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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#include <linux/utsname.h>
19#include <trace/events/sched.h>
20
21/*
22 * The number of tasks checked:
23 */
24int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
25
26/*
27 * Limit number of tasks checked in a batch.
28 *
29 * This value controls the preemptibility of khungtaskd since preemption
30 * is disabled during the critical section. It also controls the size of
31 * the RCU grace period. So it needs to be upper-bound.
32 */
33#define HUNG_TASK_BATCHING 1024
34
35/*
36 * Zero means infinite timeout - no checking done:
37 */
38unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
39
40int __read_mostly sysctl_hung_task_warnings = 10;
41
42static int __read_mostly did_panic;
43
44static struct task_struct *watchdog_task;
45
46/*
47 * Should we panic (and reboot, if panic_timeout= is set) when a
48 * hung task is detected:
49 */
50unsigned int __read_mostly sysctl_hung_task_panic =
51 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
52
53static int __init hung_task_panic_setup(char *str)
54{
55 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
56
57 if (rc)
58 return rc;
59 return 1;
60}
61__setup("hung_task_panic=", hung_task_panic_setup);
62
63static int
64hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
65{
66 did_panic = 1;
67
68 return NOTIFY_DONE;
69}
70
71static struct notifier_block panic_block = {
72 .notifier_call = hung_task_panic,
73};
74
75static void check_hung_task(struct task_struct *t, unsigned long timeout)
76{
77 unsigned long switch_count = t->nvcsw + t->nivcsw;
78
79 /*
80 * Ensure the task is not frozen.
81 * Also, skip vfork and any other user process that freezer should skip.
82 */
83 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
84 return;
85
86 /*
87 * When a freshly created task is scheduled once, changes its state to
88 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
89 * musn't be checked.
90 */
91 if (unlikely(!switch_count))
92 return;
93
94 if (switch_count != t->last_switch_count) {
95 t->last_switch_count = switch_count;
96 return;
97 }
98
99 trace_sched_process_hang(t);
100
101 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
102 return;
103
104 /*
105 * Ok, the task did not get scheduled for more than 2 minutes,
106 * complain:
107 */
108 if (sysctl_hung_task_warnings) {
109 if (sysctl_hung_task_warnings > 0)
110 sysctl_hung_task_warnings--;
111 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
112 t->comm, t->pid, timeout);
113 pr_err(" %s %s %.*s\n",
114 print_tainted(), init_utsname()->release,
115 (int)strcspn(init_utsname()->version, " "),
116 init_utsname()->version);
117 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
118 " disables this message.\n");
119 sched_show_task(t);
120 debug_show_all_locks();
121 }
122
123 touch_nmi_watchdog();
124
125 if (sysctl_hung_task_panic) {
126 trigger_all_cpu_backtrace();
127 panic("hung_task: blocked tasks");
128 }
129}
130
131/*
132 * To avoid extending the RCU grace period for an unbounded amount of time,
133 * periodically exit the critical section and enter a new one.
134 *
135 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
136 * to exit the grace period. For classic RCU, a reschedule is required.
137 */
138static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
139{
140 bool can_cont;
141
142 get_task_struct(g);
143 get_task_struct(t);
144 rcu_read_unlock();
145 cond_resched();
146 rcu_read_lock();
147 can_cont = pid_alive(g) && pid_alive(t);
148 put_task_struct(t);
149 put_task_struct(g);
150
151 return can_cont;
152}
153
154/*
155 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
156 * a really long time (120 seconds). If that happens, print out
157 * a warning.
158 */
159static void check_hung_uninterruptible_tasks(unsigned long timeout)
160{
161 int max_count = sysctl_hung_task_check_count;
162 int batch_count = HUNG_TASK_BATCHING;
163 struct task_struct *g, *t;
164
165 /*
166 * If the system crashed already then all bets are off,
167 * do not report extra hung tasks:
168 */
169 if (test_taint(TAINT_DIE) || did_panic)
170 return;
171
172 rcu_read_lock();
173 for_each_process_thread(g, t) {
174 if (!max_count--)
175 goto unlock;
176 if (!--batch_count) {
177 batch_count = HUNG_TASK_BATCHING;
178 if (!rcu_lock_break(g, t))
179 goto unlock;
180 }
181 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
182 if (t->state == TASK_UNINTERRUPTIBLE)
183 check_hung_task(t, timeout);
184 }
185 unlock:
186 rcu_read_unlock();
187}
188
189static long hung_timeout_jiffies(unsigned long last_checked,
190 unsigned long timeout)
191{
192 /* timeout of 0 will disable the watchdog */
193 return timeout ? last_checked - jiffies + timeout * HZ :
194 MAX_SCHEDULE_TIMEOUT;
195}
196
197/*
198 * Process updating of timeout sysctl
199 */
200int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
201 void __user *buffer,
202 size_t *lenp, loff_t *ppos)
203{
204 int ret;
205
206 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
207
208 if (ret || !write)
209 goto out;
210
211 wake_up_process(watchdog_task);
212
213 out:
214 return ret;
215}
216
217static atomic_t reset_hung_task = ATOMIC_INIT(0);
218
219void reset_hung_task_detector(void)
220{
221 atomic_set(&reset_hung_task, 1);
222}
223EXPORT_SYMBOL_GPL(reset_hung_task_detector);
224
225/*
226 * kthread which checks for tasks stuck in D state
227 */
228static int watchdog(void *dummy)
229{
230 unsigned long hung_last_checked = jiffies;
231
232 set_user_nice(current, 0);
233
234 for ( ; ; ) {
235 unsigned long timeout = sysctl_hung_task_timeout_secs;
236 long t = hung_timeout_jiffies(hung_last_checked, timeout);
237
238 if (t <= 0) {
239 if (!atomic_xchg(&reset_hung_task, 0))
240 check_hung_uninterruptible_tasks(timeout);
241 hung_last_checked = jiffies;
242 continue;
243 }
244 schedule_timeout_interruptible(t);
245 }
246
247 return 0;
248}
249
250static int __init hung_task_init(void)
251{
252 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
253 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
254
255 return 0;
256}
257subsys_initcall(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/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);