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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/export.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 = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
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, skip vfork and any other user process that freezer should skip.
78 */
79 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
80 return;
81
82 /*
83 * When a freshly created task is scheduled once, changes its state to
84 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
85 * musn't be checked.
86 */
87 if (unlikely(!switch_count))
88 return;
89
90 if (switch_count != t->last_switch_count) {
91 t->last_switch_count = switch_count;
92 return;
93 }
94 if (!sysctl_hung_task_warnings)
95 return;
96 sysctl_hung_task_warnings--;
97
98 /*
99 * Ok, the task did not get scheduled for more than 2 minutes,
100 * complain:
101 */
102 printk(KERN_ERR "INFO: task %s:%d blocked for more than "
103 "%ld seconds.\n", t->comm, t->pid, timeout);
104 printk(KERN_ERR "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
105 " disables this message.\n");
106 sched_show_task(t);
107 debug_show_held_locks(t);
108
109 touch_nmi_watchdog();
110
111 if (sysctl_hung_task_panic) {
112 trigger_all_cpu_backtrace();
113 panic("hung_task: blocked tasks");
114 }
115}
116
117/*
118 * To avoid extending the RCU grace period for an unbounded amount of time,
119 * periodically exit the critical section and enter a new one.
120 *
121 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
122 * to exit the grace period. For classic RCU, a reschedule is required.
123 */
124static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
125{
126 bool can_cont;
127
128 get_task_struct(g);
129 get_task_struct(t);
130 rcu_read_unlock();
131 cond_resched();
132 rcu_read_lock();
133 can_cont = pid_alive(g) && pid_alive(t);
134 put_task_struct(t);
135 put_task_struct(g);
136
137 return can_cont;
138}
139
140/*
141 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
142 * a really long time (120 seconds). If that happens, print out
143 * a warning.
144 */
145static void check_hung_uninterruptible_tasks(unsigned long timeout)
146{
147 int max_count = sysctl_hung_task_check_count;
148 int batch_count = HUNG_TASK_BATCHING;
149 struct task_struct *g, *t;
150
151 /*
152 * If the system crashed already then all bets are off,
153 * do not report extra hung tasks:
154 */
155 if (test_taint(TAINT_DIE) || did_panic)
156 return;
157
158 rcu_read_lock();
159 do_each_thread(g, t) {
160 if (!max_count--)
161 goto unlock;
162 if (!--batch_count) {
163 batch_count = HUNG_TASK_BATCHING;
164 if (!rcu_lock_break(g, t))
165 goto unlock;
166 }
167 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
168 if (t->state == TASK_UNINTERRUPTIBLE)
169 check_hung_task(t, timeout);
170 } while_each_thread(g, t);
171 unlock:
172 rcu_read_unlock();
173}
174
175static unsigned long timeout_jiffies(unsigned long timeout)
176{
177 /* timeout of 0 will disable the watchdog */
178 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
179}
180
181/*
182 * Process updating of timeout sysctl
183 */
184int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
185 void __user *buffer,
186 size_t *lenp, loff_t *ppos)
187{
188 int ret;
189
190 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
191
192 if (ret || !write)
193 goto out;
194
195 wake_up_process(watchdog_task);
196
197 out:
198 return ret;
199}
200
201/*
202 * kthread which checks for tasks stuck in D state
203 */
204static int watchdog(void *dummy)
205{
206 set_user_nice(current, 0);
207
208 for ( ; ; ) {
209 unsigned long timeout = sysctl_hung_task_timeout_secs;
210
211 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
212 timeout = sysctl_hung_task_timeout_secs;
213
214 check_hung_uninterruptible_tasks(timeout);
215 }
216
217 return 0;
218}
219
220static int __init hung_task_init(void)
221{
222 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
223 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
224
225 return 0;
226}
227
228module_init(hung_task_init);
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 = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
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 * to 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);