xref: /linux/kernel/hung_task.c (revision e406d57be7bd2a4e73ea512c1ae36a40a44e499e)
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 #include <linux/hung_task.h>
26 #include <linux/rwsem.h>
27 
28 #include <trace/events/sched.h>
29 
30 /*
31  * The number of tasks checked:
32  */
33 static int __read_mostly sysctl_hung_task_check_count = PID_MAX_LIMIT;
34 
35 /*
36  * Total number of tasks detected as hung since boot:
37  */
38 static unsigned long __read_mostly sysctl_hung_task_detect_count;
39 
40 /*
41  * Limit number of tasks checked in a batch.
42  *
43  * This value controls the preemptibility of khungtaskd since preemption
44  * is disabled during the critical section. It also controls the size of
45  * the RCU grace period. So it needs to be upper-bound.
46  */
47 #define HUNG_TASK_LOCK_BREAK (HZ / 10)
48 
49 /*
50  * Zero means infinite timeout - no checking done:
51  */
52 unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
53 EXPORT_SYMBOL_GPL(sysctl_hung_task_timeout_secs);
54 
55 /*
56  * Zero (default value) means use sysctl_hung_task_timeout_secs:
57  */
58 static unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
59 
60 static int __read_mostly sysctl_hung_task_warnings = 10;
61 
62 static int __read_mostly did_panic;
63 static bool hung_task_show_lock;
64 static bool hung_task_call_panic;
65 static bool hung_task_show_all_bt;
66 
67 static struct task_struct *watchdog_task;
68 
69 #ifdef CONFIG_SMP
70 /*
71  * Should we dump all CPUs backtraces in a hung task event?
72  * Defaults to 0, can be changed via sysctl.
73  */
74 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
75 #else
76 #define sysctl_hung_task_all_cpu_backtrace 0
77 #endif /* CONFIG_SMP */
78 
79 /*
80  * Should we panic (and reboot, if panic_timeout= is set) when a
81  * hung task is detected:
82  */
83 static unsigned int __read_mostly sysctl_hung_task_panic =
84 	IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
85 
86 static int
hung_task_panic(struct notifier_block * this,unsigned long event,void * ptr)87 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
88 {
89 	did_panic = 1;
90 
91 	return NOTIFY_DONE;
92 }
93 
94 static struct notifier_block panic_block = {
95 	.notifier_call = hung_task_panic,
96 };
97 
task_is_hung(struct task_struct * t,unsigned long timeout)98 static bool task_is_hung(struct task_struct *t, unsigned long timeout)
99 {
100 	unsigned long switch_count = t->nvcsw + t->nivcsw;
101 	unsigned int state = READ_ONCE(t->__state);
102 
103 	/*
104 	 * skip the TASK_KILLABLE tasks -- these can be killed
105 	 * skip the TASK_IDLE tasks -- those are genuinely idle
106 	 * skip the TASK_FROZEN task -- it reasonably stops scheduling by freezer
107 	 */
108 	if (!(state & TASK_UNINTERRUPTIBLE) ||
109 	    (state & (TASK_WAKEKILL | TASK_NOLOAD | TASK_FROZEN)))
110 		return false;
111 
112 	/*
113 	 * When a freshly created task is scheduled once, changes its state to
114 	 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
115 	 * musn't be checked.
116 	 */
117 	if (unlikely(!switch_count))
118 		return false;
119 
120 	if (switch_count != t->last_switch_count) {
121 		t->last_switch_count = switch_count;
122 		t->last_switch_time = jiffies;
123 		return false;
124 	}
125 	if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
126 		return false;
127 
128 	return true;
129 }
130 
131 #ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
debug_show_blocker(struct task_struct * task,unsigned long timeout)132 static void debug_show_blocker(struct task_struct *task, unsigned long timeout)
133 {
134 	struct task_struct *g, *t;
135 	unsigned long owner, blocker, blocker_type;
136 	const char *rwsem_blocked_by, *rwsem_blocked_as;
137 
138 	RCU_LOCKDEP_WARN(!rcu_read_lock_held(), "No rcu lock held");
139 
140 	blocker = READ_ONCE(task->blocker);
141 	if (!blocker)
142 		return;
143 
144 	blocker_type = hung_task_get_blocker_type(blocker);
145 
146 	switch (blocker_type) {
147 	case BLOCKER_TYPE_MUTEX:
148 		owner = mutex_get_owner(hung_task_blocker_to_lock(blocker));
149 		break;
150 	case BLOCKER_TYPE_SEM:
151 		owner = sem_last_holder(hung_task_blocker_to_lock(blocker));
152 		break;
153 	case BLOCKER_TYPE_RWSEM_READER:
154 	case BLOCKER_TYPE_RWSEM_WRITER:
155 		owner = (unsigned long)rwsem_owner(
156 					hung_task_blocker_to_lock(blocker));
157 		rwsem_blocked_as = (blocker_type == BLOCKER_TYPE_RWSEM_READER) ?
158 					"reader" : "writer";
159 		rwsem_blocked_by = is_rwsem_reader_owned(
160 					hung_task_blocker_to_lock(blocker)) ?
161 					"reader" : "writer";
162 		break;
163 	default:
164 		WARN_ON_ONCE(1);
165 		return;
166 	}
167 
168 
169 	if (unlikely(!owner)) {
170 		switch (blocker_type) {
171 		case BLOCKER_TYPE_MUTEX:
172 			pr_err("INFO: task %s:%d is blocked on a mutex, but the owner is not found.\n",
173 			       task->comm, task->pid);
174 			break;
175 		case BLOCKER_TYPE_SEM:
176 			pr_err("INFO: task %s:%d is blocked on a semaphore, but the last holder is not found.\n",
177 			       task->comm, task->pid);
178 			break;
179 		case BLOCKER_TYPE_RWSEM_READER:
180 		case BLOCKER_TYPE_RWSEM_WRITER:
181 			pr_err("INFO: task %s:%d is blocked on an rw-semaphore, but the owner is not found.\n",
182 			       task->comm, task->pid);
183 			break;
184 		}
185 		return;
186 	}
187 
188 	/* Ensure the owner information is correct. */
189 	for_each_process_thread(g, t) {
190 		if ((unsigned long)t != owner)
191 			continue;
192 
193 		switch (blocker_type) {
194 		case BLOCKER_TYPE_MUTEX:
195 			pr_err("INFO: task %s:%d is blocked on a mutex likely owned by task %s:%d.\n",
196 			       task->comm, task->pid, t->comm, t->pid);
197 			break;
198 		case BLOCKER_TYPE_SEM:
199 			pr_err("INFO: task %s:%d blocked on a semaphore likely last held by task %s:%d\n",
200 			       task->comm, task->pid, t->comm, t->pid);
201 			break;
202 		case BLOCKER_TYPE_RWSEM_READER:
203 		case BLOCKER_TYPE_RWSEM_WRITER:
204 			pr_err("INFO: task %s:%d <%s> blocked on an rw-semaphore likely owned by task %s:%d <%s>\n",
205 			       task->comm, task->pid, rwsem_blocked_as, t->comm,
206 			       t->pid, rwsem_blocked_by);
207 			break;
208 		}
209 		/* Avoid duplicated task dump, skip if the task is also hung. */
210 		if (!task_is_hung(t, timeout))
211 			sched_show_task(t);
212 		return;
213 	}
214 }
215 #else
debug_show_blocker(struct task_struct * task,unsigned long timeout)216 static inline void debug_show_blocker(struct task_struct *task, unsigned long timeout)
217 {
218 }
219 #endif
220 
check_hung_task(struct task_struct * t,unsigned long timeout)221 static void check_hung_task(struct task_struct *t, unsigned long timeout)
222 {
223 	if (!task_is_hung(t, timeout))
224 		return;
225 
226 	/*
227 	 * This counter tracks the total number of tasks detected as hung
228 	 * since boot.
229 	 */
230 	sysctl_hung_task_detect_count++;
231 
232 	trace_sched_process_hang(t);
233 
234 	if (sysctl_hung_task_panic) {
235 		console_verbose();
236 		hung_task_show_lock = true;
237 		hung_task_call_panic = true;
238 	}
239 
240 	/*
241 	 * Ok, the task did not get scheduled for more than 2 minutes,
242 	 * complain:
243 	 */
244 	if (sysctl_hung_task_warnings || hung_task_call_panic) {
245 		if (sysctl_hung_task_warnings > 0)
246 			sysctl_hung_task_warnings--;
247 		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
248 		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
249 		pr_err("      %s %s %.*s\n",
250 			print_tainted(), init_utsname()->release,
251 			(int)strcspn(init_utsname()->version, " "),
252 			init_utsname()->version);
253 		if (t->flags & PF_POSTCOREDUMP)
254 			pr_err("      Blocked by coredump.\n");
255 		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
256 			" disables this message.\n");
257 		sched_show_task(t);
258 		debug_show_blocker(t, timeout);
259 		hung_task_show_lock = true;
260 
261 		if (sysctl_hung_task_all_cpu_backtrace)
262 			hung_task_show_all_bt = true;
263 		if (!sysctl_hung_task_warnings)
264 			pr_info("Future hung task reports are suppressed, see sysctl kernel.hung_task_warnings\n");
265 	}
266 
267 	touch_nmi_watchdog();
268 }
269 
270 /*
271  * To avoid extending the RCU grace period for an unbounded amount of time,
272  * periodically exit the critical section and enter a new one.
273  *
274  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
275  * to exit the grace period. For classic RCU, a reschedule is required.
276  */
rcu_lock_break(struct task_struct * g,struct task_struct * t)277 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
278 {
279 	bool can_cont;
280 
281 	get_task_struct(g);
282 	get_task_struct(t);
283 	rcu_read_unlock();
284 	cond_resched();
285 	rcu_read_lock();
286 	can_cont = pid_alive(g) && pid_alive(t);
287 	put_task_struct(t);
288 	put_task_struct(g);
289 
290 	return can_cont;
291 }
292 
293 /*
294  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
295  * a really long time (120 seconds). If that happens, print out
296  * a warning.
297  */
check_hung_uninterruptible_tasks(unsigned long timeout)298 static void check_hung_uninterruptible_tasks(unsigned long timeout)
299 {
300 	int max_count = sysctl_hung_task_check_count;
301 	unsigned long last_break = jiffies;
302 	struct task_struct *g, *t;
303 
304 	/*
305 	 * If the system crashed already then all bets are off,
306 	 * do not report extra hung tasks:
307 	 */
308 	if (test_taint(TAINT_DIE) || did_panic)
309 		return;
310 
311 	hung_task_show_lock = false;
312 	rcu_read_lock();
313 	for_each_process_thread(g, t) {
314 
315 		if (!max_count--)
316 			goto unlock;
317 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
318 			if (!rcu_lock_break(g, t))
319 				goto unlock;
320 			last_break = jiffies;
321 		}
322 
323 		check_hung_task(t, timeout);
324 	}
325  unlock:
326 	rcu_read_unlock();
327 	if (hung_task_show_lock)
328 		debug_show_all_locks();
329 
330 	if (hung_task_show_all_bt) {
331 		hung_task_show_all_bt = false;
332 		trigger_all_cpu_backtrace();
333 	}
334 
335 	if (hung_task_call_panic)
336 		panic("hung_task: blocked tasks");
337 }
338 
hung_timeout_jiffies(unsigned long last_checked,unsigned long timeout)339 static long hung_timeout_jiffies(unsigned long last_checked,
340 				 unsigned long timeout)
341 {
342 	/* timeout of 0 will disable the watchdog */
343 	return timeout ? last_checked - jiffies + timeout * HZ :
344 		MAX_SCHEDULE_TIMEOUT;
345 }
346 
347 #ifdef CONFIG_SYSCTL
348 /*
349  * Process updating of timeout sysctl
350  */
proc_dohung_task_timeout_secs(const struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)351 static int proc_dohung_task_timeout_secs(const struct ctl_table *table, int write,
352 				  void *buffer,
353 				  size_t *lenp, loff_t *ppos)
354 {
355 	int ret;
356 
357 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
358 
359 	if (ret || !write)
360 		goto out;
361 
362 	wake_up_process(watchdog_task);
363 
364  out:
365 	return ret;
366 }
367 
368 /*
369  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
370  * and hung_task_check_interval_secs
371  */
372 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
373 static const struct ctl_table hung_task_sysctls[] = {
374 #ifdef CONFIG_SMP
375 	{
376 		.procname	= "hung_task_all_cpu_backtrace",
377 		.data		= &sysctl_hung_task_all_cpu_backtrace,
378 		.maxlen		= sizeof(int),
379 		.mode		= 0644,
380 		.proc_handler	= proc_dointvec_minmax,
381 		.extra1		= SYSCTL_ZERO,
382 		.extra2		= SYSCTL_ONE,
383 	},
384 #endif /* CONFIG_SMP */
385 	{
386 		.procname	= "hung_task_panic",
387 		.data		= &sysctl_hung_task_panic,
388 		.maxlen		= sizeof(int),
389 		.mode		= 0644,
390 		.proc_handler	= proc_dointvec_minmax,
391 		.extra1		= SYSCTL_ZERO,
392 		.extra2		= SYSCTL_ONE,
393 	},
394 	{
395 		.procname	= "hung_task_check_count",
396 		.data		= &sysctl_hung_task_check_count,
397 		.maxlen		= sizeof(int),
398 		.mode		= 0644,
399 		.proc_handler	= proc_dointvec_minmax,
400 		.extra1		= SYSCTL_ZERO,
401 	},
402 	{
403 		.procname	= "hung_task_timeout_secs",
404 		.data		= &sysctl_hung_task_timeout_secs,
405 		.maxlen		= sizeof(unsigned long),
406 		.mode		= 0644,
407 		.proc_handler	= proc_dohung_task_timeout_secs,
408 		.extra2		= (void *)&hung_task_timeout_max,
409 	},
410 	{
411 		.procname	= "hung_task_check_interval_secs",
412 		.data		= &sysctl_hung_task_check_interval_secs,
413 		.maxlen		= sizeof(unsigned long),
414 		.mode		= 0644,
415 		.proc_handler	= proc_dohung_task_timeout_secs,
416 		.extra2		= (void *)&hung_task_timeout_max,
417 	},
418 	{
419 		.procname	= "hung_task_warnings",
420 		.data		= &sysctl_hung_task_warnings,
421 		.maxlen		= sizeof(int),
422 		.mode		= 0644,
423 		.proc_handler	= proc_dointvec_minmax,
424 		.extra1		= SYSCTL_NEG_ONE,
425 	},
426 	{
427 		.procname	= "hung_task_detect_count",
428 		.data		= &sysctl_hung_task_detect_count,
429 		.maxlen		= sizeof(unsigned long),
430 		.mode		= 0444,
431 		.proc_handler	= proc_doulongvec_minmax,
432 	},
433 };
434 
hung_task_sysctl_init(void)435 static void __init hung_task_sysctl_init(void)
436 {
437 	register_sysctl_init("kernel", hung_task_sysctls);
438 }
439 #else
440 #define hung_task_sysctl_init() do { } while (0)
441 #endif /* CONFIG_SYSCTL */
442 
443 
444 static atomic_t reset_hung_task = ATOMIC_INIT(0);
445 
reset_hung_task_detector(void)446 void reset_hung_task_detector(void)
447 {
448 	atomic_set(&reset_hung_task, 1);
449 }
450 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
451 
452 static bool hung_detector_suspended;
453 
hungtask_pm_notify(struct notifier_block * self,unsigned long action,void * hcpu)454 static int hungtask_pm_notify(struct notifier_block *self,
455 			      unsigned long action, void *hcpu)
456 {
457 	switch (action) {
458 	case PM_SUSPEND_PREPARE:
459 	case PM_HIBERNATION_PREPARE:
460 	case PM_RESTORE_PREPARE:
461 		hung_detector_suspended = true;
462 		break;
463 	case PM_POST_SUSPEND:
464 	case PM_POST_HIBERNATION:
465 	case PM_POST_RESTORE:
466 		hung_detector_suspended = false;
467 		break;
468 	default:
469 		break;
470 	}
471 	return NOTIFY_OK;
472 }
473 
474 /*
475  * kthread which checks for tasks stuck in D state
476  */
watchdog(void * dummy)477 static int watchdog(void *dummy)
478 {
479 	unsigned long hung_last_checked = jiffies;
480 
481 	set_user_nice(current, 0);
482 
483 	for ( ; ; ) {
484 		unsigned long timeout = sysctl_hung_task_timeout_secs;
485 		unsigned long interval = sysctl_hung_task_check_interval_secs;
486 		long t;
487 
488 		if (interval == 0)
489 			interval = timeout;
490 		interval = min_t(unsigned long, interval, timeout);
491 		t = hung_timeout_jiffies(hung_last_checked, interval);
492 		if (t <= 0) {
493 			if (!atomic_xchg(&reset_hung_task, 0) &&
494 			    !hung_detector_suspended)
495 				check_hung_uninterruptible_tasks(timeout);
496 			hung_last_checked = jiffies;
497 			continue;
498 		}
499 		schedule_timeout_interruptible(t);
500 	}
501 
502 	return 0;
503 }
504 
hung_task_init(void)505 static int __init hung_task_init(void)
506 {
507 	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
508 
509 	/* Disable hung task detector on suspend */
510 	pm_notifier(hungtask_pm_notify, 0);
511 
512 	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
513 	hung_task_sysctl_init();
514 
515 	return 0;
516 }
517 subsys_initcall(hung_task_init);
518