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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 <linux/sched/signal.h>
20#include <linux/sched/debug.h>
21
22#include <trace/events/sched.h>
23
24/*
25 * The number of tasks checked:
26 */
27int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
28
29/*
30 * Limit number of tasks checked in a batch.
31 *
32 * This value controls the preemptibility of khungtaskd since preemption
33 * is disabled during the critical section. It also controls the size of
34 * the RCU grace period. So it needs to be upper-bound.
35 */
36#define HUNG_TASK_BATCHING 1024
37
38/*
39 * Zero means infinite timeout - no checking done:
40 */
41unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
42
43int __read_mostly sysctl_hung_task_warnings = 10;
44
45static int __read_mostly did_panic;
46static bool hung_task_show_lock;
47
48static struct task_struct *watchdog_task;
49
50/*
51 * Should we panic (and reboot, if panic_timeout= is set) when a
52 * hung task is detected:
53 */
54unsigned int __read_mostly sysctl_hung_task_panic =
55 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
56
57static int __init hung_task_panic_setup(char *str)
58{
59 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
60
61 if (rc)
62 return rc;
63 return 1;
64}
65__setup("hung_task_panic=", hung_task_panic_setup);
66
67static int
68hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
69{
70 did_panic = 1;
71
72 return NOTIFY_DONE;
73}
74
75static struct notifier_block panic_block = {
76 .notifier_call = hung_task_panic,
77};
78
79static void check_hung_task(struct task_struct *t, unsigned long timeout)
80{
81 unsigned long switch_count = t->nvcsw + t->nivcsw;
82
83 /*
84 * Ensure the task is not frozen.
85 * Also, skip vfork and any other user process that freezer should skip.
86 */
87 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
88 return;
89
90 /*
91 * When a freshly created task is scheduled once, changes its state to
92 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
93 * musn't be checked.
94 */
95 if (unlikely(!switch_count))
96 return;
97
98 if (switch_count != t->last_switch_count) {
99 t->last_switch_count = switch_count;
100 return;
101 }
102
103 trace_sched_process_hang(t);
104
105 if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
106 return;
107
108 /*
109 * Ok, the task did not get scheduled for more than 2 minutes,
110 * complain:
111 */
112 if (sysctl_hung_task_warnings) {
113 if (sysctl_hung_task_warnings > 0)
114 sysctl_hung_task_warnings--;
115 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
116 t->comm, t->pid, timeout);
117 pr_err(" %s %s %.*s\n",
118 print_tainted(), init_utsname()->release,
119 (int)strcspn(init_utsname()->version, " "),
120 init_utsname()->version);
121 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
122 " disables this message.\n");
123 sched_show_task(t);
124 hung_task_show_lock = true;
125 }
126
127 touch_nmi_watchdog();
128
129 if (sysctl_hung_task_panic) {
130 if (hung_task_show_lock)
131 debug_show_all_locks();
132 trigger_all_cpu_backtrace();
133 panic("hung_task: blocked tasks");
134 }
135}
136
137/*
138 * To avoid extending the RCU grace period for an unbounded amount of time,
139 * periodically exit the critical section and enter a new one.
140 *
141 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
142 * to exit the grace period. For classic RCU, a reschedule is required.
143 */
144static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
145{
146 bool can_cont;
147
148 get_task_struct(g);
149 get_task_struct(t);
150 rcu_read_unlock();
151 cond_resched();
152 rcu_read_lock();
153 can_cont = pid_alive(g) && pid_alive(t);
154 put_task_struct(t);
155 put_task_struct(g);
156
157 return can_cont;
158}
159
160/*
161 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
162 * a really long time (120 seconds). If that happens, print out
163 * a warning.
164 */
165static void check_hung_uninterruptible_tasks(unsigned long timeout)
166{
167 int max_count = sysctl_hung_task_check_count;
168 int batch_count = HUNG_TASK_BATCHING;
169 struct task_struct *g, *t;
170
171 /*
172 * If the system crashed already then all bets are off,
173 * do not report extra hung tasks:
174 */
175 if (test_taint(TAINT_DIE) || did_panic)
176 return;
177
178 hung_task_show_lock = false;
179 rcu_read_lock();
180 for_each_process_thread(g, t) {
181 if (!max_count--)
182 goto unlock;
183 if (!--batch_count) {
184 batch_count = HUNG_TASK_BATCHING;
185 if (!rcu_lock_break(g, t))
186 goto unlock;
187 }
188 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
189 if (t->state == TASK_UNINTERRUPTIBLE)
190 check_hung_task(t, timeout);
191 }
192 unlock:
193 rcu_read_unlock();
194 if (hung_task_show_lock)
195 debug_show_all_locks();
196}
197
198static long hung_timeout_jiffies(unsigned long last_checked,
199 unsigned long timeout)
200{
201 /* timeout of 0 will disable the watchdog */
202 return timeout ? last_checked - jiffies + timeout * HZ :
203 MAX_SCHEDULE_TIMEOUT;
204}
205
206/*
207 * Process updating of timeout sysctl
208 */
209int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
210 void __user *buffer,
211 size_t *lenp, loff_t *ppos)
212{
213 int ret;
214
215 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
216
217 if (ret || !write)
218 goto out;
219
220 wake_up_process(watchdog_task);
221
222 out:
223 return ret;
224}
225
226static atomic_t reset_hung_task = ATOMIC_INIT(0);
227
228void reset_hung_task_detector(void)
229{
230 atomic_set(&reset_hung_task, 1);
231}
232EXPORT_SYMBOL_GPL(reset_hung_task_detector);
233
234/*
235 * kthread which checks for tasks stuck in D state
236 */
237static int watchdog(void *dummy)
238{
239 unsigned long hung_last_checked = jiffies;
240
241 set_user_nice(current, 0);
242
243 for ( ; ; ) {
244 unsigned long timeout = sysctl_hung_task_timeout_secs;
245 long t = hung_timeout_jiffies(hung_last_checked, timeout);
246
247 if (t <= 0) {
248 if (!atomic_xchg(&reset_hung_task, 0))
249 check_hung_uninterruptible_tasks(timeout);
250 hung_last_checked = jiffies;
251 continue;
252 }
253 schedule_timeout_interruptible(t);
254 }
255
256 return 0;
257}
258
259static int __init hung_task_init(void)
260{
261 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
262 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
263
264 return 0;
265}
266subsys_initcall(hung_task_init);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Detect Hung Task
4 *
5 * kernel/hung_task.c - kernel thread for detecting tasks stuck in D state
6 *
7 */
8
9#include <linux/mm.h>
10#include <linux/cpu.h>
11#include <linux/nmi.h>
12#include <linux/init.h>
13#include <linux/delay.h>
14#include <linux/freezer.h>
15#include <linux/kthread.h>
16#include <linux/lockdep.h>
17#include <linux/export.h>
18#include <linux/sysctl.h>
19#include <linux/suspend.h>
20#include <linux/utsname.h>
21#include <linux/sched/signal.h>
22#include <linux/sched/debug.h>
23#include <linux/sched/sysctl.h>
24
25#include <trace/events/sched.h>
26
27/*
28 * The number of tasks checked:
29 */
30int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
31
32/*
33 * Limit number of tasks checked in a batch.
34 *
35 * This value controls the preemptibility of khungtaskd since preemption
36 * is disabled during the critical section. It also controls the size of
37 * the RCU grace period. So it needs to be upper-bound.
38 */
39#define HUNG_TASK_LOCK_BREAK (HZ / 10)
40
41/*
42 * Zero means infinite timeout - no checking done:
43 */
44unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
45
46/*
47 * Zero (default value) means use sysctl_hung_task_timeout_secs:
48 */
49unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
50
51int __read_mostly sysctl_hung_task_warnings = 10;
52
53static int __read_mostly did_panic;
54static bool hung_task_show_lock;
55static bool hung_task_call_panic;
56static bool hung_task_show_all_bt;
57
58static struct task_struct *watchdog_task;
59
60#ifdef CONFIG_SMP
61/*
62 * Should we dump all CPUs backtraces in a hung task event?
63 * Defaults to 0, can be changed via sysctl.
64 */
65unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
66#endif /* CONFIG_SMP */
67
68/*
69 * Should we panic (and reboot, if panic_timeout= is set) when a
70 * hung task is detected:
71 */
72unsigned int __read_mostly sysctl_hung_task_panic =
73 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
74
75static int
76hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
77{
78 did_panic = 1;
79
80 return NOTIFY_DONE;
81}
82
83static struct notifier_block panic_block = {
84 .notifier_call = hung_task_panic,
85};
86
87static void check_hung_task(struct task_struct *t, unsigned long timeout)
88{
89 unsigned long switch_count = t->nvcsw + t->nivcsw;
90
91 /*
92 * Ensure the task is not frozen.
93 * Also, skip vfork and any other user process that freezer should skip.
94 */
95 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
96 return;
97
98 /*
99 * When a freshly created task is scheduled once, changes its state to
100 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
101 * musn't be checked.
102 */
103 if (unlikely(!switch_count))
104 return;
105
106 if (switch_count != t->last_switch_count) {
107 t->last_switch_count = switch_count;
108 t->last_switch_time = jiffies;
109 return;
110 }
111 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
112 return;
113
114 trace_sched_process_hang(t);
115
116 if (sysctl_hung_task_panic) {
117 console_verbose();
118 hung_task_show_lock = true;
119 hung_task_call_panic = true;
120 }
121
122 /*
123 * Ok, the task did not get scheduled for more than 2 minutes,
124 * complain:
125 */
126 if (sysctl_hung_task_warnings) {
127 if (sysctl_hung_task_warnings > 0)
128 sysctl_hung_task_warnings--;
129 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
130 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
131 pr_err(" %s %s %.*s\n",
132 print_tainted(), init_utsname()->release,
133 (int)strcspn(init_utsname()->version, " "),
134 init_utsname()->version);
135 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
136 " disables this message.\n");
137 sched_show_task(t);
138 hung_task_show_lock = true;
139
140 if (sysctl_hung_task_all_cpu_backtrace)
141 hung_task_show_all_bt = true;
142 }
143
144 touch_nmi_watchdog();
145}
146
147/*
148 * To avoid extending the RCU grace period for an unbounded amount of time,
149 * periodically exit the critical section and enter a new one.
150 *
151 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
152 * to exit the grace period. For classic RCU, a reschedule is required.
153 */
154static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
155{
156 bool can_cont;
157
158 get_task_struct(g);
159 get_task_struct(t);
160 rcu_read_unlock();
161 cond_resched();
162 rcu_read_lock();
163 can_cont = pid_alive(g) && pid_alive(t);
164 put_task_struct(t);
165 put_task_struct(g);
166
167 return can_cont;
168}
169
170/*
171 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
172 * a really long time (120 seconds). If that happens, print out
173 * a warning.
174 */
175static void check_hung_uninterruptible_tasks(unsigned long timeout)
176{
177 int max_count = sysctl_hung_task_check_count;
178 unsigned long last_break = jiffies;
179 struct task_struct *g, *t;
180
181 /*
182 * If the system crashed already then all bets are off,
183 * do not report extra hung tasks:
184 */
185 if (test_taint(TAINT_DIE) || did_panic)
186 return;
187
188 hung_task_show_lock = false;
189 rcu_read_lock();
190 for_each_process_thread(g, t) {
191 if (!max_count--)
192 goto unlock;
193 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
194 if (!rcu_lock_break(g, t))
195 goto unlock;
196 last_break = jiffies;
197 }
198 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
199 if (t->state == TASK_UNINTERRUPTIBLE)
200 check_hung_task(t, timeout);
201 }
202 unlock:
203 rcu_read_unlock();
204 if (hung_task_show_lock)
205 debug_show_all_locks();
206
207 if (hung_task_show_all_bt) {
208 hung_task_show_all_bt = false;
209 trigger_all_cpu_backtrace();
210 }
211
212 if (hung_task_call_panic)
213 panic("hung_task: blocked tasks");
214}
215
216static long hung_timeout_jiffies(unsigned long last_checked,
217 unsigned long timeout)
218{
219 /* timeout of 0 will disable the watchdog */
220 return timeout ? last_checked - jiffies + timeout * HZ :
221 MAX_SCHEDULE_TIMEOUT;
222}
223
224/*
225 * Process updating of timeout sysctl
226 */
227int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
228 void __user *buffer,
229 size_t *lenp, loff_t *ppos)
230{
231 int ret;
232
233 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
234
235 if (ret || !write)
236 goto out;
237
238 wake_up_process(watchdog_task);
239
240 out:
241 return ret;
242}
243
244static atomic_t reset_hung_task = ATOMIC_INIT(0);
245
246void reset_hung_task_detector(void)
247{
248 atomic_set(&reset_hung_task, 1);
249}
250EXPORT_SYMBOL_GPL(reset_hung_task_detector);
251
252static bool hung_detector_suspended;
253
254static int hungtask_pm_notify(struct notifier_block *self,
255 unsigned long action, void *hcpu)
256{
257 switch (action) {
258 case PM_SUSPEND_PREPARE:
259 case PM_HIBERNATION_PREPARE:
260 case PM_RESTORE_PREPARE:
261 hung_detector_suspended = true;
262 break;
263 case PM_POST_SUSPEND:
264 case PM_POST_HIBERNATION:
265 case PM_POST_RESTORE:
266 hung_detector_suspended = false;
267 break;
268 default:
269 break;
270 }
271 return NOTIFY_OK;
272}
273
274/*
275 * kthread which checks for tasks stuck in D state
276 */
277static int watchdog(void *dummy)
278{
279 unsigned long hung_last_checked = jiffies;
280
281 set_user_nice(current, 0);
282
283 for ( ; ; ) {
284 unsigned long timeout = sysctl_hung_task_timeout_secs;
285 unsigned long interval = sysctl_hung_task_check_interval_secs;
286 long t;
287
288 if (interval == 0)
289 interval = timeout;
290 interval = min_t(unsigned long, interval, timeout);
291 t = hung_timeout_jiffies(hung_last_checked, interval);
292 if (t <= 0) {
293 if (!atomic_xchg(&reset_hung_task, 0) &&
294 !hung_detector_suspended)
295 check_hung_uninterruptible_tasks(timeout);
296 hung_last_checked = jiffies;
297 continue;
298 }
299 schedule_timeout_interruptible(t);
300 }
301
302 return 0;
303}
304
305static int __init hung_task_init(void)
306{
307 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
308
309 /* Disable hung task detector on suspend */
310 pm_notifier(hungtask_pm_notify, 0);
311
312 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
313
314 return 0;
315}
316subsys_initcall(hung_task_init);