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