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", this_cpu);
139 print_modules();
140 print_irqtrace_events(current);
141 if (regs)
142 show_regs(regs);
143 else
144 dump_stack();
145
146 /*
147 * Perform all-CPU dump only once to avoid multiple hardlockups
148 * generating interleaving traces
149 */
150 if (sysctl_hardlockup_all_cpu_backtrace &&
151 !test_and_set_bit(0, &hardlockup_allcpu_dumped))
152 trigger_allbutself_cpu_backtrace();
153
154 if (hardlockup_panic)
155 nmi_panic(regs, "Hard LOCKUP");
156
157 __this_cpu_write(hard_watchdog_warn, true);
158 return;
159 }
160
161 __this_cpu_write(hard_watchdog_warn, false);
162 return;
163}
164
165static int hardlockup_detector_event_create(void)
166{
167 unsigned int cpu = smp_processor_id();
168 struct perf_event_attr *wd_attr;
169 struct perf_event *evt;
170
171 wd_attr = &wd_hw_attr;
172 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
173
174 /* Try to register using hardware perf events */
175 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
176 watchdog_overflow_callback, NULL);
177 if (IS_ERR(evt)) {
178 pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
179 PTR_ERR(evt));
180 return PTR_ERR(evt);
181 }
182 this_cpu_write(watchdog_ev, evt);
183 return 0;
184}
185
186/**
187 * hardlockup_detector_perf_enable - Enable the local event
188 */
189void hardlockup_detector_perf_enable(void)
190{
191 if (hardlockup_detector_event_create())
192 return;
193
194 /* use original value for check */
195 if (!atomic_fetch_inc(&watchdog_cpus))
196 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
197
198 perf_event_enable(this_cpu_read(watchdog_ev));
199}
200
201/**
202 * hardlockup_detector_perf_disable - Disable the local event
203 */
204void hardlockup_detector_perf_disable(void)
205{
206 struct perf_event *event = this_cpu_read(watchdog_ev);
207
208 if (event) {
209 perf_event_disable(event);
210 this_cpu_write(watchdog_ev, NULL);
211 this_cpu_write(dead_event, event);
212 cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
213 atomic_dec(&watchdog_cpus);
214 }
215}
216
217/**
218 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
219 *
220 * Called from lockup_detector_cleanup(). Serialized by the caller.
221 */
222void hardlockup_detector_perf_cleanup(void)
223{
224 int cpu;
225
226 for_each_cpu(cpu, &dead_events_mask) {
227 struct perf_event *event = per_cpu(dead_event, cpu);
228
229 /*
230 * Required because for_each_cpu() reports unconditionally
231 * CPU0 as set on UP kernels. Sigh.
232 */
233 if (event)
234 perf_event_release_kernel(event);
235 per_cpu(dead_event, cpu) = NULL;
236 }
237 cpumask_clear(&dead_events_mask);
238}
239
240/**
241 * hardlockup_detector_perf_stop - Globally stop watchdog events
242 *
243 * Special interface for x86 to handle the perf HT bug.
244 */
245void __init hardlockup_detector_perf_stop(void)
246{
247 int cpu;
248
249 lockdep_assert_cpus_held();
250
251 for_each_online_cpu(cpu) {
252 struct perf_event *event = per_cpu(watchdog_ev, cpu);
253
254 if (event)
255 perf_event_disable(event);
256 }
257}
258
259/**
260 * hardlockup_detector_perf_restart - Globally restart watchdog events
261 *
262 * Special interface for x86 to handle the perf HT bug.
263 */
264void __init hardlockup_detector_perf_restart(void)
265{
266 int cpu;
267
268 lockdep_assert_cpus_held();
269
270 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
271 return;
272
273 for_each_online_cpu(cpu) {
274 struct perf_event *event = per_cpu(watchdog_ev, cpu);
275
276 if (event)
277 perf_event_enable(event);
278 }
279}
280
281/**
282 * hardlockup_detector_perf_init - Probe whether NMI event is available at all
283 */
284int __init hardlockup_detector_perf_init(void)
285{
286 int ret = hardlockup_detector_event_create();
287
288 if (ret) {
289 pr_info("Perf NMI watchdog permanently disabled\n");
290 } else {
291 perf_event_release_kernel(this_cpu_read(watchdog_ev));
292 this_cpu_write(watchdog_ev, NULL);
293 }
294 return ret;
295}
296