1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Detect hard lockups on a system using perf
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
23 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
24 static DEFINE_PER_CPU(struct perf_event *, dead_event);
25 static struct cpumask dead_events_mask;
26
27 static atomic_t watchdog_cpus = ATOMIC_INIT(0);
28
29 #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
30 static DEFINE_PER_CPU(ktime_t, last_timestamp);
31 static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
32 static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
33
watchdog_update_hrtimer_threshold(u64 period)34 void watchdog_update_hrtimer_threshold(u64 period)
35 {
36 /*
37 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
38 *
39 * So it runs effectively with 2.5 times the rate of the NMI
40 * watchdog. That means the hrtimer should fire 2-3 times before
41 * the NMI watchdog expires. The NMI watchdog on x86 is based on
42 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
43 * might run way faster than expected and the NMI fires in a
44 * smaller period than the one deduced from the nominal CPU
45 * frequency. Depending on the Turbo-Mode factor this might be fast
46 * enough to get the NMI period smaller than the hrtimer watchdog
47 * period and trigger false positives.
48 *
49 * The sample threshold is used to check in the NMI handler whether
50 * the minimum time between two NMI samples has elapsed. That
51 * prevents false positives.
52 *
53 * Set this to 4/5 of the actual watchdog threshold period so the
54 * hrtimer is guaranteed to fire at least once within the real
55 * watchdog threshold.
56 */
57 watchdog_hrtimer_sample_threshold = period * 2;
58 }
59
watchdog_check_timestamp(void)60 static bool watchdog_check_timestamp(void)
61 {
62 ktime_t delta, now = ktime_get_mono_fast_ns();
63
64 delta = now - __this_cpu_read(last_timestamp);
65 if (delta < watchdog_hrtimer_sample_threshold) {
66 /*
67 * If ktime is jiffies based, a stalled timer would prevent
68 * jiffies from being incremented and the filter would look
69 * at a stale timestamp and never trigger.
70 */
71 if (__this_cpu_inc_return(nmi_rearmed) < 10)
72 return false;
73 }
74 __this_cpu_write(nmi_rearmed, 0);
75 __this_cpu_write(last_timestamp, now);
76 return true;
77 }
78 #else
watchdog_check_timestamp(void)79 static inline bool watchdog_check_timestamp(void)
80 {
81 return true;
82 }
83 #endif
84
85 static struct perf_event_attr wd_hw_attr = {
86 .type = PERF_TYPE_HARDWARE,
87 .config = PERF_COUNT_HW_CPU_CYCLES,
88 .size = sizeof(struct perf_event_attr),
89 .pinned = 1,
90 .disabled = 1,
91 };
92
93 /* Callback function for perf event subsystem */
watchdog_overflow_callback(struct perf_event * event,struct perf_sample_data * data,struct pt_regs * regs)94 static void watchdog_overflow_callback(struct perf_event *event,
95 struct perf_sample_data *data,
96 struct pt_regs *regs)
97 {
98 /* Ensure the watchdog never gets throttled */
99 event->hw.interrupts = 0;
100
101 if (!watchdog_check_timestamp())
102 return;
103
104 watchdog_hardlockup_check(smp_processor_id(), regs);
105 }
106
hardlockup_detector_event_create(void)107 static int hardlockup_detector_event_create(void)
108 {
109 unsigned int cpu;
110 struct perf_event_attr *wd_attr;
111 struct perf_event *evt;
112
113 /*
114 * Preemption is not disabled because memory will be allocated.
115 * Ensure CPU-locality by calling this in per-CPU kthread.
116 */
117 WARN_ON(!is_percpu_thread());
118 cpu = raw_smp_processor_id();
119 wd_attr = &wd_hw_attr;
120 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
121
122 /* Try to register using hardware perf events */
123 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
124 watchdog_overflow_callback, NULL);
125 if (IS_ERR(evt)) {
126 pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
127 PTR_ERR(evt));
128 return PTR_ERR(evt);
129 }
130 this_cpu_write(watchdog_ev, evt);
131 return 0;
132 }
133
134 /**
135 * watchdog_hardlockup_enable - Enable the local event
136 *
137 * @cpu: The CPU to enable hard lockup on.
138 */
watchdog_hardlockup_enable(unsigned int cpu)139 void watchdog_hardlockup_enable(unsigned int cpu)
140 {
141 WARN_ON_ONCE(cpu != smp_processor_id());
142
143 if (hardlockup_detector_event_create())
144 return;
145
146 /* use original value for check */
147 if (!atomic_fetch_inc(&watchdog_cpus))
148 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
149
150 perf_event_enable(this_cpu_read(watchdog_ev));
151 }
152
153 /**
154 * watchdog_hardlockup_disable - Disable the local event
155 *
156 * @cpu: The CPU to enable hard lockup on.
157 */
watchdog_hardlockup_disable(unsigned int cpu)158 void watchdog_hardlockup_disable(unsigned int cpu)
159 {
160 struct perf_event *event = this_cpu_read(watchdog_ev);
161
162 WARN_ON_ONCE(cpu != smp_processor_id());
163
164 if (event) {
165 perf_event_disable(event);
166 this_cpu_write(watchdog_ev, NULL);
167 this_cpu_write(dead_event, event);
168 cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
169 atomic_dec(&watchdog_cpus);
170 }
171 }
172
173 /**
174 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
175 *
176 * Called from lockup_detector_cleanup(). Serialized by the caller.
177 */
hardlockup_detector_perf_cleanup(void)178 void hardlockup_detector_perf_cleanup(void)
179 {
180 int cpu;
181
182 for_each_cpu(cpu, &dead_events_mask) {
183 struct perf_event *event = per_cpu(dead_event, cpu);
184
185 /*
186 * Required because for_each_cpu() reports unconditionally
187 * CPU0 as set on UP kernels. Sigh.
188 */
189 if (event)
190 perf_event_release_kernel(event);
191 per_cpu(dead_event, cpu) = NULL;
192 }
193 cpumask_clear(&dead_events_mask);
194 }
195
196 /**
197 * hardlockup_detector_perf_stop - Globally stop watchdog events
198 *
199 * Special interface for x86 to handle the perf HT bug.
200 */
hardlockup_detector_perf_stop(void)201 void __init hardlockup_detector_perf_stop(void)
202 {
203 int cpu;
204
205 lockdep_assert_cpus_held();
206
207 for_each_online_cpu(cpu) {
208 struct perf_event *event = per_cpu(watchdog_ev, cpu);
209
210 if (event)
211 perf_event_disable(event);
212 }
213 }
214
215 /**
216 * hardlockup_detector_perf_restart - Globally restart watchdog events
217 *
218 * Special interface for x86 to handle the perf HT bug.
219 */
hardlockup_detector_perf_restart(void)220 void __init hardlockup_detector_perf_restart(void)
221 {
222 int cpu;
223
224 lockdep_assert_cpus_held();
225
226 if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
227 return;
228
229 for_each_online_cpu(cpu) {
230 struct perf_event *event = per_cpu(watchdog_ev, cpu);
231
232 if (event)
233 perf_event_enable(event);
234 }
235 }
236
arch_perf_nmi_is_available(void)237 bool __weak __init arch_perf_nmi_is_available(void)
238 {
239 return true;
240 }
241
242 /**
243 * watchdog_hardlockup_probe - Probe whether NMI event is available at all
244 */
watchdog_hardlockup_probe(void)245 int __init watchdog_hardlockup_probe(void)
246 {
247 int ret;
248
249 if (!arch_perf_nmi_is_available())
250 return -ENODEV;
251
252 ret = hardlockup_detector_event_create();
253
254 if (ret) {
255 pr_info("Perf NMI watchdog permanently disabled\n");
256 } else {
257 perf_event_release_kernel(this_cpu_read(watchdog_ev));
258 this_cpu_write(watchdog_ev, NULL);
259 }
260 return ret;
261 }
262