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