softlockup: s/99/MAX_RT_PRIO/
[linux-2.6.git] / 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/kthread.h>
14 #include <linux/notifier.h>
15 #include <linux/module.h>
16
17 static DEFINE_SPINLOCK(print_lock);
18
19 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
20 static DEFINE_PER_CPU(unsigned long, print_timestamp);
21 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
22
23 static int did_panic = 0;
24
25 static int
26 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
27 {
28         did_panic = 1;
29
30         return NOTIFY_DONE;
31 }
32
33 static struct notifier_block panic_block = {
34         .notifier_call = softlock_panic,
35 };
36
37 void touch_softlockup_watchdog(void)
38 {
39         __raw_get_cpu_var(touch_timestamp) = jiffies;
40 }
41 EXPORT_SYMBOL(touch_softlockup_watchdog);
42
43 /*
44  * This callback runs from the timer interrupt, and checks
45  * whether the watchdog thread has hung or not:
46  */
47 void softlockup_tick(void)
48 {
49         int this_cpu = smp_processor_id();
50         unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
51
52         /* prevent double reports: */
53         if (per_cpu(print_timestamp, this_cpu) == touch_timestamp ||
54                 did_panic ||
55                         !per_cpu(watchdog_task, this_cpu))
56                 return;
57
58         /* do not print during early bootup: */
59         if (unlikely(system_state != SYSTEM_RUNNING)) {
60                 touch_softlockup_watchdog();
61                 return;
62         }
63
64         /* Wake up the high-prio watchdog task every second: */
65         if (time_after(jiffies, touch_timestamp + HZ))
66                 wake_up_process(per_cpu(watchdog_task, this_cpu));
67
68         /* Warn about unreasonable 10+ seconds delays: */
69         if (time_after(jiffies, touch_timestamp + 10*HZ)) {
70                 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
71
72                 spin_lock(&print_lock);
73                 printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
74                         this_cpu);
75                 dump_stack();
76                 spin_unlock(&print_lock);
77         }
78 }
79
80 /*
81  * The watchdog thread - runs every second and touches the timestamp.
82  */
83 static int watchdog(void * __bind_cpu)
84 {
85         struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
86
87         sched_setscheduler(current, SCHED_FIFO, &param);
88         current->flags |= PF_NOFREEZE;
89
90         /*
91          * Run briefly once per second to reset the softlockup timestamp.
92          * If this gets delayed for more than 10 seconds then the
93          * debug-printout triggers in softlockup_tick().
94          */
95         while (!kthread_should_stop()) {
96                 set_current_state(TASK_INTERRUPTIBLE);
97                 touch_softlockup_watchdog();
98                 schedule();
99         }
100
101         return 0;
102 }
103
104 /*
105  * Create/destroy watchdog threads as CPUs come and go:
106  */
107 static int __cpuinit
108 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
109 {
110         int hotcpu = (unsigned long)hcpu;
111         struct task_struct *p;
112
113         switch (action) {
114         case CPU_UP_PREPARE:
115                 BUG_ON(per_cpu(watchdog_task, hotcpu));
116                 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
117                 if (IS_ERR(p)) {
118                         printk("watchdog for %i failed\n", hotcpu);
119                         return NOTIFY_BAD;
120                 }
121                 per_cpu(touch_timestamp, hotcpu) = jiffies;
122                 per_cpu(watchdog_task, hotcpu) = p;
123                 kthread_bind(p, hotcpu);
124                 break;
125         case CPU_ONLINE:
126                 wake_up_process(per_cpu(watchdog_task, hotcpu));
127                 break;
128 #ifdef CONFIG_HOTPLUG_CPU
129         case CPU_UP_CANCELED:
130                 if (!per_cpu(watchdog_task, hotcpu))
131                         break;
132                 /* Unbind so it can run.  Fall thru. */
133                 kthread_bind(per_cpu(watchdog_task, hotcpu),
134                              any_online_cpu(cpu_online_map));
135         case CPU_DEAD:
136                 p = per_cpu(watchdog_task, hotcpu);
137                 per_cpu(watchdog_task, hotcpu) = NULL;
138                 kthread_stop(p);
139                 break;
140 #endif /* CONFIG_HOTPLUG_CPU */
141         }
142         return NOTIFY_OK;
143 }
144
145 static struct notifier_block __cpuinitdata cpu_nfb = {
146         .notifier_call = cpu_callback
147 };
148
149 __init void spawn_softlockup_task(void)
150 {
151         void *cpu = (void *)(long)smp_processor_id();
152         int err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
153
154         BUG_ON(err == NOTIFY_BAD);
155         cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
156         register_cpu_notifier(&cpu_nfb);
157
158         atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
159 }