigned long touch_ts
)
218 unsigned long now
= get_timestamp();
220 /* Warn about unreasonable delays: */
221 if (time_after(now
, touch_ts
+ get_softlockup_thresh()))
222 return now
- touch_ts
;
227 #ifdef CONFIG_HARDLOCKUP_DETECTOR
229 static struct perf_event_attr wd_hw_attr
= {
230 .type
= PERF_TYPE_HARDWARE
,
231 .config
= PERF_COUNT_HW_CPU_CYCLES
,
232 .size
= sizeof(struct perf_event_attr
),
237 /* Callback function for perf event subsystem */
238 static void watchdog_overflow_callback(struct perf_event
*event
,
239 struct perf_sample_data
*data
,
240 struct pt_regs
*regs
)
242 /* Ensure the watchdog never gets throttled */
243 event
->hw
.interrupts
= 0;
245 if (__this_cpu_read(watchdog_nmi_touch
) == true) {
246 __this_cpu_write(watchdog_nmi_touch
, false);
250 /* check for a hardlockup
251 * This is done by making sure our timer interrupt
252 * is incrementing. The timer interrupt should have
253 * fired multiple times before we overflow'd. If it hasn't
254 * then this is a good indication the cpu is stuck
256 if (is_hardlockup()) {
257 int this_cpu
= smp_processor_id();
259 /* only print hardlockups once */
260 if (__this_cpu_read(hard_watchdog_warn
) == true)
263 if (hardlockup_panic
)
264 panic("Watchdog detected hard LOCKUP on cpu %d",
267 WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
270 __this_cpu_write(hard_watchdog_warn
, true);
274 __this_cpu_write(hard_watchdog_warn
, false);
277 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
279 static void watchdog_interrupt_count(void)
281 __this_cpu_inc(hrtimer_interrupts
);
284 static int watchdog_nmi_enable(unsigned int cpu
);
285 static void watchdog_nmi_disable(unsigned int cpu
);
287 /* watchdog kicker functions */
288 static enum hrtimer_restart
watchdog_timer_fn(struct hrtimer
*hrtimer
)
290 unsigned long touch_ts
= __this_cpu_read(watchdog_touch_ts
);
291 struct pt_regs
*regs
= get_irq_regs();
293 int softlockup_all_cpu_backtrace
= sysctl_softlockup_all_cpu_backtrace
;
295 /* kick the hardlockup detector */
296 watchdog_interrupt_count();
298 /* kick the softlockup detector */
299 wake_up_process(__this_cpu_read(softlockup_watchdog
));
302 hrtimer_forward_now(hrtimer
, ns_to_ktime(sample_period
));
305 if (unlikely(__this_cpu_read(softlockup_touch_sync
))) {
307 * If the time stamp was touched atomically
308 * make sure the scheduler tick is up to date.
310 __this_cpu_write(softlockup_touch_sync
, false);
314 /* Clear the guest paused flag on watchdog reset */
315 kvm_check_and_clear_guest_paused();
317 return HRTIMER_RESTART
;
320 /* check for a softlockup
321 * This is done by making sure a high priority task is
322 * being scheduled. The task touches the watchdog to
323 * indicate it is getting cpu time. If it hasn't then
324 * this is a good indication some task is hogging the cpu
326 duration
= is_softlockup(touch_ts
);
327 if (unlikely(duration
)) {
329 * If a virtual machine is stopped by the host it can look to
330 * the watchdog like a soft lockup, check to see if the host
331 * stopped the vm before we issue the warning
333 if (kvm_check_and_clear_guest_paused())
334 return HRTIMER_RESTART
;
337 if (__this_cpu_read(soft_watchdog_warn
) == true) {
339 * When multiple processes are causing softlockups the
340 * softlockup detector only warns on the first one
341 * because the code relies on a full quiet cycle to
342 * re-arm. The second process prevents the quiet cycle
343 * and never gets reported. Use task pointers to detect
346 if (__this_cpu_read(softlockup_task_ptr_saved
) !=
348 __this_cpu_write(soft_watchdog_warn
, false);
351 return HRTIMER_RESTART
;
354 if (softlockup_all_cpu_backtrace
) {
355 /* Prevent multiple soft-lockup reports if one cpu is already
356 * engaged in dumping cpu back traces
358 if (test_and_set_bit(0, &soft_lockup_nmi_warn
)) {
359 /* Someone else will report us. Let's give up */
360 __this_cpu_write(soft_watchdog_warn
, true);
361 return HRTIMER_RESTART
;
365 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
366 smp_processor_id(), duration
,
367 current
->comm
, task_pid_nr(current
));
368 __this_cpu_write(softlockup_task_ptr_saved
, current
);
370 print_irqtrace_events(current
);
376 if (softlockup_all_cpu_backtrace
) {
377 /* Avoid generating two back traces for current
378 * given that one is already made above
380 trigger_allbutself_cpu_backtrace();
382 clear_bit(0, &soft_lockup_nmi_warn
);
383 /* Barrier to sync with other cpus */
384 smp_mb__after_atomic();
387 add_taint(TAINT_SOFTLOCKUP
, LOCKDEP_STILL_OK
);
388 if (softlockup_panic
)
389 panic("softlockup: hung tasks");
390 __this_cpu_write(soft_watchdog_warn
, true);
392 __this_cpu_write(soft_watchdog_warn
, false);
394 return HRTIMER_RESTART
;
397 static void watchdog_set_prio(unsigned int policy
, unsigned int prio
)
399 struct sched_param param
= { .sched_priority
= prio
};
401 sched_setscheduler(current
, policy
, ¶m
);
404 static void watchdog_enable(unsigned int cpu
)
406 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
408 /* kick off the timer for the hardlockup detector */
409 hrtimer_init(hrtimer
, CLOCK_MONOTONIC
, HRTIMER_MODE_REL
);
410 hrtimer
->function
= watchdog_timer_fn
;
412 /* Enable the perf event */
413 watchdog_nmi_enable(cpu
);
415 /* done here because hrtimer_start can only pin to smp_processor_id() */
416 hrtimer_start(hrtimer
, ns_to_ktime(sample_period
),
417 HRTIMER_MODE_REL_PINNED
);
419 /* initialize timestamp */
420 watchdog_set_prio(SCHED_FIFO
, MAX_RT_PRIO
- 1);
424 static void watchdog_disable(unsigned int cpu
)
426 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
428 watchdog_set_prio(SCHED_NORMAL
, 0);
429 hrtimer_cancel(hrtimer
);
430 /* disable the perf event */
431 watchdog_nmi_disable(cpu
);
434 static void watchdog_cleanup(unsigned int cpu
, bool online
)
436 watchdog_disable(cpu
);
439 static int watchdog_should_run(unsigned int cpu
)
441 return __this_cpu_read(hrtimer_interrupts
) !=
442 __this_cpu_read(soft_lockup_hrtimer_cnt
);
446 * The watchdog thread function - touches the timestamp.
448 * It only runs once every sample_period seconds (4 seconds by
449 * default) to reset the softlockup timestamp. If this gets delayed
450 * for more than 2*watchdog_thresh seconds then the debug-printout
451 * triggers in watchdog_timer_fn().
453 static void watchdog(unsigned int cpu
)
455 __this_cpu_write(soft_lockup_hrtimer_cnt
,
456 __this_cpu_read(hrtimer_interrupts
));
460 #ifdef CONFIG_HARDLOCKUP_DETECTOR
462 * People like the simple clean cpu node info on boot.
463 * Reduce the watchdog noise by only printing messages
464 * that are different from what cpu0 displayed.
466 static unsigned long cpu0_err
;
468 static int watchdog_nmi_enable(unsigned int cpu
)
470 struct perf_event_attr
*wd_attr
;
471 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
473 /* is it already setup and enabled? */
474 if (event
&& event
->state
> PERF_EVENT_STATE_OFF
)
477 /* it is setup but not enabled */
481 wd_attr
= &wd_hw_attr
;
482 wd_attr
->sample_period
= hw_nmi_get_sample_period(watchdog_thresh
);
484 /* Try to register using hardware perf events */
485 event
= perf_event_create_kernel_counter(wd_attr
, cpu
, NULL
, watchdog_overflow_callback
, NULL
);
487 /* save cpu0 error for future comparision */
488 if (cpu
== 0 && IS_ERR(event
))
489 cpu0_err
= PTR_ERR(event
);
491 if (!IS_ERR(event
)) {
492 /* only print for cpu0 or different than cpu0 */
493 if (cpu
== 0 || cpu0_err
)
494 pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
498 /* skip displaying the same error again */
499 if (cpu
> 0 && (PTR_ERR(event
) == cpu0_err
))
500 return PTR_ERR(event
);
502 /* vary the KERN level based on the returned errno */
503 if (PTR_ERR(event
) == -EOPNOTSUPP
)
504 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu
);
505 else if (PTR_ERR(event
) == -ENOENT
)
506 pr_warn("disabled (cpu%i): hardware events not enabled\n",
509 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
510 cpu
, PTR_ERR(event
));
511 return PTR_ERR(event
);
515 per_cpu(watchdog_ev
, cpu
) = event
;
517 perf_event_enable(per_cpu(watchdog_ev
, cpu
));
522 static void watchdog_nmi_disable(unsigned int cpu
)
524 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
527 perf_event_disable(event
);
528 per_cpu(watchdog_ev
, cpu
) = NULL
;
530 /* should be in cleanup, but blocks oprofile */
531 perf_event_release_kernel(event
);
536 static int watchdog_nmi_enable(unsigned int cpu
) { return 0; }
537 static void watchdog_nmi_disable(unsigned int cpu
) { return; }
538 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
540 static struct smp_hotplug_thread watchdog_threads
= {
541 .store
= &softlockup_watchdog
,
542 .thread_should_run
= watchdog_should_run
,
543 .thread_fn
= watchdog
,
544 .thread_comm
= "watchdog/%u",
545 .setup
= watchdog_enable
,
546 .cleanup
= watchdog_cleanup
,
547 .park
= watchdog_disable
,
548 .unpark
= watchdog_enable
,
551 static void restart_watchdog_hrtimer(void *info
)
553 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
557 * No need to cancel and restart hrtimer if it is currently executing
558 * because it will reprogram itself with the new period now.
559 * We should never see it unqueued here because we are running per-cpu
560 * with interrupts disabled.
562 ret
= hrtimer_try_to_cancel(hrtimer
);
564 hrtimer_start(hrtimer
, ns_to_ktime(sample_period
),
565 HRTIMER_MODE_REL_PINNED
);
568 static void update_timers(int cpu
)
571 * Make sure that perf event counter will adopt to a new
572 * sampling period. Updating the sampling period directly would
573 * be much nicer but we do not have an API for that now so
574 * let's use a big hammer.
575 * Hrtimer will adopt the new period on the next tick but this
576 * might be late already so we have to restart the timer as well.
578 watchdog_nmi_disable(cpu
);
579 smp_call_function_single(cpu
, restart_watchdog_hrtimer
, NULL
, 1);
580 watchdog_nmi_enable(cpu
);
583 static void update_timers_all_cpus(void)
588 for_each_online_cpu(cpu
)
593 static int watchdog_enable_all_cpus(bool sample_period_changed
)
597 if (!watchdog_running
) {
598 err
= smpboot_register_percpu_thread(&watchdog_threads
);
600 pr_err("Failed to create watchdog threads, disabled\n");
602 watchdog_running
= 1;
603 } else if (sample_period_changed
) {
604 update_timers_all_cpus();
610 /* prepare/enable/disable routines */
611 /* sysctl functions */
613 static void watchdog_disable_all_cpus(void)
615 if (watchdog_running
) {
616 watchdog_running
= 0;
617 smpboot_unregister_percpu_thread(&watchdog_threads
);
622 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
625 int proc_dowatchdog(struct ctl_table
*table
, int write
,
626 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
628 int err
, old_thresh
, old_enabled
;
629 static DEFINE_MUTEX(watchdog_proc_mutex
);
631 mutex_lock(&watchdog_proc_mutex
);
632 old_thresh
= ACCESS_ONCE(watchdog_thresh
);
633 old_enabled
= ACCESS_ONCE(watchdog_user_enabled
);
635 err
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
641 * Watchdog threads shouldn't be enabled if they are
642 * disabled. The 'watchdog_running' variable check in
643 * watchdog_*_all_cpus() function takes care of this.
645 if (watchdog_user_enabled
&& watchdog_thresh
)
646 err
= watchdog_enable_all_cpus(old_thresh
!= watchdog_thresh
);
648 watchdog_disable_all_cpus();
650 /* Restore old values on failure */
652 watchdog_thresh
= old_thresh
;
653 watchdog_user_enabled
= old_enabled
;
656 mutex_unlock(&watchdog_proc_mutex
);
659 #endif /* CONFIG_SYSCTL */
661 void __init
lockup_detector_init(void)
665 if (watchdog_user_enabled
)
666 watchdog_enable_all_cpus(false);