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 /* 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 }