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(int this_cpu)
  44 {
  45         return cpu_clock(this_cpu) >> 30;  /* 2^30 ~= 10^9 */
  46 }
  47
  48 void touch_softlockup_watchdog(void)
  49 {
  50         int this_cpu = raw_smp_processor_id();
  51
  52         __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
  53 }
  54 EXPORT_SYMBOL(touch_softlockup_watchdog);
  55
  56 void touch_all_softlockup_watchdogs(void)
  57 {
  58         int cpu;
  59
  60         /* Cause each CPU to re-update its timestamp rather than complain */
  61         for_each_online_cpu(cpu)
  62                 per_cpu(touch_timestamp, cpu) = 0;
  63 }
  64 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  65
  66 /*
  67  * This callback runs from the timer interrupt, and checks
  68  * whether the watchdog thread has hung or not:
  69  */
  70 void softlockup_tick(void)
  71 {
  72         int this_cpu = smp_processor_id();
  73         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  74         unsigned long print_timestamp;
  75         unsigned long now;
  76
  77         if (touch_timestamp == 0) {
  78                 touch_softlockup_watchdog();
  79                 return;
  80         }
  81
  82         print_timestamp = per_cpu(print_timestamp, this_cpu);
  83
  84         /* report at most once a second */
  85         if ((print_timestamp >= touch_timestamp &&
  86                         print_timestamp < (touch_timestamp + 1)) ||
  87                         did_panic || !per_cpu(watchdog_task, this_cpu)) {
  88                 return;
  89         }
  90
  91         /* do not print during early bootup: */
  92         if (unlikely(system_state != SYSTEM_RUNNING)) {
  93                 touch_softlockup_watchdog();
  94                 return;
  95         }
  96
  97         now = get_timestamp(this_cpu);
  98
  99         /* Wake up the high-prio watchdog task every second: */
 100         if (now > (touch_timestamp + 1))
 101                 wake_up_process(per_cpu(watchdog_task, this_cpu));
 102
 103         /* Warn about unreasonable 10+ seconds delays: */
 104         if (now > (touch_timestamp + 10)) {
 105                 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 106
 107                 spin_lock(&print_lock);
 108                 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
 109                         this_cpu);
 110                 dump_stack();
 111                 spin_unlock(&print_lock);
 112         }
 113 }
 114
 115 /*
 116  * The watchdog thread - runs every second and touches the timestamp.
 117  */
 118 static int watchdog(void * __bind_cpu)
 119 {
 120         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 121
 122         sched_setscheduler(current, SCHED_FIFO, &param);
 123
 124         /* initialize timestamp */
 125         touch_softlockup_watchdog();
 126
 127         /*
 128          * Run briefly once per second to reset the softlockup timestamp.
 129          * If this gets delayed for more than 10 seconds then the
 130          * debug-printout triggers in softlockup_tick().
 131          */
 132         while (!kthread_should_stop()) {
 133                 set_current_state(TASK_INTERRUPTIBLE);
 134                 touch_softlockup_watchdog();
 135                 schedule();
 136         }
 137
 138         return 0;
 139 }
 140
 141 /*
 142  * Create/destroy watchdog threads as CPUs come and go:
 143  */
 144 static int __cpuinit
 145 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 146 {
 147         int hotcpu = (unsigned long)hcpu;
 148         struct task_struct *p;
 149
 150         switch (action) {
 151         case CPU_UP_PREPARE:
 152         case CPU_UP_PREPARE_FROZEN:
 153                 BUG_ON(per_cpu(watchdog_task, hotcpu));
 154                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 155                 if (IS_ERR(p)) {
 156                         printk("watchdog for %i failed\n", hotcpu);
 157                         return NOTIFY_BAD;
 158                 }
 159                 per_cpu(touch_timestamp, hotcpu) = 0;
 160                 per_cpu(watchdog_task, hotcpu) = p;
 161                 kthread_bind(p, hotcpu);
 162                 break;
 163         case CPU_ONLINE:
 164         case CPU_ONLINE_FROZEN:
 165                 wake_up_process(per_cpu(watchdog_task, hotcpu));
 166                 break;
 167 #ifdef CONFIG_HOTPLUG_CPU
 168         case CPU_UP_CANCELED:
 169         case CPU_UP_CANCELED_FROZEN:
 170                 if (!per_cpu(watchdog_task, hotcpu))
 171                         break;
 172                 /* Unbind so it can run.  Fall thru. */
 173                 kthread_bind(per_cpu(watchdog_task, hotcpu),
 174                              any_online_cpu(cpu_online_map));
 175         case CPU_DEAD:
 176         case CPU_DEAD_FROZEN:
 177                 p = per_cpu(watchdog_task, hotcpu);
 178                 per_cpu(watchdog_task, hotcpu) = NULL;
 179                 kthread_stop(p);
 180                 break;
 181 #endif /* CONFIG_HOTPLUG_CPU */
 182         }
 183         return NOTIFY_OK;
 184 }
 185
 186 static struct notifier_block __cpuinitdata cpu_nfb = {
 187         .notifier_call = cpu_callback
 188 };
 189
 190 __init void spawn_softlockup_task(void)
 191 {
 192         void *cpu = (void *)(long)smp_processor_id();
 193         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 194
 195         BUG_ON(err == NOTIFY_BAD);
 196         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 197         register_cpu_notifier(&cpu_nfb);
 198
 199         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 200 }