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 #else 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 */ 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 } 106 107 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 */ 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 */ 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 */ 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 */ 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 */ 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 } 236 237 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 */ 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