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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 sysctl_hung_task_panic = simple_strtoul(str, NULL, 0);
56
57 return 1;
58}
59__setup("hung_task_panic=", hung_task_panic_setup);
60
61static int
62hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
63{
64 did_panic = 1;
65
66 return NOTIFY_DONE;
67}
68
69static struct notifier_block panic_block = {
70 .notifier_call = hung_task_panic,
71};
72
73static void check_hung_task(struct task_struct *t, unsigned long timeout)
74{
75 unsigned long switch_count = t->nvcsw + t->nivcsw;
76
77 /*
78 * Ensure the task is not frozen.
79 * Also, skip vfork and any other user process that freezer should skip.
80 */
81 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
82 return;
83
84 /*
85 * When a freshly created task is scheduled once, changes its state to
86 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
87 * musn't be checked.
88 */
89 if (unlikely(!switch_count))
90 return;
91
92 if (switch_count != t->last_switch_count) {
93 t->last_switch_count = switch_count;
94 return;
95 }
96
97 trace_sched_process_hang(t);
98
99 if (!sysctl_hung_task_warnings)
100 return;
101
102 if (sysctl_hung_task_warnings > 0)
103 sysctl_hung_task_warnings--;
104
105 /*
106 * Ok, the task did not get scheduled for more than 2 minutes,
107 * complain:
108 */
109 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
110 t->comm, t->pid, timeout);
111 pr_err(" %s %s %.*s\n",
112 print_tainted(), init_utsname()->release,
113 (int)strcspn(init_utsname()->version, " "),
114 init_utsname()->version);
115 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
116 " disables this message.\n");
117 sched_show_task(t);
118 debug_show_held_locks(t);
119
120 touch_nmi_watchdog();
121
122 if (sysctl_hung_task_panic) {
123 trigger_all_cpu_backtrace();
124 panic("hung_task: blocked tasks");
125 }
126}
127
128/*
129 * To avoid extending the RCU grace period for an unbounded amount of time,
130 * periodically exit the critical section and enter a new one.
131 *
132 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
133 * to exit the grace period. For classic RCU, a reschedule is required.
134 */
135static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
136{
137 bool can_cont;
138
139 get_task_struct(g);
140 get_task_struct(t);
141 rcu_read_unlock();
142 cond_resched();
143 rcu_read_lock();
144 can_cont = pid_alive(g) && pid_alive(t);
145 put_task_struct(t);
146 put_task_struct(g);
147
148 return can_cont;
149}
150
151/*
152 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
153 * a really long time (120 seconds). If that happens, print out
154 * a warning.
155 */
156static void check_hung_uninterruptible_tasks(unsigned long timeout)
157{
158 int max_count = sysctl_hung_task_check_count;
159 int batch_count = HUNG_TASK_BATCHING;
160 struct task_struct *g, *t;
161
162 /*
163 * If the system crashed already then all bets are off,
164 * do not report extra hung tasks:
165 */
166 if (test_taint(TAINT_DIE) || did_panic)
167 return;
168
169 rcu_read_lock();
170 do_each_thread(g, t) {
171 if (!max_count--)
172 goto unlock;
173 if (!--batch_count) {
174 batch_count = HUNG_TASK_BATCHING;
175 if (!rcu_lock_break(g, t))
176 goto unlock;
177 }
178 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
179 if (t->state == TASK_UNINTERRUPTIBLE)
180 check_hung_task(t, timeout);
181 } while_each_thread(g, t);
182 unlock:
183 rcu_read_unlock();
184}
185
186static unsigned long timeout_jiffies(unsigned long timeout)
187{
188 /* timeout of 0 will disable the watchdog */
189 return timeout ? timeout * HZ : MAX_SCHEDULE_TIMEOUT;
190}
191
192/*
193 * Process updating of timeout sysctl
194 */
195int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
196 void __user *buffer,
197 size_t *lenp, loff_t *ppos)
198{
199 int ret;
200
201 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
202
203 if (ret || !write)
204 goto out;
205
206 wake_up_process(watchdog_task);
207
208 out:
209 return ret;
210}
211
212static atomic_t reset_hung_task = ATOMIC_INIT(0);
213
214void reset_hung_task_detector(void)
215{
216 atomic_set(&reset_hung_task, 1);
217}
218EXPORT_SYMBOL_GPL(reset_hung_task_detector);
219
220/*
221 * kthread which checks for tasks stuck in D state
222 */
223static int watchdog(void *dummy)
224{
225 set_user_nice(current, 0);
226
227 for ( ; ; ) {
228 unsigned long timeout = sysctl_hung_task_timeout_secs;
229
230 while (schedule_timeout_interruptible(timeout_jiffies(timeout)))
231 timeout = sysctl_hung_task_timeout_secs;
232
233 if (atomic_xchg(&reset_hung_task, 0))
234 continue;
235
236 check_hung_uninterruptible_tasks(timeout);
237 }
238
239 return 0;
240}
241
242static int __init hung_task_init(void)
243{
244 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
245 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
246
247 return 0;
248}
249subsys_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#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)
102 return;
103
104 if (sysctl_hung_task_warnings > 0)
105 sysctl_hung_task_warnings--;
106
107 /*
108 * Ok, the task did not get scheduled for more than 2 minutes,
109 * complain:
110 */
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_held_locks(t);
121
122 touch_nmi_watchdog();
123
124 if (sysctl_hung_task_panic) {
125 trigger_all_cpu_backtrace();
126 panic("hung_task: blocked tasks");
127 }
128}
129
130/*
131 * To avoid extending the RCU grace period for an unbounded amount of time,
132 * periodically exit the critical section and enter a new one.
133 *
134 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
135 * to exit the grace period. For classic RCU, a reschedule is required.
136 */
137static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
138{
139 bool can_cont;
140
141 get_task_struct(g);
142 get_task_struct(t);
143 rcu_read_unlock();
144 cond_resched();
145 rcu_read_lock();
146 can_cont = pid_alive(g) && pid_alive(t);
147 put_task_struct(t);
148 put_task_struct(g);
149
150 return can_cont;
151}
152
153/*
154 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
155 * a really long time (120 seconds). If that happens, print out
156 * a warning.
157 */
158static void check_hung_uninterruptible_tasks(unsigned long timeout)
159{
160 int max_count = sysctl_hung_task_check_count;
161 int batch_count = HUNG_TASK_BATCHING;
162 struct task_struct *g, *t;
163
164 /*
165 * If the system crashed already then all bets are off,
166 * do not report extra hung tasks:
167 */
168 if (test_taint(TAINT_DIE) || did_panic)
169 return;
170
171 rcu_read_lock();
172 for_each_process_thread(g, t) {
173 if (!max_count--)
174 goto unlock;
175 if (!--batch_count) {
176 batch_count = HUNG_TASK_BATCHING;
177 if (!rcu_lock_break(g, t))
178 goto unlock;
179 }
180 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
181 if (t->state == TASK_UNINTERRUPTIBLE)
182 check_hung_task(t, timeout);
183 }
184 unlock:
185 rcu_read_unlock();
186}
187
188static long hung_timeout_jiffies(unsigned long last_checked,
189 unsigned long timeout)
190{
191 /* timeout of 0 will disable the watchdog */
192 return timeout ? last_checked - jiffies + timeout * HZ :
193 MAX_SCHEDULE_TIMEOUT;
194}
195
196/*
197 * Process updating of timeout sysctl
198 */
199int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
200 void __user *buffer,
201 size_t *lenp, loff_t *ppos)
202{
203 int ret;
204
205 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
206
207 if (ret || !write)
208 goto out;
209
210 wake_up_process(watchdog_task);
211
212 out:
213 return ret;
214}
215
216static atomic_t reset_hung_task = ATOMIC_INIT(0);
217
218void reset_hung_task_detector(void)
219{
220 atomic_set(&reset_hung_task, 1);
221}
222EXPORT_SYMBOL_GPL(reset_hung_task_detector);
223
224/*
225 * kthread which checks for tasks stuck in D state
226 */
227static int watchdog(void *dummy)
228{
229 unsigned long hung_last_checked = jiffies;
230
231 set_user_nice(current, 0);
232
233 for ( ; ; ) {
234 unsigned long timeout = sysctl_hung_task_timeout_secs;
235 long t = hung_timeout_jiffies(hung_last_checked, timeout);
236
237 if (t <= 0) {
238 if (!atomic_xchg(&reset_hung_task, 0))
239 check_hung_uninterruptible_tasks(timeout);
240 hung_last_checked = jiffies;
241 continue;
242 }
243 schedule_timeout_interruptible(t);
244 }
245
246 return 0;
247}
248
249static int __init hung_task_init(void)
250{
251 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
252 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
253
254 return 0;
255}
256subsys_initcall(hung_task_init);