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
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
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
79 static void watchdog_init_timestamp(void)
80 {
81 __this_cpu_write(nmi_rearmed, 0);
82 __this_cpu_write(last_timestamp, ktime_get_mono_fast_ns());
83 }
84 #else
85 static inline bool watchdog_check_timestamp(void) { return true; }
86 static inline void watchdog_init_timestamp(void) { }
87 #endif
88
89 static struct perf_event_attr wd_hw_attr = {
90 .type = PERF_TYPE_HARDWARE,
91 .config = PERF_COUNT_HW_CPU_CYCLES,
92 .size = sizeof(struct perf_event_attr),
93 .pinned = 1,
94 .disabled = 1,
95 };
96
97 static struct perf_event_attr fallback_wd_hw_attr = {
98 .type = PERF_TYPE_HARDWARE,
99 .config = PERF_COUNT_HW_CPU_CYCLES,
100 .size = sizeof(struct perf_event_attr),
101 .pinned = 1,
102 .disabled = 1,
103 };
104
105 /* Callback function for perf event subsystem */
106 static void watchdog_overflow_callback(struct perf_event *event,
107 struct perf_sample_data *data,
108 struct pt_regs *regs)
109 {
110 /* Ensure the watchdog never gets throttled */
111 event->hw.interrupts = 0;
112
113 if (!watchdog_check_timestamp())
114 return;
115
116 watchdog_hardlockup_check(smp_processor_id(), regs);
117 }
118
119 static int hardlockup_detector_event_create(void)
120 {
121 unsigned int cpu;
122 struct perf_event_attr *wd_attr;
123 struct perf_event *evt;
124
125 /*
126 * Preemption is not disabled because memory will be allocated.
127 * Ensure CPU-locality by calling this in per-CPU kthread.
128 */
129 WARN_ON(!is_percpu_thread());
130 cpu = raw_smp_processor_id();
131 wd_attr = &wd_hw_attr;
132 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
133
134 /* Try to register using hardware perf events */
135 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
136 watchdog_overflow_callback, NULL);
137 if (IS_ERR(evt)) {
138 wd_attr = &fallback_wd_hw_attr;
139 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
140 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
141 watchdog_overflow_callback, NULL);
142 }
143
144 if (IS_ERR(evt)) {
145 pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
146 PTR_ERR(evt));
147 return PTR_ERR(evt);
148 }
149 this_cpu_write(watchdog_ev, evt);
150 return 0;
151 }
152
153 /**
154 * watchdog_hardlockup_enable - Enable the local event
155 * @cpu: The CPU to enable hard lockup on.
156 */
157 void watchdog_hardlockup_enable(unsigned int cpu)
158 {
159 WARN_ON_ONCE(cpu != smp_processor_id());
160
161 if (hardlockup_detector_event_create())
162 return;
163
164 /* use original value for check */
165 if (!atomic_fetch_inc(&watchdog_cpus))
166 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
167
168 watchdog_init_timestamp();
169 perf_event_enable(this_cpu_read(watchdog_ev));
170 }
171
172 /**
173 * watchdog_hardlockup_disable - Disable the local event
174 * @cpu: The CPU to enable hard lockup on.
175 */
176 void watchdog_hardlockup_disable(unsigned int cpu)
177 {
178 struct perf_event *event = this_cpu_read(watchdog_ev);
179
180 WARN_ON_ONCE(cpu != smp_processor_id());
181
182 if (event) {
183 perf_event_disable(event);
184 this_cpu_write(watchdog_ev, NULL);
185 this_cpu_write(dead_event, event);
186 cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
187 atomic_dec(&watchdog_cpus);
188 }
189 }
190
191 /**
192 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
193 *
194 * Called from lockup_detector_cleanup(). Serialized by the caller.
195 */
196 void hardlockup_detector_perf_cleanup(void)
197 {
198 int cpu;
199
200 for_each_cpu(cpu, &dead_events_mask) {
201 struct perf_event *event = per_cpu(dead_event, cpu);
202
203 /*
204 * Required because for_each_cpu() reports unconditionally
205 * CPU0 as set on UP kernels. Sigh.
206 */
207 if (event)
208 perf_event_release_kernel(event);
209 per_cpu(dead_event, cpu) = NULL;
210 }
211 cpumask_clear(&dead_events_mask);
212 }
213
214 /**
215 * hardlockup_detector_perf_stop - Globally stop watchdog events
216 *
217 * Special interface for x86 to handle the perf HT bug.
218 */
219 void __init hardlockup_detector_perf_stop(void)
220 {
221 int cpu;
222
223 lockdep_assert_cpus_held();
224
225 for_each_online_cpu(cpu) {
226 struct perf_event *event = per_cpu(watchdog_ev, cpu);
227
228 if (event)
229 perf_event_disable(event);
230 }
231 }
232
233 /**
234 * hardlockup_detector_perf_restart - Globally restart watchdog events
235 *
236 * Special interface for x86 to handle the perf HT bug.
237 */
238 void __init hardlockup_detector_perf_restart(void)
239 {
240 int cpu;
241
242 lockdep_assert_cpus_held();
243
244 if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
245 return;
246
247 for_each_online_cpu(cpu) {
248 struct perf_event *event = per_cpu(watchdog_ev, cpu);
249
250 if (event)
251 perf_event_enable(event);
252 }
253 }
254
255 bool __weak __init arch_perf_nmi_is_available(void)
256 {
257 return true;
258 }
259
260 /**
261 * watchdog_hardlockup_probe - Probe whether NMI event is available at all
262 */
263 int __init watchdog_hardlockup_probe(void)
264 {
265 int ret;
266
267 if (!arch_perf_nmi_is_available())
268 return -ENODEV;
269
270 ret = hardlockup_detector_event_create();
271
272 if (ret) {
273 pr_info("Perf NMI watchdog permanently disabled\n");
274 } else {
275 perf_event_release_kernel(this_cpu_read(watchdog_ev));
276 this_cpu_write(watchdog_ev, NULL);
277 }
278 return ret;
279 }
280
281 /**
282 * hardlockup_config_perf_event - Overwrite config of wd_hw_attr.
283 * @str: number which identifies the raw perf event to use
284 */
285 void __init hardlockup_config_perf_event(const char *str)
286 {
287 u64 config;
288 char buf[24];
289 char *comma = strchr(str, ',');
290
291 if (!comma) {
292 if (kstrtoull(str, 16, &config))
293 return;
294 } else {
295 unsigned int len = comma - str;
296
297 if (len >= sizeof(buf))
298 return;
299
300 if (strscpy(buf, str, sizeof(buf)) < 0)
301 return;
302 buf[len] = 0;
303 if (kstrtoull(buf, 16, &config))
304 return;
305 }
306
307 wd_hw_attr.type = PERF_TYPE_RAW;
308 wd_hw_attr.config = config;
309 }
310
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