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 #include <asm/irq_regs.h>
20 static DEFINE_SPINLOCK(print_lock);
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);
26 static int did_panic = 0;
29 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
36 static struct notifier_block panic_block = {
37 .notifier_call = softlock_panic,
41 * Returns seconds, approximately. We don't need nanosecond
42 * resolution, and we don't need to waste time with a big divide when
45 static unsigned long get_timestamp(int this_cpu)
47 return cpu_clock(this_cpu) >> 30; /* 2^30 ~= 10^9 */
50 void touch_softlockup_watchdog(void)
52 int this_cpu = raw_smp_processor_id();
54 __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
56 EXPORT_SYMBOL(touch_softlockup_watchdog);
58 void touch_all_softlockup_watchdogs(void)
62 /* Cause each CPU to re-update its timestamp rather than complain */
63 for_each_online_cpu(cpu)
64 per_cpu(touch_timestamp, cpu) = 0;
66 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
69 * This callback runs from the timer interrupt, and checks
70 * whether the watchdog thread has hung or not:
72 void softlockup_tick(void)
74 int this_cpu = smp_processor_id();
75 unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
76 unsigned long print_timestamp;
77 struct pt_regs *regs = get_irq_regs();
80 if (touch_timestamp == 0) {
81 touch_softlockup_watchdog();
85 print_timestamp = per_cpu(print_timestamp, this_cpu);
87 /* report at most once a second */
88 if ((print_timestamp >= touch_timestamp &&
89 print_timestamp < (touch_timestamp + 1)) ||
90 did_panic || !per_cpu(watchdog_task, this_cpu)) {
94 /* do not print during early bootup: */
95 if (unlikely(system_state != SYSTEM_RUNNING)) {
96 touch_softlockup_watchdog();
100 now = get_timestamp(this_cpu);
102 /* Wake up the high-prio watchdog task every second: */
103 if (now > (touch_timestamp + 1))
104 wake_up_process(per_cpu(watchdog_task, this_cpu));
106 /* Warn about unreasonable 10+ seconds delays: */
107 if (now <= (touch_timestamp + 10))
110 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
112 spin_lock(&print_lock);
113 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n", this_cpu);
118 spin_unlock(&print_lock);
122 * The watchdog thread - runs every second and touches the timestamp.
124 static int watchdog(void * __bind_cpu)
126 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
128 sched_setscheduler(current, SCHED_FIFO, ¶m);
130 /* initialize timestamp */
131 touch_softlockup_watchdog();
134 * Run briefly once per second to reset the softlockup timestamp.
135 * If this gets delayed for more than 10 seconds then the
136 * debug-printout triggers in softlockup_tick().
138 while (!kthread_should_stop()) {
139 set_current_state(TASK_INTERRUPTIBLE);
140 touch_softlockup_watchdog();
148 * Create/destroy watchdog threads as CPUs come and go:
151 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
153 int hotcpu = (unsigned long)hcpu;
154 struct task_struct *p;
158 case CPU_UP_PREPARE_FROZEN:
159 BUG_ON(per_cpu(watchdog_task, hotcpu));
160 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
162 printk("watchdog for %i failed\n", hotcpu);
165 per_cpu(touch_timestamp, hotcpu) = 0;
166 per_cpu(watchdog_task, hotcpu) = p;
167 kthread_bind(p, hotcpu);
170 case CPU_ONLINE_FROZEN:
171 wake_up_process(per_cpu(watchdog_task, hotcpu));
173 #ifdef CONFIG_HOTPLUG_CPU
174 case CPU_UP_CANCELED:
175 case CPU_UP_CANCELED_FROZEN:
176 if (!per_cpu(watchdog_task, hotcpu))
178 /* Unbind so it can run. Fall thru. */
179 kthread_bind(per_cpu(watchdog_task, hotcpu),
180 any_online_cpu(cpu_online_map));
182 case CPU_DEAD_FROZEN:
183 p = per_cpu(watchdog_task, hotcpu);
184 per_cpu(watchdog_task, hotcpu) = NULL;
187 #endif /* CONFIG_HOTPLUG_CPU */
192 static struct notifier_block __cpuinitdata cpu_nfb = {
193 .notifier_call = cpu_callback
196 __init void spawn_softlockup_task(void)
198 void *cpu = (void *)(long)smp_processor_id();
199 int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
201 BUG_ON(err == NOTIFY_BAD);
202 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
203 register_cpu_notifier(&cpu_nfb);
205 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);