kernel/softlockup.c

   1 /*
   2  * Detect Soft Lockups
   3  *
   4  * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
   5  *
   6  * this code detects soft lockups: incidents in where on a CPU
   7  * the kernel does not reschedule for 10 seconds or more.
   8  */
   9 #include <linux/mm.h>
  10 #include <linux/cpu.h>
  11 #include <linux/init.h>
  12 #include <linux/delay.h>
  13 #include <linux/kthread.h>
  14 #include <linux/notifier.h>
  15 #include <linux/module.h>
  16
  17 static DEFINE_SPINLOCK(print_lock);
  18
  19 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  20 static DEFINE_PER_CPU(unsigned long, print_timestamp);
  21 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  22
  23 static int did_panic = 0;
  24
  25 static int
  26 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  27 {
  28         did_panic = 1;
  29
  30         return NOTIFY_DONE;
  31 }
  32
  33 static struct notifier_block panic_block = {
  34         .notifier_call = softlock_panic,
  35 };
  36
  37 /*
  38  * Returns seconds, approximately.  We don't need nanosecond
  39  * resolution, and we don't need to waste time with a big divide when
  40  * 2^30ns == 1.074s.
  41  */
  42 static unsigned long get_timestamp(void)
  43 {
  44         return sched_clock() >> 30;  /* 2^30 ~= 10^9 */
  45 }
  46
  47 void touch_softlockup_watchdog(void)
  48 {
  49         __raw_get_cpu_var(touch_timestamp) = get_timestamp();
  50 }
  51 EXPORT_SYMBOL(touch_softlockup_watchdog);
  52
  53 void touch_all_softlockup_watchdogs(void)
  54 {
  55         int cpu;
  56
  57         /* Cause each CPU to re-update its timestamp rather than complain */
  58         for_each_online_cpu(cpu)
  59                 per_cpu(touch_timestamp, cpu) = 0;
  60 }
  61 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  62
  63 /*
  64  * This callback runs from the timer interrupt, and checks
  65  * whether the watchdog thread has hung or not:
  66  */
  67 void softlockup_tick(void)
  68 {
  69         int this_cpu = smp_processor_id();
  70         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  71         unsigned long print_timestamp;
  72         unsigned long now;
  73
  74         if (touch_timestamp == 0) {
  75                 touch_softlockup_watchdog();
  76                 return;
  77         }
  78
  79         print_timestamp = per_cpu(print_timestamp, this_cpu);
  80
  81         /* report at most once a second */
  82         if (print_timestamp < (touch_timestamp + 1) ||
  83                 did_panic ||
  84                         !per_cpu(watchdog_task, this_cpu))
  85                 return;
  86
  87         /* do not print during early bootup: */
  88         if (unlikely(system_state != SYSTEM_RUNNING)) {
  89                 touch_softlockup_watchdog();
  90                 return;
  91         }
  92
  93         now = get_timestamp();
  94
  95         /* Wake up the high-prio watchdog task every second: */
  96         if (now > (touch_timestamp + 1))
  97                 wake_up_process(per_cpu(watchdog_task, this_cpu));
  98
  99         /* Warn about unreasonable 10+ seconds delays: */
 100         if (now > (touch_timestamp + 10)) {
 101                 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 102
 103                 spin_lock(&print_lock);
 104                 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
 105                         this_cpu);
 106                 dump_stack();
 107                 spin_unlock(&print_lock);
 108         }
 109 }
 110
 111 /*
 112  * The watchdog thread - runs every second and touches the timestamp.
 113  */
 114 static int watchdog(void * __bind_cpu)
 115 {
 116         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 117
 118         sched_setscheduler(current, SCHED_FIFO, &param);
 119         current->flags |= PF_NOFREEZE;
 120
 121         /* initialize timestamp */
 122         touch_softlockup_watchdog();
 123
 124         /*
 125          * Run briefly once per second to reset the softlockup timestamp.
 126          * If this gets delayed for more than 10 seconds then the
 127          * debug-printout triggers in softlockup_tick().
 128          */
 129         while (!kthread_should_stop()) {
 130                 set_current_state(TASK_INTERRUPTIBLE);
 131                 touch_softlockup_watchdog();
 132                 schedule();
 133         }
 134
 135         return 0;
 136 }
 137
 138 /*
 139  * Create/destroy watchdog threads as CPUs come and go:
 140  */
 141 static int __cpuinit
 142 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 143 {
 144         int hotcpu = (unsigned long)hcpu;
 145         struct task_struct *p;
 146
 147         switch (action) {
 148         case CPU_UP_PREPARE:
 149         case CPU_UP_PREPARE_FROZEN:
 150                 BUG_ON(per_cpu(watchdog_task, hotcpu));
 151                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 152                 if (IS_ERR(p)) {
 153                         printk("watchdog for %i failed\n", hotcpu);
 154                         return NOTIFY_BAD;
 155                 }
 156                 per_cpu(touch_timestamp, hotcpu) = 0;
 157                 per_cpu(watchdog_task, hotcpu) = p;
 158                 kthread_bind(p, hotcpu);
 159                 break;
 160         case CPU_ONLINE:
 161         case CPU_ONLINE_FROZEN:
 162                 wake_up_process(per_cpu(watchdog_task, hotcpu));
 163                 break;
 164 #ifdef CONFIG_HOTPLUG_CPU
 165         case CPU_UP_CANCELED:
 166         case CPU_UP_CANCELED_FROZEN:
 167                 if (!per_cpu(watchdog_task, hotcpu))
 168                         break;
 169                 /* Unbind so it can run.  Fall thru. */
 170                 kthread_bind(per_cpu(watchdog_task, hotcpu),
 171                              any_online_cpu(cpu_online_map));
 172         case CPU_DEAD:
 173         case CPU_DEAD_FROZEN:
 174                 p = per_cpu(watchdog_task, hotcpu);
 175                 per_cpu(watchdog_task, hotcpu) = NULL;
 176                 kthread_stop(p);
 177                 break;
 178 #endif /* CONFIG_HOTPLUG_CPU */
 179         }
 180         return NOTIFY_OK;
 181 }
 182
 183 static struct notifier_block __cpuinitdata cpu_nfb = {
 184         .notifier_call = cpu_callback
 185 };
 186
 187 __init void spawn_softlockup_task(void)
 188 {
 189         void *cpu = (void *)(long)smp_processor_id();
 190         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 191
 192         BUG_ON(err == NOTIFY_BAD);
 193         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 194         register_cpu_notifier(&cpu_nfb);
 195
 196         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 197 }