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/module.h>
19 #include <linux/sysctl.h>
20 #include <linux/smpboot.h>
21 #include <linux/sched/rt.h>
23 #include <asm/irq_regs.h>
24 #include <linux/kvm_para.h>
25 #include <linux/perf_event.h>
27 int watchdog_user_enabled
= 1;
28 int __read_mostly watchdog_thresh
= 10;
30 int __read_mostly sysctl_softlockup_all_cpu_backtrace
;
32 #define sysctl_softlockup_all_cpu_backtrace 0
35 static int __read_mostly watchdog_running
;
36 static u64 __read_mostly sample_period
;
38 static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts
);
39 static DEFINE_PER_CPU(struct task_struct
*, softlockup_watchdog
);
40 static DEFINE_PER_CPU(struct hrtimer
, watchdog_hrtimer
);
41 static DEFINE_PER_CPU(bool, softlockup_touch_sync
);
42 static DEFINE_PER_CPU(bool, soft_watchdog_warn
);
43 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts
);
44 static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt
);
45 static DEFINE_PER_CPU(struct task_struct
*, softlockup_task_ptr_saved
);
46 #ifdef CONFIG_HARDLOCKUP_DETECTOR
47 static DEFINE_PER_CPU(bool, hard_watchdog_warn
);
48 static DEFINE_PER_CPU(bool, watchdog_nmi_touch
);
49 static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved
);
50 static DEFINE_PER_CPU(struct perf_event
*, watchdog_ev
);
52 static unsigned long soft_lockup_nmi_warn
;
56 * Should we panic when a soft-lockup or hard-lockup occurs:
58 #ifdef CONFIG_HARDLOCKUP_DETECTOR
59 static int hardlockup_panic
=
60 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE
;
62 static int __init
hardlockup_panic_setup(char *str
)
64 if (!strncmp(str
, "panic", 5))
66 else if (!strncmp(str
, "nopanic", 7))
68 else if (!strncmp(str
, "0", 1))
69 watchdog_user_enabled
= 0;
72 __setup("nmi_watchdog=", hardlockup_panic_setup
);
75 unsigned int __read_mostly softlockup_panic
=
76 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE
;
78 static int __init
softlockup_panic_setup(char *str
)
80 softlockup_panic
= simple_strtoul(str
, NULL
, 0);
84 __setup("softlockup_panic=", softlockup_panic_setup
);
86 static int __init
nowatchdog_setup(char *str
)
88 watchdog_user_enabled
= 0;
91 __setup("nowatchdog", nowatchdog_setup
);
94 static int __init
nosoftlockup_setup(char *str
)
96 watchdog_user_enabled
= 0;
99 __setup("nosoftlockup", nosoftlockup_setup
);
102 static int __init
softlockup_all_cpu_backtrace_setup(char *str
)
104 sysctl_softlockup_all_cpu_backtrace
=
105 !!simple_strtol(str
, NULL
, 0);
108 __setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup
);
112 * Hard-lockup warnings should be triggered after just a few seconds. Soft-
113 * lockups can have false positives under extreme conditions. So we generally
114 * want a higher threshold for soft lockups than for hard lockups. So we couple
115 * the thresholds with a factor: we make the soft threshold twice the amount of
116 * time the hard threshold is.
118 static int get_softlockup_thresh(void)
120 return watchdog_thresh
* 2;
124 * Returns seconds, approximately. We don't need nanosecond
125 * resolution, and we don't need to waste time with a big divide when
128 static unsigned long get_timestamp(void)
130 return local_clock() >> 30LL; /* 2^30 ~= 10^9 */
133 static void set_sample_period(void)
136 * convert watchdog_thresh from seconds to ns
137 * the divide by 5 is to give hrtimer several chances (two
138 * or three with the current relation between the soft
139 * and hard thresholds) to increment before the
140 * hardlockup detector generates a warning
142 sample_period
= get_softlockup_thresh() * ((u64
)NSEC_PER_SEC
/ 5);
145 /* Commands for resetting the watchdog */
146 static void __touch_watchdog(void)
148 __this_cpu_write(watchdog_touch_ts
, get_timestamp());
151 void touch_softlockup_watchdog(void)
154 * Preemption can be enabled. It doesn't matter which CPU's timestamp
155 * gets zeroed here, so use the raw_ operation.
157 raw_cpu_write(watchdog_touch_ts
, 0);
159 EXPORT_SYMBOL(touch_softlockup_watchdog
);
161 void touch_all_softlockup_watchdogs(void)
166 * this is done lockless
167 * do we care if a 0 races with a timestamp?
168 * all it means is the softlock check starts one cycle later
170 for_each_online_cpu(cpu
)
171 per_cpu(watchdog_touch_ts
, cpu
) = 0;
174 #ifdef CONFIG_HARDLOCKUP_DETECTOR
175 void touch_nmi_watchdog(void)
178 * Using __raw here because some code paths have
179 * preemption enabled. If preemption is enabled
180 * then interrupts should be enabled too, in which
181 * case we shouldn't have to worry about the watchdog
184 __raw_get_cpu_var(watchdog_nmi_touch
) = true;
185 touch_softlockup_watchdog();
187 EXPORT_SYMBOL(touch_nmi_watchdog
);
191 void touch_softlockup_watchdog_sync(void)
193 __raw_get_cpu_var(softlockup_touch_sync
) = true;
194 __raw_get_cpu_var(watchdog_touch_ts
) = 0;
197 #ifdef CONFIG_HARDLOCKUP_DETECTOR
198 /* watchdog detector functions */
199 static int is_hardlockup(void)
201 unsigned long hrint
= __this_cpu_read(hrtimer_interrupts
);
203 if (__this_cpu_read(hrtimer_interrupts_saved
) == hrint
)
206 __this_cpu_write(hrtimer_interrupts_saved
, hrint
);
211 static int is_softlockup(unsigned long touch_ts
)
213 unsigned long now
= get_timestamp();
215 /* Warn about unreasonable delays: */
216 if (time_after(now
, touch_ts
+ get_softlockup_thresh()))
217 return now
- touch_ts
;
222 #ifdef CONFIG_HARDLOCKUP_DETECTOR
224 static struct perf_event_attr wd_hw_attr
= {
225 .type
= PERF_TYPE_HARDWARE
,
226 .config
= PERF_COUNT_HW_CPU_CYCLES
,
227 .size
= sizeof(struct perf_event_attr
),
232 /* Callback function for perf event subsystem */
233 static void watchdog_overflow_callback(struct perf_event
*event
,
234 struct perf_sample_data
*data
,
235 struct pt_regs
*regs
)
237 /* Ensure the watchdog never gets throttled */
238 event
->hw
.interrupts
= 0;
240 if (__this_cpu_read(watchdog_nmi_touch
) == true) {
241 __this_cpu_write(watchdog_nmi_touch
, false);
245 /* check for a hardlockup
246 * This is done by making sure our timer interrupt
247 * is incrementing. The timer interrupt should have
248 * fired multiple times before we overflow'd. If it hasn't
249 * then this is a good indication the cpu is stuck
251 if (is_hardlockup()) {
252 int this_cpu
= smp_processor_id();
254 /* only print hardlockups once */
255 if (__this_cpu_read(hard_watchdog_warn
) == true)
258 if (hardlockup_panic
)
259 panic("Watchdog detected hard LOCKUP on cpu %d",
262 WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
265 __this_cpu_write(hard_watchdog_warn
, true);
269 __this_cpu_write(hard_watchdog_warn
, false);
272 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
274 static void watchdog_interrupt_count(void)
276 __this_cpu_inc(hrtimer_interrupts
);
279 static int watchdog_nmi_enable(unsigned int cpu
);
280 static void watchdog_nmi_disable(unsigned int cpu
);
282 /* watchdog kicker functions */
283 static enum hrtimer_restart
watchdog_timer_fn(struct hrtimer
*hrtimer
)
285 unsigned long touch_ts
= __this_cpu_read(watchdog_touch_ts
);
286 struct pt_regs
*regs
= get_irq_regs();
288 int softlockup_all_cpu_backtrace
= sysctl_softlockup_all_cpu_backtrace
;
290 /* kick the hardlockup detector */
291 watchdog_interrupt_count();
293 /* kick the softlockup detector */
294 wake_up_process(__this_cpu_read(softlockup_watchdog
));
297 hrtimer_forward_now(hrtimer
, ns_to_ktime(sample_period
));
300 if (unlikely(__this_cpu_read(softlockup_touch_sync
))) {
302 * If the time stamp was touched atomically
303 * make sure the scheduler tick is up to date.
305 __this_cpu_write(softlockup_touch_sync
, false);
309 /* Clear the guest paused flag on watchdog reset */
310 kvm_check_and_clear_guest_paused();
312 return HRTIMER_RESTART
;
315 /* check for a softlockup
316 * This is done by making sure a high priority task is
317 * being scheduled. The task touches the watchdog to
318 * indicate it is getting cpu time. If it hasn't then
319 * this is a good indication some task is hogging the cpu
321 duration
= is_softlockup(touch_ts
);
322 if (unlikely(duration
)) {
324 * If a virtual machine is stopped by the host it can look to
325 * the watchdog like a soft lockup, check to see if the host
326 * stopped the vm before we issue the warning
328 if (kvm_check_and_clear_guest_paused())
329 return HRTIMER_RESTART
;
332 if (__this_cpu_read(soft_watchdog_warn
) == true) {
334 * When multiple processes are causing softlockups the
335 * softlockup detector only warns on the first one
336 * because the code relies on a full quiet cycle to
337 * re-arm. The second process prevents the quiet cycle
338 * and never gets reported. Use task pointers to detect
341 if (__this_cpu_read(softlockup_task_ptr_saved
) !=
343 __this_cpu_write(soft_watchdog_warn
, false);
346 return HRTIMER_RESTART
;
349 if (softlockup_all_cpu_backtrace
) {
350 /* Prevent multiple soft-lockup reports if one cpu is already
351 * engaged in dumping cpu back traces
353 if (test_and_set_bit(0, &soft_lockup_nmi_warn
)) {
354 /* Someone else will report us. Let's give up */
355 __this_cpu_write(soft_watchdog_warn
, true);
356 return HRTIMER_RESTART
;
360 pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
361 smp_processor_id(), duration
,
362 current
->comm
, task_pid_nr(current
));
363 __this_cpu_write(softlockup_task_ptr_saved
, current
);
365 print_irqtrace_events(current
);
371 if (softlockup_all_cpu_backtrace
) {
372 /* Avoid generating two back traces for current
373 * given that one is already made above
375 trigger_allbutself_cpu_backtrace();
377 clear_bit(0, &soft_lockup_nmi_warn
);
378 /* Barrier to sync with other cpus */
379 smp_mb__after_atomic();
382 add_taint(TAINT_SOFTLOCKUP
, LOCKDEP_STILL_OK
);
383 if (softlockup_panic
)
384 panic("softlockup: hung tasks");
385 __this_cpu_write(soft_watchdog_warn
, true);
387 __this_cpu_write(soft_watchdog_warn
, false);
389 return HRTIMER_RESTART
;
392 static void watchdog_set_prio(unsigned int policy
, unsigned int prio
)
394 struct sched_param param
= { .sched_priority
= prio
};
396 sched_setscheduler(current
, policy
, ¶m
);
399 static void watchdog_enable(unsigned int cpu
)
401 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
403 /* kick off the timer for the hardlockup detector */
404 hrtimer_init(hrtimer
, CLOCK_MONOTONIC
, HRTIMER_MODE_REL
);
405 hrtimer
->function
= watchdog_timer_fn
;
407 /* Enable the perf event */
408 watchdog_nmi_enable(cpu
);
410 /* done here because hrtimer_start can only pin to smp_processor_id() */
411 hrtimer_start(hrtimer
, ns_to_ktime(sample_period
),
412 HRTIMER_MODE_REL_PINNED
);
414 /* initialize timestamp */
415 watchdog_set_prio(SCHED_FIFO
, MAX_RT_PRIO
- 1);
419 static void watchdog_disable(unsigned int cpu
)
421 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
423 watchdog_set_prio(SCHED_NORMAL
, 0);
424 hrtimer_cancel(hrtimer
);
425 /* disable the perf event */
426 watchdog_nmi_disable(cpu
);
429 static void watchdog_cleanup(unsigned int cpu
, bool online
)
431 watchdog_disable(cpu
);
434 static int watchdog_should_run(unsigned int cpu
)
436 return __this_cpu_read(hrtimer_interrupts
) !=
437 __this_cpu_read(soft_lockup_hrtimer_cnt
);
441 * The watchdog thread function - touches the timestamp.
443 * It only runs once every sample_period seconds (4 seconds by
444 * default) to reset the softlockup timestamp. If this gets delayed
445 * for more than 2*watchdog_thresh seconds then the debug-printout
446 * triggers in watchdog_timer_fn().
448 static void watchdog(unsigned int cpu
)
450 __this_cpu_write(soft_lockup_hrtimer_cnt
,
451 __this_cpu_read(hrtimer_interrupts
));
455 #ifdef CONFIG_HARDLOCKUP_DETECTOR
457 * People like the simple clean cpu node info on boot.
458 * Reduce the watchdog noise by only printing messages
459 * that are different from what cpu0 displayed.
461 static unsigned long cpu0_err
;
463 static int watchdog_nmi_enable(unsigned int cpu
)
465 struct perf_event_attr
*wd_attr
;
466 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
468 /* is it already setup and enabled? */
469 if (event
&& event
->state
> PERF_EVENT_STATE_OFF
)
472 /* it is setup but not enabled */
476 wd_attr
= &wd_hw_attr
;
477 wd_attr
->sample_period
= hw_nmi_get_sample_period(watchdog_thresh
);
479 /* Try to register using hardware perf events */
480 event
= perf_event_create_kernel_counter(wd_attr
, cpu
, NULL
, watchdog_overflow_callback
, NULL
);
482 /* save cpu0 error for future comparision */
483 if (cpu
== 0 && IS_ERR(event
))
484 cpu0_err
= PTR_ERR(event
);
486 if (!IS_ERR(event
)) {
487 /* only print for cpu0 or different than cpu0 */
488 if (cpu
== 0 || cpu0_err
)
489 pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
493 /* skip displaying the same error again */
494 if (cpu
> 0 && (PTR_ERR(event
) == cpu0_err
))
495 return PTR_ERR(event
);
497 /* vary the KERN level based on the returned errno */
498 if (PTR_ERR(event
) == -EOPNOTSUPP
)
499 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu
);
500 else if (PTR_ERR(event
) == -ENOENT
)
501 pr_warn("disabled (cpu%i): hardware events not enabled\n",
504 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
505 cpu
, PTR_ERR(event
));
506 return PTR_ERR(event
);
510 per_cpu(watchdog_ev
, cpu
) = event
;
512 perf_event_enable(per_cpu(watchdog_ev
, cpu
));
517 static void watchdog_nmi_disable(unsigned int cpu
)
519 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
522 perf_event_disable(event
);
523 per_cpu(watchdog_ev
, cpu
) = NULL
;
525 /* should be in cleanup, but blocks oprofile */
526 perf_event_release_kernel(event
);
529 /* watchdog_nmi_enable() expects this to be zero initially. */
534 static int watchdog_nmi_enable(unsigned int cpu
) { return 0; }
535 static void watchdog_nmi_disable(unsigned int cpu
) { return; }
536 #endif /* CONFIG_HARDLOCKUP_DETECTOR */
538 static struct smp_hotplug_thread watchdog_threads
= {
539 .store
= &softlockup_watchdog
,
540 .thread_should_run
= watchdog_should_run
,
541 .thread_fn
= watchdog
,
542 .thread_comm
= "watchdog/%u",
543 .setup
= watchdog_enable
,
544 .cleanup
= watchdog_cleanup
,
545 .park
= watchdog_disable
,
546 .unpark
= watchdog_enable
,
549 static void restart_watchdog_hrtimer(void *info
)
551 struct hrtimer
*hrtimer
= &__raw_get_cpu_var(watchdog_hrtimer
);
555 * No need to cancel and restart hrtimer if it is currently executing
556 * because it will reprogram itself with the new period now.
557 * We should never see it unqueued here because we are running per-cpu
558 * with interrupts disabled.
560 ret
= hrtimer_try_to_cancel(hrtimer
);
562 hrtimer_start(hrtimer
, ns_to_ktime(sample_period
),
563 HRTIMER_MODE_REL_PINNED
);
566 static void update_timers(int cpu
)
569 * Make sure that perf event counter will adopt to a new
570 * sampling period. Updating the sampling period directly would
571 * be much nicer but we do not have an API for that now so
572 * let's use a big hammer.
573 * Hrtimer will adopt the new period on the next tick but this
574 * might be late already so we have to restart the timer as well.
576 watchdog_nmi_disable(cpu
);
577 smp_call_function_single(cpu
, restart_watchdog_hrtimer
, NULL
, 1);
578 watchdog_nmi_enable(cpu
);
581 static void update_timers_all_cpus(void)
586 for_each_online_cpu(cpu
)
591 static int watchdog_enable_all_cpus(bool sample_period_changed
)
595 if (!watchdog_running
) {
596 err
= smpboot_register_percpu_thread(&watchdog_threads
);
598 pr_err("Failed to create watchdog threads, disabled\n");
600 watchdog_running
= 1;
601 } else if (sample_period_changed
) {
602 update_timers_all_cpus();
608 /* prepare/enable/disable routines */
609 /* sysctl functions */
611 static void watchdog_disable_all_cpus(void)
613 if (watchdog_running
) {
614 watchdog_running
= 0;
615 smpboot_unregister_percpu_thread(&watchdog_threads
);
620 * proc handler for /proc/sys/kernel/nmi_watchdog,watchdog_thresh
623 int proc_dowatchdog(struct ctl_table
*table
, int write
,
624 void __user
*buffer
, size_t *lenp
, loff_t
*ppos
)
626 int err
, old_thresh
, old_enabled
;
627 static DEFINE_MUTEX(watchdog_proc_mutex
);
629 mutex_lock(&watchdog_proc_mutex
);
630 old_thresh
= ACCESS_ONCE(watchdog_thresh
);
631 old_enabled
= ACCESS_ONCE(watchdog_user_enabled
);
633 err
= proc_dointvec_minmax(table
, write
, buffer
, lenp
, ppos
);
639 * Watchdog threads shouldn't be enabled if they are
640 * disabled. The 'watchdog_running' variable check in
641 * watchdog_*_all_cpus() function takes care of this.
643 if (watchdog_user_enabled
&& watchdog_thresh
)
644 err
= watchdog_enable_all_cpus(old_thresh
!= watchdog_thresh
);
646 watchdog_disable_all_cpus();
648 /* Restore old values on failure */
650 watchdog_thresh
= old_thresh
;
651 watchdog_user_enabled
= old_enabled
;
654 mutex_unlock(&watchdog_proc_mutex
);
657 #endif /* CONFIG_SYSCTL */
659 void __init
lockup_detector_init(void)
663 if (watchdog_user_enabled
)
664 watchdog_enable_all_cpus(false);