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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/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 */
31static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
32
33/*
34 * Total number of tasks detected as hung since boot:
35 */
36static unsigned long __read_mostly sysctl_hung_task_detect_count;
37
38/*
39 * Limit number of tasks checked in a batch.
40 *
41 * This value controls the preemptibility of khungtaskd since preemption
42 * is disabled during the critical section. It also controls the size of
43 * the RCU grace period. So it needs to be upper-bound.
44 */
45#define HUNG_TASK_LOCK_BREAK (HZ / 10)
46
47/*
48 * Zero means infinite timeout - no checking done:
49 */
50unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
51EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
52
53/*
54 * Zero (default value) means use sysctl_hung_task_timeout_secs:
55 */
56static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
57
58static int __read_mostly sysctl_hung_task_warnings = 10;
59
60static int __read_mostly did_panic;
61static bool hung_task_show_lock;
62static bool hung_task_call_panic;
63static bool hung_task_show_all_bt;
64
65static struct task_struct *watchdog_task;
66
67#ifdef CONFIG_SMP
68/*
69 * Should we dump all CPUs backtraces in a hung task event?
70 * Defaults to 0, can be changed via sysctl.
71 */
72static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
73#else
74#define sysctl_hung_task_all_cpu_backtrace 0
75#endif /* CONFIG_SMP */
76
77/*
78 * Should we panic (and reboot, if panic_timeout= is set) when a
79 * hung task is detected:
80 */
81static unsigned int __read_mostly sysctl_hung_task_panic =
82 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
83
84static int
85hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
86{
87 did_panic = 1;
88
89 return NOTIFY_DONE;
90}
91
92static struct notifier_block panic_block = {
93 .notifier_call = hung_task_panic,
94};
95
96static void check_hung_task(struct task_struct *t, unsigned long timeout)
97{
98 unsigned long switch_count = t->nvcsw + t->nivcsw;
99
100 /*
101 * Ensure the task is not frozen.
102 * Also, skip vfork and any other user process that freezer should skip.
103 */
104 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
105 return;
106
107 /*
108 * When a freshly created task is scheduled once, changes its state to
109 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
110 * musn't be checked.
111 */
112 if (unlikely(!switch_count))
113 return;
114
115 if (switch_count != t->last_switch_count) {
116 t->last_switch_count = switch_count;
117 t->last_switch_time = jiffies;
118 return;
119 }
120 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
121 return;
122
123 /*
124 * This counter tracks the total number of tasks detected as hung
125 * since boot.
126 */
127 sysctl_hung_task_detect_count++;
128
129 trace_sched_process_hang(t);
130
131 if (sysctl_hung_task_panic) {
132 console_verbose();
133 hung_task_show_lock = true;
134 hung_task_call_panic = true;
135 }
136
137 /*
138 * Ok, the task did not get scheduled for more than 2 minutes,
139 * complain:
140 */
141 if (sysctl_hung_task_warnings || hung_task_call_panic) {
142 if (sysctl_hung_task_warnings > 0)
143 sysctl_hung_task_warnings--;
144 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
145 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
146 pr_err(" %s %s %.*s\n",
147 print_tainted(), init_utsname()->release,
148 (int)strcspn(init_utsname()->version, " "),
149 init_utsname()->version);
150 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
151 " disables this message.\n");
152 sched_show_task(t);
153 hung_task_show_lock = true;
154
155 if (sysctl_hung_task_all_cpu_backtrace)
156 hung_task_show_all_bt = true;
157 if (!sysctl_hung_task_warnings)
158 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
159 }
160
161 touch_nmi_watchdog();
162}
163
164/*
165 * To avoid extending the RCU grace period for an unbounded amount of time,
166 * periodically exit the critical section and enter a new one.
167 *
168 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
169 * to exit the grace period. For classic RCU, a reschedule is required.
170 */
171static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
172{
173 bool can_cont;
174
175 get_task_struct(g);
176 get_task_struct(t);
177 rcu_read_unlock();
178 cond_resched();
179 rcu_read_lock();
180 can_cont = pid_alive(g) && pid_alive(t);
181 put_task_struct(t);
182 put_task_struct(g);
183
184 return can_cont;
185}
186
187/*
188 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
189 * a really long time (120 seconds). If that happens, print out
190 * a warning.
191 */
192static void check_hung_uninterruptible_tasks(unsigned long timeout)
193{
194 int max_count = sysctl_hung_task_check_count;
195 unsigned long last_break = jiffies;
196 struct task_struct *g, *t;
197
198 /*
199 * If the system crashed already then all bets are off,
200 * do not report extra hung tasks:
201 */
202 if (test_taint(TAINT_DIE) || did_panic)
203 return;
204
205 hung_task_show_lock = false;
206 rcu_read_lock();
207 for_each_process_thread(g, t) {
208 unsigned int state;
209
210 if (!max_count--)
211 goto unlock;
212 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
213 if (!rcu_lock_break(g, t))
214 goto unlock;
215 last_break = jiffies;
216 }
217 /*
218 * skip the TASK_KILLABLE tasks -- these can be killed
219 * skip the TASK_IDLE tasks -- those are genuinely idle
220 */
221 state = READ_ONCE(t->__state);
222 if ((state & TASK_UNINTERRUPTIBLE) &&
223 !(state & TASK_WAKEKILL) &&
224 !(state & TASK_NOLOAD))
225 check_hung_task(t, timeout);
226 }
227 unlock:
228 rcu_read_unlock();
229 if (hung_task_show_lock)
230 debug_show_all_locks();
231
232 if (hung_task_show_all_bt) {
233 hung_task_show_all_bt = false;
234 trigger_all_cpu_backtrace();
235 }
236
237 if (hung_task_call_panic)
238 panic("hung_task: blocked tasks");
239}
240
241static long hung_timeout_jiffies(unsigned long last_checked,
242 unsigned long timeout)
243{
244 /* timeout of 0 will disable the watchdog */
245 return timeout ? last_checked - jiffies + timeout * HZ :
246 MAX_SCHEDULE_TIMEOUT;
247}
248
249#ifdef CONFIG_SYSCTL
250/*
251 * Process updating of timeout sysctl
252 */
253static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write,
254 void *buffer,
255 size_t *lenp, loff_t *ppos)
256{
257 int ret;
258
259 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
260
261 if (ret || !write)
262 goto out;
263
264 wake_up_process(watchdog_task);
265
266 out:
267 return ret;
268}
269
270/*
271 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
272 * and hung_task_check_interval_secs
273 */
274static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
275static struct ctl_table hung_task_sysctls[] = {
276#ifdef CONFIG_SMP
277 {
278 .procname = "hung_task_all_cpu_backtrace",
279 .data = &sysctl_hung_task_all_cpu_backtrace,
280 .maxlen = sizeof(int),
281 .mode = 0644,
282 .proc_handler = proc_dointvec_minmax,
283 .extra1 = SYSCTL_ZERO,
284 .extra2 = SYSCTL_ONE,
285 },
286#endif /* CONFIG_SMP */
287 {
288 .procname = "hung_task_panic",
289 .data = &sysctl_hung_task_panic,
290 .maxlen = sizeof(int),
291 .mode = 0644,
292 .proc_handler = proc_dointvec_minmax,
293 .extra1 = SYSCTL_ZERO,
294 .extra2 = SYSCTL_ONE,
295 },
296 {
297 .procname = "hung_task_check_count",
298 .data = &sysctl_hung_task_check_count,
299 .maxlen = sizeof(int),
300 .mode = 0644,
301 .proc_handler = proc_dointvec_minmax,
302 .extra1 = SYSCTL_ZERO,
303 },
304 {
305 .procname = "hung_task_timeout_secs",
306 .data = &sysctl_hung_task_timeout_secs,
307 .maxlen = sizeof(unsigned long),
308 .mode = 0644,
309 .proc_handler = proc_dohung_task_timeout_secs,
310 .extra2 = (void *)&hung_task_timeout_max,
311 },
312 {
313 .procname = "hung_task_check_interval_secs",
314 .data = &sysctl_hung_task_check_interval_secs,
315 .maxlen = sizeof(unsigned long),
316 .mode = 0644,
317 .proc_handler = proc_dohung_task_timeout_secs,
318 .extra2 = (void *)&hung_task_timeout_max,
319 },
320 {
321 .procname = "hung_task_warnings",
322 .data = &sysctl_hung_task_warnings,
323 .maxlen = sizeof(int),
324 .mode = 0644,
325 .proc_handler = proc_dointvec_minmax,
326 .extra1 = SYSCTL_NEG_ONE,
327 },
328 {
329 .procname = "hung_task_detect_count",
330 .data = &sysctl_hung_task_detect_count,
331 .maxlen = sizeof(unsigned long),
332 .mode = 0444,
333 .proc_handler = proc_doulongvec_minmax,
334 },
335};
336
337static void __init hung_task_sysctl_init(void)
338{
339 register_sysctl_init("kernel", hung_task_sysctls);
340}
341#else
342#define hung_task_sysctl_init() do { } while (0)
343#endif /* CONFIG_SYSCTL */
344
345
346static atomic_t reset_hung_task = ATOMIC_INIT(0);
347
348void reset_hung_task_detector(void)
349{
350 atomic_set(&reset_hung_task, 1);
351}
352EXPORT_SYMBOL_GPL(reset_hung_task_detector);
353
354static bool hung_detector_suspended;
355
356static int hungtask_pm_notify(struct notifier_block *self,
357 unsigned long action, void *hcpu)
358{
359 switch (action) {
360 case PM_SUSPEND_PREPARE:
361 case PM_HIBERNATION_PREPARE:
362 case PM_RESTORE_PREPARE:
363 hung_detector_suspended = true;
364 break;
365 case PM_POST_SUSPEND:
366 case PM_POST_HIBERNATION:
367 case PM_POST_RESTORE:
368 hung_detector_suspended = false;
369 break;
370 default:
371 break;
372 }
373 return NOTIFY_OK;
374}
375
376/*
377 * kthread which checks for tasks stuck in D state
378 */
379static int watchdog(void *dummy)
380{
381 unsigned long hung_last_checked = jiffies;
382
383 set_user_nice(current, 0);
384
385 for ( ; ; ) {
386 unsigned long timeout = sysctl_hung_task_timeout_secs;
387 unsigned long interval = sysctl_hung_task_check_interval_secs;
388 long t;
389
390 if (interval == 0)
391 interval = timeout;
392 interval = min_t(unsigned long, interval, timeout);
393 t = hung_timeout_jiffies(hung_last_checked, interval);
394 if (t <= 0) {
395 if (!atomic_xchg(&reset_hung_task, 0) &&
396 !hung_detector_suspended)
397 check_hung_uninterruptible_tasks(timeout);
398 hung_last_checked = jiffies;
399 continue;
400 }
401 schedule_timeout_interruptible(t);
402 }
403
404 return 0;
405}
406
407static int __init hung_task_init(void)
408{
409 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
410
411 /* Disable hung task detector on suspend */
412 pm_notifier(hungtask_pm_notify, 0);
413
414 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
415 hung_task_sysctl_init();
416
417 return 0;
418}
419subsys_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);