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/kthread.h>
14#include <linux/notifier.h>
15#include <linux/module.h>
16
17static DEFINE_SPINLOCK(print_lock);
18
19static DEFINE_PER_CPU(unsigned long, touch_timestamp);
20static DEFINE_PER_CPU(unsigned long, print_timestamp);
21static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
22
23static int did_panic = 0;
24
25static int
26softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
27{
28	did_panic = 1;
29
30	return NOTIFY_DONE;
31}
32
33static struct notifier_block panic_block = {
34	.notifier_call = softlock_panic,
35};
36
37/*
38 * Returns seconds, approximately.  We don't need nanosecond
39 * resolution, and we don't need to waste time with a big divide when
40 * 2^30ns == 1.074s.
41 */
42static unsigned long get_timestamp(void)
43{
44	return sched_clock() >> 30;  /* 2^30 ~= 10^9 */
45}
46
47void touch_softlockup_watchdog(void)
48{
49	__raw_get_cpu_var(touch_timestamp) = get_timestamp();
50}
51EXPORT_SYMBOL(touch_softlockup_watchdog);
52
53void touch_all_softlockup_watchdogs(void)
54{
55	int cpu;
56
57	/* Cause each CPU to re-update its timestamp rather than complain */
58	for_each_online_cpu(cpu)
59		per_cpu(touch_timestamp, cpu) = 0;
60}
61EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
62
63/*
64 * This callback runs from the timer interrupt, and checks
65 * whether the watchdog thread has hung or not:
66 */
67void softlockup_tick(void)
68{
69	int this_cpu = smp_processor_id();
70	unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
71	unsigned long print_timestamp;
72	unsigned long now;
73
74	if (touch_timestamp == 0) {
75		touch_softlockup_watchdog();
76		return;
77	}
78
79	print_timestamp = per_cpu(print_timestamp, this_cpu);
80
81	/* report at most once a second */
82	if (print_timestamp < (touch_timestamp + 1) ||
83		did_panic ||
84			!per_cpu(watchdog_task, this_cpu))
85		return;
86
87	/* do not print during early bootup: */
88	if (unlikely(system_state != SYSTEM_RUNNING)) {
89		touch_softlockup_watchdog();
90		return;
91	}
92
93	now = get_timestamp();
94
95	/* Wake up the high-prio watchdog task every second: */
96	if (now > (touch_timestamp + 1))
97		wake_up_process(per_cpu(watchdog_task, this_cpu));
98
99	/* Warn about unreasonable 10+ seconds delays: */
100	if (now > (touch_timestamp + 10)) {
101		per_cpu(print_timestamp, this_cpu) = touch_timestamp;
102
103		spin_lock(&print_lock);
104		printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
105			this_cpu);
106		dump_stack();
107		spin_unlock(&print_lock);
108	}
109}
110
111/*
112 * The watchdog thread - runs every second and touches the timestamp.
113 */
114static int watchdog(void * __bind_cpu)
115{
116	struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
117
118	sched_setscheduler(current, SCHED_FIFO, &param);
119	current->flags |= PF_NOFREEZE;
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 */
141static int __cpuinit
142cpu_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
183static 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}
198