1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Detect hard lockups on a system
  4 *
  5 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
  6 *
  7 * Note: Most of this code is borrowed heavily from the original softlockup
  8 * detector, so thanks to Ingo for the initial implementation.
  9 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
 10 * to those contributors as well.
 11 */
 12
 13#define pr_fmt(fmt) "NMI watchdog: " fmt
 14
 15#include <linux/nmi.h>
 16#include <linux/atomic.h>
 17#include <linux/module.h>
 18#include <linux/sched/debug.h>
 19
 20#include <asm/irq_regs.h>
 21#include <linux/perf_event.h>
 22
 23static DEFINE_PER_CPU(bool, hard_watchdog_warn);
 24static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
 25static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
 26static DEFINE_PER_CPU(struct perf_event *, dead_event);
 27static struct cpumask dead_events_mask;
 28
 29static unsigned long hardlockup_allcpu_dumped;
 30static atomic_t watchdog_cpus = ATOMIC_INIT(0);
 31
 32notrace void arch_touch_nmi_watchdog(void)
 33{
 34	/*
 35	 * Using __raw here because some code paths have
 36	 * preemption enabled.  If preemption is enabled
 37	 * then interrupts should be enabled too, in which
 38	 * case we shouldn't have to worry about the watchdog
 39	 * going off.
 40	 */
 41	raw_cpu_write(watchdog_nmi_touch, true);
 42}
 43EXPORT_SYMBOL(arch_touch_nmi_watchdog);
 44
 45#ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
 46static DEFINE_PER_CPU(ktime_t, last_timestamp);
 47static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
 48static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
 49
 50void watchdog_update_hrtimer_threshold(u64 period)
 51{
 52	/*
 53	 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
 54	 *
 55	 * So it runs effectively with 2.5 times the rate of the NMI
 56	 * watchdog. That means the hrtimer should fire 2-3 times before
 57	 * the NMI watchdog expires. The NMI watchdog on x86 is based on
 58	 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
 59	 * might run way faster than expected and the NMI fires in a
 60	 * smaller period than the one deduced from the nominal CPU
 61	 * frequency. Depending on the Turbo-Mode factor this might be fast
 62	 * enough to get the NMI period smaller than the hrtimer watchdog
 63	 * period and trigger false positives.
 64	 *
 65	 * The sample threshold is used to check in the NMI handler whether
 66	 * the minimum time between two NMI samples has elapsed. That
 67	 * prevents false positives.
 68	 *
 69	 * Set this to 4/5 of the actual watchdog threshold period so the
 70	 * hrtimer is guaranteed to fire at least once within the real
 71	 * watchdog threshold.
 72	 */
 73	watchdog_hrtimer_sample_threshold = period * 2;
 74}
 75
 76static bool watchdog_check_timestamp(void)
 77{
 78	ktime_t delta, now = ktime_get_mono_fast_ns();
 79
 80	delta = now - __this_cpu_read(last_timestamp);
 81	if (delta < watchdog_hrtimer_sample_threshold) {
 82		/*
 83		 * If ktime is jiffies based, a stalled timer would prevent
 84		 * jiffies from being incremented and the filter would look
 85		 * at a stale timestamp and never trigger.
 86		 */
 87		if (__this_cpu_inc_return(nmi_rearmed) < 10)
 88			return false;
 89	}
 90	__this_cpu_write(nmi_rearmed, 0);
 91	__this_cpu_write(last_timestamp, now);
 92	return true;
 93}
 94#else
 95static inline bool watchdog_check_timestamp(void)
 96{
 97	return true;
 98}
 99#endif
100
101static struct perf_event_attr wd_hw_attr = {
102	.type		= PERF_TYPE_HARDWARE,
103	.config		= PERF_COUNT_HW_CPU_CYCLES,
104	.size		= sizeof(struct perf_event_attr),
105	.pinned		= 1,
106	.disabled	= 1,
107};
108
109/* Callback function for perf event subsystem */
110static void watchdog_overflow_callback(struct perf_event *event,
111				       struct perf_sample_data *data,
112				       struct pt_regs *regs)
113{
114	/* Ensure the watchdog never gets throttled */
115	event->hw.interrupts = 0;
116
117	if (__this_cpu_read(watchdog_nmi_touch) == true) {
118		__this_cpu_write(watchdog_nmi_touch, false);
119		return;
120	}
121
122	if (!watchdog_check_timestamp())
123		return;
124
125	/* check for a hardlockup
126	 * This is done by making sure our timer interrupt
127	 * is incrementing.  The timer interrupt should have
128	 * fired multiple times before we overflow'd.  If it hasn't
129	 * then this is a good indication the cpu is stuck
130	 */
131	if (is_hardlockup()) {
132		int this_cpu = smp_processor_id();
133
134		/* only print hardlockups once */
135		if (__this_cpu_read(hard_watchdog_warn) == true)
136			return;
137
138		pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n",
139			 this_cpu);
140		print_modules();
141		print_irqtrace_events(current);
142		if (regs)
143			show_regs(regs);
144		else
145			dump_stack();
146
147		/*
148		 * Perform all-CPU dump only once to avoid multiple hardlockups
149		 * generating interleaving traces
150		 */
151		if (sysctl_hardlockup_all_cpu_backtrace &&
152				!test_and_set_bit(0, &hardlockup_allcpu_dumped))
153			trigger_allbutself_cpu_backtrace();
154
155		if (hardlockup_panic)
156			nmi_panic(regs, "Hard LOCKUP");
157
158		__this_cpu_write(hard_watchdog_warn, true);
159		return;
160	}
161
162	__this_cpu_write(hard_watchdog_warn, false);
163	return;
164}
165
166static int hardlockup_detector_event_create(void)
167{
168	unsigned int cpu = smp_processor_id();
169	struct perf_event_attr *wd_attr;
170	struct perf_event *evt;
171
172	wd_attr = &wd_hw_attr;
173	wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
174
175	/* Try to register using hardware perf events */
176	evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
177					       watchdog_overflow_callback, NULL);
178	if (IS_ERR(evt)) {
179		pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
180			 PTR_ERR(evt));
181		return PTR_ERR(evt);
182	}
183	this_cpu_write(watchdog_ev, evt);
184	return 0;
185}
186
187/**
188 * hardlockup_detector_perf_enable - Enable the local event
189 */
190void hardlockup_detector_perf_enable(void)
191{
192	if (hardlockup_detector_event_create())
193		return;
194
195	/* use original value for check */
196	if (!atomic_fetch_inc(&watchdog_cpus))
197		pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
198
199	perf_event_enable(this_cpu_read(watchdog_ev));
200}
201
202/**
203 * hardlockup_detector_perf_disable - Disable the local event
204 */
205void hardlockup_detector_perf_disable(void)
206{
207	struct perf_event *event = this_cpu_read(watchdog_ev);
208
209	if (event) {
210		perf_event_disable(event);
211		this_cpu_write(watchdog_ev, NULL);
212		this_cpu_write(dead_event, event);
213		cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
214		atomic_dec(&watchdog_cpus);
215	}
216}
217
218/**
219 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
220 *
221 * Called from lockup_detector_cleanup(). Serialized by the caller.
222 */
223void hardlockup_detector_perf_cleanup(void)
224{
225	int cpu;
226
227	for_each_cpu(cpu, &dead_events_mask) {
228		struct perf_event *event = per_cpu(dead_event, cpu);
229
230		/*
231		 * Required because for_each_cpu() reports  unconditionally
232		 * CPU0 as set on UP kernels. Sigh.
233		 */
234		if (event)
235			perf_event_release_kernel(event);
236		per_cpu(dead_event, cpu) = NULL;
237	}
238	cpumask_clear(&dead_events_mask);
239}
240
241/**
242 * hardlockup_detector_perf_stop - Globally stop watchdog events
243 *
244 * Special interface for x86 to handle the perf HT bug.
245 */
246void __init hardlockup_detector_perf_stop(void)
247{
248	int cpu;
249
250	lockdep_assert_cpus_held();
251
252	for_each_online_cpu(cpu) {
253		struct perf_event *event = per_cpu(watchdog_ev, cpu);
254
255		if (event)
256			perf_event_disable(event);
257	}
258}
259
260/**
261 * hardlockup_detector_perf_restart - Globally restart watchdog events
262 *
263 * Special interface for x86 to handle the perf HT bug.
264 */
265void __init hardlockup_detector_perf_restart(void)
266{
267	int cpu;
268
269	lockdep_assert_cpus_held();
270
271	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
272		return;
273
274	for_each_online_cpu(cpu) {
275		struct perf_event *event = per_cpu(watchdog_ev, cpu);
276
277		if (event)
278			perf_event_enable(event);
279	}
280}
281
282/**
283 * hardlockup_detector_perf_init - Probe whether NMI event is available at all
284 */
285int __init hardlockup_detector_perf_init(void)
286{
287	int ret = hardlockup_detector_event_create();
288
289	if (ret) {
290		pr_info("Perf NMI watchdog permanently disabled\n");
291	} else {
292		perf_event_release_kernel(this_cpu_read(watchdog_ev));
293		this_cpu_write(watchdog_ev, NULL);
294	}
295	return ret;
296}