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 #include <asm/irq_regs.h>
  19
  20 static DEFINE_SPINLOCK(print_lock);
  21
  22 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
  23 static DEFINE_PER_CPU(unsigned long, print_timestamp);
  24 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
  25
  26 static int did_panic;
  27 int softlockup_thresh = 10;
  28
  29 static int
  30 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
  31 {
  32         did_panic = 1;
  33
  34         return NOTIFY_DONE;
  35 }
  36
  37 static struct notifier_block panic_block = {
  38         .notifier_call = softlock_panic,
  39 };
  40
  41 /*
  42  * Returns seconds, approximately.  We don't need nanosecond
  43  * resolution, and we don't need to waste time with a big divide when
  44  * 2^30ns == 1.074s.
  45  */
  46 static unsigned long get_timestamp(int this_cpu)
  47 {
  48         return cpu_clock(this_cpu) >> 30;  /* 2^30 ~= 10^9 */
  49 }
  50
  51 void touch_softlockup_watchdog(void)
  52 {
  53         int this_cpu = raw_smp_processor_id();
  54
  55         __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
  56 }
  57 EXPORT_SYMBOL(touch_softlockup_watchdog);
  58
  59 void touch_all_softlockup_watchdogs(void)
  60 {
  61         int cpu;
  62
  63         /* Cause each CPU to re-update its timestamp rather than complain */
  64         for_each_online_cpu(cpu)
  65                 per_cpu(touch_timestamp, cpu) = 0;
  66 }
  67 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
  68
  69 /*
  70  * This callback runs from the timer interrupt, and checks
  71  * whether the watchdog thread has hung or not:
  72  */
  73 void softlockup_tick(void)
  74 {
  75         int this_cpu = smp_processor_id();
  76         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
  77         unsigned long print_timestamp;
  78         struct pt_regs *regs = get_irq_regs();
  79         unsigned long now;
  80
  81         if (touch_timestamp == 0) {
  82                 touch_softlockup_watchdog();
  83                 return;
  84         }
  85
  86         print_timestamp = per_cpu(print_timestamp, this_cpu);
  87
  88         /* report at most once a second */
  89         if ((print_timestamp >= touch_timestamp &&
  90                         print_timestamp < (touch_timestamp + 1)) ||
  91                         did_panic || !per_cpu(watchdog_task, this_cpu)) {
  92                 return;
  93         }
  94
  95         /* do not print during early bootup: */
  96         if (unlikely(system_state != SYSTEM_RUNNING)) {
  97                 touch_softlockup_watchdog();
  98                 return;
  99         }
 100
 101         now = get_timestamp(this_cpu);
 102
 103         /* Wake up the high-prio watchdog task every second: */
 104         if (now > (touch_timestamp + 1))
 105                 wake_up_process(per_cpu(watchdog_task, this_cpu));
 106
 107         /* Warn about unreasonable 10+ seconds delays: */
 108         if (now <= (touch_timestamp + softlockup_thresh))
 109                 return;
 110
 111         per_cpu(print_timestamp, this_cpu) = touch_timestamp;
 112
 113         spin_lock(&print_lock);
 114         printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
 115                         this_cpu, now - touch_timestamp,
 116                         current->comm, task_pid_nr(current));
 117         if (regs)
 118                 show_regs(regs);
 119         else
 120                 dump_stack();
 121         spin_unlock(&print_lock);
 122 }
 123
 124 /*
 125  * The watchdog thread - runs every second and touches the timestamp.
 126  */
 127 static int watchdog(void *__bind_cpu)
 128 {
 129         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
 130
 131         sched_setscheduler(current, SCHED_FIFO, &param);
 132
 133         /* initialize timestamp */
 134         touch_softlockup_watchdog();
 135
 136         /*
 137          * Run briefly once per second to reset the softlockup timestamp.
 138          * If this gets delayed for more than 10 seconds then the
 139          * debug-printout triggers in softlockup_tick().
 140          */
 141         while (!kthread_should_stop()) {
 142                 set_current_state(TASK_INTERRUPTIBLE);
 143                 touch_softlockup_watchdog();
 144                 schedule();
 145         }
 146
 147         return 0;
 148 }
 149
 150 /*
 151  * Create/destroy watchdog threads as CPUs come and go:
 152  */
 153 static int __cpuinit
 154 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
 155 {
 156         int hotcpu = (unsigned long)hcpu;
 157         struct task_struct *p;
 158
 159         switch (action) {
 160         case CPU_UP_PREPARE:
 161         case CPU_UP_PREPARE_FROZEN:
 162                 BUG_ON(per_cpu(watchdog_task, hotcpu));
 163                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
 164                 if (IS_ERR(p)) {
 165                         printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
 166                         return NOTIFY_BAD;
 167                 }
 168                 per_cpu(touch_timestamp, hotcpu) = 0;
 169                 per_cpu(watchdog_task, hotcpu) = p;
 170                 kthread_bind(p, hotcpu);
 171                 break;
 172         case CPU_ONLINE:
 173         case CPU_ONLINE_FROZEN:
 174                 wake_up_process(per_cpu(watchdog_task, hotcpu));
 175                 break;
 176 #ifdef CONFIG_HOTPLUG_CPU
 177         case CPU_UP_CANCELED:
 178         case CPU_UP_CANCELED_FROZEN:
 179                 if (!per_cpu(watchdog_task, hotcpu))
 180                         break;
 181                 /* Unbind so it can run.  Fall thru. */
 182                 kthread_bind(per_cpu(watchdog_task, hotcpu),
 183                              any_online_cpu(cpu_online_map));
 184         case CPU_DEAD:
 185         case CPU_DEAD_FROZEN:
 186                 p = per_cpu(watchdog_task, hotcpu);
 187                 per_cpu(watchdog_task, hotcpu) = NULL;
 188                 kthread_stop(p);
 189                 break;
 190 #endif /* CONFIG_HOTPLUG_CPU */
 191         }
 192         return NOTIFY_OK;
 193 }
 194
 195 static struct notifier_block __cpuinitdata cpu_nfb = {
 196         .notifier_call = cpu_callback
 197 };
 198
 199 __init void spawn_softlockup_task(void)
 200 {
 201         void *cpu = (void *)(long)smp_processor_id();
 202         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
 203
 204         BUG_ON(err == NOTIFY_BAD);
 205         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
 206         register_cpu_notifier(&cpu_nfb);
 207
 208         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
 209 }