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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// 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);