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