xref: /openbmc/linux/kernel/hung_task.c (revision acf50233) 
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  */
31 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  */
45 unsigned 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  */
50 unsigned long __read_mostly sysctl_hung_task_check_interval_secs;
51 
52 int __read_mostly sysctl_hung_task_warnings = 10;
53 
54 static int __read_mostly did_panic;
55 static bool hung_task_show_lock;
56 static bool hung_task_call_panic;
57 static bool hung_task_show_all_bt;
58 
59 static 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  */
66 static unsigned int __read_mostly sysctl_hung_task_all_cpu_backtrace;
67 #else
68 #define sysctl_hung_task_all_cpu_backtrace 0
69 #endif /* CONFIG_SMP */
70 
71 /*
72  * Should we panic (and reboot, if panic_timeout= is set) when a
73  * hung task is detected:
74  */
75 unsigned int __read_mostly sysctl_hung_task_panic =
76 				IS_ENABLED(CONFIG_BOOTPARAM_HUNG_TASK_PANIC);
77 
78 static int
79 hung_task_panic(struct notifier_block *this, unsigned long event, void *ptr)
80 {
81 	did_panic = 1;
82 
83 	return NOTIFY_DONE;
84 }
85 
86 static struct notifier_block panic_block = {
87 	.notifier_call = hung_task_panic,
88 };
89 
90 static void check_hung_task(struct task_struct *t, unsigned long timeout)
91 {
92 	unsigned long switch_count = t->nvcsw + t->nivcsw;
93 
94 	/*
95 	 * Ensure the task is not frozen.
96 	 * Also, skip vfork and any other user process that freezer should skip.
97 	 */
98 	if (unlikely(t->flags & (PF_FROZEN | PF_FREEZER_SKIP)))
99 	    return;
100 
101 	/*
102 	 * When a freshly created task is scheduled once, changes its state to
103 	 * TASK_UNINTERRUPTIBLE without having ever been switched out once, it
104 	 * musn't be checked.
105 	 */
106 	if (unlikely(!switch_count))
107 		return;
108 
109 	if (switch_count != t->last_switch_count) {
110 		t->last_switch_count = switch_count;
111 		t->last_switch_time = jiffies;
112 		return;
113 	}
114 	if (time_is_after_jiffies(t->last_switch_time + timeout * HZ))
115 		return;
116 
117 	trace_sched_process_hang(t);
118 
119 	if (sysctl_hung_task_panic) {
120 		console_verbose();
121 		hung_task_show_lock = true;
122 		hung_task_call_panic = true;
123 	}
124 
125 	/*
126 	 * Ok, the task did not get scheduled for more than 2 minutes,
127 	 * complain:
128 	 */
129 	if (sysctl_hung_task_warnings) {
130 		if (sysctl_hung_task_warnings > 0)
131 			sysctl_hung_task_warnings--;
132 		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
133 		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
134 		pr_err("      %s %s %.*s\n",
135 			print_tainted(), init_utsname()->release,
136 			(int)strcspn(init_utsname()->version, " "),
137 			init_utsname()->version);
138 		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
139 			" disables this message.\n");
140 		sched_show_task(t);
141 		hung_task_show_lock = true;
142 
143 		if (sysctl_hung_task_all_cpu_backtrace)
144 			hung_task_show_all_bt = true;
145 	}
146 
147 	touch_nmi_watchdog();
148 }
149 
150 /*
151  * To avoid extending the RCU grace period for an unbounded amount of time,
152  * periodically exit the critical section and enter a new one.
153  *
154  * For preemptible RCU it is sufficient to call rcu_read_unlock in order
155  * to exit the grace period. For classic RCU, a reschedule is required.
156  */
157 static bool rcu_lock_break(struct task_struct *g, struct task_struct *t)
158 {
159 	bool can_cont;
160 
161 	get_task_struct(g);
162 	get_task_struct(t);
163 	rcu_read_unlock();
164 	cond_resched();
165 	rcu_read_lock();
166 	can_cont = pid_alive(g) && pid_alive(t);
167 	put_task_struct(t);
168 	put_task_struct(g);
169 
170 	return can_cont;
171 }
172 
173 /*
174  * Check whether a TASK_UNINTERRUPTIBLE does not get woken up for
175  * a really long time (120 seconds). If that happens, print out
176  * a warning.
177  */
178 static void check_hung_uninterruptible_tasks(unsigned long timeout)
179 {
180 	int max_count = sysctl_hung_task_check_count;
181 	unsigned long last_break = jiffies;
182 	struct task_struct *g, *t;
183 
184 	/*
185 	 * If the system crashed already then all bets are off,
186 	 * do not report extra hung tasks:
187 	 */
188 	if (test_taint(TAINT_DIE) || did_panic)
189 		return;
190 
191 	hung_task_show_lock = false;
192 	rcu_read_lock();
193 	for_each_process_thread(g, t) {
194 		if (!max_count--)
195 			goto unlock;
196 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
197 			if (!rcu_lock_break(g, t))
198 				goto unlock;
199 			last_break = jiffies;
200 		}
201 		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */
202 		if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)
203 			check_hung_task(t, timeout);
204 	}
205  unlock:
206 	rcu_read_unlock();
207 	if (hung_task_show_lock)
208 		debug_show_all_locks();
209 
210 	if (hung_task_show_all_bt) {
211 		hung_task_show_all_bt = false;
212 		trigger_all_cpu_backtrace();
213 	}
214 
215 	if (hung_task_call_panic)
216 		panic("hung_task: blocked tasks");
217 }
218 
219 static long hung_timeout_jiffies(unsigned long last_checked,
220 				 unsigned long timeout)
221 {
222 	/* timeout of 0 will disable the watchdog */
223 	return timeout ? last_checked - jiffies + timeout * HZ :
224 		MAX_SCHEDULE_TIMEOUT;
225 }
226 
227 #ifdef CONFIG_SYSCTL
228 /*
229  * Process updating of timeout sysctl
230  */
231 static int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
232 				  void __user *buffer,
233 				  size_t *lenp, loff_t *ppos)
234 {
235 	int ret;
236 
237 	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
238 
239 	if (ret || !write)
240 		goto out;
241 
242 	wake_up_process(watchdog_task);
243 
244  out:
245 	return ret;
246 }
247 
248 /*
249  * This is needed for proc_doulongvec_minmax of sysctl_hung_task_timeout_secs
250  * and hung_task_check_interval_secs
251  */
252 static const unsigned long hung_task_timeout_max = (LONG_MAX / HZ);
253 static struct ctl_table hung_task_sysctls[] = {
254 #ifdef CONFIG_SMP
255 	{
256 		.procname	= "hung_task_all_cpu_backtrace",
257 		.data		= &sysctl_hung_task_all_cpu_backtrace,
258 		.maxlen		= sizeof(int),
259 		.mode		= 0644,
260 		.proc_handler	= proc_dointvec_minmax,
261 		.extra1		= SYSCTL_ZERO,
262 		.extra2		= SYSCTL_ONE,
263 	},
264 #endif /* CONFIG_SMP */
265 	{
266 		.procname	= "hung_task_panic",
267 		.data		= &sysctl_hung_task_panic,
268 		.maxlen		= sizeof(int),
269 		.mode		= 0644,
270 		.proc_handler	= proc_dointvec_minmax,
271 		.extra1		= SYSCTL_ZERO,
272 		.extra2		= SYSCTL_ONE,
273 	},
274 	{
275 		.procname	= "hung_task_check_count",
276 		.data		= &sysctl_hung_task_check_count,
277 		.maxlen		= sizeof(int),
278 		.mode		= 0644,
279 		.proc_handler	= proc_dointvec_minmax,
280 		.extra1		= SYSCTL_ZERO,
281 	},
282 	{
283 		.procname	= "hung_task_timeout_secs",
284 		.data		= &sysctl_hung_task_timeout_secs,
285 		.maxlen		= sizeof(unsigned long),
286 		.mode		= 0644,
287 		.proc_handler	= proc_dohung_task_timeout_secs,
288 		.extra2		= (void *)&hung_task_timeout_max,
289 	},
290 	{
291 		.procname	= "hung_task_check_interval_secs",
292 		.data		= &sysctl_hung_task_check_interval_secs,
293 		.maxlen		= sizeof(unsigned long),
294 		.mode		= 0644,
295 		.proc_handler	= proc_dohung_task_timeout_secs,
296 		.extra2		= (void *)&hung_task_timeout_max,
297 	},
298 	{
299 		.procname	= "hung_task_warnings",
300 		.data		= &sysctl_hung_task_warnings,
301 		.maxlen		= sizeof(int),
302 		.mode		= 0644,
303 		.proc_handler	= proc_dointvec_minmax,
304 		.extra1		= SYSCTL_NEG_ONE,
305 	},
306 	{}
307 };
308 
309 static void __init hung_task_sysctl_init(void)
310 {
311 	register_sysctl_init("kernel", hung_task_sysctls);
312 }
313 #else
314 #define hung_task_sysctl_init() do { } while (0)
315 #endif /* CONFIG_SYSCTL */
316 
317 
318 static atomic_t reset_hung_task = ATOMIC_INIT(0);
319 
320 void reset_hung_task_detector(void)
321 {
322 	atomic_set(&reset_hung_task, 1);
323 }
324 EXPORT_SYMBOL_GPL(reset_hung_task_detector);
325 
326 static bool hung_detector_suspended;
327 
328 static int hungtask_pm_notify(struct notifier_block *self,
329 			      unsigned long action, void *hcpu)
330 {
331 	switch (action) {
332 	case PM_SUSPEND_PREPARE:
333 	case PM_HIBERNATION_PREPARE:
334 	case PM_RESTORE_PREPARE:
335 		hung_detector_suspended = true;
336 		break;
337 	case PM_POST_SUSPEND:
338 	case PM_POST_HIBERNATION:
339 	case PM_POST_RESTORE:
340 		hung_detector_suspended = false;
341 		break;
342 	default:
343 		break;
344 	}
345 	return NOTIFY_OK;
346 }
347 
348 /*
349  * kthread which checks for tasks stuck in D state
350  */
351 static int watchdog(void *dummy)
352 {
353 	unsigned long hung_last_checked = jiffies;
354 
355 	set_user_nice(current, 0);
356 
357 	for ( ; ; ) {
358 		unsigned long timeout = sysctl_hung_task_timeout_secs;
359 		unsigned long interval = sysctl_hung_task_check_interval_secs;
360 		long t;
361 
362 		if (interval == 0)
363 			interval = timeout;
364 		interval = min_t(unsigned long, interval, timeout);
365 		t = hung_timeout_jiffies(hung_last_checked, interval);
366 		if (t <= 0) {
367 			if (!atomic_xchg(&reset_hung_task, 0) &&
368 			    !hung_detector_suspended)
369 				check_hung_uninterruptible_tasks(timeout);
370 			hung_last_checked = jiffies;
371 			continue;
372 		}
373 		schedule_timeout_interruptible(t);
374 	}
375 
376 	return 0;
377 }
378 
379 static int __init hung_task_init(void)
380 {
381 	atomic_notifier_chain_register(&panic_notifier_list, &panic_block);
382 
383 	/* Disable hung task detector on suspend */
384 	pm_notifier(hungtask_pm_notify, 0);
385 
386 	watchdog_task = kthread_run(watchdog, NULL, "khungtaskd");
387 	hung_task_sysctl_init();
388 
389 	return 0;
390 }
391 subsys_initcall(hung_task_init);
392