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);
403