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Mandeep Singh Bainese162b392009-01-15 11:08:40 -08001/*
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/*
Mandeep Singh Bainesce9dbe22009-02-04 20:35:48 -080020 * The number of tasks checked:
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080021 */
Mandeep Singh Bainesce9dbe22009-02-04 20:35:48 -080022unsigned 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
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080032
33/*
34 * Zero means infinite timeout - no checking done:
35 */
36unsigned long __read_mostly sysctl_hung_task_timeout_secs = 120;
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080037
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
Mandeep Singh Baines17406b82009-02-06 15:37:47 -080071static void check_hung_task(struct task_struct *t, unsigned long timeout)
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080072{
73 unsigned long switch_count = t->nvcsw + t->nivcsw;
74
Frederic Weisbeckercf2592f2009-02-10 16:52:37 +010075 /*
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))
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080082 return;
83
Mandeep Singh Baines17406b82009-02-06 15:37:47 -080084 if (switch_count != t->last_switch_count) {
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080085 t->last_switch_count = switch_count;
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080086 return;
87 }
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080088 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 "
Mandeep Singh Baines603a1482009-01-17 10:31:48 -080097 "%ld seconds.\n", t->comm, t->pid, timeout);
Mandeep Singh Bainese162b392009-01-15 11:08:40 -080098 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
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800103 touch_nmi_watchdog();
104
105 if (sysctl_hung_task_panic)
106 panic("hung_task: blocked tasks");
107}
108
109/*
Mandeep Singh Bainesce9dbe22009-02-04 20:35:48 -0800110 * 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/*
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800128 * 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 */
Mandeep Singh Baines603a1482009-01-17 10:31:48 -0800132static void check_hung_uninterruptible_tasks(unsigned long timeout)
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800133{
134 int max_count = sysctl_hung_task_check_count;
Mandeep Singh Bainesce9dbe22009-02-04 20:35:48 -0800135 int batch_count = HUNG_TASK_BATCHING;
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800136 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
Mandeep Singh Baines94be52d2009-02-05 09:56:08 -0800145 rcu_read_lock();
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800146 do_each_thread(g, t) {
147 if (!--max_count)
148 goto unlock;
Mandeep Singh Bainesce9dbe22009-02-04 20:35:48 -0800149 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 }
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800156 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
157 if (t->state == TASK_UNINTERRUPTIBLE)
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800158 check_hung_task(t, timeout);
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800159 } while_each_thread(g, t);
160 unlock:
Mandeep Singh Baines94be52d2009-02-05 09:56:08 -0800161 rcu_read_unlock();
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800162}
163
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800164static unsigned long timeout_jiffies(unsigned long timeout)
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800165{
166 /* timeout of 0 will disable the watchdog */
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800167 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800168}
169
170/*
171 * Process updating of timeout sysctl
172 */
173int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
174 struct file *filp, void __user *buffer,
175 size_t *lenp, loff_t *ppos)
176{
177 int ret;
178
179 ret = proc_doulongvec_minmax(table, write, filp, buffer, lenp, ppos);
180
181 if (ret || !write)
182 goto out;
183
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800184 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);
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800196
197 for ( ; ; ) {
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800198 unsigned long timeout = sysctl_hung_task_timeout_secs;
Mandeep Singh Baines603a1482009-01-17 10:31:48 -0800199
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800200 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
201 timeout = sysctl_hung_task_timeout_secs;
Mandeep Singh Baines603a1482009-01-17 10:31:48 -0800202
Mandeep Singh Baines17406b82009-02-06 15:37:47 -0800203 check_hung_uninterruptible_tasks(timeout);
Mandeep Singh Bainese162b392009-01-15 11:08:40 -0800204 }
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);