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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// 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/panic_notifier.h>
19#include <linux/sysctl.h>
20#include <linux/suspend.h>
21#include <linux/utsname.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/debug.h>
24#include <linux/sched/sysctl.h>
25
26#include <trace/events/sched.h>
27
28/*
29 * The number of tasks checked:
30 */
31int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
32
33/*
34 * Limit number of tasks checked in a batch.
35 *
36 * This value controls the preemptibility of khungtaskd since preemption
37 * is disabled during the critical section. It also controls the size of
38 * the RCU grace period. So it needs to be upper-bound.
39 */
40#define HUNG_TASK_LOCK_BREAK (HZ / 10)
41
42/*
43 * Zero means infinite timeout - no checking done:
44 */
45unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
46
47/*
48 * Zero (default value) means use sysctl_hung_task_timeout_secs:
49 */
50unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
51
52int __read_mostly sysctl_hung_task_warnings = 10;
53
54static int __read_mostly did_panic;
55static bool hung_task_show_lock;
56static bool hung_task_call_panic;
57static bool hung_task_show_all_bt;
58
59static struct task_struct *watchdog_task;
60
61#ifdef CONFIG_SMP
62/*
63 * Should we dump all CPUs backtraces in a hung task event?
64 * Defaults to 0, can be changed via sysctl.
65 */
66unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
67#endif /* CONFIG_SMP */
68
69/*
70 * Should we panic (and reboot, if panic_timeout= is set) when a
71 * hung task is detected:
72 */
73unsigned int __read_mostly sysctl_hung_task_panic =
74 CONFIG_BOOTPARAM_HUNG_TASK_PANIC_VALUE;
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 if (sysctl_hung_task_all_cpu_backtrace)
142 hung_task_show_all_bt = true;
143 }
144
145 touch_nmi_watchdog();
146}
147
148/*
149 * To avoid extending the RCU grace period for an unbounded amount of time,
150 * periodically exit the critical section and enter a new one.
151 *
152 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
153 * to exit the grace period. For classic RCU, a reschedule is required.
154 */
155static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
156{
157 bool can_cont;
158
159 get_task_struct(g);
160 get_task_struct(t);
161 rcu_read_unlock();
162 cond_resched();
163 rcu_read_lock();
164 can_cont = pid_alive(g) && pid_alive(t);
165 put_task_struct(t);
166 put_task_struct(g);
167
168 return can_cont;
169}
170
171/*
172 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
173 * a really long time (120 seconds). If that happens, print out
174 * a warning.
175 */
176static void check_hung_uninterruptible_tasks(unsigned long timeout)
177{
178 int max_count = sysctl_hung_task_check_count;
179 unsigned long last_break = jiffies;
180 struct task_struct *g, *t;
181
182 /*
183 * If the system crashed already then all bets are off,
184 * do not report extra hung tasks:
185 */
186 if (test_taint(TAINT_DIE) || did_panic)
187 return;
188
189 hung_task_show_lock = false;
190 rcu_read_lock();
191 for_each_process_thread(g, t) {
192 if (!max_count--)
193 goto unlock;
194 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
195 if (!rcu_lock_break(g, t))
196 goto unlock;
197 last_break = jiffies;
198 }
199 /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
200 if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
201 check_hung_task(t, timeout);
202 }
203 unlock:
204 rcu_read_unlock();
205 if (hung_task_show_lock)
206 debug_show_all_locks();
207
208 if (hung_task_show_all_bt) {
209 hung_task_show_all_bt = false;
210 trigger_all_cpu_backtrace();
211 }
212
213 if (hung_task_call_panic)
214 panic("hung_task: blocked tasks");
215}
216
217static long hung_timeout_jiffies(unsigned long last_checked,
218 unsigned long timeout)
219{
220 /* timeout of 0 will disable the watchdog */
221 return timeout ? last_checked - jiffies + timeout * HZ :
222 MAX_SCHEDULE_TIMEOUT;
223}
224
225/*
226 * Process updating of timeout sysctl
227 */
228int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
229 void *buffer, 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);