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/freezer.h>
  14 #include <linux/kthread.h>
  15 #include <linux/notifier.h>
  16 #include <linux/module.h>
  17
  18 static DEFINE_SPINLOCK(print_lock);
  19
  20 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  21 static DEFINE_PER_CPU(unsigned long, print_timestamp);
  22 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  23
  24 static int did_panic = 0;
  25
  26 static int
  27 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  28 {
  29         did_panic = 1;
  30
  31         return NOTIFY_DONE;
  32 }
  33
  34 static struct notifier_block panic_block = {
  35         .notifier_call = softlock_panic,
  36 };
  37
  38 /*
  39  * Returns seconds, approximately.  We don't need nanosecond
  40  * resolution, and we don't need to waste time with a big divide when
  41  * 2^30ns == 1.074s.
  42  */
  43 static unsigned long get_timestamp(void)
  44 {
  45         return sched_clock() >> 30;  /* 2^30 ~= 10^9 */
  46 }
  47
  48 void touch_softlockup_watchdog(void)
  49 {
  50         __raw_get_cpu_var(touch_timestamp) = get_timestamp();
  51 }
  52 EXPORT_SYMBOL(touch_softlockup_watchdog);
  53
  54 void touch_all_softlockup_watchdogs(void)
  55 {
  56         int cpu;
  57
  58         /* Cause each CPU to re-update its timestamp rather than complain */
  59         for_each_online_cpu(cpu)
  60                 per_cpu(touch_timestamp, cpu) = 0;
  61 }
  62 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  63
  64 /*
  65  * This callback runs from the timer interrupt, and checks
  66  * whether the watchdog thread has hung or not:
  67  */
  68 void softlockup_tick(void)
  69 {
  70         int this_cpu = smp_processor_id();
  71         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  72         unsigned long print_timestamp;
  73         unsigned long now;
  74
  75         if (touch_timestamp == 0) {
  76                 touch_softlockup_watchdog();
  77                 return;
  78         }
  79
  80         print_timestamp = per_cpu(print_timestamp, this_cpu);
  81
  82         /* report at most once a second */
  83         if (print_timestamp < (touch_timestamp + 1) ||
  84                 did_panic ||
  85                         !per_cpu(watchdog_task, this_cpu))
  86                 return;
  87
  88         /* do not print during early bootup: */
  89         if (unlikely(system_state != SYSTEM_RUNNING)) {
  90                 touch_softlockup_watchdog();
  91                 return;
  92         }
  93
  94         now = get_timestamp();
  95
  96         /* Wake up the high-prio watchdog task every second: */
  97         if (now > (touch_timestamp + 1))
  98                 wake_up_process(per_cpu(watchdog_task, this_cpu));
  99
 100         /* Warn about unreasonable 10+ seconds delays: */
 101         if (now > (touch_timestamp + 10)) {
 102                 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 103
 104                 spin_lock(&print_lock);
 105                 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
 106                         this_cpu);
 107                 dump_stack();
 108                 spin_unlock(&print_lock);
 109         }
 110 }
 111
 112 /*
 113  * The watchdog thread - runs every second and touches the timestamp.
 114  */
 115 static int watchdog(void * __bind_cpu)
 116 {
 117         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 118
 119         sched_setscheduler(current, SCHED_FIFO, &param);
 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 }