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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;
56
57static struct task_struct *watchdog_task;
58
59/*
60 * Should we panic (and reboot, if panic_timeout= is set) when a
61 * hung task is detected:
62 */
63unsigned int __read_mostly sysctl_hung_task_panic =
64 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
65
66static int __init hung_task_panic_setup(char *str)
67{
68 int rc = kstrtouint(str, 0, &sysctl_hung_task_panic);
69
70 if (rc)
71 return rc;
72 return 1;
73}
74__setup("hung_task_panic=", hung_task_panic_setup);
75
76static int
77hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
78{
79 did_panic = 1;
80
81 return NOTIFY_DONE;
82}
83
84static struct notifier_block panic_block = {
85 .notifier_call = hung_task_panic,
86};
87
88static void check_hung_task(struct task_struct *t, unsigned long timeout)
89{
90 unsigned long switch_count = t->nvcsw + t->nivcsw;
91
92 /*
93 * Ensure the task is not frozen.
94 * Also, skip vfork and any other user process that freezer should skip.
95 */
96 if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
97 return;
98
99 /*
100 * When a freshly created task is scheduled once, changes its state to
101 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
102 * musn't be checked.
103 */
104 if (unlikely(!switch_count))
105 return;
106
107 if (switch_count != t->last_switch_count) {
108 t->last_switch_count = switch_count;
109 t->last_switch_time = jiffies;
110 return;
111 }
112 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
113 return;
114
115 trace_sched_process_hang(t);
116
117 if (sysctl_hung_task_panic) {
118 console_verbose();
119 hung_task_show_lock = true;
120 hung_task_call_panic = true;
121 }
122
123 /*
124 * Ok, the task did not get scheduled for more than 2 minutes,
125 * complain:
126 */
127 if (sysctl_hung_task_warnings) {
128 if (sysctl_hung_task_warnings > 0)
129 sysctl_hung_task_warnings--;
130 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
131 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
132 pr_err(" %s %s %.*s\n",
133 print_tainted(), init_utsname()->release,
134 (int)strcspn(init_utsname()->version, " "),
135 init_utsname()->version);
136 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
137 " disables this message.\n");
138 sched_show_task(t);
139 hung_task_show_lock = true;
140 }
141
142 touch_nmi_watchdog();
143}
144
145/*
146 * To avoid extending the RCU grace period for an unbounded amount of time,
147 * periodically exit the critical section and enter a new one.
148 *
149 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
150 * to exit the grace period. For classic RCU, a reschedule is required.
151 */
152static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
153{
154 bool can_cont;
155
156 get_task_struct(g);
157 get_task_struct(t);
158 rcu_read_unlock();
159 cond_resched();
160 rcu_read_lock();
161 can_cont = pid_alive(g) && pid_alive(t);
162 put_task_struct(t);
163 put_task_struct(g);
164
165 return can_cont;
166}
167
168/*
169 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
170 * a really long time (120 seconds). If that happens, print out
171 * a warning.
172 */
173static void check_hung_uninterruptible_tasks(unsigned long timeout)
174{
175 int max_count = sysctl_hung_task_check_count;
176 unsigned long last_break = jiffies;
177 struct task_struct *g, *t;
178
179 /*
180 * If the system crashed already then all bets are off,
181 * do not report extra hung tasks:
182 */
183 if (test_taint(TAINT_DIE) || did_panic)
184 return;
185
186 hung_task_show_lock = false;
187 rcu_read_lock();
188 for_each_process_thread(g, t) {
189 if (!max_count--)
190 goto unlock;
191 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
192 if (!rcu_lock_break(g, t))
193 goto unlock;
194 last_break = jiffies;
195 }
196 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
197 if (t->state == TASK_UNINTERRUPTIBLE)
198 check_hung_task(t, timeout);
199 }
200 unlock:
201 rcu_read_unlock();
202 if (hung_task_show_lock)
203 debug_show_all_locks();
204 if (hung_task_call_panic) {
205 trigger_all_cpu_backtrace();
206 panic("hung_task: blocked tasks");
207 }
208}
209
210static long hung_timeout_jiffies(unsigned long last_checked,
211 unsigned long timeout)
212{
213 /* timeout of 0 will disable the watchdog */
214 return timeout ? last_checked - jiffies + timeout * HZ :
215 MAX_SCHEDULE_TIMEOUT;
216}
217
218/*
219 * Process updating of timeout sysctl
220 */
221int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
222 void __user *buffer,
223 size_t *lenp, loff_t *ppos)
224{
225 int ret;
226
227 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
228
229 if (ret || !write)
230 goto out;
231
232 wake_up_process(watchdog_task);
233
234 out:
235 return ret;
236}
237
238static atomic_t reset_hung_task = ATOMIC_INIT(0);
239
240void reset_hung_task_detector(void)
241{
242 atomic_set(&reset_hung_task, 1);
243}
244EXPORT_SYMBOL_GPL(reset_hung_task_detector);
245
246static bool hung_detector_suspended;
247
248static int hungtask_pm_notify(struct notifier_block *self,
249 unsigned long action, void *hcpu)
250{
251 switch (action) {
252 case PM_SUSPEND_PREPARE:
253 case PM_HIBERNATION_PREPARE:
254 case PM_RESTORE_PREPARE:
255 hung_detector_suspended = true;
256 break;
257 case PM_POST_SUSPEND:
258 case PM_POST_HIBERNATION:
259 case PM_POST_RESTORE:
260 hung_detector_suspended = false;
261 break;
262 default:
263 break;
264 }
265 return NOTIFY_OK;
266}
267
268/*
269 * kthread which checks for tasks stuck in D state
270 */
271static int watchdog(void *dummy)
272{
273 unsigned long hung_last_checked = jiffies;
274
275 set_user_nice(current, 0);
276
277 for ( ; ; ) {
278 unsigned long timeout = sysctl_hung_task_timeout_secs;
279 unsigned long interval = sysctl_hung_task_check_interval_secs;
280 long t;
281
282 if (interval == 0)
283 interval = timeout;
284 interval = min_t(unsigned long, interval, timeout);
285 t = hung_timeout_jiffies(hung_last_checked, interval);
286 if (t <= 0) {
287 if (!atomic_xchg(&reset_hung_task, 0) &&
288 !hung_detector_suspended)
289 check_hung_uninterruptible_tasks(timeout);
290 hung_last_checked = jiffies;
291 continue;
292 }
293 schedule_timeout_interruptible(t);
294 }
295
296 return 0;
297}
298
299static int __init hung_task_init(void)
300{
301 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
302
303 /* Disable hung task detector on suspend */
304 pm_notifier(hungtask_pm_notify, 0);
305
306 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
307
308 return 0;
309}
310subsys_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 && !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);