1/*
2 * Detect Hung Task
3 *
4 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
5 *
6 */
7
8#include <linux/mm.h>
9#include <linux/cpu.h>
10#include <linux/nmi.h>
11#include <linux/init.h>
12#include <linux/delay.h>
13#include <linux/freezer.h>
14#include <linux/kthread.h>
15#include <linux/lockdep.h>
16#include <linux/module.h>
17#include <linux/sysctl.h>
18
19/*
20 * The number of tasks checked:
21 */
22unsigned long __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
23
24/*
25 * Limit number of tasks checked in a batch.
26 *
27 * This value controls the preemptibility of khungtaskd since preemption
28 * is disabled during the critical section. It also controls the size of
29 * the RCU grace period. So it needs to be upper-bound.
30 */
31#define HUNG_TASK_BATCHING 1024
32
33/*
34 * Zero means infinite timeout - no checking done:
35 */
36unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
37
38unsigned long __read_mostly sysctl_hung_task_warnings = 10;
39
40static int __read_mostly did_panic;
41
42static struct task_struct *watchdog_task;
43
44/*
45 * Should we panic (and reboot, if panic_timeout= is set) when a
46 * hung task is detected:
47 */
48unsigned int __read_mostly sysctl_hung_task_panic =
49				CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
50
51static int __init hung_task_panic_setup(char *str)
52{
53	sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
54
55	return 1;
56}
57__setup("hung_task_panic=", hung_task_panic_setup);
58
59static int
60hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
61{
62	did_panic = 1;
63
64	return NOTIFY_DONE;
65}
66
67static struct notifier_block panic_block = {
68	.notifier_call = hung_task_panic,
69};
70
71static void check_hung_task(struct task_struct *t, unsigned long timeout)
72{
73	unsigned long switch_count = t->nvcsw + t->nivcsw;
74
75	/*
76	 * Ensure the task is not frozen.
77	 * Also, when a freshly created task is scheduled once, changes
78	 * its state to TASK_UNINTERRUPTIBLE without having ever been
79	 * switched out once, it musn't be checked.
80	 */
81	if (unlikely(t->flags & PF_FROZEN || !switch_count))
82		return;
83
84	if (switch_count != t->last_switch_count) {
85		t->last_switch_count = switch_count;
86		return;
87	}
88	if (!sysctl_hung_task_warnings)
89		return;
90	sysctl_hung_task_warnings--;
91
92	/*
93	 * Ok, the task did not get scheduled for more than 2 minutes,
94	 * complain:
95	 */
96	printk(KERN_ERR "INFO: task %s:%d blocked for more than "
97			"%ld seconds.\n", t->comm, t->pid, timeout);
98	printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
99			" disables this message.\n");
100	sched_show_task(t);
101	__debug_show_held_locks(t);
102
103	touch_nmi_watchdog();
104
105	if (sysctl_hung_task_panic)
106		panic("hung_task: blocked tasks");
107}
108
109/*
110 * To avoid extending the RCU grace period for an unbounded amount of time,
111 * periodically exit the critical section and enter a new one.
112 *
113 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
114 * exit the grace period. For classic RCU, a reschedule is required.
115 */
116static void rcu_lock_break(struct task_struct *g, struct task_struct *t)
117{
118	get_task_struct(g);
119	get_task_struct(t);
120	rcu_read_unlock();
121	cond_resched();
122	rcu_read_lock();
123	put_task_struct(t);
124	put_task_struct(g);
125}
126
127/*
128 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
129 * a really long time (120 seconds). If that happens, print out
130 * a warning.
131 */
132static void check_hung_uninterruptible_tasks(unsigned long timeout)
133{
134	int max_count = sysctl_hung_task_check_count;
135	int batch_count = HUNG_TASK_BATCHING;
136	struct task_struct *g, *t;
137
138	/*
139	 * If the system crashed already then all bets are off,
140	 * do not report extra hung tasks:
141	 */
142	if (test_taint(TAINT_DIE) || did_panic)
143		return;
144
145	rcu_read_lock();
146	do_each_thread(g, t) {
147		if (!max_count--)
148			goto unlock;
149		if (!--batch_count) {
150			batch_count = HUNG_TASK_BATCHING;
151			rcu_lock_break(g, t);
152			/* Exit if t or g was unhashed during refresh. */
153			if (t->state == TASK_DEAD || g->state == TASK_DEAD)
154				goto unlock;
155		}
156		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
157		if (t->state == TASK_UNINTERRUPTIBLE)
158			check_hung_task(t, timeout);
159	} while_each_thread(g, t);
160 unlock:
161	rcu_read_unlock();
162}
163
164static unsigned long timeout_jiffies(unsigned long timeout)
165{
166	/* timeout of 0 will disable the watchdog */
167	return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
168}
169
170/*
171 * Process updating of timeout sysctl
172 */
173int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
174				  void __user *buffer,
175				  size_t *lenp, loff_t *ppos)
176{
177	int ret;
178
179	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
180
181	if (ret || !write)
182		goto out;
183
184	wake_up_process(watchdog_task);
185
186 out:
187	return ret;
188}
189
190/*
191 * kthread which checks for tasks stuck in D state
192 */
193static int watchdog(void *dummy)
194{
195	set_user_nice(current, 0);
196
197	for ( ; ; ) {
198		unsigned long timeout = sysctl_hung_task_timeout_secs;
199
200		while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
201			timeout = sysctl_hung_task_timeout_secs;
202
203		check_hung_uninterruptible_tasks(timeout);
204	}
205
206	return 0;
207}
208
209static int __init hung_task_init(void)
210{
211	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
212	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
213
214	return 0;
215}
216
217module_init(hung_task_init);
218