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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 */
31static int __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;
46EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
47
48/*
49 * Zero (default value) means use sysctl_hung_task_timeout_secs:
50 */
51static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
52
53static int __read_mostly sysctl_hung_task_warnings = 10;
54
55static int __read_mostly did_panic;
56static bool hung_task_show_lock;
57static bool hung_task_call_panic;
58static bool hung_task_show_all_bt;
59
60static struct task_struct *watchdog_task;
61
62#ifdef CONFIG_SMP
63/*
64 * Should we dump all CPUs backtraces in a hung task event?
65 * Defaults to 0, can be changed via sysctl.
66 */
67static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
68#else
69#define sysctl_hung_task_all_cpu_backtrace 0
70#endif /* CONFIG_SMP */
71
72/*
73 * Should we panic (and reboot, if panic_timeout= is set) when a
74 * hung task is detected:
75 */
76static unsigned int __read_mostly sysctl_hung_task_panic =
77 IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
78
79static int
80hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
81{
82 did_panic = 1;
83
84 return NOTIFY_DONE;
85}
86
87static struct notifier_block panic_block = {
88 .notifier_call = hung_task_panic,
89};
90
91static void check_hung_task(struct task_struct *t, unsigned long timeout)
92{
93 unsigned long switch_count = t->nvcsw + t->nivcsw;
94
95 /*
96 * Ensure the task is not frozen.
97 * Also, skip vfork and any other user process that freezer should skip.
98 */
99 if (unlikely(READ_ONCE(t->__state) & TASK_FROZEN))
100 return;
101
102 /*
103 * When a freshly created task is scheduled once, changes its state to
104 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
105 * musn't be checked.
106 */
107 if (unlikely(!switch_count))
108 return;
109
110 if (switch_count != t->last_switch_count) {
111 t->last_switch_count = switch_count;
112 t->last_switch_time = jiffies;
113 return;
114 }
115 if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
116 return;
117
118 trace_sched_process_hang(t);
119
120 if (sysctl_hung_task_panic) {
121 console_verbose();
122 hung_task_show_lock = true;
123 hung_task_call_panic = true;
124 }
125
126 /*
127 * Ok, the task did not get scheduled for more than 2 minutes,
128 * complain:
129 */
130 if (sysctl_hung_task_warnings) {
131 if (sysctl_hung_task_warnings > 0)
132 sysctl_hung_task_warnings--;
133 pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
134 t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
135 pr_err(" %s %s %.*s\n",
136 print_tainted(), init_utsname()->release,
137 (int)strcspn(init_utsname()->version, " "),
138 init_utsname()->version);
139 pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
140 " disables this message.\n");
141 sched_show_task(t);
142 hung_task_show_lock = true;
143
144 if (sysctl_hung_task_all_cpu_backtrace)
145 hung_task_show_all_bt = true;
146 if (!sysctl_hung_task_warnings)
147 pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
148 }
149
150 touch_nmi_watchdog();
151}
152
153/*
154 * To avoid extending the RCU grace period for an unbounded amount of time,
155 * periodically exit the critical section and enter a new one.
156 *
157 * For preemptible RCU it is sufficient to call rcu_read_unlock in order
158 * to exit the grace period. For classic RCU, a reschedule is required.
159 */
160static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
161{
162 bool can_cont;
163
164 get_task_struct(g);
165 get_task_struct(t);
166 rcu_read_unlock();
167 cond_resched();
168 rcu_read_lock();
169 can_cont = pid_alive(g) && pid_alive(t);
170 put_task_struct(t);
171 put_task_struct(g);
172
173 return can_cont;
174}
175
176/*
177 * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
178 * a really long time (120 seconds). If that happens, print out
179 * a warning.
180 */
181static void check_hung_uninterruptible_tasks(unsigned long timeout)
182{
183 int max_count = sysctl_hung_task_check_count;
184 unsigned long last_break = jiffies;
185 struct task_struct *g, *t;
186
187 /*
188 * If the system crashed already then all bets are off,
189 * do not report extra hung tasks:
190 */
191 if (test_taint(TAINT_DIE) || did_panic)
192 return;
193
194 hung_task_show_lock = false;
195 rcu_read_lock();
196 for_each_process_thread(g, t) {
197 unsigned int state;
198
199 if (!max_count--)
200 goto unlock;
201 if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
202 if (!rcu_lock_break(g, t))
203 goto unlock;
204 last_break = jiffies;
205 }
206 /*
207 * skip the TASK_KILLABLE tasks -- these can be killed
208 * skip the TASK_IDLE tasks -- those are genuinely idle
209 */
210 state = READ_ONCE(t->__state);
211 if ((state & TASK_UNINTERRUPTIBLE) &&
212 !(state & TASK_WAKEKILL) &&
213 !(state & TASK_NOLOAD))
214 check_hung_task(t, timeout);
215 }
216 unlock:
217 rcu_read_unlock();
218 if (hung_task_show_lock)
219 debug_show_all_locks();
220
221 if (hung_task_show_all_bt) {
222 hung_task_show_all_bt = false;
223 trigger_all_cpu_backtrace();
224 }
225
226 if (hung_task_call_panic)
227 panic("hung_task: blocked tasks");
228}
229
230static long hung_timeout_jiffies(unsigned long last_checked,
231 unsigned long timeout)
232{
233 /* timeout of 0 will disable the watchdog */
234 return timeout ? last_checked - jiffies + timeout * HZ :
235 MAX_SCHEDULE_TIMEOUT;
236}
237
238#ifdef CONFIG_SYSCTL
239/*
240 * Process updating of timeout sysctl
241 */
242static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
243 void *buffer,
244 size_t *lenp, loff_t *ppos)
245{
246 int ret;
247
248 ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
249
250 if (ret || !write)
251 goto out;
252
253 wake_up_process(watchdog_task);
254
255 out:
256 return ret;
257}
258
259/*
260 * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
261 * and hung_task_check_interval_secs
262 */
263static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
264static struct ctl_table hung_task_sysctls[] = {
265#ifdef CONFIG_SMP
266 {
267 .procname = "hung_task_all_cpu_backtrace",
268 .data = &sysctl_hung_task_all_cpu_backtrace,
269 .maxlen = sizeof(int),
270 .mode = 0644,
271 .proc_handler = proc_dointvec_minmax,
272 .extra1 = SYSCTL_ZERO,
273 .extra2 = SYSCTL_ONE,
274 },
275#endif /* CONFIG_SMP */
276 {
277 .procname = "hung_task_panic",
278 .data = &sysctl_hung_task_panic,
279 .maxlen = sizeof(int),
280 .mode = 0644,
281 .proc_handler = proc_dointvec_minmax,
282 .extra1 = SYSCTL_ZERO,
283 .extra2 = SYSCTL_ONE,
284 },
285 {
286 .procname = "hung_task_check_count",
287 .data = &sysctl_hung_task_check_count,
288 .maxlen = sizeof(int),
289 .mode = 0644,
290 .proc_handler = proc_dointvec_minmax,
291 .extra1 = SYSCTL_ZERO,
292 },
293 {
294 .procname = "hung_task_timeout_secs",
295 .data = &sysctl_hung_task_timeout_secs,
296 .maxlen = sizeof(unsigned long),
297 .mode = 0644,
298 .proc_handler = proc_dohung_task_timeout_secs,
299 .extra2 = (void *)&hung_task_timeout_max,
300 },
301 {
302 .procname = "hung_task_check_interval_secs",
303 .data = &sysctl_hung_task_check_interval_secs,
304 .maxlen = sizeof(unsigned long),
305 .mode = 0644,
306 .proc_handler = proc_dohung_task_timeout_secs,
307 .extra2 = (void *)&hung_task_timeout_max,
308 },
309 {
310 .procname = "hung_task_warnings",
311 .data = &sysctl_hung_task_warnings,
312 .maxlen = sizeof(int),
313 .mode = 0644,
314 .proc_handler = proc_dointvec_minmax,
315 .extra1 = SYSCTL_NEG_ONE,
316 },
317 {}
318};
319
320static void __init hung_task_sysctl_init(void)
321{
322 register_sysctl_init("kernel", hung_task_sysctls);
323}
324#else
325#define hung_task_sysctl_init() do { } while (0)
326#endif /* CONFIG_SYSCTL */
327
328
329static atomic_t reset_hung_task = ATOMIC_INIT(0);
330
331void reset_hung_task_detector(void)
332{
333 atomic_set(&reset_hung_task, 1);
334}
335EXPORT_SYMBOL_GPL(reset_hung_task_detector);
336
337static bool hung_detector_suspended;
338
339static int hungtask_pm_notify(struct notifier_block *self,
340 unsigned long action, void *hcpu)
341{
342 switch (action) {
343 case PM_SUSPEND_PREPARE:
344 case PM_HIBERNATION_PREPARE:
345 case PM_RESTORE_PREPARE:
346 hung_detector_suspended = true;
347 break;
348 case PM_POST_SUSPEND:
349 case PM_POST_HIBERNATION:
350 case PM_POST_RESTORE:
351 hung_detector_suspended = false;
352 break;
353 default:
354 break;
355 }
356 return NOTIFY_OK;
357}
358
359/*
360 * kthread which checks for tasks stuck in D state
361 */
362static int watchdog(void *dummy)
363{
364 unsigned long hung_last_checked = jiffies;
365
366 set_user_nice(current, 0);
367
368 for ( ; ; ) {
369 unsigned long timeout = sysctl_hung_task_timeout_secs;
370 unsigned long interval = sysctl_hung_task_check_interval_secs;
371 long t;
372
373 if (interval == 0)
374 interval = timeout;
375 interval = min_t(unsigned long, interval, timeout);
376 t = hung_timeout_jiffies(hung_last_checked, interval);
377 if (t <= 0) {
378 if (!atomic_xchg(&reset_hung_task, 0) &&
379 !hung_detector_suspended)
380 check_hung_uninterruptible_tasks(timeout);
381 hung_last_checked = jiffies;
382 continue;
383 }
384 schedule_timeout_interruptible(t);
385 }
386
387 return 0;
388}
389
390static int __init hung_task_init(void)
391{
392 atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
393
394 /* Disable hung task detector on suspend */
395 pm_notifier(hungtask_pm_notify, 0);
396
397 watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
398 hung_task_sysctl_init();
399
400 return 0;
401}
402subsys_initcall(hung_task_init);