4 * started by Ingo Molnar, Copyright (C) 2005, 2006 Red Hat, Inc.
6 * this code detects soft lockups: incidents in where on a CPU
7 * the kernel does not reschedule for 10 seconds or more.
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>
18 static DEFINE_SPINLOCK(print_lock);
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);
24 static int did_panic = 0;
27 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
34 static struct notifier_block panic_block = {
35 .notifier_call = softlock_panic,
39 * Returns seconds, approximately. We don't need nanosecond
40 * resolution, and we don't need to waste time with a big divide when
43 static unsigned long get_timestamp(int this_cpu)
45 return cpu_clock(this_cpu) >> 30; /* 2^30 ~= 10^9 */
48 void touch_softlockup_watchdog(void)
50 int this_cpu = raw_smp_processor_id();
52 __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
54 EXPORT_SYMBOL(touch_softlockup_watchdog);
56 void touch_all_softlockup_watchdogs(void)
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;
64 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
67 * This callback runs from the timer interrupt, and checks
68 * whether the watchdog thread has hung or not:
70 void softlockup_tick(void)
72 int this_cpu = smp_processor_id();
73 unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
74 unsigned long print_timestamp;
77 if (touch_timestamp == 0) {
78 touch_softlockup_watchdog();
82 print_timestamp = per_cpu(print_timestamp, this_cpu);
84 /* report at most once a second */
85 if (print_timestamp < (touch_timestamp + 1) ||
87 !per_cpu(watchdog_task, this_cpu))
90 /* do not print during early bootup: */
91 if (unlikely(system_state != SYSTEM_RUNNING)) {
92 touch_softlockup_watchdog();
96 now = get_timestamp(this_cpu);
98 /* Wake up the high-prio watchdog task every second: */
99 if (now > (touch_timestamp + 1))
100 wake_up_process(per_cpu(watchdog_task, this_cpu));
102 /* Warn about unreasonable 10+ seconds delays: */
103 if (now > (touch_timestamp + 10)) {
104 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
106 spin_lock(&print_lock);
107 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
110 spin_unlock(&print_lock);
115 * The watchdog thread - runs every second and touches the timestamp.
117 static int watchdog(void * __bind_cpu)
119 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
121 sched_setscheduler(current, SCHED_FIFO, ¶m);
123 /* initialize timestamp */
124 touch_softlockup_watchdog();
127 * Run briefly once per second to reset the softlockup timestamp.
128 * If this gets delayed for more than 10 seconds then the
129 * debug-printout triggers in softlockup_tick().
131 while (!kthread_should_stop()) {
132 set_current_state(TASK_INTERRUPTIBLE);
133 touch_softlockup_watchdog();
141 * Create/destroy watchdog threads as CPUs come and go:
144 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
146 int hotcpu = (unsigned long)hcpu;
147 struct task_struct *p;
151 case CPU_UP_PREPARE_FROZEN:
152 BUG_ON(per_cpu(watchdog_task, hotcpu));
153 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
155 printk("watchdog for %i failed\n", hotcpu);
158 per_cpu(touch_timestamp, hotcpu) = 0;
159 per_cpu(watchdog_task, hotcpu) = p;
160 kthread_bind(p, hotcpu);
163 case CPU_ONLINE_FROZEN:
164 wake_up_process(per_cpu(watchdog_task, hotcpu));
166 #ifdef CONFIG_HOTPLUG_CPU
167 case CPU_UP_CANCELED:
168 case CPU_UP_CANCELED_FROZEN:
169 if (!per_cpu(watchdog_task, hotcpu))
171 /* Unbind so it can run. Fall thru. */
172 kthread_bind(per_cpu(watchdog_task, hotcpu),
173 any_online_cpu(cpu_online_map));
175 case CPU_DEAD_FROZEN:
176 p = per_cpu(watchdog_task, hotcpu);
177 per_cpu(watchdog_task, hotcpu) = NULL;
180 #endif /* CONFIG_HOTPLUG_CPU */
185 static struct notifier_block __cpuinitdata cpu_nfb = {
186 .notifier_call = cpu_callback
189 __init void spawn_softlockup_task(void)
191 void *cpu = (void *)(long)smp_processor_id();
192 int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
194 BUG_ON(err == NOTIFY_BAD);
195 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
196 register_cpu_notifier(&cpu_nfb);
198 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);