kernel/watchdog_hld.c

   1 /*
   2  * Detect hard lockups on a system
   3  *
   4  * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
   5  *
   6  * Note: Most of this code is borrowed heavily from the original softlockup
   7  * detector, so thanks to Ingo for the initial implementation.
   8  * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
   9  * to those contributors as well.
  10  */
  11
  12 #define pr_fmt(fmt) "NMI watchdog: " fmt
  13
  14 #include <linux/nmi.h>
  15 #include <linux/atomic.h>
  16 #include <linux/module.h>
  17 #include <linux/sched/debug.h>
  18
  19 #include <asm/irq_regs.h>
  20 #include <linux/perf_event.h>
  21
  22 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
  23 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
  24 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
  25 static DEFINE_PER_CPU(struct perf_event *, dead_event);
  26 static struct cpumask dead_events_mask;
  27
  28 static unsigned long hardlockup_allcpu_dumped;
  29 static atomic_t watchdog_cpus = ATOMIC_INIT(0);
  30
  31 void arch_touch_nmi_watchdog(void)
  32 {
  33         /*
  34          * Using __raw here because some code paths have
  35          * preemption enabled.  If preemption is enabled
  36          * then interrupts should be enabled too, in which
  37          * case we shouldn't have to worry about the watchdog
  38          * going off.
  39          */
  40         raw_cpu_write(watchdog_nmi_touch, true);
  41 }
  42 EXPORT_SYMBOL(arch_touch_nmi_watchdog);
  43
  44 #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
  45 static DEFINE_PER_CPU(ktime_t, last_timestamp);
  46 static DEFINE_PER_CPU(unsigned int, nmi_rearmed);
  47 static ktime_t watchdog_hrtimer_sample_threshold __read_mostly;
  48
  49 void watchdog_update_hrtimer_threshold(u64 period)
  50 {
  51         /*
  52          * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
  53          *
  54          * So it runs effectively with 2.5 times the rate of the NMI
  55          * watchdog. That means the hrtimer should fire 2-3 times before
  56          * the NMI watchdog expires. The NMI watchdog on x86 is based on
  57          * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
  58          * might run way faster than expected and the NMI fires in a
  59          * smaller period than the one deduced from the nominal CPU
  60          * frequency. Depending on the Turbo-Mode factor this might be fast
  61          * enough to get the NMI period smaller than the hrtimer watchdog
  62          * period and trigger false positives.
  63          *
  64          * The sample threshold is used to check in the NMI handler whether
  65          * the minimum time between two NMI samples has elapsed. That
  66          * prevents false positives.
  67          *
  68          * Set this to 4/5 of the actual watchdog threshold period so the
  69          * hrtimer is guaranteed to fire at least once within the real
  70          * watchdog threshold.
  71          */
  72         watchdog_hrtimer_sample_threshold = period * 2;
  73 }
  74
  75 static bool watchdog_check_timestamp(void)
  76 {
  77         ktime_t delta, now = ktime_get_mono_fast_ns();
  78
  79         delta = now - __this_cpu_read(last_timestamp);
  80         if (delta < watchdog_hrtimer_sample_threshold) {
  81                 /*
  82                  * If ktime is jiffies based, a stalled timer would prevent
  83                  * jiffies from being incremented and the filter would look
  84                  * at a stale timestamp and never trigger.
  85                  */
  86                 if (__this_cpu_inc_return(nmi_rearmed) < 10)
  87                         return false;
  88         }
  89         __this_cpu_write(nmi_rearmed, 0);
  90         __this_cpu_write(last_timestamp, now);
  91         return true;
  92 }
  93 #else
  94 static inline bool watchdog_check_timestamp(void)
  95 {
  96         return true;
  97 }
  98 #endif
  99
 100 static struct perf_event_attr wd_hw_attr = {
 101         .type           = PERF_TYPE_HARDWARE,
 102         .config         = PERF_COUNT_HW_CPU_CYCLES,
 103         .size           = sizeof(struct perf_event_attr),
 104         .pinned         = 1,
 105         .disabled       = 1,
 106 };
 107
 108 /* Callback function for perf event subsystem */
 109 static void watchdog_overflow_callback(struct perf_event *event,
 110                                        struct perf_sample_data *data,
 111                                        struct pt_regs *regs)
 112 {
 113         /* Ensure the watchdog never gets throttled */
 114         event->hw.interrupts = 0;
 115
 116         if (__this_cpu_read(watchdog_nmi_touch) == true) {
 117                 __this_cpu_write(watchdog_nmi_touch, false);
 118                 return;
 119         }
 120
 121         if (!watchdog_check_timestamp())
 122                 return;
 123
 124         /* check for a hardlockup
 125          * This is done by making sure our timer interrupt
 126          * is incrementing.  The timer interrupt should have
 127          * fired multiple times before we overflow'd.  If it hasn't
 128          * then this is a good indication the cpu is stuck
 129          */
 130         if (is_hardlockup()) {
 131                 int this_cpu = smp_processor_id();
 132
 133                 /* only print hardlockups once */
 134                 if (__this_cpu_read(hard_watchdog_warn) == true)
 135                         return;
 136
 137                 pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
 138                 print_modules();
 139                 print_irqtrace_events(current);
 140                 if (regs)
 141                         show_regs(regs);
 142                 else
 143                         dump_stack();
 144
 145                 /*
 146                  * Perform all-CPU dump only once to avoid multiple hardlockups
 147                  * generating interleaving traces
 148                  */
 149                 if (sysctl_hardlockup_all_cpu_backtrace &&
 150                                 !test_and_set_bit(0, &hardlockup_allcpu_dumped))
 151                         trigger_allbutself_cpu_backtrace();
 152
 153                 if (hardlockup_panic)
 154                         nmi_panic(regs, "Hard LOCKUP");
 155
 156                 __this_cpu_write(hard_watchdog_warn, true);
 157                 return;
 158         }
 159
 160         __this_cpu_write(hard_watchdog_warn, false);
 161         return;
 162 }
 163
 164 static int hardlockup_detector_event_create(void)
 165 {
 166         unsigned int cpu = smp_processor_id();
 167         struct perf_event_attr *wd_attr;
 168         struct perf_event *evt;
 169
 170         wd_attr = &wd_hw_attr;
 171         wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
 172
 173         /* Try to register using hardware perf events */
 174         evt = perf_event_create_kernel_counter(wd_attr, cpu, NULL,
 175                                                watchdog_overflow_callback, NULL);
 176         if (IS_ERR(evt)) {
 177                 pr_info("Perf event create on CPU %d failed with %ld\n", cpu,
 178                         PTR_ERR(evt));
 179                 return PTR_ERR(evt);
 180         }
 181         this_cpu_write(watchdog_ev, evt);
 182         return 0;
 183 }
 184
 185 /**
 186  * hardlockup_detector_perf_enable - Enable the local event
 187  */
 188 void hardlockup_detector_perf_enable(void)
 189 {
 190         if (hardlockup_detector_event_create())
 191                 return;
 192
 193         /* use original value for check */
 194         if (!atomic_fetch_inc(&watchdog_cpus))
 195                 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
 196
 197         perf_event_enable(this_cpu_read(watchdog_ev));
 198 }
 199
 200 /**
 201  * hardlockup_detector_perf_disable - Disable the local event
 202  */
 203 void hardlockup_detector_perf_disable(void)
 204 {
 205         struct perf_event *event = this_cpu_read(watchdog_ev);
 206
 207         if (event) {
 208                 perf_event_disable(event);
 209                 this_cpu_write(watchdog_ev, NULL);
 210                 this_cpu_write(dead_event, event);
 211                 cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
 212                 atomic_dec(&watchdog_cpus);
 213         }
 214 }
 215
 216 /**
 217  * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
 218  *
 219  * Called from lockup_detector_cleanup(). Serialized by the caller.
 220  */
 221 void hardlockup_detector_perf_cleanup(void)
 222 {
 223         int cpu;
 224
 225         for_each_cpu(cpu, &dead_events_mask) {
 226                 struct perf_event *event = per_cpu(dead_event, cpu);
 227
 228                 /*
 229                  * Required because for_each_cpu() reports  unconditionally
 230                  * CPU0 as set on UP kernels. Sigh.
 231                  */
 232                 if (event)
 233                         perf_event_release_kernel(event);
 234                 per_cpu(dead_event, cpu) = NULL;
 235         }
 236         cpumask_clear(&dead_events_mask);
 237 }
 238
 239 /**
 240  * hardlockup_detector_perf_stop - Globally stop watchdog events
 241  *
 242  * Special interface for x86 to handle the perf HT bug.
 243  */
 244 void __init hardlockup_detector_perf_stop(void)
 245 {
 246         int cpu;
 247
 248         lockdep_assert_cpus_held();
 249
 250         for_each_online_cpu(cpu) {
 251                 struct perf_event *event = per_cpu(watchdog_ev, cpu);
 252
 253                 if (event)
 254                         perf_event_disable(event);
 255         }
 256 }
 257
 258 /**
 259  * hardlockup_detector_perf_restart - Globally restart watchdog events
 260  *
 261  * Special interface for x86 to handle the perf HT bug.
 262  */
 263 void __init hardlockup_detector_perf_restart(void)
 264 {
 265         int cpu;
 266
 267         lockdep_assert_cpus_held();
 268
 269         if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
 270                 return;
 271
 272         for_each_online_cpu(cpu) {
 273                 struct perf_event *event = per_cpu(watchdog_ev, cpu);
 274
 275                 if (event)
 276                         perf_event_enable(event);
 277         }
 278 }
 279
 280 /**
 281  * hardlockup_detector_perf_init - Probe whether NMI event is available at all
 282  */
 283 int __init hardlockup_detector_perf_init(void)
 284 {
 285         int ret = hardlockup_detector_event_create();
 286
 287         if (ret) {
 288                 pr_info("Perf NMI watchdog permanently disabled\n");
 289         } else {
 290                 perf_event_release_kernel(this_cpu_read(watchdog_ev));
 291                 this_cpu_write(watchdog_ev, NULL);
 292         }
 293         return ret;
 294 }