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/nmi.h>
12 #include <linux/init.h>
13 #include <linux/delay.h>
14 #include <linux/freezer.h>
15 #include <linux/kthread.h>
16 #include <linux/lockdep.h>
17 #include <linux/notifier.h>
18 #include <linux/module.h>
20 #include <asm/irq_regs.h>
22 static DEFINE_SPINLOCK(print_lock);
24 static DEFINE_PER_CPU(unsigned long, touch_timestamp);
25 static DEFINE_PER_CPU(unsigned long, print_timestamp);
26 static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
28 static int __read_mostly did_panic;
29 int __read_mostly softlockup_thresh = 60;
32 * Should we panic (and reboot, if panic_timeout= is set) when a
35 unsigned int __read_mostly softlockup_panic =
36 CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE;
38 static int __init softlockup_panic_setup(char *str)
40 softlockup_panic = simple_strtoul(str, NULL, 0);
44 __setup("softlockup_panic=", softlockup_panic_setup);
47 softlock_panic(struct notifier_block *this, unsigned long event, void *ptr)
54 static struct notifier_block panic_block = {
55 .notifier_call = softlock_panic,
59 * Returns seconds, approximately. We don't need nanosecond
60 * resolution, and we don't need to waste time with a big divide when
63 static unsigned long get_timestamp(int this_cpu)
65 return cpu_clock(this_cpu) >> 30LL; /* 2^30 ~= 10^9 */
68 static void __touch_softlockup_watchdog(void)
70 int this_cpu = raw_smp_processor_id();
72 __raw_get_cpu_var(touch_timestamp) = get_timestamp(this_cpu);
75 void touch_softlockup_watchdog(void)
77 __raw_get_cpu_var(touch_timestamp) = 0;
79 EXPORT_SYMBOL(touch_softlockup_watchdog);
81 void touch_all_softlockup_watchdogs(void)
85 /* Cause each CPU to re-update its timestamp rather than complain */
86 for_each_online_cpu(cpu)
87 per_cpu(touch_timestamp, cpu) = 0;
89 EXPORT_SYMBOL(touch_all_softlockup_watchdogs);
92 * This callback runs from the timer interrupt, and checks
93 * whether the watchdog thread has hung or not:
95 void softlockup_tick(void)
97 int this_cpu = smp_processor_id();
98 unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
99 unsigned long print_timestamp;
100 struct pt_regs *regs = get_irq_regs();
103 /* Is detection switched off? */
104 if (!per_cpu(watchdog_task, this_cpu) || softlockup_thresh <= 0) {
105 /* Be sure we don't false trigger if switched back on */
107 per_cpu(touch_timestamp, this_cpu) = 0;
111 if (touch_timestamp == 0) {
112 __touch_softlockup_watchdog();
116 print_timestamp = per_cpu(print_timestamp, this_cpu);
118 /* report at most once a second */
119 if (print_timestamp == touch_timestamp || did_panic)
122 /* do not print during early bootup: */
123 if (unlikely(system_state != SYSTEM_RUNNING)) {
124 __touch_softlockup_watchdog();
128 now = get_timestamp(this_cpu);
131 * Wake up the high-prio watchdog task twice per
132 * threshold timespan.
134 if (now > touch_timestamp + softlockup_thresh/2)
135 wake_up_process(per_cpu(watchdog_task, this_cpu));
137 /* Warn about unreasonable delays: */
138 if (now <= (touch_timestamp + softlockup_thresh))
141 per_cpu(print_timestamp, this_cpu) = touch_timestamp;
143 spin_lock(&print_lock);
144 printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
145 this_cpu, now - touch_timestamp,
146 current->comm, task_pid_nr(current));
148 print_irqtrace_events(current);
153 spin_unlock(&print_lock);
155 if (softlockup_panic)
156 panic("softlockup: hung tasks");
160 * Have a reasonable limit on the number of tasks checked:
162 unsigned long __read_mostly sysctl_hung_task_check_count = 1024;
165 * Zero means infinite timeout - no checking done:
167 unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
169 unsigned long __read_mostly sysctl_hung_task_warnings = 10;
172 * Only do the hung-tasks check on one CPU:
174 static int check_cpu __read_mostly = -1;
176 static void check_hung_task(struct task_struct *t, unsigned long now)
178 unsigned long switch_count = t->nvcsw + t->nivcsw;
180 if (t->flags & PF_FROZEN)
183 if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
184 t->last_switch_count = switch_count;
185 t->last_switch_timestamp = now;
188 if ((long)(now - t->last_switch_timestamp) <
189 sysctl_hung_task_timeout_secs)
191 if (sysctl_hung_task_warnings < 0)
193 sysctl_hung_task_warnings--;
196 * Ok, the task did not get scheduled for more than 2 minutes,
199 printk(KERN_ERR "INFO: task %s:%d blocked for more than "
200 "%ld seconds.\n", t->comm, t->pid,
201 sysctl_hung_task_timeout_secs);
202 printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
203 " disables this message.\n");
205 __debug_show_held_locks(t);
207 t->last_switch_timestamp = now;
208 touch_nmi_watchdog();
210 if (softlockup_panic)
211 panic("softlockup: blocked tasks");
215 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
216 * a really long time (120 seconds). If that happens, print out
219 static void check_hung_uninterruptible_tasks(int this_cpu)
221 int max_count = sysctl_hung_task_check_count;
222 unsigned long now = get_timestamp(this_cpu);
223 struct task_struct *g, *t;
226 * If the system crashed already then all bets are off,
227 * do not report extra hung tasks:
229 if (test_taint(TAINT_DIE) || did_panic)
232 read_lock(&tasklist_lock);
233 do_each_thread(g, t) {
236 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
237 if (t->state == TASK_UNINTERRUPTIBLE)
238 check_hung_task(t, now);
239 } while_each_thread(g, t);
241 read_unlock(&tasklist_lock);
245 * The watchdog thread - runs every second and touches the timestamp.
247 static int watchdog(void *__bind_cpu)
249 struct sched_param param = { .sched_priority = MAX_RT_PRIO-1 };
250 int this_cpu = (long)__bind_cpu;
252 sched_setscheduler(current, SCHED_FIFO, ¶m);
254 /* initialize timestamp */
255 __touch_softlockup_watchdog();
257 set_current_state(TASK_INTERRUPTIBLE);
259 * Run briefly once per second to reset the softlockup timestamp.
260 * If this gets delayed for more than 60 seconds then the
261 * debug-printout triggers in softlockup_tick().
263 while (!kthread_should_stop()) {
264 __touch_softlockup_watchdog();
267 if (kthread_should_stop())
270 if (this_cpu == check_cpu) {
271 if (sysctl_hung_task_timeout_secs)
272 check_hung_uninterruptible_tasks(this_cpu);
275 set_current_state(TASK_INTERRUPTIBLE);
277 __set_current_state(TASK_RUNNING);
283 * Create/destroy watchdog threads as CPUs come and go:
286 cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
288 int hotcpu = (unsigned long)hcpu;
289 struct task_struct *p;
293 case CPU_UP_PREPARE_FROZEN:
294 BUG_ON(per_cpu(watchdog_task, hotcpu));
295 p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
297 printk(KERN_ERR "watchdog for %i failed\n", hotcpu);
300 per_cpu(touch_timestamp, hotcpu) = 0;
301 per_cpu(watchdog_task, hotcpu) = p;
302 kthread_bind(p, hotcpu);
305 case CPU_ONLINE_FROZEN:
306 check_cpu = any_online_cpu(cpu_online_map);
307 wake_up_process(per_cpu(watchdog_task, hotcpu));
309 #ifdef CONFIG_HOTPLUG_CPU
310 case CPU_DOWN_PREPARE:
311 case CPU_DOWN_PREPARE_FROZEN:
312 if (hotcpu == check_cpu) {
313 cpumask_t temp_cpu_online_map = cpu_online_map;
315 cpu_clear(hotcpu, temp_cpu_online_map);
316 check_cpu = any_online_cpu(temp_cpu_online_map);
320 case CPU_UP_CANCELED:
321 case CPU_UP_CANCELED_FROZEN:
322 if (!per_cpu(watchdog_task, hotcpu))
324 /* Unbind so it can run. Fall thru. */
325 kthread_bind(per_cpu(watchdog_task, hotcpu),
326 any_online_cpu(cpu_online_map));
328 case CPU_DEAD_FROZEN:
329 p = per_cpu(watchdog_task, hotcpu);
330 per_cpu(watchdog_task, hotcpu) = NULL;
333 #endif /* CONFIG_HOTPLUG_CPU */
338 static struct notifier_block __cpuinitdata cpu_nfb = {
339 .notifier_call = cpu_callback
342 static int __initdata nosoftlockup;
344 static int __init nosoftlockup_setup(char *str)
349 __setup("nosoftlockup", nosoftlockup_setup);
351 static int __init spawn_softlockup_task(void)
353 void *cpu = (void *)(long)smp_processor_id();
359 err = cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
360 if (err == NOTIFY_BAD) {
364 cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
365 register_cpu_notifier(&cpu_nfb);
367 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
371 early_initcall(spawn_softlockup_task);