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/panic.h>
16 #include <linux/nmi.h>
17 #include <linux/atomic.h>
18 #include <linux/module.h>
19 #include <linux/sched/debug.h>
20
21 #include <asm/irq_regs.h>
22 #include <linux/perf_event.h>
23
24 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
25
26 static atomic_t watchdog_cpus = ATOMIC_INIT(0);
27
28 #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
29 static DEFINE_PER_CPU(ktime_t, last_timestamp);
30 static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
31 static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
32
watchdog_update_hrtimer_threshold(u64 period)33 void watchdog_update_hrtimer_threshold(u64 period)
34 {
35 /*
36 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
37 *
38 * So it runs effectively with 2.5 times the rate of the NMI
39 * watchdog. That means the hrtimer should fire 2-3 times before
40 * the NMI watchdog expires. The NMI watchdog on x86 is based on
41 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
42 * might run way faster than expected and the NMI fires in a
43 * smaller period than the one deduced from the nominal CPU
44 * frequency. Depending on the Turbo-Mode factor this might be fast
45 * enough to get the NMI period smaller than the hrtimer watchdog
46 * period and trigger false positives.
47 *
48 * The sample threshold is used to check in the NMI handler whether
49 * the minimum time between two NMI samples has elapsed. That
50 * prevents false positives.
51 *
52 * Set this to 4/5 of the actual watchdog threshold period so the
53 * hrtimer is guaranteed to fire at least once within the real
54 * watchdog threshold.
55 */
56 watchdog_hrtimer_sample_threshold = period * 2;
57 }
58
watchdog_check_timestamp(void)59 static bool watchdog_check_timestamp(void)
60 {
61 ktime_t delta, now = ktime_get_mono_fast_ns();
62
63 delta = now - __this_cpu_read(last_timestamp);
64 if (delta < watchdog_hrtimer_sample_threshold) {
65 /*
66 * If ktime is jiffies based, a stalled timer would prevent
67 * jiffies from being incremented and the filter would look
68 * at a stale timestamp and never trigger.
69 */
70 if (__this_cpu_inc_return(nmi_rearmed) < 10)
71 return false;
72 }
73 __this_cpu_write(nmi_rearmed, 0);
74 __this_cpu_write(last_timestamp, now);
75 return true;
76 }
77
watchdog_init_timestamp(void)78 static void watchdog_init_timestamp(void)
79 {
80 __this_cpu_write(nmi_rearmed, 0);
81 __this_cpu_write(last_timestamp, ktime_get_mono_fast_ns());
82 }
83 #else
watchdog_check_timestamp(void)84 static inline bool watchdog_check_timestamp(void) { return true; }
watchdog_init_timestamp(void)85 static inline void watchdog_init_timestamp(void) { }
86 #endif
87
88 static struct perf_event_attr wd_hw_attr = {
89 .type = PERF_TYPE_HARDWARE,
90 .config = PERF_COUNT_HW_CPU_CYCLES,
91 .size = sizeof(struct perf_event_attr),
92 .pinned = 1,
93 .disabled = 1,
94 };
95
96 static struct perf_event_attr fallback_wd_hw_attr = {
97 .type = PERF_TYPE_HARDWARE,
98 .config = PERF_COUNT_HW_CPU_CYCLES,
99 .size = sizeof(struct perf_event_attr),
100 .pinned = 1,
101 .disabled = 1,
102 };
103
104 /* Callback function for perf event subsystem */
watchdog_overflow_callback(struct perf_event * event,struct perf_sample_data * data,struct pt_regs * regs)105 static void watchdog_overflow_callback(struct perf_event *event,
106 struct perf_sample_data *data,
107 struct pt_regs *regs)
108 {
109 /* Ensure the watchdog never gets throttled */
110 event->hw.interrupts = 0;
111
112 if (panic_in_progress())
113 return;
114
115 if (!watchdog_check_timestamp())
116 return;
117
118 watchdog_hardlockup_check(smp_processor_id(), regs);
119 }
120
hardlockup_detector_event_create(void)121 static int hardlockup_detector_event_create(void)
122 {
123 unsigned int cpu;
124 struct perf_event_attr *wd_attr;
125 struct perf_event *evt;
126
127 /*
128 * Preemption is not disabled because memory will be allocated.
129 * Ensure CPU-locality by calling this in per-CPU kthread.
130 */
131 WARN_ON(!is_percpu_thread());
132 cpu = raw_smp_processor_id();
133 wd_attr = &wd_hw_attr;
134 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
135
136 /* Try to register using hardware perf events */
137 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
138 watchdog_overflow_callback, NULL);
139 if (IS_ERR(evt)) {
140 wd_attr = &fallback_wd_hw_attr;
141 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
142 evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
143 watchdog_overflow_callback, NULL);
144 }
145
146 if (IS_ERR(evt)) {
147 pr_debug("Perf event create on CPU %d failed with %ld\n", cpu,
148 PTR_ERR(evt));
149 return PTR_ERR(evt);
150 }
151 WARN_ONCE(this_cpu_read(watchdog_ev), "unexpected watchdog_ev leak");
152 this_cpu_write(watchdog_ev, evt);
153 return 0;
154 }
155
156 /**
157 * watchdog_hardlockup_enable - Enable the local event
158 * @cpu: The CPU to enable hard lockup on.
159 */
watchdog_hardlockup_enable(unsigned int cpu)160 void watchdog_hardlockup_enable(unsigned int cpu)
161 {
162 WARN_ON_ONCE(cpu != smp_processor_id());
163
164 if (hardlockup_detector_event_create())
165 return;
166
167 /* use original value for check */
168 if (!atomic_fetch_inc(&watchdog_cpus))
169 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
170
171 watchdog_init_timestamp();
172 perf_event_enable(this_cpu_read(watchdog_ev));
173 }
174
175 /**
176 * watchdog_hardlockup_disable - Disable the local event
177 * @cpu: The CPU to enable hard lockup on.
178 */
watchdog_hardlockup_disable(unsigned int cpu)179 void watchdog_hardlockup_disable(unsigned int cpu)
180 {
181 struct perf_event *event = this_cpu_read(watchdog_ev);
182
183 WARN_ON_ONCE(cpu != smp_processor_id());
184
185 if (event) {
186 perf_event_disable(event);
187 perf_event_release_kernel(event);
188 this_cpu_write(watchdog_ev, NULL);
189 atomic_dec(&watchdog_cpus);
190 }
191 }
192
193 /**
194 * hardlockup_detector_perf_adjust_period - Adjust the event period due
195 * to current cpu frequency change
196 * @period: The target period to be set
197 */
hardlockup_detector_perf_adjust_period(u64 period)198 void hardlockup_detector_perf_adjust_period(u64 period)
199 {
200 struct perf_event *event = this_cpu_read(watchdog_ev);
201
202 if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
203 return;
204
205 if (!event)
206 return;
207
208 if (event->attr.sample_period == period)
209 return;
210
211 if (perf_event_period(event, period))
212 pr_err("failed to change period to %llu\n", period);
213 }
214
215 /**
216 * hardlockup_detector_perf_stop - Globally stop watchdog events
217 *
218 * Special interface for x86 to handle the perf HT bug.
219 */
hardlockup_detector_perf_stop(void)220 void __init hardlockup_detector_perf_stop(void)
221 {
222 int cpu;
223
224 lockdep_assert_cpus_held();
225
226 for_each_online_cpu(cpu) {
227 struct perf_event *event = per_cpu(watchdog_ev, cpu);
228
229 if (event)
230 perf_event_disable(event);
231 }
232 }
233
234 /**
235 * hardlockup_detector_perf_restart - Globally restart watchdog events
236 *
237 * Special interface for x86 to handle the perf HT bug.
238 */
hardlockup_detector_perf_restart(void)239 void __init hardlockup_detector_perf_restart(void)
240 {
241 int cpu;
242
243 lockdep_assert_cpus_held();
244
245 if (!(watchdog_enabled & WATCHDOG_HARDLOCKUP_ENABLED))
246 return;
247
248 for_each_online_cpu(cpu) {
249 struct perf_event *event = per_cpu(watchdog_ev, cpu);
250
251 if (event)
252 perf_event_enable(event);
253 }
254 }
255
arch_perf_nmi_is_available(void)256 bool __weak __init arch_perf_nmi_is_available(void)
257 {
258 return true;
259 }
260
261 /**
262 * watchdog_hardlockup_probe - Probe whether NMI event is available at all
263 */
watchdog_hardlockup_probe(void)264 int __init watchdog_hardlockup_probe(void)
265 {
266 int ret;
267
268 if (!arch_perf_nmi_is_available())
269 return -ENODEV;
270
271 ret = hardlockup_detector_event_create();
272
273 if (ret) {
274 pr_info("Perf NMI watchdog permanently disabled\n");
275 } else {
276 perf_event_release_kernel(this_cpu_read(watchdog_ev));
277 this_cpu_write(watchdog_ev, NULL);
278 }
279 return ret;
280 }
281
282 /**
283 * hardlockup_config_perf_event - Overwrite config of wd_hw_attr.
284 * @str: number which identifies the raw perf event to use
285 */
hardlockup_config_perf_event(const char * str)286 void __init hardlockup_config_perf_event(const char *str)
287 {
288 u64 config;
289 char buf[24];
290 char *comma = strchr(str, ',');
291
292 if (!comma) {
293 if (kstrtoull(str, 16, &config))
294 return;
295 } else {
296 unsigned int len = comma - str;
297
298 if (len > sizeof(buf))
299 return;
300
301 strscpy(buf, str, len);
302 if (kstrtoull(buf, 16, &config))
303 return;
304 }
305
306 wd_hw_attr.type = PERF_TYPE_RAW;
307 wd_hw_attr.config = config;
308 }
309