kernel/watchdog_perf.c

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